System and method for preparing carbon nanotubes

Abstract

The present disclosure relates to a carbon nanotube preparation system and method, which uses catalytic diesel as a carbon source, carries out a cracking reaction in a fluidized bed reactor, generates an agglomerate of catalyst and carbon nanotubes, and then physically breaks the agglomerate by using a grinding device to obtain carbon nanotubes. Through this process, the tolerance of the catalyst to catalytic diesel can be significantly improved, and efficient, low-cost and continuous preparation of carbon nanotubes can be achieved. The carbon nanotube preparation system and method of the present disclosure have good prospects for industrial application.

Description

Technical Field

[0001] This disclosure relates to a system and method for preparing 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. Simultaneously, the catalyst is susceptible to impurities in the carbon source (such as sulfur and nitrogen), leading to catalyst deactivation, reduced reaction stability, and lower carbon nanotube yield. Summary of the Invention

[0003] The purpose of this disclosure is to provide a system and method for preparing carbon nanotubes using catalytic diesel as a carbon source, thereby improving the yield of carbon nanotubes.

[0004] To achieve the above objectives, the first aspect of this disclosure provides a system for preparing carbon nanotubes, the system comprising: A fluidized bed reactor is used to allow catalytic diesel fuel to contact with a catalyst for a cracking reaction, resulting in agglomerates of catalyst and carbon nanotubes, wherein the particle size of the agglomerates is 30 μm to 30 mm. A grinding device is used to break down the aggregates to obtain carbon nanotubes.

[0005] Optionally, the fluidized bed reactor has a catalyst inlet, a first carrier gas inlet, and an agglomerate outlet, wherein the catalytic diesel is carried into the fluidized bed reactor by the first carrier gas to carry out the cracking reaction; The grinding device has an agglomerate inlet, a carbon nanotube outlet, and a catalyst outlet. The agglomerate outlet and the agglomerate inlet are connected by an agglomerate conveying pipeline. The agglomerate conveying pipeline has a second carrier gas inlet. The agglomerates are carried into the grinding device by the second carrier gas for crushing. The carbon nanotubes are carried by the second carrier gas and leave the grinding device through the carbon nanotube outlet. Preferably, the flow rate of the second carrier gas is configured to be different from the flow rate of the first carrier gas.

[0006] Optionally, the first carrier gas and the second carrier gas each independently include at least one of nitrogen, argon, hydrogen and methane.

[0007] Optionally, the agglomerates exchange heat through a cooling medium and / or the second carrier gas; Preferably, the grinding apparatus further comprises a cooling medium inlet and a cooling medium outlet; and / or, the temperature of the second carrier gas is 0~50°C.

[0008] Optionally, the fluidized bed reactor further includes a catalyst circulation port, and the catalyst outlet is connected to the catalyst circulation port.

[0009] Optionally, the catalytic diesel oil has a distillation temperature range of 200~300℃, a sulfur content of 0~10000 mg / kg, and a nitrogen content of 200~2000 mg / kg.

[0010] Optionally, the catalyst includes a support and an active metal and an additive supported on the support, wherein the support includes at least one of alumina, silicon oxide and magnesium oxide, the active metal includes at least one of iron, cobalt and nickel, and the additive includes molybdenum and / or tungsten; Preferably, the initial grain size of the active metal is 1~3 nm.

[0011] A second aspect of this disclosure provides a method for preparing carbon nanotubes using the system described in the first aspect of this disclosure, the method comprising: Catalytic diesel oil and catalyst are brought into contact in a fluidized bed reactor to carry out a cracking reaction, resulting in agglomerates of catalyst and carbon nanotubes, wherein the particle size of the agglomerates is 30 μm to 30 mm. The aggregates are broken down in a grinding device to obtain carbon nanotubes.

[0012] Optionally, the weight ratio of the catalytic diesel to the catalyst is (0.2~3):1; the conditions for the cracking reaction include: a temperature of 600~900℃ and a time of 2~14h; The crushing conditions include a temperature of 20~300℃ and a time of 0.1~3h.

[0013] Optionally, the method further includes: carrying the catalytic diesel fuel into the fluidized bed reactor via a first carrier gas for the pyrolysis reaction, carrying the agglomerates into the grinding device via a second carrier gas for the crushing, and carrying the carbon nanotubes out of the grinding device via the second carrier gas. Preferably, the flow rate of the first carrier gas is 0.02~0.1m / s, and the flow rate of the second carrier gas is 0.08~0.15m / s.

[0014] Through the above technical solution, this disclosure utilizes catalytic diesel as a carbon source to carry out a cracking reaction in a fluidized bed reactor to obtain catalyst and carbon nanotube aggregates. Then, the aggregates are physically broken up by a grinding device to obtain carbon nanotubes, which effectively improves the catalyst's tolerance to catalytic diesel and realizes efficient, low-cost, and continuous carbon nanotube preparation, with good prospects for industrial application.

[0015] Other features and advantages of this disclosure will be described in detail in the following detailed description section. Attached Figure Description

[0016] 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 diagram of the structure and process of a system for preparing carbon nanotubes according to a specific embodiment of the present disclosure.

[0017] Figure 2 This is a schematic diagram of the system structure and process used in Comparative Example 1.

[0018] Explanation of reference numerals in the attached figures 1—Fluidized bed reactor; 2—Grinding device; 3—First carrier gas inlet; 4—Catalyst inlet; 5—Fluidized bed gas outlet; 6—Agglomerate outlet; 7—Agglomerate conveying pipeline; 8—Agglomerate inlet; 9—Catalyst outlet; 10—Second carrier gas inlet; 11—Cooling medium inlet; 12—Cooling medium outlet; 13—Carbon nanotube outlet; 14—Catalyst circulation port. Detailed Implementation

[0019] 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.

[0020] In a first aspect, this disclosure provides a system for preparing carbon nanotubes, with reference to... Figure 1 The system includes a fluidized bed reactor 1 and a grinding device 2. The fluidized bed reactor 1 is used to allow catalytic diesel to contact with the catalyst for a cracking reaction, resulting in agglomerates of catalyst and carbon nanotubes. The grinding device 2 is used to break up the agglomerates to obtain carbon nanotubes.

[0021] This disclosure utilizes catalytic diesel as a carbon source in a fluidized bed reactor for pyrolysis, allowing carbon nanotubes to grow directly on the catalyst surface. A grinding device then physically breaks up the agglomerates of catalyst and carbon nanotubes, separating them. This effectively improves the catalyst's tolerance to catalytic diesel, reduces catalyst deactivation, and increases the yield of carbon nanotubes. Furthermore, it eliminates the need for complex fluidized bed control, significantly reducing equipment investment and operating costs. This enables efficient, low-cost, continuous, and high-purity carbon nanotube production, making it suitable for industrial applications and possessing promising prospects for widespread adoption.

[0022] This disclosure discloses the preparation of carbon nanotubes using catalytic diesel as raw material, realizing the high added value utilization of catalytic diesel. The catalytic diesel refers to heavy distillate oil obtained from the catalytic cracking process in the petroleum refining process, and its distillation range can be 200~300℃. It is particularly suitable for catalytic diesel with a certain sulfur and nitrogen content. Specifically, the sulfur content of the catalytic diesel can be 0~10000 mg / kg, preferably 50~500ppm, and the nitrogen content can be 200~2000 mg / kg, preferably 300~1500 mg / kg.

[0023] According to this disclosure, in the fluidized bed reactor 1, catalytic diesel undergoes single-step thermal cracking in the presence of a catalyst, allowing the carbon source in the catalytic diesel to directly deposit and grow carbon nanotubes on the catalyst surface. This helps reduce the loss of intermediate products and improve the yield of carbon nanotubes. In one embodiment, the fluidized bed reactor 1 may have a catalyst inlet 4, a first carrier gas inlet 3, and an agglomerate outlet 6. The catalyst inlet 4 is used to introduce fresh catalyst, the first carrier gas inlet 3 is used to introduce a first carrier gas, through which the catalytic diesel can be carried into the fluidized bed reactor 1 for cracking reaction, and the agglomerate outlet 6 is used to extract the catalyst and carbon nanotube agglomerates obtained after the cracking reaction. Further, the catalyst inlet 4 may be located at the upper part of the fluidized bed reactor 1, and the first carrier gas inlet 3 may be located at the bottom of the fluidized bed reactor 1. Thus, the mixture of catalytic diesel and the first carrier gas can enter the fluidized bed reactor 1 from bottom to top, and the catalyst, flowing from top to bottom, can be in a suspended fluidized state when it comes into contact with the first carrier gas carrying the catalytic diesel, which helps improve the contact reaction efficiency.

[0024] Furthermore, the fluidized bed reactor 1 may also have a catalyst circulation port 14, connected to the catalyst outlet of the grinding device 2, for receiving the recycled catalyst from the grinding device 2. Thus, the crushed catalyst can be returned to the fluidized bed reactor 1 to continue participating in the reaction, improving catalyst utilization. The catalyst circulation port 14 may be located at the top of the fluidized bed reactor 1.

[0025] In addition, the fluidized bed reactor 1 may also have a fluidized bed gas outlet 5 located at the top for extracting the gaseous products (i.e., pyrolysis gas) obtained after the pyrolysis reaction, including methane, hydrogen, and a small amount of light hydrocarbons. The gaseous products can be further purified or partially recycled for the preheating of catalytic diesel, thereby reducing the external heating requirement, further improving energy utilization efficiency, and reducing overall operating costs.

[0026] In one specific embodiment, the first carrier gas may include at least one of nitrogen (N2), argon (Ar), hydrogen (H2), and methane (CH4).

[0027] The catalyst is a hydrocarbon cracking catalyst. In one embodiment, the catalyst may include a support and an active metal and an additive supported on the support. Based on the total dry weight of the catalyst, the content of the active metal, calculated as an element, may be 5-20% by weight, and the content of the additive, calculated as an element, may be 3-15% by weight. 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 particle size of the catalyst may be 30-100 μm. Further, the initial grain size of the active metal may be 1-3 nm, and the active metal and the additive components are dispersed together on the support. The catalyst can be prepared by co-precipitation. For example, the preparation steps of the catalyst may include: (1) calculating the weight ratio of the corresponding support, active metal salt and auxiliary 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.

[0028] The catalyst and carbon nanotube agglomerates obtained from the fluidized bed reactor 1 have suitable particle sizes, which is beneficial to improving the subsequent separation efficiency and the purity of carbon nanotubes. Specifically, the particle size of the agglomerates is 30 μm to 30 mm, preferably 50 μm to 2 mm.

[0029] According to this disclosure, in the grinding device 2, the carbon nanotubes on the catalyst surface are detached by physically breaking up the agglomerates, achieving efficient separation of the catalyst and carbon nanotubes. This obtains high-quality carbon nanotubes while maintaining the particle uniformity and activity of the catalyst, further enabling catalyst recycling and reducing the difficulty of fluidized bed operation control. In one embodiment, the grinding device 2 may have an agglomerate inlet 8, a carbon nanotube outlet 13, and a catalyst outlet 9. The agglomerate inlet 8 is used to introduce agglomerates from the fluidized bed reactor 1 into the grinding device 2, and the carbon nanotube outlet 13 and the catalyst outlet 9 are used to lead out the crushed carbon nanotubes and catalyst from the grinding device 2, respectively. The agglomerate outlet 8 of the fluidized bed reactor 1 and the agglomerate inlet 8 of the grinding device 2 are connected by an agglomerate conveying pipeline 7. Furthermore, the agglomerate inlet 8 of the grinding device 2 may be set lower than the agglomerate outlet 8 of the fluidized bed reactor 1 to allow the agglomerates to smoothly enter the grinding device 2. The agglomerate delivery line 7 may have a second carrier gas inlet 10 for introducing a second carrier gas. The agglomerates can be carried into the grinding device 2 by the second carrier gas and broken down under gas impact grinding. The resulting carbon nanotubes, due to their lower density, can be carried by the second carrier gas and exit the grinding device 2 through the carbon nanotube outlet 13. The flow rate of the second carrier gas can be configured to be different from that of the first carrier gas, preferably configured to be greater than that of the first carrier gas. For example, the flow rates of the first and second carrier gases can be configured as follows: the flow rate of the first carrier gas is 0.02~0.1 m / s, and the flow rate of the second carrier gas is 0.08~0.15 m / s. In addition, the catalyst outlet 9 can be connected to the catalyst circulation port 14 of the fluidized bed reactor 1 so that the broken catalyst particles can be returned to the fluidized bed reactor 1 for continued use in the growth of carbon nanotubes. The grinding device 2 may include grinding components that facilitate the breaking down and separation of agglomerates, and this disclosure does not impose any particular limitation on its specific form.

[0030] Furthermore, the grinding device 2 can also be equipped with a heat exchange unit to control the grinding temperature, prevent thermal damage to the carbon nanotubes, and improve grinding and crushing efficiency. In one embodiment, the agglomerates can exchange heat through a cooling medium. In this case, the grinding device 2 can have a cooling medium inlet 11 and a cooling medium outlet 12, with a cooling medium pipeline connecting the cooling medium inlet 11 and the cooling medium outlet 12. For example, a jacket can be set on the outer wall of the grinding device 2, and a cooling medium pipeline can be set inside the jacket to introduce cooling medium to cool the inside of the grinding device 2, so that the grinding device 2 can operate smoothly. The cooling medium can be water, etc. In another embodiment, the agglomerates can also exchange heat through the second carrier gas. The lower-temperature second carrier gas can directly contact the agglomerates for cooling while being used for auxiliary transportation. In this case, the temperature of the second carrier gas can be 0~50℃.

[0031] The second carrier gas can be an oxygen-free gas. In one specific embodiment, the second carrier gas may include at least one of N2, argon (Ar), hydrogen (H2), and methane (CH4).

[0032] The carbon nanotubes prepared in this disclosure have suitable diameter characteristics and uniform morphology. Specifically, the diameter of the carbon nanotubes can be 7~70 nm, the length can be 3~10 μm, and the specific surface area can be 100~350 m². 2 / g, especially, the carbon nanotubes have a narrower diameter distribution, with the proportion of carbon nanotubes with a diameter of 10~20 nm reaching more than 65% by weight, preferably more than 70%, which has important application prospects in the fields of high-performance electronic devices, energy storage materials and nanocomposite materials.

[0033] The system disclosed herein uses a fluidized bed reactor in conjunction with a grinding device, which optimizes energy utilization, effectively solves the engineering problem of catalyst agglomeration due to the influence of sulfur and nitrogen in catalytic diesel, significantly improves the yield of carbon nanotubes, and at the same time helps to reduce the difficulty of fluidized bed operation and control and reduce preparation costs. Specifically, the yield of carbon nanotubes can reach more than 70%.

[0034] A second aspect of this disclosure provides a method for preparing carbon nanotubes using the system described in the first aspect of this disclosure, the method comprising the following steps S1-S2: S1. Catalytic diesel and catalyst are brought into contact in a fluidized bed reactor to carry out a cracking reaction, resulting in agglomerates of catalyst and carbon nanotubes; In one embodiment, the step may further include: carrying the catalytic diesel fuel into the fluidized bed reactor via a first carrier gas to carry out the pyrolysis reaction; furthermore, by reasonably controlling the flow rate of the first carrier gas, it is beneficial to fully pyrolyze the catalytic diesel fuel and allow carbon nanotubes to grow in an orderly manner on the catalyst surface. Specifically, the flow rate of the first carrier gas may be 0.02~0.1m / s. The weight ratio of the catalytic diesel to the catalyst can be (0.2~3):1, preferably (1.4~2.8):1; the conditions for the cracking reaction can include: a temperature of 600~900℃, preferably 650~850℃; and a time of 2~14h, preferably 6~12h. S2. The aggregates are broken down in a grinding device to obtain carbon nanotubes.

[0035] In one embodiment, the step may further include: carrying the agglomerates into the grinding device via a second carrier gas for crushing, and carrying the carbon nanotubes via the second carrier gas and exiting the grinding device through the carbon nanotube outlet; the flow rate of the second carrier gas is different from the flow rate of the first carrier gas, preferably greater than the flow rate of the first carrier gas; furthermore, the flow rate of the second carrier gas can be 0.08~0.15m / s, which is beneficial to improving the yield of carbon nanotubes and the recycling efficiency of the catalyst; In one embodiment, the step may further include: allowing the agglomerates to exchange heat through a cooling medium and / or the second carrier gas to achieve stable and efficient operation of the grinding device; The crushing conditions may include: a temperature of 20~300℃ and a time of 0.1~3h.

[0036] The method described in the second aspect of this disclosure has all the beneficial effects of the system described in the first aspect of this disclosure, which will not be repeated here.

[0037] The present disclosure will be described in detail below through examples, but it is not intended to limit the present disclosure.

[0038] Example 1 This embodiment uses, as follows: Figure 1 The system shown is used to prepare carbon nanotubes from catalytic diesel. The catalytic diesel has a distillation range of 250–300 °C (at atmospheric pressure), a sulfur content of 300 mg / kg, and a nitrogen content of 1500 mg / kg. The active metal in the catalyst is 18 wt% iron and 2 wt% nickel, the additive is 3.5 wt% molybdenum, and the support is alumina. The initial grain size of the active metal is 1 nm, and the active metal and additive components are dispersed together on the support. The particle size of the catalyst is 50 μm.

[0039] A catalyst is added to the fluidized bed reactor 1 through catalyst inlet 4, and a first carrier gas (50% H2, 50% CH4) is introduced through the first carrier gas inlet 3, keeping the catalyst in a suspended fluidized state. Preheated catalytic diesel (catalytic diesel to catalyst weight ratio of 1.42) is introduced into the fluidized bed reactor 1 via gas entrainment through the first carrier gas inlet 3. The catalyst is pyrolyzed at 650℃ for 6 hours, resulting in the growth of carbon nanotubes on the catalyst, yielding agglomerates of catalyst and carbon nanotubes (particle size 50~100μm). The operating gas velocity of the first carrier gas is controlled at 0.1m / s. The pyrolysis gas (mainly methane and hydrogen) is exited from the fluidized bed reactor 1 through the fluidized bed gas outlet 5, partially used for preheating the catalytic diesel. The agglomerates of catalyst and carbon nanotubes are exited from the fluidized bed reactor 1 through the agglomerate outlet 6 and then enter the grinding device 2 through the agglomerate transport pipeline 7 and the agglomerate inlet 8. Cooling water is circulated into the cooling medium inlet 11 to ensure the smooth operation of the grinding device 2. The cooled water after heat exchange is led out from the cooling medium outlet 12. A second carrier gas (100% N2) at 50°C is introduced into the second carrier gas inlet 10 on the agglomerate conveying pipeline 7. The operating gas velocity of the second carrier gas is controlled at 0.15 m / s to transport, cool, and break up the agglomerates. The agglomerates are broken up in the grinding device 2 at 80°C for 0.2 h. The carbon nanotubes detach from the catalyst and leave the grinding device 2 from the carbon nanotube outlet 13 under the gas carrying, which is the carbon nanotube product prepared in this embodiment. The broken catalyst particles exit from the catalyst outlet 9 and return to the fluidized bed reactor 1 through the catalyst circulation port 14 to continue the growth of carbon nanotubes.

[0040] The diameter characteristics of carbon nanotubes were detected by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), and the specific surface area of ​​carbon nanotubes was detected by physical adsorption (BET). The results are listed in Table 1.

[0041] The yield and preparation cost of carbon nanotubes were calculated according to the following formula, and the results are listed in Table 2.

[0042] Carbon nanotube yield (%) = (actual weight of carbon nanotubes produced / theoretical weight of carbon nanotubes produced) × 100% Preparation cost (RMB / kg) = (Raw material cost + Equipment energy consumption cost + Labor cost, etc.) / Weight of carbon nanotube product Example 2 This embodiment uses, as follows: Figure 1The system shown is used to prepare carbon nanotubes from catalytic diesel. The catalytic diesel has a distillation 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 active metal of the catalyst is 17 wt% iron, the additive is 3.5 wt% molybdenum, and the support is silicon dioxide. The initial grain size of the active metal is 2 nm, and the active metal and additive components are dispersed together on the support. The particle size of the catalyst is 45 μm.

[0043] A catalyst is added to the fluidized bed reactor 1 through catalyst inlet 4, and a first carrier gas (50% N2, 50% CH4) is introduced through the first carrier gas inlet 3, keeping the catalyst in a suspended fluidized state. Preheated catalytic diesel (catalytic diesel to catalyst weight ratio of 0.474) is introduced into the fluidized bed reactor 1 via gas entrainment through the first carrier gas inlet 3. The catalyst is pyrolyzed at 900℃ for 2 hours, resulting in the growth of carbon nanotubes on the catalyst, yielding agglomerates of catalyst and carbon nanotubes (particle size 40~90 μm). The operating gas velocity of the first carrier gas is controlled at 0.06 m / s. The pyrolysis gas (mainly methane and hydrogen) is exited from the fluidized bed reactor 1 through the fluidized bed gas outlet 5, partially used for preheating the catalytic diesel. The agglomerates of catalyst and carbon nanotubes are exited from the fluidized bed reactor 1 through the agglomerate outlet 6 and then enter the grinding device 2 through the agglomerate transport pipeline 7 and the agglomerate inlet 8. Cooling water is circulated into the cooling medium inlet 11 to ensure the smooth operation of the grinding device 2. The cooled water after heat exchange is led out from the cooling medium outlet 12. A second carrier gas (100% Ar) at 0°C is introduced into the second carrier gas inlet 10 on the agglomerate conveying pipeline 7. The operating gas velocity of the second carrier gas is controlled at 0.12 m / s to transport, cool, and break up the agglomerates. The agglomerates are broken up in the grinding device 2 at 70°C for 3 hours. The carbon nanotubes detach from the catalyst and leave the grinding device 2 from the carbon nanotube outlet 13 under the gas carrying, which is the carbon nanotube product prepared in this embodiment. The broken catalyst particles exit from the catalyst outlet 9 and return to the fluidized bed reactor 1 through the catalyst circulation port 14 to continue the growth of carbon nanotubes.

[0044] The diameter characteristics and other results of the carbon nanotubes prepared in this embodiment are listed in Table 1, and the yield of carbon nanotubes is listed in Table 2.

[0045] Example 3 This embodiment uses, as follows: Figure 1The system shown is used to prepare carbon nanotubes from catalytic diesel. The catalytic diesel has a distillation range of 200–280 °C (atmospheric pressure), a sulfur content of 300 mg / kg, and a nitrogen content of 1000 mg / kg. The active metals of the catalyst are 4 wt% iron and 16 wt% cobalt, the additive is 5 wt% tungsten, and the support is magnesium oxide. The initial grain size of the active metal is 1 nm, and the active metal and additive components are dispersed together on the support. The particle size of the catalyst is 60 μm.

[0046] Catalyst is added to fluidized bed reactor 1 through catalyst inlet 4, and first carrier gas (50% N2, 40% Ar, 10% H2) is introduced through first carrier gas inlet 3, keeping the catalyst in a suspended fluidized state. Preheated catalytic diesel (catalytic diesel to catalyst weight ratio of 2.8) is introduced into fluidized bed reactor 1 through first carrier gas inlet 3 via gas entrainment. The catalyst is pyrolyzed at 750℃ for 12 hours, resulting in the growth of carbon nanotubes on the catalyst, yielding agglomerates of catalyst and carbon nanotubes (particle size 60~120μm). The operating gas velocity of the first carrier gas is controlled at 0.05m / s. The pyrolysis gas (mainly methane and hydrogen) is led out of fluidized bed reactor 1 through fluidized bed gas outlet 5, partially used for preheating the catalytic diesel. The agglomerates of catalyst and carbon nanotubes are led out of fluidized bed reactor 1 through agglomerate outlet 6 and enter grinding device 2 through agglomerate conveying pipeline 7 and agglomerate inlet 8. Cooling water is circulated into the cooling medium inlet 11 to ensure the smooth operation of the grinding device 2. The cooled water after heat exchange is led out from the cooling medium outlet 12. A second carrier gas (90% CH4, 10% H2) at 10°C is introduced into the second carrier gas inlet 10 on the agglomerate conveying pipeline 7. The operating gas velocity of the second carrier gas is controlled at 0.08 m / s to transport, cool, and break up the agglomerates. The agglomerates are broken up in the grinding device 2 at 50°C for 3 hours. The carbon nanotubes detach from the catalyst and leave the grinding device 2 from the carbon nanotube outlet 13 under the gas carrying, which is the carbon nanotube product prepared in this embodiment. The broken catalyst particles exit from the catalyst outlet 9 and return to the fluidized bed reactor 1 through the catalyst circulation port 14 to continue the growth of carbon nanotubes.

[0047] The diameter characteristics and other results of the carbon nanotubes prepared in this embodiment are listed in Table 1, and the yield of carbon nanotubes is listed in Table 2.

[0048] Example 4 This embodiment uses, as follows: Figure 1The system shown is used to prepare carbon nanotubes from catalytic diesel. The catalytic diesel has a distillation temperature range of 210–240 °C (at atmospheric pressure), a sulfur content of 1500 mg / kg, and a nitrogen content of 2000 mg / kg. The active metal of the catalyst is 15% by weight nickel, the promoter is 3% by weight molybdenum, and the support is magnesium oxide. The initial grain size of the active metal is 2.5 nm, and the active metal and promoter are dispersed together on the support. The particle size of the catalyst is 70 μm.

[0049] Catalyst is added to fluidized bed reactor 1 through catalyst inlet 4, and first carrier gas (100% Ar) is introduced through first carrier gas inlet 3, keeping the catalyst in a suspended fluidized state. Preheated catalytic diesel (catalytic diesel to catalyst weight ratio of 2.5) is introduced into fluidized bed reactor 1 through first carrier gas inlet 3 via gas entrainment. The catalyst is pyrolyzed at 750℃ for 12 hours, resulting in the growth of carbon nanotubes on the catalyst, yielding agglomerates of catalyst and carbon nanotubes (particle size 70~130μm). The operating gas velocity of the first carrier gas is controlled at 0.1m / s. The pyrolysis gas (mainly methane and hydrogen) is led out of fluidized bed reactor 1 through fluidized bed gas outlet 5, partially used for preheating the catalytic diesel. The agglomerates of catalyst and carbon nanotubes are led out of fluidized bed reactor 1 through agglomerate outlet 6 and enter grinding device 2 through agglomerate conveying pipeline 7 and agglomerate inlet 8. Cooling water is introduced into cooling medium inlet 11 to ensure stable operation of grinding device 2. The cooled water after heat exchange is led out through cooling medium outlet 12. A second carrier gas (50% CH4, 50% H2) at 10°C is introduced into the second carrier gas inlet 10 on the agglomerate transport pipeline 7. The operating gas velocity of the second carrier gas is controlled at 0.15 m / s. This second carrier gas is used to transport, cool, and break up the agglomerates. The agglomerates are broken up in the grinding device 2 at 65°C for 3 hours. The carbon nanotubes detach from the catalyst and leave the grinding device 2 from the carbon nanotube outlet 13 under gas carrying, which is the carbon nanotube product prepared in this embodiment. The broken catalyst particles exit from the catalyst outlet 9 and return to the fluidized bed reactor 1 through the catalyst circulation port 14 to continue the growth of carbon nanotubes.

[0050] The diameter characteristics and other results of the carbon nanotubes prepared in this embodiment are listed in Table 1, and the yield of carbon nanotubes is listed in Table 2.

[0051] 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 240–280 °C (at atmospheric pressure), a sulfur content of 7000 mg / kg, and a nitrogen content of 200 mg / kg. The active metal of the catalyst is 15 wt% iron, the additive is 4 wt% tungsten, and the support is alumina. The initial grain size of the active metal is 2.2 nm, and the active metal and additive components are dispersed together on the support. The particle size of the catalyst is 80 μm.

[0052] Catalyst is added to fluidized bed reactor 1 through catalyst inlet 4, and first carrier gas (10% Ar, 90% CH4) is introduced through first carrier gas inlet 3, keeping the catalyst in a suspended fluidized state. Preheated catalytic diesel (catalytic diesel to catalyst weight ratio of 2.2) is introduced into fluidized bed reactor 1 through first carrier gas inlet 3 via gas entrainment. The catalyst is pyrolyzed at 750℃ for 12 hours, resulting in the growth of carbon nanotubes on the catalyst, yielding agglomerates of catalyst and carbon nanotubes (particle size 80~150μm). The operating gas velocity of the first carrier gas is controlled at 0.05m / s. The pyrolysis gas (mainly methane and hydrogen) is led out of fluidized bed reactor 1 through fluidized bed gas outlet 5, partially used for preheating the catalytic diesel. The agglomerates of catalyst and carbon nanotubes are led out of fluidized bed reactor 1 through agglomerate outlet 6 and enter grinding device 2 through agglomerate conveying pipeline 7 and agglomerate inlet 8. Cooling water is circulated into the cooling medium inlet 11 to ensure the smooth operation of the grinding device 2. The cooled water after heat exchange is led out from the cooling medium outlet 12. A second carrier gas (90% CH4, 10% Ar) at 20°C is introduced into the second carrier gas inlet 10 on the agglomerate conveying pipeline 7. The operating gas velocity of the second carrier gas is controlled at 0.12 m / s to transport, cool, and break up the agglomerates. The agglomerates are broken up in the grinding device 2 at 75°C for 3 hours. The carbon nanotubes detach from the catalyst and leave the grinding device 2 from the carbon nanotube outlet 13 under the gas carrying, which is the carbon nanotube product prepared in this embodiment. The broken catalyst particles exit from the catalyst outlet 9 and return to the fluidized bed reactor 1 through the catalyst circulation port 14 to continue the growth of carbon nanotubes.

[0053] The diameter characteristics and other results of the carbon nanotubes prepared in this embodiment are listed in Table 1, and the yield of carbon nanotubes is listed in Table 2.

[0054] Comparative Example 1 Adopting such Figure 2 The 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.

[0055] 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.

[0056] 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.

[0057] 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.

[0058] 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.

[0059] The catalyst is added to the upward-flowing fluidized bed B for 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 for catalytic cracking through outlet 32, forming a carbon material product.

[0060] 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.

[0061] The diameter characteristics and other results of the carbon nanotubes prepared in this comparative example are listed in Table 1, and the yield of carbon nanotubes is listed in Table 2.

[0062] Table 1

[0063] Table 2

[0064] As can be seen from Tables 1 and 2, the system and method disclosed herein are beneficial for improving the yield of carbon nanotubes and reducing the preparation cost.

[0065] 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.

[0066] 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.

[0067] 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 system for preparing carbon nanotubes, characterized in that, The system includes: A fluidized bed reactor is used to allow catalytic diesel fuel to contact with a catalyst for a cracking reaction, resulting in agglomerates of catalyst and carbon nanotubes, wherein the particle size of the agglomerates is 30 μm to 30 mm. A grinding device is used to break down the aggregates to obtain carbon nanotubes.

2. The system according to claim 1, wherein, The fluidized bed reactor has a catalyst inlet, a first carrier gas inlet, and an agglomerate outlet. The catalytic diesel fuel is carried into the fluidized bed reactor by the first carrier gas to carry out the cracking reaction. The grinding device has an agglomerate inlet, a carbon nanotube outlet, and a catalyst outlet. The agglomerate outlet and the agglomerate inlet are connected by an agglomerate conveying pipeline. The agglomerate conveying pipeline has a second carrier gas inlet. The agglomerates are carried into the grinding device by the second carrier gas for crushing. The carbon nanotubes are carried by the second carrier gas and leave the grinding device through the carbon nanotube outlet. Preferably, the flow rate of the second carrier gas is configured to be different from the flow rate of the first carrier gas.

3. The system according to claim 2, wherein, The first carrier gas and the second carrier gas each independently include at least one of nitrogen, argon, hydrogen and methane.

4. The system according to claim 2, wherein, The agglomerates exchange heat through a cooling medium and / or the second carrier gas; Preferably, the grinding apparatus further comprises a cooling medium inlet and a cooling medium outlet; and / or, the temperature of the second carrier gas is 0~50°C.

5. The system according to claim 2, wherein, The fluidized bed reactor also has a catalyst circulation port, and the catalyst outlet is connected to the catalyst circulation port.

6. The system according to claim 1, wherein, The catalytic diesel oil has a distillation temperature range of 200~300℃, a sulfur content of 0~10000 mg / kg, and a nitrogen content of 200~2000 mg / kg.

7. The system according to claim 1, wherein, The catalyst includes a support and an active metal and an additive supported on the support, wherein the support includes at least one of alumina, silicon oxide and magnesium oxide, the active metal includes at least one of iron, cobalt and nickel, and the additive includes molybdenum and / or tungsten; Preferably, the initial grain size of the active metal is 1~3 nm.

8. A method for preparing carbon nanotubes using the system described in any one of claims 1 to 7, characterized in that, The method includes: Catalytic diesel oil and catalyst are brought into contact in a fluidized bed reactor to carry out a cracking reaction, resulting in agglomerates of catalyst and carbon nanotubes, wherein the particle size of the agglomerates is 30 μm to 30 mm. The aggregates are broken down in a grinding device to obtain carbon nanotubes.

9. The method according to claim 8, wherein, The weight ratio of the catalytic diesel to the catalyst is (0.2~3):1; the conditions for the pyrolysis reaction include: a temperature of 600~900℃ and a time of 2~14h. The crushing conditions include a temperature of 20~300℃ and a time of 0.1~3h.

10. The method according to claim 8, wherein, The method further includes: carrying the catalytic diesel fuel into the fluidized bed reactor via a first carrier gas to carry out the pyrolysis reaction, carrying the agglomerates into the grinding device via a second carrier gas to carry out the crushing, and carrying the carbon nanotubes out of the grinding device via the second carrier gas. Preferably, the flow rate of the first carrier gas is 0.02~0.1m / s, and the flow rate of the second carrier gas is 0.08~0.15m / s.

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