Catalyst for manufacturing carbon nanotubes

Abstract

A method of forming carbon nanotubes may include: volatilizing a metal alloy in a plasma to form an active catalyst; flowing the active catalyst and the carbon source into a floating catalyst chemical vapor deposition reactor; and pyrolyzing at least a portion of the carbon source on the active catalyst in a pyrolysis zone in the floating catalyst chemical vapor deposition reactor to form carbon nanotubes on the active catalyst.

Description

TECHNICAL FIELD

[0001] The present application relates to systems and methods for producing carbon nanoscale structures such as carbon nanotubes or carbon nanofibers. BACKGROUND

[0002] Floating catalyst chemical vapor deposition (FC-CVD) is a method for producing carbon nanotubes (CNTs). A typical FC-CVD process involves introducing a feed comprising a pre-catalyst and a carbon source into a tubular reactor at a relatively high temperature of about 1,000 °C or higher. In the tubular reactor, the pre-catalyst is converted to an active catalyst and the carbon source is decomposed to produce reactive carbon intermediates that further react with the catalyst to form carbon nanotubes. The pre-catalyst is typically an organometallic iron source, such as ferrocene.

[0003] Attempts to scale up conventional reactors for carbon nanotube production present various challenges. First, as the diameter of the reactor increases, it becomes increasingly difficult, if not physically impossible, to transfer enough heat through the reactor wall to maintain the temperature needed to thermally decompose the pre-catalyst to form an active catalyst. Additionally, the thermal decomposition temperature of a particular pre-catalyst and the reaction temperature needed to produce carbon nanotubes can be substantially different, requiring additional quench gas and process steps, resulting in a more complex reactor design. For example, attempting to cool the gas stream in the reactor after the active catalyst is formed can result in the catalyst surface temperature becoming too cool to effectively catalyze carbon nanotube formation. Furthermore, when the pre-catalyst decomposes, iron (or other metal) from the catalyst precursor tends to deposit on the walls of the reactor. This can result in a loss of 50 mol% or more of the metal from the pre-catalyst. Additionally, after this metal deposition begins, coke formation is also observed on the walls of conventional reactors. Deposition occurs because when the pre-catalyst is decomposed at temperatures typically between 700 °C and 1000 °C, the resulting metal has a higher phase stability as an atom deposited on a surface rather than remaining in the gas phase. As a result, when the pre-catalyst is heated through the temperature range of 700 °C to 1000 °C, deposition of the metal on the exposed surface can occur. This deposition of the metal can continue up to temperatures higher than 1000 °C where the metal atom has a higher phase stability in the gas phase. In conventional FC-CVD reactors, a significant amount of metal deposition can be deposited on the reactor walls, thereby reducing or minimizing the amount of active catalyst formed.

[0004] Accordingly, scaling up of FC-CVD processes is hindered by the high cost and low utilization efficiency of the pre-catalyst. Only a small fraction of the pre-catalyst is activated in FC-CVD processes, which requires a relatively high catalyst feed rate, long reactor residence times, and large reactor volumes. SUMMARY

[0006] An exemplary method of forming carbon nanotubes is disclosed herein, the method comprising: volatilizing a metal alloy in a plasma to form an active catalyst; flowing the active catalyst and a carbon source into a floating catalyst chemical vapor deposition reactor; and pyrolyzing at least a portion of the carbon source on the active catalyst in a pyrolysis zone in the floating catalyst chemical vapor deposition reactor to form carbon nanotubes on the active catalyst.

[0007] A reaction system for forming carbon nanotubes is further disclosed herein, the reaction system comprising: a carbon source; a floating catalyst chemical vapor deposition reactor, the reactor comprising: a pyrolysis zone; an inlet for the carbon source to flow into the pyrolysis zone; and a heater configured to heat the pyrolysis zone to a pyrolysis temperature, wherein the floating catalyst chemical vapor deposition reactor is configured to pyrolyze the carbon source in the pyrolysis zone to produce pyrolyzed carbon; a metal alloy; and a plasma generator configured to generate a plasma, wherein the metal alloy is disposed within the plasma such that the plasma volatilizes the metal alloy to form an active catalyst; wherein the plasma generator and the floating catalyst chemical vapor deposition reactor are fluidly coupled such that the active catalyst and the pyrolyzed carbon contact in the pyrolysis zone.

[0008] These and other features and attributes of the methods and systems disclosed herein, as well as the advantages thereof over prior solutions, will become more fully apparent in light of the following detailed description.

[0009] BRIEF DESCRIPTION OF DRAWINGS

[0010] To assist a person of ordinary skill in the relevant art in making and using the subject matter of the present application, reference is made to the accompanying drawings, in which:

[0011] Figure 1 is an illustrative depiction of an FC-CVD method according to certain embodiments of the disclosure herein.

[0012] Figure 2 is a scanning electron microscope micrograph of carbon nanotubes produced according to certain embodiments of the disclosure herein.

[0013] Figure 3 is a scanning electron microscope micrograph of carbon nanotubes produced according to certain embodiments of the disclosure herein.

[0014] Figure 4 is a scanning electron microscope micrograph of carbon nanotubes produced according to certain embodiments of the disclosure herein.

[0015] Figure 5 is a scanning electron microscope micrograph of carbon nanotubes produced according to certain embodiments of the disclosure herein.

[0016] Figure 6 is a scanning electron microscope micrograph of carbon nanotubes produced according to certain embodiments of the disclosure.

[0017] Figure 7 is a scanning electron microscope micrograph of carbon nanotubes produced according to certain embodiments of the disclosure.

[0018] Figure 8 is a scanning electron microscope micrograph of carbon nanotubes produced according to certain embodiments of the disclosure.

[0019] Figure 9 is a scanning electron microscope micrograph of carbon nanotubes produced according to certain embodiments of the disclosure.

[0020] Figure 10 is a plot of experimental results for carbon nanotubes produced according to certain embodiments of the disclosure.

[0021] Figure 11 is a bar graph of experimental results for carbon nanotubes produced according to certain embodiments of the disclosure.

[0022] DETAILED DESCRIPTION

[0023] Disclosed herein are systems and methods for producing carbon nanoscale structures such as carbon nanotubes or carbon nanofibers, and more specifically, systems and methods for producing carbon nanoscale structures using an active catalyst generated by a plasma produced from a metal alloy.

[0024] DEFINITIONS

[0025] The words and phrases used herein should be understood and interpreted to have a meaning that is consistent with the understanding of those words and phrases by those of ordinary skill in the relevant art. The consistent use of a term or phrase in this document is not intended to imply a special definition of the term or phrase that is different from the ordinary and customary meaning as understood by those of ordinary skill in the art. In the event that a term or phrase is intended to have a special meaning (i.e., a meaning other than the broadest meaning understood by those of ordinary skill in the art), such special or clarified definition will be set forth explicitly in the specification in definition form, which provides the special or clarified definition for the term or phrase.

[0026] For example, the following discussion contains a non-exhaustive list of definitions for several specific terms used in the disclosure (other terms can be defined or clarified in definition form elsewhere herein). These definitions are intended to clarify the meaning of the terms used herein. It is believed that these terms are used in a manner consistent with their ordinary meanings, but the definitions are nevertheless specified here for the sake of clarity.

[0027] Carbon fibers, nanofibers, and nanotubes are allotropes of carbon having a cylindrical nanostructure. Carbon nanofibers and nanotubes are members of the fullerene family of structures, which includes spherical carbon spheres known as "fullerenes." The walls of carbon nanotubes are formed from sheets of carbon in a graphene structure. As used herein, nanotubes include single-walled nanotubes 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.

[0028] FC-CVD method

[0029] As noted above, there are several challenges to scaling up floating catalyst chemical vapor deposition (FC-CVD) processes to produce carbon nanotubes. Conventional FC-CVD processes for producing carbon nanotubes include forming an active catalyst in situ within the FC-CVD reactor by thermal decomposition of a pre-catalyst to form an active catalyst. Commonly used pre-catalysts include compounds containing iron, cobalt, and / or nickel, with some specific examples including Fe(CO)5and organometallic compounds such as ferrocene. The metal in the pre-catalyst is converted to an active metal catalyst.

[0030] Disclosed herein are systems and methods for producing carbon nanoscale structures, including carbon nanotubes, using plasma-generated active catalysts in a floating catalyst-chemical vapor deposition (FC-CVD) reactor. The methods disclosed herein utilize a variety of metals to produce active catalysts by directly vaporizing a variety of metals using plasma to form an active catalyst that can be directly fed into the FC-CVD reactor without additional quenching. The methods disclosed herein for producing carbon nanotubes in FC-CVD have several advantages over conventional methods of producing carbon nanotubes, including that the active catalyst can be produced directly from cheaper metal sources such as metal alloy samples. The disclosed methods have a higher elemental metal utilization compared to conventional FC-CVD methods, resulting in less catalyst needed per unit of carbon nanotubes produced. The active catalyst produced by the methods disclosed herein allows for increased rates of carbon nanotube production by reducing reactor residence times and facilitating reactor scaling to use reactor volume more efficiently. The active catalyst produced by the methods disclosed herein also has a smaller tendency to deposit on reactor walls. Additionally, the plasma vaporization step allows for fine control of catalyst morphology and particle size, giving additional process control variables to influence the physical properties of the carbon nanotubes produced and control coke formation.

[0031] Another advantage of the disclosed systems and methods for producing carbon nanotubes includes that the hydrocarbon source and active catalyst can be well mixed prior to introduction into the FC-CVD reactor. It is desirable to have a flow of the activated catalyst and hydrocarbon into the FC-CVD reactor that is well mixed such that the formation of carbon nanotubes is increased.

[0032] Conventional FC-CVD reactors require a mixing device that includes introducing turbulence into the hydrocarbon source and pre-catalyst to thoroughly mix the hydrocarbon source and pre-catalyst prior to the pre-catalyst decomposing into the active catalyst. However, by having a substantially laminar flow with little or no mixing, the efficient formation of carbon nanotubes at the product end of the reactor is facilitated. In smaller scale conventional FC-CVD reactors, the initial mixing of the reactants can be achieved in various ways such that the fluid is well mixed even with a reduced or minimized amount of turbulence in the fluid. In other words, the reactants can be mixed sufficiently in a small scale reactor while keeping the Reynolds number below 1,000, or even below 500. In contrast, in a relatively larger scale reactor, producing a fluid that is well mixed at the beginning of the reactor would result in a turbulent flow with a Reynolds number greater than 5,000. Thus, for larger scale conventional FC-CVD reactors, a device is needed to reduce the Reynolds number of the fluid to about 500 or lower, preferably to about 10, when the fluid reaches the product end of the reactor.

[0033] The systems and methods disclosed herein for producing carbon nanoscale structures allow for sufficient mixing of the hydrocarbon source and active catalyst and do not require additional reactor components to reduce the Reynolds number below 5,000. The plasma generated active catalyst allows for turbulent flow to produce carbon nanoscale structures where the fluid through the FC-CVD reactor has a Reynolds number greater than 5,000. In various embodiments, the fluid through the FC-CVD reactor has a Reynolds number ranging from 5,000 to 20,000. Alternatively, the fluid through the FC-CVD reactor has a Reynolds number ranging from 5,000 to 8,000, 5,000 to 10,000, 5,000 to 15,000, or 5,000 to 20,000.

[0034] The turbulent production of carbon nanoscale structures can have several advantages compared to conventional FC-CVD methods, including that the active catalyst and carbon source are mixed sufficiently within the FC-CVD reactor, the heat transfer in turbulent flow is much greater than in laminar flow, and carbon nanostructures with a relatively low level of entanglement can be produced.

[0035] The reactor system for carbon nanotube formation carries out at least three types of reactions. One reaction is the use of heat generated by the plasma to volatilize the metal alloy (MA) to form the active catalyst (MA ), as shown in Reaction 1:

[0036] Reaction 1

[0037] The second reaction is pyrolysis of a carbon source, such as methane, to provide H2and pyrolyzed carbon (C ) for forming carbon nanotubes, as shown in Reaction 2.

[0038] Reaction 2

[0039] The third reaction is the formation of carbon nanotubes by depositing pyrolyzed carbon (C ) on the active catalyst MA , as shown in Reaction 3. It should be noted that the term "catalyst" is used to describe the active catalyst (MA ) in that it facilitates the formation of carbon nanotubes by participating in the pyrolysis of the carbon source and allowing carbon nanotubes to form on the surface of the active catalyst. 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 to include materials that function in the manner of an FC-CVD catalyst.

[0040] Reaction 3

[0041] The volatilization of the metal alloy in Reaction 1 can be performed by any suitable plasma. In embodiments, the plasma can be generated by any suitable type of plasma generator, including but not limited to a DC plasma generator, an RF plasma generator, a microwave plasma generator, an inductively coupled plasma generator, an arc plasma generator, or combinations thereof. In various embodiments, the plasma generator generates a plasma by various means. For example, the plasma is generated by an arc discharge between two electrodes, and the metal alloy is fed into the resulting plasma. Alternatively or additionally, the metal alloy can constitute the electrodes themselves, which are ablated away. Alternatively or additionally, the metal alloy is fed into a plasma torch maintained by a microwave plasma generator. In embodiments, the temperature of the plasma is in the range of 4,000 K to 7,000 K, or any suitable temperature to volatilize the metal alloy. Alternatively, 4,000 k to 5,000 k, 5,000 k to 6,000 k, 6,000 k to 7,000 k, or any range therebetween.

[0042] In various embodiments, the metal alloy comprises an alloy of metals, including but not limited to alloys of iron, nickel, cobalt, manganese, tungsten, and molybdenum. In various embodiments, the metal alloy comprises one or more metals in an amount of 1 wt% to 99 wt% or any value therebetween. 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. Another specific example of a suitable metal alloy includes iron / cobalt alloy compositions containing 12 wt% to 25 wt% cobalt, with the balance comprising iron and trace impurities, if present. Another specific example of a suitable metal alloy includes iron / cobalt / manganese alloy compositions containing 12 wt% to 25 wt% cobalt, 10 wt% to 25 wt% manganese, with the balance comprising iron and trace impurities, if present. Another specific example of a suitable metal alloy includes iron / molybdenum alloy compositions containing 10 wt% to 25 wt% molybdenum, with the balance comprising iron and trace impurities, if present.

[0043] In various embodiments, the metal alloy is disposed on a catalyst support, including but not limited to activated carbon, alumina, zeolites, silica, and / or titania. In various embodiments, the metal alloy is disposed on the support in an amount of 1 wt% to 99 wt% of the total weight of the metal alloy and the support. Alternatively, 1 wt% to 10 wt%, 10 wt% to 20 wt%, 20 wt% to 50 wt%, 50 wt% to 99 wt%, or any range therebetween.

[0044] In various embodiments, the metal alloy is introduced into the plasma by any suitable means. In various embodiments, the metal alloy is introduced into the plasma in liquid or solid form. In various embodiments, the metal alloy is in powder form, particulate form, as an electrode within the plasma, as a solid piece (such as a rod or wire), or combinations thereof. In further embodiments, the metal alloy is introduced into the plasma in liquid form, such as molten metal form.

[0045] Plasma volatilization of the metal alloy forms an active catalyst (MA ) of the nanoparticulate catalyst in an aerosol state. In various embodiments, the FC-CVD reactor is directly coupled to the plasma, and the FC-CVD reactor is operated at a temperature cool enough to coalesce the volatilized metal alloy to form nanoparticles of the active catalyst (MA ) of the nanoparticulate catalyst. In various embodiments, the active catalyst (MA ) in the range of 1 nm to 100 nm. Alternatively, in the range of 1 nm to 75 nm, 1 nm to 50 nm, 1 nm to 25 nm, 1 nm to 10 nm, or any range therebetween. In various embodiments, the plasma volatilization of the metal alloy forms an aerosol having a metal alloy concentration suitable for forming carbon nanotubes, such as a metal alloy concentration in the range of 1,000 pg / m 3 to 100,000 pg / m 3 Alternatively, 1,000 pg / m 3 to 5,000 pg / m 3 , 5,000 pg / m 3 to 10,000 pg / m 3 , 10,000 pg / m 3 to 100,000 pg / m 3 , or any range therebetween.

[0046] In various embodiments, a carrier gas is used with the plasma to carry the active catalyst (MA ) particles. The carrier gas includes, but is not limited to, a noble gas, such as argon, and, for example, nitrogen, helium, and / or hydrogen.

[0047] In various embodiments, the carbon source that produces pyrolytic carbon (C ) for production of nanotubes includes a Ci-Cio hydrocarbon alkane, alkene, alkyne, arene, and / or cycloalkane. Some specific examples of carbon sources include methane, ethane, ethylene, acetylene, propane, propylene, butane, butadiene, benzene, and combinations thereof. Alternatively or additionally, the carbon source includes hydrocarbons from refinery streams, such as ethane steam cracker effluent and / or fluid catalytic cracker (FCC) off-gas. In further embodiments, the carbon source includes a Ci-Cio alcohol.

[0048] Pyrolysis of the carbon source in Reaction 2 can be performed by any suitable method. In various embodiments, the carbon source can be introduced into an FC-CVD reactor operating at a temperature suitable for pyrolyzing at least a portion of the carbon source. Alternatively or additionally, the carbon source is contacted with a plasma to pyrolyze the carbon source. In various embodiments, the carbon source is used as a carrier gas in the plasma, thereby producing pyrolyzed carbon and active catalyst (MA ). In further embodiments, the carbon source is introduced into a plasma separate from the plasma that produces the active catalyst (MA ).

[0049] While some pyrolysis of the carbon source occurs at temperatures below 1000 °C, when methane and / or other relatively lighter hydrocarbons are introduced into the FC-CVD reactor, the temperature in the pyrolysis environment can be up to 1000 °C or more, or up to 1100 °C or more, or up to 1200 °C or more, such as up to 1600 °C or possibly more. In various embodiments, the carbon source can be pre-heated prior to introduction into the pyrolysis zone (e.g., in the FC-CVD reactor). In various embodiments, the pyrolysis zone is heated to the pyrolysis temperature by any suitable heater means, such as by a flame heater, an induction heater, or by a heat exchanger.

[0050] In various embodiments, the feed to the FC-CVD reactor includes an active catalyst (MA ) and a carbon source. In further embodiments, the feed to the FC-CVD reactor includes an active catalyst (MA ) and a pyrolyzed carbon source (C ). In further embodiments, the feed to the FC-CVD reactor includes a carrier gas. In further embodiments, the feed to the FC-CVD reactor includes a hydrogen co-feed and / or a carrier gas. When present, the hydrogen co-feed can be introduced into the FC-CVD reactor in an amount of 500 mole % to 5000 mole % of the carbon source or pyrolyzed carbon source (C ) introduced into the FC-CVD reactor. Alternatively, the hydrogen co-feed can be introduced into the FC-CVD reactor in an amount of 500 mole % to 1000 mole %, 1000 mole % to 2000 mole %, 2000 mole % to 5000 mole %, or any range therein. Additionally, in embodiments where a carrier gas is present, the carrier gas can be introduced into the FC-CVD reactor in an amount of 1500 mole % to 10,000 mole % of the carbon source or pyrolyzed carbon source (C ) introduced into the FC-CVD reactor. Alternatively, the carrier gas can be introduced into the FC-CVD reactor in an amount of 1500 mole % to 3000 mole %, 3000 mole % to 5000 mole %, 5000 mole % to 10,000 mole %, or any range therein. Optionally, when a hydrogen-containing gas is used, the hydrogen-containing gas can also include CO, such that the hydrogen-containing gas corresponds to a syngas. The syngas can also optionally contain water and / or CO2. In some embodiments, the use of a hydrogen co-feed can provide the additional advantage of further reducing or minimizing carbon deposition within the reactor. Under pyrolysis conditions, both carbon atoms and hydrogen gas are formed. The carbon atoms can tend to deposit on the surfaces of the reactor. However, having a hydrogen co-feed can reduce or minimize the tendency of carbon atoms to deposit on the surfaces and / or can facilitate removal of carbon atoms that can deposit on the surfaces. In such an environment, increased amounts of carbon can remain in the gas phase in some form until the gas stream reaches the cooler temperatures in the region used to form carbon nanotubes.

[0051] In various embodiments, the feed to the FC-CVD reactor includes 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 source introduced into the reactor.

[0052] In various embodiments, the feed to the FC-CVD reactor includes a carbon source in an amount of 1 vol% to 10 vol% of the feed. Alternatively, the feed to the FC-CVD reactor includes a carbon source in an amount of 1 vol% to 3 vol%, 3 vol% to 6 vol%, or 6 vol% to 10 vol%, or any range therebetween. In various embodiments, the feed to the FC-CVD reactor includes a hydrogen co-feed in an amount of 20 vol% to 50 vol%. Alternatively, the feed to the FC-CVD reactor includes a hydrogen co-feed in an amount of 20 vol% to 30 vol%, 30 vol% to 40 vol%, 40 vol% to 50 vol%, or any other range therebetween. In various embodiments, the feed to the FC-CVD reactor includes a carrier gas in an amount of 50 vol% to 80 vol%. Alternatively, the feed to the FC-CVD reactor includes a carrier gas in an amount of 50 vol% to 60 vol%, 60 vol% to 70 vol%, 70 vol% to 80 vol%, or any range therebetween.

[0053] In some embodiments, the carbon source can be supplemented by a hydrocarbon that forms free radicals under pyrolysis conditions. By forming free radicals, the temperature required for methane pyrolysis can be reduced. One option can be to introduce propane and / or butane with the methane feed. Propane and butane are often available as part of the “condensate” stream at natural gas production sites. Another option can be to use a free radical precursor that provides free radicals with a longer lifetime. Toluene is an example of a hydrocarbon that can provide stable free radicals within a pyrolysis environment. When an additional hydrocarbon is used to provide free radicals in a pyrolysis environment, the amount of additional hydrocarbon can correspond to 0.1 mol% to 5.0 mol% of the amount of methane or other carbon source introduced into the reactor.

[0054] Before being introduced into the FC-CVD reactor, one or more components in the feed to the FC-CVD reactor can be heated. One option for heating the gas stream is to use multiple heating stages. For example, the initial heating stage could correspond to a furnace used to heat the reactor, such as the type of furnace used in a steam cracking reaction system. A conventional furnace can be used to heat one or more components in the FC-CVD feed to temperatures of 1000°C or higher. Additional heating can be provided through various methods to further increase the temperature to 1100°C or higher, or 1200°C or higher. One option is to use electric heating to heat the walls of the duct containing the gas stream. Despite the reactor's large size, the duct used to heat the gas stream before it enters the reactor can be appropriately sized to allow for efficient heat transfer. Other options can include induction heating or plasma heating. Because pyrolysis is an endothermic process, the gas stream temperature can decrease as the pyrolysis reaction proceeds. Therefore, it may be desirable to heat the gas stream to temperatures above 1000°C so that a sufficient volume within the reactor will be above 1000°C when the endothermic pyrolysis process cools the fluid. Even after the fluid is cooled to below 1000°C, some additional pyrolysis can still occur, but the reaction rate is slower. Another option is to include an electric heating element within the gas flow.

[0055] In some implementations, the carbon source used for pyrolysis and / or the pyrolyzed carbon source (C ) and / or active catalyst (MA The components can be mixed before being introduced into the FC-CVD reactor and / or mixed in the reactor by introducing the feed components into the FC-CVD reactor. In other embodiments, the carbon source and active catalyst (MA) used for pyrolysis At least one of the following can be mixed with the heated gas stream before entering the reactor. Optionally, a portion of the heated gas stream and / or a portion of the hydrocarbons for pyrolysis can be introduced into the reactor at a downstream location relative to the flow direction. Introducing different portions of the gas stream at different locations within the reactor can help manage the reaction distribution within the reactor. For example, by adding a portion of methane at a downstream location in the reactor, the amount of methane available for pyrolysis in the early stages of the reactor can be reduced or minimized, further reducing the likelihood of early carbon nanotube formation and / or early carbon deposition on the reactor surface.

[0056] In several embodiments, the FC-CVD reactor operates at a temperature ranging from 800 to 1600°C, or 800 to 1000°C, 1000 to 1200°C, 1200 to 1600°C, or any range thereof. In several embodiments, the FC-CVD reactor operates at a pressure ranging from 50 kPa to 200 kPa. In several embodiments, the FC-CVD reactor operates at atmospheric pressure (101.325 kPa), or at a pressure ranging from 50 kPa to 100 kPa, 100 kPa to 150 kPa, 150 kPa to 200 kPa, or any range thereof.

[0057] In several embodiments, 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 high velocities combined with low concentrations of hydrocarbons in the total fluid and temperatures above 1000°C, high levels of conversion can be achieved while maintaining low residence times. Low residence times in the reactor's pyrolysis zone reduce or minimize carbon deposition on the reactor surfaces before the products reach the carbon nanotube formation zone. In several embodiments, the average residence time in the reactor can range from 0.05 seconds to 5.0 seconds, or 0.05 seconds to 1.0 seconds, or 0.1 seconds to 5.0 seconds, or any range in between.

[0058] In several embodiments, the FC-CVD reactor includes a horizontal FC-CVD reactor and / or a vertical FC-CVD reactor. The FC-CVD reactor may include any suitable configuration, including but not limited to a flat-flame reactor in which reactants are introduced into plasma and then deposited onto a substrate; a co-current reactor in which reactants are introduced into plasma from top and bottom to generate a co-current flame and then deposited onto a substrate; a counter-current reactor in which reactants are introduced into plasma from the opposite direction and deposited onto a substrate; and / or a slit burner configuration in which plasma is emitted from a slit introducing reactants and then directed to a slit burner on a substrate.

[0059] Example configuration

[0060] Figure 1 This is an illustrative depiction of an FC-CVD method 100 based on certain embodiments disclosed in this application. Although Figure 1 Only the components necessary for understanding the main operations of the FC-CVD method 100 are shown; however, those skilled in the art will readily understand that additional components and / or steps can be integrated into it. Figure 1Without departing from the disclosed embodiments, the FC-CVD method 100 begins by introducing a carrier gas flow 102 into a plasma 104. In the plasma 104, a metal alloy is volatilized by the plasma to form a metal aerosol. The metal alloy can be in any form, such as powder, granules, as an electrode within the plasma, as a solid (e.g., a rod or wire), or as a metal solution in an aqueous carrier. The carrier gas combines with the metal aerosol to form an activated catalyst stream 138. In several embodiments, the activated catalyst stream 138 is combined with a recycle stream 122 and a feed stream 134 to form a reactor feed stream 112. The hydrocarbon stream 124 contains a carbon source for the production of carbon nanotubes. In some embodiments, the hydrocarbon stream 124 is preheated in a heat exchanger 126. In several embodiments, a portion of the hydrocarbon stream can be fractionated into stream 128 and introduced into an FC-CVD reactor 106. In the FC-CVD reactor 106, components introduced into the FC-CVD reactor react to form carbon nanotubes. Carbon nanotubes can be removed from the FC-CVD reactor 106 via stream 130 to collection unit 110. Collection unit 110 may include a spool-type collection unit or any other type of collector suitable for collecting carbon nanotubes to produce product nanotube stream 132. Reactor effluent stream 114 is taken from the FC-CVD reactor 106 and may include unreacted components from the feed to the FC-CVD reactor 106, which is introduced into separation unit 108. Separation unit 108 includes equipment for separating the components in reactor effluent stream 114 into recycle stream 118 and waste stream 116. Recycle stream 118 may include components in reactor effluent stream 114, such as hydrogen, carrier gas, unreacted hydrocarbons, and other components that can be reacted to form additional carbon nanotube products. Recycle stream 118 may be heated in heat exchanger 120 and may optionally be split into recycle stream 122 for combination with activated catalyst stream 138 and recycle stream 136 for introduction into the FC-CVD reactor 106.

[0061] Additional Implementation Plan

[0062] Therefore, this application discloses systems and methods for producing carbon nanoscale structures such as carbon nanotubes or carbon nanofibers, and more specifically, discloses systems and methods for producing carbon nanoscale structures using plasma-generated active catalysts. The methods and systems may include any of the various features disclosed herein, including one or more of the following statements.

[0063] Implementation Scheme 1. A method for forming carbon nanotubes, the method comprising: volatilizing a metal alloy in plasma to form an active catalyst; flowing the active catalyst and a carbon source into a floating catalyst chemical vapor deposition reactor; and pyrolyzing at least a portion of the carbon source on the active catalyst in a pyrolysis zone of the floating catalyst chemical vapor deposition reactor to form carbon nanotubes on the active catalyst.

[0064] Implementation Scheme 2. The method according to Implementation Scheme 1, wherein the metal alloy comprises at least two metals selected from iron, nickel, cobalt, manganese, tungsten, molybdenum and combinations thereof.

[0065] Implementation Scheme 3. The method according to any one of Implementation Schemes 1-2, wherein the metal alloy comprises iron and about 10% by weight to about 25% by weight of nickel.

[0066] Implementation Scheme 4. The method according to any one of Implementation Schemes 1-3, wherein the metal alloy comprises iron and about 12% by weight to about 25% by weight of cobalt.

[0067] Implementation Scheme 5. The method according to any one of Implementation Schemes 1-4, wherein the metal alloy comprises iron and about 10% to about 25% by weight of molybdenum.

[0068] Implementation Scheme 6. The method according to any one of Implementation Schemes 1-5, wherein the metal alloy comprises iron, about 10% to 25% manganese and about 12% to 25% cobalt.

[0069] Implementation Scheme 7. The method according to any one of Implementation Schemes 1-6, wherein the metal alloy further comprises a carrier selected from activated carbon, alumina, zeolite, silicon dioxide, titanium dioxide, and combinations thereof.

[0070] Implementation Scheme 8. The method according to any one of Implementation Schemes 1-7, wherein the active catalyst and carbon source flow turbulently through a floating catalyst chemical vapor deposition reactor.

[0071] Implementation Scheme 9. The method according to any one of Implementation Schemes 1-8, 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.

[0072] Implementation Scheme 10. The method according to any one of Implementation Schemes 1-9, wherein the active catalyst is introduced into the floating catalyst chemical vapor deposition reactor without quenching.

[0073] Implementation Scheme 11. The method according to any one of Implementation Schemes 1-10, wherein the carbon source comprises C1-C10 hydrocarbons.

[0074] Implementation Scheme 12. The method according to any one of Implementation Schemes 1-11, wherein the carbon source comprises C1-C10 alcohols.

[0075] Implementation Scheme 13. The method according to any one of Implementation Schemes 1-12, wherein the carbon source comprises ethane steam cracker effluent and / or fluidized catalytic cracker exhaust gas.

[0076] Implementation Scheme 14. The method according to any one of Implementation Schemes 1-13 further includes introducing a carrier gas into the plasma, and wherein the feed of the floating catalyst chemical vapor deposition reactor comprises the active catalyst suspended in the carrier gas.

[0077] Implementation Scheme 15. The method according to any one of Implementation Schemes 1-14, wherein the carrier gas comprises at least one gas selected from inert gases, hydrogen, helium, and combinations thereof.

[0078] Implementation Scheme 16. A reaction system for forming carbon nanotubes, comprising: a carbon source; a floating catalyst chemical vapor deposition reactor, the reactor including: a pyrolysis zone; an inlet for the carbon source to flow into the pyrolysis zone; and a heater configured to heat the pyrolysis zone to a pyrolysis temperature, wherein the floating catalyst chemical vapor deposition reactor is configured to pyrolyze the carbon source in the pyrolysis zone to produce pyrolyzed carbon; 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; wherein the plasma generator and the floating catalyst chemical vapor deposition reactor are fluidly coupled such that the active catalyst and the pyrolyzed carbon are contacted in the pyrolysis zone.

[0079] Implementation Scheme 17. The reaction system according to Implementation Scheme 16, wherein the metal alloy comprises at least two metals selected from iron, nickel, cobalt, manganese, tungsten, molybdenum and combinations thereof.

[0080] Implementation Scheme 18. The reaction system according to any one of Implementation Schemes 16-17, wherein the metal alloy comprises iron and about 10% by weight to about 25% by weight nickel.

[0081] Implementation Scheme 19. The reaction system according to any one of Implementation Schemes 16-18, wherein the metal alloy comprises iron and about 12% by weight to about 25% by weight of cobalt.

[0082] Implementation Scheme 20. The reaction system according to any one of Implementation Schemes 16-19, wherein the metal alloy comprises iron and about 10% by weight to about 25% by weight of molybdenum.

[0083] Implementation Scheme 21. The reaction system according to any one of Implementation Schemes 16-20, wherein the metal alloy comprises iron, about 10% to 25% manganese and about 12% to 25% cobalt.

[0084] Implementation Scheme 22. The reaction system according to any one of Implementation Schemes 16-21, wherein the carbon source comprises C1-C10 hydrocarbons.

[0085] Implementation Scheme 23. The reaction system according to any one of Implementation Schemes 16-22, wherein the carbon source comprises a C1-C10 alcohol.

[0086] Implementation Scheme 24. The reaction system according to any one of Implementation Schemes 16-23, wherein the carbon source comprises ethane steam cracker effluent, fluidized catalytic cracker exhaust gas, wherein the carbon source comprises syngas, or a combination thereof.

[0087] Implementation Scheme 25. The reaction system according to any one of Implementation Schemes 16-24 further includes a feed for the floating catalyst chemical vapor deposition reactor, wherein the feed comprises about 1 vol% to about 10 vol% of a carbon source, about 20 vol% to about 50 vol% of a hydrogen co-feed, and about 50 vol% to about 80 vol% of a carrier gas.

[0088] To facilitate a better understanding of the present invention, the following embodiments of certain aspects of some implementation schemes are provided. These embodiments should not in any way be construed as limiting or restricting the entire scope of the disclosure herein.

[0089] Example 1

[0090] In this embodiment, carbon nanotubes were synthesized using ethylene feed and an iron nanoparticle catalyst generated via plasma. The experiment was conducted in a downflow quartz reactor at 900°C and ambient pressure. The reactor feed consisted of 12 standard cubic centimeters (sccm) of ethylene (measured at T=273.15 K and P=1.01 bar), 131.4 sccm of hydrogen, and a catalyst feed comprising 300 sccm of N2 containing iron nanoparticles. The catalyst feed was generated by passing nitrogen through a particle generator, which produced the iron nanoparticle catalyst via spark ablation of an iron electrode. During the experiment, the particle generator operated at 1.3 kV and 10 mA. The flux of the generated nanoparticles was measured using a differential mobility analyzer before and after the reaction, and the flux was observed to stabilize at approximately 10. 4 μg / m 3 At the reaction temperature, the nominal residence time in the reactor is approximately 1.4 seconds.

[0091] The reaction proceeded for 2 hours, with continuous analysis of gaseous products from the reactor effluent using a gas chromatography-thermal conductivity detector (GC-TCD) to measure methane, ethane, and acetylene. Afterward, the feed was stopped, and the reactor was cooled under flowing nitrogen. Carbon products deposited on the reactor tubes were recovered for SEM analysis. Figure 2 and Figure 3 These are SEM images of the recovered carbon products. Single-walled and multi-walled carbon nanotubes were observed.

[0092] Example 2

[0093] In this embodiment, carbon nanotubes were synthesized using an ethylene feedstock and an iron-cobalt nanoparticle catalyst generated via plasma co-feeding with ethane / helium. The experiment was conducted in a downflow quartz reactor at 900°C and ambient pressure. The reactor feed consisted of 12 standard cubic centimeters (sccm) of ethylene (95% ethane / 5% helium), 131.4 sccm of hydrogen, and a catalyst feed comprising 300 sccm of nitrogen containing iron / cobalt nanoparticles. The catalyst feed was generated by passing nitrogen through a particle generator, which produced the nanoparticle catalyst via spark ablation of a pair of iron / cobalt (75 / 25) alloy electrodes. During the experiment, the particle generator operated at 1.3 kV and 10 mA. The flux of the generated nanoparticles was measured using a differential mobility analyzer before and after the reaction, and the flux was observed to stabilize at approximately 10. 4 μg / m 3 At the reaction temperature, the nominal residence time in the reactor is approximately 1.4 seconds.

[0094] The reaction proceeded for 2 hours, with continuous analysis of gaseous products from the reactor effluent using a gas chromatography-thermal conductivity detector (GC-TCD) to measure methane, ethane, and acetylene. Afterward, the feed was stopped, and the reactor was cooled under flowing nitrogen. Carbon products deposited on the reactor tubes were recovered for SEM analysis. Figure 4 and Figure 5 These are SEM images of the recovered carbon products. Single-walled and multi-walled carbon nanotubes were observed.

[0095] Example 3

[0096] In this embodiment, carbon nanotubes were synthesized using an ethylene feedstock and an iron-cobalt-manganese nanoparticle catalyst generated via plasma co-feeding with ethane / helium. The experiment was conducted in a downward-flowing quartz reactor at 900°C and ambient pressure. The reactor feed consisted of 12 standard cubic centimeters (sccm) of ethylene (95% ethane / 5% helium), 131.4 sccm of hydrogen, and a catalyst feed comprising 300 sccm of nitrogen containing iron / cobalt nanoparticles. The catalyst feed was generated by passing nitrogen through a particle generator, which produced the nanoparticle catalyst via spark ablation of a pair of iron-cobalt-manganese alloy electrodes. During the experiment, the particle generator operated at 1.3 kV and 10 mA. The flux of the generated nanoparticles was measured using a differential mobility analyzer before and after the reaction, and the flux was observed to stabilize at approximately 10. 4 μg / m 3 At the reaction temperature, the nominal residence time in the reactor is approximately 1.4 seconds.

[0097] During the 2-hour reaction period, gaseous products from the reactor effluent were continuously analyzed using a gas chromatograph-thermal conductivity detector (GC-TCD) to measure methane, ethane, and acetylene. Afterward, the feed was stopped, and the reactor was cooled under flowing nitrogen. Carbon products deposited on the reactor tubes were recovered for SEM analysis. Figure 6 and Figure 7 These are SEM images of the recovered carbon products. Single-walled and multi-walled carbon nanotubes were observed.

[0098] Example 4

[0099] In this embodiment, carbon nanotubes were synthesized using an ethylene feedstock and an iron-molybdenum nanoparticle catalyst generated via plasma co-feeding with ethane / helium. The experiment was conducted in a downflow quartz reactor at 900°C and ambient pressure. The reactor feed consisted of 12 standard cubic centimeters (sccm) of ethylene (95% ethane / 5% helium), 131.4 sccm of hydrogen, and a catalyst feed comprising 300 sccm of nitrogen containing iron / cobalt nanoparticles. The catalyst feed was generated by passing nitrogen through a particle generator, which produced the nanoparticle catalyst via spark ablation of a pair of iron-molybdenum alloy electrodes. During the experiment, the particle generator operated at 1.3 kV and 10 mA. The flux of the generated nanoparticles was measured using a differential mobility analyzer before and after the reaction, and the flux was observed to stabilize at approximately 10. 4 μg / m 3 At the reaction temperature, the nominal residence time in the reactor is approximately 1.4 seconds.

[0100] During the 2-hour reaction period, gaseous products from the reactor effluent were continuously analyzed using a gas chromatograph-thermal conductivity detector (GC-TCD) to measure methane, ethane, and acetylene. Afterward, the feed was stopped, and the reactor was cooled under flowing nitrogen. Carbon products deposited on the reactor tubes were recovered for SEM analysis. Figure 8 and Figure 9 These are SEM images of the recovered carbon products. Single-walled and multi-walled carbon nanotubes were observed.

[0101] Example 5

[0102] In this embodiment, carbon nanotubes were synthesized using various metal alloy catalysts deposited on an alumina (Al₂O₃) support. The catalysts used were iron, iron / nickel, iron / manganese, and iron / cobalt, with 20% by weight of the metal deposited on the alumina. The experiment was conducted in a downward-flowing quartz reactor at 675°C and ambient pressure. The reactor feed contained 9 standard cubic centimeters (sccm) of ethylene and 190 sccm of argon. At the reaction temperature, the nominal residence time in the reactor was approximately 1 second.

[0103] The reaction proceeded for 100 minutes, and the amount of carbon nanotubes produced was continuously measured throughout the experiment. The experimental results showed... Figure 10 and Figure 11 middle. Figure 10 This graph shows the carbon nanotube production rate during the experiment. The iron / cobalt and iron / nickel catalysts were observed to have the highest carbon nanotube production rates. Further observation showed that the iron and iron / manganese catalysts produced carbon nanotubes at slightly lower rates. Figure 11 This is a bar chart showing the total carbon nanotube yield for each tested catalyst. It was observed that the total carbon nanotube yield reported as dimensionless values ​​of conversion number (TON) (which is the number of carbon atoms relative to the number of metal atoms) was 85 for iron / nickel, 331 for iron / magnesium, 116 for iron / magnesium, and 227 for iron / cobalt.

[0104] While this application disclosure has described various embodiments and examples, those skilled in the art who benefit from it will understand that other embodiments can be devised without departing from the scope and spirit of this application disclosure as disclosed herein. Although individual embodiments have been discussed, this application disclosure covers all combinations of all such embodiments.

[0105] Although compositions, methods, and processes are described herein in the form of “comprising,” “containing,” “having,” or “including” various components or steps, compositions and methods may also be described as “consists essentially of” or “consisting essentially of”. Unless otherwise stated, the phrases “consists essentially of” and “consisting essentially 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 the disclosure of this application. Furthermore, they do not exclude impurities and variations typically associated with the elements and materials used.

[0106] All numerical values ​​in the detailed description are modified with “approximately” and take into account experimental errors and variations expected by those skilled in the art.

[0107] As used in the disclosure of this application and in the subsequent claims, the phrase “a” and any grammatical variations mean one or more. References to steps, elements, materials, etc., cover one step, one element and one material, as well as one or more steps, one or more elements and one or more materials.

[0108] Based on the foregoing description, many changes, modifications and variations will be apparent to those skilled in the art without departing from the spirit or scope of the invention, and when lower and upper limits of values ​​are listed herein, they cover a range from any lower limit to any upper limit.

Claims

1. A method for forming carbon nanotubes, the method comprising: Metal alloys are volatilized in plasma to form active catalysts; The active catalyst and carbon source are fed into a floating catalyst chemical vapor deposition reactor; and At least a portion of the carbon source on the active catalyst is pyrolyzed in the pyrolysis zone of the floating catalyst chemical vapor deposition reactor to form carbon nanotubes on the active catalyst.

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

3. The method according to any one of claims 1-2, wherein the metal alloy comprises iron and about 10% to about 25% by weight of nickel.

4. The method according to any one of claims 1-3, wherein the metal alloy comprises iron and about 12% to about 25% cobalt.

5. The method according to any one of claims 1-4, wherein the metal alloy comprises iron and about 10% to about 25% by weight of molybdenum.

6. The method according to any one of claims 1-5, wherein the metal alloy comprises iron, about 10% to 25% manganese and about 12% to 25% cobalt.

7. The method according to any one of claims 1-6, wherein the metal alloy further comprises a carrier selected from activated carbon, alumina, zeolite, silica, titanium dioxide, and combinations thereof.

8. The method according to any one of claims 1-7, wherein the active catalyst and the carbon source flow turbulently through the floating catalyst chemical vapor deposition reactor.

9. The method of claim 8, 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.

10. The method according to any one of claims 1-9, wherein the active catalyst is introduced into the floating catalyst chemical vapor deposition reactor without quenching.

11. The method according to any one of claims 1-10, wherein the carbon source comprises C1-C10 hydrocarbons.

12. The method according to any one of claims 1-11, wherein the carbon source comprises C1-C10 alcohols.

13. The method according to any one of claims 1-12, wherein the carbon source comprises ethane steam cracker effluent and / or fluidized catalytic cracker exhaust gas.

14. The method according to any one of claims 1-13, further comprising introducing a carrier gas into the plasma, and wherein the feed of the floating catalyst chemical vapor deposition reactor comprises the active catalyst suspended in the carrier gas.

15. The method of claim 14, wherein the carrier gas comprises at least one gas selected from inert gases, hydrogen, helium, and combinations thereof.

16. A reaction system for forming carbon nanotubes, the system comprising: Carbon source; A floating catalyst chemical vapor deposition reactor, comprising: Pyrolysis zone; The inlet for the carbon source to flow into the pyrolysis zone; and A heater configured to heat the pyrolysis zone to a pyrolysis temperature, wherein the floating catalyst chemical vapor deposition reactor is configured to pyrolyze a carbon source in the pyrolysis zone to produce pyrolyzed carbon. 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. The plasma generator and the floating catalyst chemical vapor deposition reactor are fluidly coupled so that the active catalyst and the pyrolyzed carbon come into contact in the pyrolysis zone.

17. The reaction system of claim 16, wherein the metal alloy comprises at least two metals selected from iron, nickel, cobalt, manganese, tungsten, molybdenum, and combinations thereof.

18. The reaction system according to any one of claims 16-17, wherein the metal alloy comprises iron and about 10% to about 25% by weight of nickel.

19. The reaction system according to any one of claims 16-18, wherein the metal alloy comprises iron and about 12% to about 25% cobalt.

20. The reaction system according to any one of claims 16-19, wherein the metal alloy comprises iron and about 10% to about 25% by weight of molybdenum.

21. The reaction system according to any one of claims 16-20, wherein the metal alloy comprises iron, about 10% to 25% manganese and about 12% to 25% cobalt.

22. The reaction system according to any one of claims 16-20, wherein the carbon source comprises C1-C10 hydrocarbons.

23. The reaction system according to any one of claims 16-20, wherein the carbon source comprises C1-C10 alcohols.

24. The reaction system according to any one of claims 16-20, wherein the carbon source comprises ethane steam cracker effluent, fluidized catalytic cracker exhaust gas, wherein the carbon source comprises syngas, or a combination thereof.

25. The reaction system according to any one of claims 16-20, further comprising the feed of the floating catalyst chemical vapor deposition reactor, wherein the feed comprises about 1% to about 10% by volume of a carbon source, about 20% to about 50% by volume of a hydrogen co-feed, and about 50% to about 80% by volume of a carrier gas.

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