Method for carbon nanotube synthesis

Abstract

A method for forming carbon nanotubes can include: volatilizing a metal in a plasma to form an active catalyst; introducing a hydrocarbon stream comprising methane to a hydrocarbon conversion unit and converting at least a portion of the methane to a carbon reactant comprising ethylene, acetylene, or a combination thereof; introducing the active catalyst and the carbon reactant to a floating catalyst chemical vapor deposition reactor, wherein the floating catalyst chemical vapor deposition reactor is operated under conditions suitable for carbon nanotube formation; and contacting the active catalyst and the carbon reactant in a reaction zone in the floating catalyst chemical vapor deposition reactor to form carbon nanotubes on the active catalyst.

Description

[0001] Cross-references to related applications

[0002] This application claims priority to U.S. Provisional Patent Application No. 63 / 607,146, filed December 7, 2023, the entire contents of which are incorporated herein by reference. Technical Field

[0003] This application relates to systems and methods for producing carbon nanoscale structures, such as carbon nanotubes or carbon nanofibers. Background Technology

[0004] Due to their structure and electrical properties, carbon nanotubes are highly attractive for a wide range of applications. A major challenge to the widespread adoption of carbon nanotubes is the low productivity of current production methods, resulting in relatively high costs.

[0005] One method for fabricating carbon nanotubes is floating catalyst chemical vapor deposition (FC-CVD). Typical FC-CVD methods involve introducing a feed containing a pre-catalyst and a carbon source into a tubular reactor at a temperature of ~1,000 °C or higher. In the reactor, the pre-catalyst transforms into an active catalyst, and the carbon source decomposes to produce reactive carbon intermediates, which further react with the catalyst in the gas phase, on the catalyst surface, or both, to form carbon nanotubes. The pre-catalyst is typically an organometallic iron source, such as ferrocene, with or without a promoter such as thiophene. The components flow through the reactor under laminar flow conditions. The temperature profile in the FC-CVD method is parabolic, with temperatures starting at approximately 400 °C, reaching a maximum of approximately 1300 °C, and ending at approximately 300 °C. Residence times in the high-temperature zone are in the range of a few seconds. Some bottlenecks in this method include catalyst evaporation in the high-temperature zone and condensation of downstream active catalyst particles, which alter the size distribution of nanoparticles formed at the reactor front. The high-temperature zone (essential for hydrocarbon conversion) creates unfavorable and difficult-to-control catalyst production process conditions. Furthermore, the high-temperature zone requires the entire reactor to be made of materials capable of withstanding such high temperatures, thus increasing the reactor's capital cost. Summary of the Invention

[0006] This document discloses an exemplary method for forming carbon nanotubes, the method comprising: volatilizing a metal in a plasma to form an active catalyst; introducing a hydrocarbon feed stream containing methane into a hydrocarbon conversion unit and converting at least a portion of the methane into a carbon reactant containing ethylene, acetylene, or a combination thereof; introducing the active catalyst and the carbon reactant into a floating catalyst chemical vapor deposition reactor, wherein the floating catalyst chemical vapor deposition reactor is operated under conditions suitable for carbon nanotube formation; and contacting the active catalyst and the carbon reactant in a reaction zone within the floating catalyst chemical vapor deposition reactor to form carbon nanotubes on the active catalyst.

[0007] This document also discloses a reaction system for forming carbon nanotubes, the reaction system comprising: a catalyst generating unit comprising: a metal alloy; and a plasma generator configured to generate plasma, wherein the metal alloy is disposed within the plasma such that the plasma volatilizes the metal alloy to form an active catalyst; a hydrocarbon source comprising methane; a hydrocarbon conversion unit configured to take the hydrocarbon source as input and convert at least a portion of the methane into a carbon reactant comprising ethylene, acetylene, or a combination thereof; and a floating catalyst chemical vapor deposition reactor comprising: a reaction zone; and inlets for the active catalyst and the carbon reactant, wherein the floating catalyst chemical vapor deposition reactor is fluidly connected to the catalyst generating unit and the hydrocarbon conversion unit such that the active catalyst and the carbon reactant are in contact within the reaction zone.

[0008] These and other features and properties of the methods and systems disclosed herein, and their advantageous applications and / or uses, will become apparent from the following detailed description. Attached Figure Description

[0009] To assist those skilled in the art in creating and using the subject matter described herein, please refer to the accompanying drawings, in which:

[0010] Figure 1 This is an illustrative schematic diagram of an FC-CVD method for producing carbon nanotubes according to certain embodiments of this disclosure.

[0011] Figure 2 This is an illustrative schematic diagram of an FC-CVD method for producing carbon nanotubes according to certain embodiments of this disclosure.

[0012] Figure 3A This is an illustrative diagram of the plasma torch configuration used in a hydrocarbon conversion reactor.

[0013] Figure 3B This is an illustrative diagram of the arc plasma configuration used in a hydrocarbon conversion reactor.

[0014] Figure 3C This is an illustrative schematic diagram of the configuration of a hydrocarbon conversion reactor. Detailed Implementation

[0015] This paper discloses systems and methods for producing carbon nanoscale structures (e.g., carbon nanotubes or carbon nanofibers), and more particularly, systems and methods for producing carbon nanoscale structures using plasma-generated active catalysts and carbon reactants.

[0016] definition

[0017] The words and phrases used herein should be understood and interpreted as having the same meaning as that understood by one of skill in the art. The consistent use of terms or phrases is not intended to imply a specific definition of a term or phrase, i.e., a definition different from the usual and conventional meaning understood by one of skill in the art. Where a term or phrase is intended to have a specific meaning, i.e., a meaning different from the broadest meaning understood by one of skill in the art, such a specific or explicit definition will be clearly stated in the specification by definition (which provides the specific or explicit definition of the term or phrase).

[0018] For example, the discussion below contains a non-exhaustive list of definitions for several specific terms used in this disclosure (other terms may be defined or explicitly stated elsewhere in this document). These definitions are intended to clarify the meaning of the terms used herein. Terms are believed to be used in accordance with their usual meaning, but definitions are provided here for clarity.

[0019] Carbon fibers, nanofibers, and nanotubes are allotropes of carbon with cylindrical nanostructures. The walls of carbon nanotubes are formed from carbon sheets in a graphene structure. As used herein, nanotubes include single-walled and multi-walled nanotubes of any length. The term "carbon nanotube" as used herein and in the claims includes other fullerene allotropes of carbon, such as carbon fibers, carbon nanofibers, and other carbon nanostructures.

[0020] FC-CVD method

[0021] As mentioned above, scaling up floating catalyst chemical vapor deposition (FC-CVD) methods for producing carbon nanotubes presents several challenges. Conventional FC-CVD methods for producing carbon nanotubes involve the in-situ formation of an active catalyst within the FC-CVD reactor through the thermal decomposition of a precatalyst to form an active catalyst. Commonly used precatalysts include compounds such as thiophene or elemental sulfur, used in conjunction with organometallic compounds containing iron, cobalt, and / or nickel metals and cyclopentadiene or carbon monoxide as ligands (some specific examples include Fe(CO)5 and ferrocene). The metal in the precatalyst is converted into an active metal catalyst. Conventional FC-CVD reactors involve the mixing of hydrocarbon decomposition, precatalyst decomposition, active catalyst nucleation, growth and aggregation kinetics of catalyst nanoparticles, and the growth of CNTs on the active catalyst particles. However, the efficient formation of carbon nanotubes at the product end of the reactor is facilitated by a substantially laminar flow and little or no mixing. In smaller-scale conventional FC-CVD reactors, initial mixing of reactants can be achieved in several ways, ensuring adequate mixing of the flow even with reduced or minimized turbulence. In other words, reactants can be well mixed in small-scale reactors while maintaining a Reynolds number below 1,000, or even below 500. In contrast, in relatively large-scale reactors, generating a well-mixed flow at the beginning of the reactor will produce a turbulent gas flow with a Reynolds number greater than 5,000. Therefore, for larger-scale conventional FC-CVD reactors, it is necessary to reduce the Reynolds number of the flow to approximately 500 or lower, and more preferably to approximately 10, by the time the flow reaches the product end of the reactor.

[0022] Scaling up conventional reactors for carbon nanotube production can present various challenges. First, as reactor diameter increases, it becomes increasingly difficult, if not physically impractical, to transfer sufficient heat through the reactor walls to maintain the temperature required for the thermal decomposition of the precatalyst to form the active catalyst. Additionally, the thermal decomposition temperature of a particular precatalyst and the reaction temperature required for carbon nanotube production can differ significantly, necessitating additional quenching gases and process steps, leading to more complex reactor designs. For example, attempting to cool the gas flow in the reactor after the formation of the active catalyst may result in the catalyst surface temperature becoming too cold to effectively catalyze carbon nanotube formation. Furthermore, as the precatalyst decomposes, iron (or other metals) from the catalyst precursor tends to deposit on the reactor walls. This can result in a loss of 50 mol% or more of metal from the precatalyst. Additionally, coke formation has been observed on the walls of conventional reactors after this metal deposition has begun. Deposition occurs because the resulting metal, as atoms deposited on the surface, has higher phase stability than when retained in the gas phase, when the precatalyst is decomposed at temperatures typically between 700°C and 1000°C. Therefore, metal deposition can occur on exposed surfaces when the precatalyst is heated to temperatures between 700°C and 1000°C. This metal deposition can continue at temperatures above 1000°C, where metal atoms exhibit high phase stability in the gas phase. In conventional FC-CVD reactors, large amounts of metal can be deposited on the reactor walls, thereby reducing or minimizing the amount of activated catalyst formed.

[0023] In the implementation scheme, the method disclosed herein for producing carbon nanotubes comprises three sub-processes. The first sub-process includes generating an active catalyst in a catalyst generation unit, the second sub-process includes generating carbon reactants in a hydrocarbon conversion unit, and the third sub-process includes reacting the carbon reactants with the active catalyst in an FC-CVD reactor. One advantage of the currently disclosed method is that by separating the reactions, process parameters (e.g., temperature, pressure, and residence time) can be optimized for each sub-process.

[0024] Figure 1 This is an illustrative schematic diagram of an FC-CVD method 100 according to certain embodiments of this disclosure. Figure 1 In the process, hydrocarbon feed 102 is introduced into hydrocarbon conversion unit 104. In hydrocarbon conversion unit 104, the hydrocarbons in hydrocarbon feed 102 are converted into a form suitable for forming carbon nanotubes, referred to herein as carbon reactants. Pre-catalyst 110 is introduced into catalyst generation unit 112. In catalyst generation unit 112, the pre-catalyst is converted into an active catalyst. Active catalyst stream 114 and carbon reactant stream 106 are introduced into FC-CVD reactor 108, where the carbon reactants and active catalyst react to form carbon nanotubes. Product carbon nanotube stream 116 is removed from FC-CVD reactor 108.

[0025] The reactor system used for carbon nanotube formation performs at least three types of reactions. In the hydrocarbon conversion unit, hydrocarbons are converted into carbon reactants. Carbon reactants include, but are not limited to, C2 hydrocarbons (e.g., ethylene and / or acetylene) and hydrogen (which is a precursor for carbon nanotube formation). Reaction 1 is a generalized non-equilibrium reaction showing the conversion of methane into ethylene, acetylene, and hydrogen.

[0026] Reaction 1

[0027] Several methods exist suitable for converting hydrocarbons into carbon reactants, including, for example, conversion of methane in a plasma torch followed by quenching to maintain C2 selectivity relative to coke and endothermic cracking in a reverse flow reactor unit.

[0028] In the catalyst production unit, a metal or metal alloy is transformed into an active catalyst. In one embodiment, the metal or metal alloy is evaporated by plasma to form a volatile metal, which is then cooled and condensed into a nanoscale active catalyst. In another embodiment, the metal or metal alloy is ablated by plasma to form the active catalyst. Reaction 2 involves reacting a metal alloy (MA) with heat generated by plasma to form an active catalyst (MA). () in a broad sense.

[0029] Reaction 2

[0030] In an FC-CVD reactor, carbon nanotubes are formed by contacting carbon reactants produced in the hydrocarbon conversion unit with an active catalyst from the catalyst generation unit. Reaction 3 involves reacting the carbon reactants C2H2 and C2H4 formed in the hydrocarbon conversion unit with an active catalyst (MA) from the catalyst generation unit. The reaction is a generalized reaction that forms carbon nanotubes.

[0031] Reaction 3

[0032] It should be noted that the term "catalyst" is used to describe active catalysts (MA). This is because it promotes the formation of carbon nanotubes. However, it should be understood that at least a portion of the active catalyst is consumed during the carbon nanotube formation process, as at least a portion of the active catalyst is incorporated into the nanotube structure. In this discussion, the term "catalyst" is defined as including materials that act in a manner similar to FC-CVD catalysts. Without being theoretically limited, it is believed that the active catalyst promotes the formation and diffusion of carbon intermediates through the catalyst particles, thereby leading to carbon nanotube growth, and provides a surface for carbon nanotube nucleation.

[0033] The method disclosed herein offers several advantages over previous methods for producing carbon nanotubes, including the independence of conditions for each reaction. Temperature, pressure, and residence time are independently optimized for the hydrocarbon conversion unit, catalyst production unit, and FC-CVD reactor. Compared to conventional FC-CVD methods, the method disclosed herein exhibits higher utilization of the active catalyst, thus requiring less catalyst per unit of carbon nanotube produced. The active catalyst produced by the method disclosed herein allows for increased carbon nanotube production rates by reducing reactor residence time, facilitating reactor scalability, and enabling more efficient utilization of reactor volume. The active catalyst produced by the method disclosed herein also tends to deposit less on the reactor walls. Furthermore, the plasma volatilization step allows for fine control of catalyst morphology and particle size, providing additional process control variables to influence the physical properties of the produced carbon nanotubes and control coke formation.

[0034] Another advantage of the method disclosed herein includes the ability to use less expensive carbon sources (such as methane) to generate carbon reactants. Carbon reactants more readily generate carbon nanotubes compared to conventional FC-CVD methods, using the pyrolysis of methane or other lighter hydrocarbons to produce carbon intermediates (C2+), which are then reacted with an active catalyst to form carbon nanotubes.

[0035] Another advantage of the systems and methods disclosed herein for producing carbon nanotubes includes the ability to thoroughly mix the carbon reactants and the active catalyst before introducing them into the FC-CVD reactor. It is desirable that a well-mixed feed stream of activated catalyst and carbon reactants is introduced into the FC-CVD reactor, thereby increasing the formation of carbon nanotubes.

[0036] Hydrocarbon conversion unit

[0037] In a hydrocarbon conversion unit, a hydrocarbon feedstock is introduced into a hydrocarbon conversion reactor and converted into carbon reactants. In embodiments, the hydrocarbons used to form the carbon reactants include C1-C10 hydrocarbons such as alkanes, alkenes, alkynes, aromatic compounds, and / or cycloalkanes. Some specific examples of hydrocarbons include methane, ethane, ethylene, acetylene, propane, propylene, butane, butadiene, benzene, and combinations thereof. Alternatively or additionally, the hydrocarbon source includes hydrocarbons from refinery feed streams, such as ethane steam cracker effluent and / or fluidized catalytic cracking (FCC) exhaust gas. In another embodiment, the hydrocarbons include C1-C10 alcohols. In embodiments, the hydrocarbon feedstock is converted into carbon reactants, including but not limited to C2 hydrocarbons (e.g., ethylene and / or acetylene) and hydrogen, which are precursors for carbon nanotube formation.

[0038] In one embodiment, the hydrocarbon conversion unit includes plasma for heating the hydrocarbons to the reaction temperature. In another embodiment, the plasma can be generated by any suitable type of plasma generator, including but not limited to DC plasma generators, RF plasma generators, microwave plasma generators, inductively coupled plasma generators, arc plasma generators, or combinations thereof. In yet another embodiment, the hydrocarbons can be heated by Joule heating, flash Joule heating, pulsed Joule heating, electrofluid heating, combustion heating, arc heating, or combinations thereof.

[0039] In this embodiment, the plasma temperature is 4,000K-7,000K or any suitable temperature for heating the hydrocarbon to the reaction temperature. Alternatively, it may be 4,000K-5,000K, 5,000K-6,000K, 6,000K-7,000K, or any range therebetween.

[0040] In embodiments where the hydrocarbon conversion unit includes plasma, the hydrocarbon conversion unit can operate at any pressure suitable for converting hydrocarbons into carbon reactants, such as pressures in the range of 0.5 bar gauge pressure to 3 bar gauge pressure. Alternatively, 0.5 bar gauge pressure to 1 bar gauge pressure, 1 bar gauge pressure to 2 bar gauge pressure, 2 bar gauge pressure to 3 bar gauge pressure, or any range therebetween.

[0041] In embodiments where the hydrocarbon conversion unit includes plasma, the hydrocarbon conversion unit can operate at any residence time suitable for converting hydrocarbons into carbon reactants, such as a residence time in the range of 1 ms to 100 ms. Alternatively, any range of 1 ms to 10 ms, 10 ms to 50 ms, 50 ms to 100 ms or between, and efficient quenching to stop most of the reaction products as C2 intermediates.

[0042] The heat of reaction for the system can be supplied by plasma generated using a plasma torch (configured as a plasma jet or arc discharge). Both plasma torches and arc discharges convert electrical energy into heat, and they provide a way to reduce the CO2 footprint of carbon nanotube production methods. Plasma torches can be operated via direct current (DC) and alternating current (AC) or any of the plasma sources discussed above to convert electrical energy into heat. Both high-energy thermal plasma and microwave plasma torches can provide the required heat of reaction, and the plasma velocity enables short residence times in the hydrocarbon conversion steps.

[0043] The hydrocarbon conversion unit may also include a quench system configured to cool the product carbon reactants generated in the plasma. The quench system may include a heat exchanger, a quench tower, or any other device suitable for rapidly cooling the carbon reactants to retain the selectivity of the formed C2 and prevent the formation of amorphous carbon.

[0044] Figure 3AThis is an illustrative schematic diagram of the plasma torch configuration in a hydrocarbon conversion reactor. Figure 3A In the hydrocarbon conversion reactor 300, multiple plasma torches 302 are included, each generating plasma 304. During operation of the hydrocarbon conversion reactor 300, each plasma torch 302 can be individually controlled, for example, by adjusting the torch power or turning the torch on / off. Hydrocarbons 320 are introduced into the hydrocarbon conversion reactor 300, contacting the plasma 304 and converting the hydrocarbons 320 into carbon reactants 322, which are then extracted from the hydrocarbon conversion reactor 300.

[0045] Figure 3B This is an illustrative schematic diagram of the arc plasma configuration in a hydrocarbon conversion reactor. Figure 3B In the hydrocarbon conversion reactor 306, multiple plasma electrodes 308 are included, which generate arc plasma 310. During operation of the hydrocarbon conversion reactor 306, the multiple plasma electrodes 308 can be individually controlled, for example, by adjusting the electrode power or turning the electrodes on / off. Hydrocarbon 320 is introduced into the hydrocarbon conversion reactor 306, which contacts the arc plasma 310 and converts the hydrocarbon 320 into carbon reactant 322, which is then extracted from the hydrocarbon conversion reactor 306.

[0046] Figure 3C This is an illustrative schematic diagram of the configuration of a hydrocarbon conversion reactor. Scaling up production may include using multiple hydrocarbon conversion reactors 312 connected in parallel. Hydrocarbons 320 are introduced into each hydrocarbon conversion reactor 312, where they are converted into carbon reactants 322, which are then extracted from each hydrocarbon conversion reactor 312.

[0047] In another embodiment, the hydrocarbon conversion unit includes a shift reactor configured to convert hydrocarbons into carbon reactants. The shift reactor operates by alternating short-term endothermic cracking reactions followed by combustion of deposited coke to provide the heat of reaction required for subsequent cracking in the cycle. Suitable shift reactors are disclosed in U.S. Patent No. 9,809,506 (Hershkowitz et al.), which is incorporated herein by reference in its entirety.

[0048] In the implementation scheme, the flow-direction shift reactor includes (i) at least one thermal mass and (ii) a first zone, a second zone, and a reaction zone between the first and second zones. Hydrocarbon feed can be transferred from the first zone to the second zone of the reactor, with heat transferred from the thermal mass located near the first zone to the pyrolysis feed as the pyrolysis feed passes through the reactor. The hydrocarbon feed can be transferred near the thermal mass at a peak pyrolysis temperature of 850°C–1200°C in the reaction zone and a hydrocarbon partial pressure of ≥48 kPa absolute to convert ≥10.0% by weight of hydrocarbons in the hydrocarbon feed into carbon reactant products. The carbon reactant products may include C2 unsaturated compounds having an ethylene:acetylene molar ratio of ≥1:1. The process can be quenched by transferring heat from the pyrolysis products to the thermal mass located near the second zone to cool the carbon reactant products to a temperature below the peak pyrolysis temperature. The thermal mass located near the first zone and the thermal mass located near the second zone may be regions of the same thermal mass or alternatively, they may be separate thermal mass units.

[0049] The reactor can be a shift reactor, during which a hydrocarbon feed is transferred to the shift reactor to produce pyrolysis products during a first time interval. During a second time interval, a combustion feed (containing hydrocarbon fuel and oxidant) is transferred to the shift reactor. Heat can be transferred from the second zone to the combustion feed, and the heated combustion feed can undergo an exothermic reaction (typically near the reaction zone) to produce combustion products and heat. Heat can be transferred from the combustion reaction to the first zone to cool the combustion products. A heat storage body located in the zone receives, stores, and releases the transferred heat.

[0050] In some respects, the residence time of the hydrocarbon feed in the shift reactor is ≤1.0 second, less than ≤0.500 seconds, or less than ≤0.100 seconds. Alternatively or additionally, the hydrocarbon feed may pass through the shift reactor with a total gas residence time of ≤0.0500 seconds, and the regenerator in the reaction zone is above 800°C.

[0051] In other respects, the hydrocarbon feed may contain ≥50% by weight ethane based on the total weight of the hydrocarbons in the hydrocarbon feed. The carbon reactant products may contain unreacted hydrocarbons from the hydrocarbon feed. The pyrolysis feed may also contain a diluent, and the pyrolysis products may contain unreacted diluent.

[0052] In other respects, the hydrocarbon feed can be passed through the shift reactor at a peak pyrolysis temperature in the range of 900°C–1100°C and a hydrocarbon partial pressure of ≥137 kPa absolute. In these or alternative respects, the hydrocarbon feed can be passed through the shift reactor with a total gas residence time of ≤0.75 seconds in the shift reactor to convert ≥50.0% by weight of the hydrocarbons in the pyrolysis feed to C2 unsaturated hydrocarbons.

[0053] In the implementation scheme, the shift reactor is operated by providing ethane and / or C...3+ A hydrocarbon feedstock is provided, comprising at least one heat storage body and a flow-shifting reactor having a first zone, a second zone, and a reaction zone between the first and second zones; the hydrocarbon feedstock is transferred from the first zone to the second zone of the reactor; as the pyrolysis feedstock is transferred toward the heat storage body, heat in the first zone is transferred from the heat storage body to the hydrocarbon feedstock; the pyrolysis feedstock is transferred toward the heat storage body in the reaction zone to expose the pyrolysis feedstock to a peak pyrolysis temperature in the range of 850°C–1200°C, at a hydrocarbon partial pressure of ≥48 kPa absolute, to convert ≥10.0% by weight of hydrocarbons in the hydrocarbon feedstock into carbon reactants containing C2 unsaturated compounds, wherein the C2 unsaturated compounds, and heat in the second zone is transferred from the pyrolysis products to the heat storage body to cool the pyrolysis products to a temperature below the peak pyrolysis temperature.

[0054] Catalyst production unit

[0055] In the catalyst generation unit, a metal or metal alloy is converted into an active catalyst via plasma volatilization. The volatilization of the metal and / or metal alloy can be carried out using any suitable plasma. In some embodiments, the plasma can be generated by any suitable type of plasma generator, including but not limited to DC plasma generators, RF plasma generators, microwave plasma generators, inductively coupled plasma generators, arc plasma generators, or combinations thereof. In various embodiments, the plasma generator generates plasma in various ways. For example, plasma is generated by arc discharge between two electrodes, and a metal and / or metal alloy is fed into the resulting plasma. Alternatively, or additionally, the metal and / or metal alloy may constitute the electrode to be ablated itself. Alternatively, or additionally, the metal and / or metal alloy is fed into a plasma torch maintained by a microwave plasma generator. In some embodiments, the plasma temperature is 4,000K-7,000K or any temperature suitable for volatilizing the metal alloy. Alternatively, 4,000K-5,000K, 5,000K-6,000K, 6,000K-7,000K, or any range therein.

[0056] In embodiments, the metal and / or metal alloy is formed from metals including, but not limited to, elemental forms and alloys of iron, nickel, cobalt, manganese, tungsten, and molybdenum. In embodiments, the metal alloy comprises one or more of these metals in an amount ranging from 1 wt% to 99 wt% or any value between therewith. Some specific examples of suitable metal alloys include iron / nickel alloy compositions containing 10 wt% to 25 wt% nickel, with the balance comprising iron and trace impurities (if present). Further specific examples of suitable metal alloys include iron / cobalt alloy compositions containing 12 wt% to 25 wt% cobalt, with the balance comprising iron and trace impurities (if present). Further specific examples of suitable metal alloys include iron / cobalt / manganese alloy compositions containing 12 wt% to 25 wt% cobalt and 10 wt% to 25 wt% manganese, with the balance comprising iron and trace impurities (if present). Further specific examples of suitable metal alloys include iron / molybdenum alloy compositions containing 10 wt% to 25 wt% molybdenum, with the balance comprising iron and trace impurities (if present).

[0057] In the embodiments, metals and / or metal alloys are disposed on the catalyst support, including but not limited to activated carbon, alumina, zeolite, silica, and / or titanium dioxide. In the embodiments, the metal alloy is disposed on the support in an amount of 1% to 99% by weight of the total weight of the metal alloy and the support. Alternatively, 1% to 10% by weight, 10% to 20% by weight, 20% to 50% by weight, 50% to 99% by weight, or any range therebetween.

[0058] In some embodiments, the metal and / or metal alloy is introduced into the plasma by any suitable means. In some embodiments, the metal and / or metal alloy is introduced into the plasma in liquid or solid form. In some embodiments, the metal and / or metal alloy is in powder form, granular form, as an electrode within the plasma, as a solid element such as a rod or wire, or a combination thereof. In other embodiments, the metal and / or metal alloy is introduced into the plasma in liquid form, such as molten metal.

[0059] Plasma volatilization of metal alloys forms active catalysts (MA) as nanoparticle catalysts in the aerosol state. In this implementation, the FC-CVD reactor is directly connected to the plasma, and the FC-CVD reactor is at a sufficiently low temperature to allow the volatile metal alloys to coalesce to form an active catalyst (MA). The nanoparticles are operated at a specific temperature. In this embodiment, the active catalyst (MA) is used. The particle size has a range of 1 nm to 50 nm. Alternatively, it may be 1 nm to 15 nm, 10 nm to 20 nm, 15 nm to 25 nm, 25 nm to 35 nm, 35 nm to 50 nm, or any range therebetween. In an embodiment, the plasma volatilization of the metal alloy forms an aerosol with a metal alloy concentration suitable for the formation of carbon nanotubes, for example, a metal alloy concentration of 1,000 μg / m³. 3 -100,000 μg / m 3 Optionally, 1,000 μg / m 3 -5,000 μg / m 3 5,000 μg / m 3 -10,000 μg / m 3 10,000 μg / m 3 -100,000 μg / m 3 , or any range in between.

[0060] In the implementation plan, a carrier gas and plasma are used to transport the active catalyst (MA). Particles. Carrier gases include, but are not limited to, rare gases such as argon, as well as nitrogen, helium and / or hydrogen.

[0061] FC-CVD reactor

[0062] In one embodiment, carbon reactants and an active catalyst are contacted in the reaction zone within the FC-CVD reactor, wherein the reaction zone operates under conditions where carbon reactants form carbon nanotubes on the active catalyst. In another embodiment, the feed to the FC-CVD reactor includes an active catalyst (MA). The feed to the FC-CVD reactor comprises carbon reactants and hydrogen. In another embodiment, the feed to the FC-CVD reactor comprises carbon reactants and hydrogen in a molar ratio of 1:1 to 1:50. Alternatively, the feed to the FC-CVD reactor comprises carbon reactants and hydrogen in amounts of 1:1 to 1:10, 1:10 to 1:25, 1:25 to 1:50, or any range therebetween. In another embodiment, the feed to the FC-CVD reactor also includes an inert co-feed, such as argon, nitrogen, and / or helium. In embodiments using a co-feed, the feed to the FC-CVD reactor comprises carbon reactants and an inert co-feed in a molar ratio of carbon reactants to co-feed of 1:3 to 1:10.

[0063] Optionally, when using a hydrogen-containing gas, the hydrogen-containing gas may also contain CO so that the hydrogen-containing gas corresponds to a synthesis gas. The synthesis gas may also optionally contain water and / or CO2.

[0064] In the implementation scheme, the feed to the FC-CVD reactor contains a sulfur source such as elemental sulfur and / or thiophene, in an amount of 0.001 mol% to 5.0 mol% of the amount of methane or other carbon reactants introduced into the reactor.

[0065] One or more components of the feed gas to the FC-CVD reactor can be preheated before being introduced into the reactor. One option for heating the gas flow is to use multiple heating stages. For example, the initial heating stage could correspond to a furnace used to heat the reactor, such as a furnace of the type used in steam cracking reaction systems. Conventional furnaces can be used to heat one or more components of the FC-CVD feed gas to temperatures of 1000°C or higher. Additional heating can be provided to further increase the temperature to 1100°C or higher, or 1200°C or higher, through various methods. One option is to use electric heating to heat the walls of the duct containing the gas flow. Despite the large reactor size, the duct used to preheat the gas flow before it enters the reactor can be appropriately sized to allow for efficient heat transfer. Other options may include induction heating or plasma heating. Another option is to include electric heating elements within the gas flow.

[0066] In some implementations, carbon reactants and active catalysts (MA) Mixing before introduction into the FC-CVD reactor and / or mixing in the reactor by introducing the feed components into the FC-CVD reactor. In other embodiments, the carbon reactants and the active catalyst (MA) are introduced at a downstream (relative to the flow direction) location in the reactor. At least one of the following can be introduced into the reactor. Introducing different portions of the gas flow at different locations within the reactor can help manage the reaction profile within the reactor. For example, by adding a portion of an active catalyst or carbon reactant at a downstream location in the reactor, the amount of reactant available in each section of the reactor can be controlled, thereby further reducing the likelihood of early carbon nanotube formation and / or early carbon deposition on the reactor surface.

[0067] The systems and methods disclosed herein for producing carbon nanotubes allow for thorough mixing of carbon reactants and an active catalyst. The plasma-generated active catalyst allows turbulent flow to produce carbon nanoscale structures, wherein the flow through the FC-CVD reactor has a Reynolds number greater than 5,000. In embodiments, the flow through the FC-CVD reactor has a Reynolds number in the range of 5,000–20,000. Alternatively, the flow through the FC-CVD reactor has a Reynolds number in the ranges of 5,000–8,000, 5,000–10,000, 5,000–15,000, or 5,000–20,000.

[0068] In this embodiment, the gas velocity within the reactor can be relatively high. The velocity within the reactor determines the residence time of the reactants in the pyrolysis zone. By using a combination of high velocity with low concentrations of hydrocarbons in the total flow rate and temperatures above 1000°C, high levels of conversion can be achieved while maintaining low residence times. Low residence times in the pyrolysis zone of the reactor reduce or minimize carbon deposition on the reactor surfaces before the products reach the zone for carbon nanotube formation. In this embodiment, the average residence time in the reactor can be from 0.05 seconds to 5.0 seconds, or from 0.05 seconds to 1.0 seconds, or from 0.1 seconds to 5.0 seconds, or any range therein.

[0069] In one embodiment, the FC-CVD reactor operates at a temperature ranging from 800°C to 1600°C. Alternatively, it operates at 800°C to 1000°C, 1000°C to 1200°C, 1200°C to 1600°C, or any range therebetween. In one embodiment, the FC-CVD reactor operates at a gauge pressure ranging from 50 kPa to 200 kPa. In one embodiment, the FC-CVD reactor operates at a gauge pressure of atmospheric pressure (101.325 kPa). Alternatively, it operates at a gauge pressure ranging from 50 kPa to 100 kPa, 100 kPa to 150 kPa, 150 kPa to 200 kPa, or any range therebetween.

[0070] Example Configuration

[0071] Figure 2 This is an illustrative schematic diagram of an FC-CVD method 200 according to certain embodiments of this disclosure. Although in Figure 2 Only the elements necessary for understanding the main operations of the FC-CVD method 200 are shown, but those skilled in the art will readily understand that additional elements and / or steps can be integrated without diminishing the disclosed embodiments. Figure 2The FC-CVD method 200 begins by introducing a carrier gas stream 202 into a plasma 204. In the plasma 204, a metal alloy is volatilized by the plasma to form a metal aerosol. This metal alloy can be in any form, such as powder, granules, as an electrode within the plasma, as a solid element such as a rod or wire, or as a metal solution in an aqueous carrier. The carrier gas is combined with the metal aerosol to form an activated catalyst stream 238. In one embodiment, the activated catalyst stream 238 is combined with a recycle stream 222 and a carbon reactant stream 234 to form a reactor feed stream 212. The hydrocarbon stream 224 contains carbon reactants for the production of carbon nanotubes. The hydrocarbon stream 224 is introduced into a hydrocarbon conversion unit 226, where the hydrocarbon components of the hydrocarbon stream 224 are reacted to form the carbon reactant stream 234. In one embodiment, a portion of the carbon reactant stream may be divided into stream 228 and introduced into the FC-CVD reactor 206 at one or more points along the reactor. In FC-CVD reactor 206, the components introduced into the FC-CVD reactor are reacted to form carbon nanotubes. Carbon nanotubes can be removed from FC-CVD reactor 206 via feed stream 230 and transferred to collection unit 210. Collection unit 210 may include a spool-type collection unit or any other type suitable for collecting carbon nanotubes to produce product nanotube feed stream 232. Reactor effluent stream 214, which may contain unreacted components of the feed into FC-CVD reactor 206, is extracted from FC-CVD reactor 206 and introduced into separation unit 208. Separation unit 208 includes means for separating the components of reactor effluent stream 214 into recycle stream 218 and waste stream 216. Recycle stream 218 may contain components of reactor effluent stream 214, such as hydrogen, carrier gas, unreacted carbon reactants, and other components that can be reacted to form additional carbon nanotube products. The recirculation stream 218 can be heated in the heat exchanger 220 and can optionally be divided into a recirculation stream 222 for combination with the activated catalyst stream 238 and a recirculation stream 236 for introduction into the FC-CVD reactor 206.

[0072] Additional implementation plan

[0073] Therefore, this disclosure provides systems and methods for producing carbon nanoscale structures such as carbon nanotubes or carbon nanofibers, and more particularly, discloses systems and methods for producing carbon nanoscale structures using plasma-generated active catalysts and carbon reactants. These methods and systems may include any of the various features disclosed herein, including one or more of the following embodiments.

[0074] Implementation Scheme 1. A method for forming carbon nanotubes, comprising: volatilizing a metal in a plasma to form an active catalyst; introducing a hydrocarbon feed stream containing methane into a hydrocarbon conversion unit and converting at least a portion of the methane into a carbon reactant comprising ethylene, acetylene, or a combination thereof; introducing the active catalyst and the carbon reactant into a floating catalyst chemical vapor deposition reactor, wherein the floating catalyst chemical vapor deposition reactor is operated under conditions suitable for carbon nanotube formation; and contacting the active catalyst and the carbon reactant in a reaction zone within the floating catalyst chemical vapor deposition reactor to form carbon nanotubes on the active catalyst.

[0075] Implementation Scheme 2. The method according to Implementation Scheme 1, wherein the metal comprises a metal alloy, the metal alloy comprising at least two metals selected from iron, nickel, cobalt, manganese, tungsten, molybdenum and combinations thereof.

[0076] Implementation Scheme 3. The method according to any one of Implementation Schemes 1-2, wherein the metal comprises an elemental metal selected from iron, nickel, cobalt, manganese, tungsten and molybdenum.

[0077] Implementation Scheme 4. The method according to any one of Implementation Schemes 1-3, wherein the active catalyst comprises nanoparticles with a size of about 1 nm to about 50 nm.

[0078] Implementation Scheme 5. The method according to any one of Implementation Schemes 1-4, wherein the hydrocarbon conversion unit includes a plasma generator configured to generate a second plasma, wherein the hydrocarbon stream is contacted with the second plasma such that the plasma heats the hydrocarbon stream and reacts at least a portion of the hydrocarbons in the hydrocarbon stream to form the carbon reactant.

[0079] Implementation Scheme 6. The method according to any one of Implementation Schemes 1-5 further includes rapidly cooling the carbon reactant after contact with the second plasma.

[0080] Implementation Scheme 7. The method according to any one of Implementation Schemes 1-6, wherein the second plasma is generated by at least one generator selected from DC plasma generator, RF plasma generator, microwave plasma generator, inductively coupled plasma generator, arc plasma generator, and combinations thereof.

[0081] Implementation Scheme 8. The method according to any one of Implementation Schemes 1-7, wherein the hydrocarbon conversion unit includes a flow-shifting reactor, wherein the flow-shifting reactor includes a first zone, a second zone, and a reaction zone between the first zone and the second zone, and wherein the method further includes: transferring a hydrocarbon feed stream from the first zone to the second zone of the flow-shifting reactor; transferring heat from the heat storage body in the first zone to the hydrocarbon feed stream as the hydrocarbon feed stream is transferred toward the heat storage body; transferring the hydrocarbon feed stream toward the heat storage body in the reaction zone to expose the hydrocarbon feed stream to a peak pyrolysis temperature in the range of about 850°C to about 1200°C, at a hydrocarbon partial pressure of ≥48 kPa absolute, thereby forming carbon reactants; and transferring heat from the carbon reactants in the second zone to the heat storage body to cool the carbon reactants to a temperature below the peak pyrolysis temperature.

[0082] Implementation Scheme 9. The method according to any one of Implementation Schemes 1-8, wherein the metal is introduced into the plasma as a powder, as granules, as an electrode within the plasma, as a rod, as a wire, or a combination thereof.

[0083] Implementation Scheme 10. The method according to any one of Implementation Schemes 1-9, wherein the metal is introduced into the plasma as a metal solution in the form of molten metal and / or dissolved in a carrier fluid.

[0084] Implementation Scheme 11. The method according to any one of Implementation Schemes 1-10 further includes introducing a carrier gas into the plasma, and wherein the feed into the floating catalyst chemical vapor deposition reactor comprises an activated metal catalyst suspended in the carrier gas.

[0085] Implementation Scheme 12. The method according to any one of Implementation Schemes 1-11, wherein the carrier gas comprises at least one gas selected from rare gases, hydrogen, helium, and combinations thereof.

[0086] Implementation Scheme 13. The method according to any one of Implementation Schemes 1-12, wherein the feed into the floating catalyst chemical vapor deposition reactor comprises about 1% to about 10% by volume of carbon reactants, about 20% to about 50% by volume of hydrogen co-feed, and about 50% to about 80% by volume of carrier gas.

[0087] Implementation Scheme 14. The method according to any one of Implementation Schemes 1-13, wherein the active catalyst and the carbon reactant flow turbulently through a floating catalyst chemical vapor deposition reactor.

[0088] Implementation Scheme 15. The method according to any one of Implementation Schemes 1-14, wherein the Reynolds number of the active catalyst and carbon source flowing through the floating catalyst chemical vapor deposition reactor is in the range of about 5,000 to about 20,000.

[0089] Implementation Scheme 16. A reaction system for forming carbon nanotubes, comprising: a catalyst generating unit including: a metal alloy; and a plasma generator configured to generate plasma, wherein the metal alloy is disposed within the plasma such that the plasma causes the metal alloy to volatilize to form an active catalyst; a hydrocarbon source including methane; a hydrocarbon conversion unit configured to take the hydrocarbon source as input and convert at least a portion of the methane into a carbon reactant, the carbon reactant comprising ethylene, acetylene, or a combination thereof; and a floating catalyst chemical vapor deposition reactor including: a reaction zone; and inlets for the active catalyst and the carbon reactant, wherein the floating catalyst chemical vapor deposition reactor is fluidly connected to the catalyst generating unit and the hydrocarbon conversion unit such that the active catalyst and the carbon reactant are in contact in the reaction zone.

[0090] Implementation Scheme 17. The reaction system according to Implementation Scheme 16, wherein the hydrocarbon conversion unit includes a plasma generator configured to generate a second plasma, wherein the hydrocarbon source is in contact with the second plasma such that the plasma heats the hydrocarbon feed stream and reacts at least a portion of the hydrocarbons in the hydrocarbon source to form the carbon reactant.

[0091] Implementation Scheme 18. The reaction system according to any one of Implementation Schemes 1-17, wherein the plasma generator is at least one selected from DC plasma generators, RF plasma generators, microwave plasma generators, inductively coupled plasma generators, arc plasma generators, and combinations thereof.

[0092] Implementation Scheme 19. The reaction system according to any one of Implementation Schemes 1-18, wherein the hydrocarbon conversion unit includes a flow-shifting reactor, wherein the flow-shifting reactor includes a first zone, a second zone, and a reaction zone located between the first zone and the second zone.

[0093] Implementation Scheme 20. The reaction system according to any one of Implementation Schemes 1-19, wherein the flow-shifting reactor is configured to: transfer a hydrocarbon source from a first zone to a second zone of the flow-shifting reactor; transfer heat from the heat storage body in the first zone to the hydrocarbon source as the hydrocarbon source approaches the heat storage body; transfer the hydrocarbon stream to the heat storage body in the reaction zone to expose the hydrocarbon stream to the peak pyrolysis temperature; and transfer heat from the carbon reactants in the second zone to the heat storage body to cool the carbon reactants to a temperature below the peak pyrolysis temperature.

[0094] Although this disclosure has been described with reference to various embodiments and examples, those skilled in the art who benefit from this disclosure will understand that other embodiments can be devised without departing from the scope and spirit of the disclosure as set forth herein. While individual embodiments have been discussed, this disclosure covers all combinations of all such embodiments.

[0095] Although compositions, methods, and processes are described herein using the terms “comprising,” “containing,” “having,” or “including” various components or steps, compositions and methods may also be described as “consistently composed of various components and steps” or “comprises various components and steps.” Unless otherwise stated, the phrases “consistently composed of” and “comprises of” do not exclude the presence of other steps, elements, or materials, whether or not specifically mentioned in this specification, provided that such steps, elements, or materials do not affect the essential and novel features of this disclosure. Furthermore, they do not exclude impurities and variations commonly associated with the elements and materials used.

[0096] All numerical values ​​in the detailed description are modified with “approximate” indicators and take into account experimental errors and variations that would be expected by a person skilled in the art.

[0097] As used in this disclosure and the following claims, the terms “a”, “an”, and any grammatical variations mean one or more. References to steps, elements, materials, etc., include one step, one element, and one material, as well as one or more steps, one or more elements, and one or more materials.

[0098] For those skilled in the art based on the foregoing description, many changes, modifications and variations will be readily apparent without departing from the spirit or scope of this disclosure, and when lower limits are listed herein, they include any range from any lower limit to any upper limit.

Claims

1. A method for forming carbon nanotubes, comprising: Metals are volatilized in plasma to form active catalysts; A hydrocarbon feed stream containing methane is introduced into a hydrocarbon conversion unit and at least a portion of the methane is converted into carbon reactants, which contain ethylene, acetylene, or a combination thereof. The active catalyst and the carbon reactant are introduced into a floating catalyst chemical vapor deposition reactor, wherein the floating catalyst chemical vapor deposition reactor is operated under conditions suitable for carbon nanotube formation. and The active catalyst and the carbon reactants are brought into contact in the reaction zone of a floating catalyst chemical vapor deposition reactor to form carbon nanotubes on the active catalyst.

2. The method of claim 1, wherein the metal comprises a metal alloy, the metal alloy comprising at least two metals selected from iron, nickel, cobalt, manganese, tungsten, molybdenum and combinations thereof.

3. The method according to claim 1, wherein the metal comprises an elemental metal selected from iron, nickel, cobalt, manganese, tungsten and molybdenum.

4. The method according to claim 1, wherein the active catalyst comprises nanoparticles with a size of about 1 nm to about 50 nm.

5. The method of claim 1, wherein the hydrocarbon conversion unit includes a plasma generator configured to generate a second plasma, wherein the hydrocarbon stream is contacted with the second plasma such that the plasma heats the hydrocarbon stream and reacts at least a portion of the hydrocarbons in the hydrocarbon stream to form the carbon reactant.

6. The method of claim 5, further comprising rapidly cooling the carbon reactant after contact with the second plasma.

7. The method of claim 5, wherein the second plasma is generated by at least one generator selected from DC plasma generators, RF plasma generators, microwave plasma generators, inductively coupled plasma generators, arc plasma generators, and combinations thereof.

8. The method of claim 1, wherein the hydrocarbon conversion unit comprises a flow-shift reactor, wherein the flow-shift reactor comprises a first zone, a second zone, and a reaction zone between the first zone and the second zone, and wherein the method further comprises: The hydrocarbon feed stream is transferred from the first zone of the flow shift reactor to the second zone; As the hydrocarbon stream approaches the heat storage body, heat in the first zone is transferred from the heat storage body to the hydrocarbon stream. The hydrocarbon stream is brought close to the heat storage body in the reaction zone, exposing it to a peak pyrolysis temperature in the range of approximately 850°C to approximately 1200°C, under a hydrocarbon partial pressure of ≥48 kPa absolute, thereby forming carbon reactants; and Heat in the second zone is transferred from the carbon reactants to the heat storage body to cool the carbon reactants to a temperature below the peak pyrolysis temperature.

9. The method of claim 1, wherein the metal is introduced into the plasma as a powder, as particles, as an electrode within the plasma, as a rod, as a wire, or a combination thereof.

10. The method of claim 1, wherein the metal is introduced into the plasma as a metal solution in molten metal form and / or dissolved in a carrier fluid.

11. The method of claim 1, further comprising introducing a carrier gas into the plasma, and wherein the feed into the floating catalyst chemical vapor deposition reactor comprises an activated metal catalyst suspended in the carrier gas.

12. The method of claim 11, wherein the carrier gas comprises at least one gas selected from rare gases, hydrogen, helium, and combinations thereof.

13. The method of claim 1, wherein the feed into the floating catalyst chemical vapor deposition reactor comprises about 1% to about 10% by volume of carbon reactants, about 20% to about 50% by volume of hydrogen co-feed, and about 50% to about 80% by volume of carrier gas.

14. The method of claim 1, wherein the active catalyst and the carbon reactant flow turbulently through a floating catalyst chemical vapor deposition reactor.

15. The method of claim 14, wherein the Reynolds number of the active catalyst and carbon source flowing through the floating catalyst chemical vapor deposition reactor is in the range of about 5,000 to about 20,000.

16. A reaction system for forming carbon nanotubes, comprising: The catalyst generating unit includes: Metal alloys; and A plasma generator configured to generate plasma, wherein the metal alloy is disposed within the plasma such that the plasma causes the metal alloy to volatilize to form an active catalyst; Hydrocarbon sources, including methane; A hydrocarbon conversion unit, wherein the hydrocarbon conversion unit is configured to take a hydrocarbon source as input and convert at least a portion of methane into carbon reactants, said carbon reactants comprising ethylene, acetylene, or a combination thereof; and A floating catalyst chemical vapor deposition reactor, comprising: Reaction zone; and The inlet for the active catalyst and the carbon reactants. The floating catalyst chemical vapor deposition reactor is fluidly connected to the catalyst generation unit and the hydrocarbon conversion unit, such that the active catalyst and the carbon reactants come into contact in the reaction zone.

17. The reaction system of claim 16, wherein the hydrocarbon conversion unit includes a plasma generator configured to generate a second plasma, wherein the hydrocarbon source is contacted with the second plasma such that the plasma heats the hydrocarbon stream and reacts at least a portion of the hydrocarbons in the hydrocarbon source to form the carbon reactant.

18. The reaction system of claim 17, wherein the plasma generator is at least one selected from DC plasma generators, RF plasma generators, microwave plasma generators, inductively coupled plasma generators, arc plasma generators, and combinations thereof.

19. The reaction system of claim 16, wherein the hydrocarbon conversion unit comprises a flow-shifting reactor, wherein the flow-shifting reactor comprises a first zone, a second zone, and a reaction zone located between the first zone and the second zone.

20. The reaction system of claim 19, wherein the flow-shifting reactor is configured as follows: This allows the hydrocarbon source to be transferred from the first zone of the shift reactor to the second zone; As the hydrocarbon source approaches the heat storage body, the heat in the first zone is transferred from the heat storage body to the hydrocarbon source. The hydrocarbon stream is brought close to the heat storage body in the reaction zone to expose it to the peak pyrolysis temperature; and Heat in the second zone is transferred from the carbon reactants to the heat storage body to cool the carbon reactants to a temperature below the peak pyrolysis temperature.

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