Process for carbon nanotube synthesis

Abstract

A method for forming carbon nanotubes may include: volatilizing a metal in a plasma to form an active catalyst; introducing a hydrocarbon stream comprising methane into a hydrocarbon conversion unit and converting at least a portion of the methane into 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 at 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

PROCESS FOR CARBON NANOTUBE SYNTHESISCROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the priority ofU.S. Provisional Patent Application No. 63 / 607,146, filed December 7, 2023, which is incorporated by reference in its entirety.FIELD

[0002] This application relates to sy stems and methods for production of carbon nano-scale structures, such as carbon nanotubes or carbon nanofibers.BACKGROUND

[0003] Carbon nanotubes are very attractive for various applications due to their structural and electrical properties. One major challenge with the wider adoption of carbon nanotubes is that current methods of producing carbon nanotubes have low production rates leading to relatively high cost of the carbon nanotubes.

[0004] One method to fabricate carbon nanotubes is floating catalyst chemical vapor deposition (FC-CVD). A typical FC-CVD process includes introducing a feed comprising a pre-catalyst and a carbon source into a tubular reactor at relatively high temperature of -1,000 °C or greater. In the reactor, the pre-catalyst is transformed into active catalyst, and the carbon source is decomposed to generate a reactive carbon intermediate either in the gas phase or on the catalyst surface or on both, which is further reacted with the catalyst to form carbon nanotubes. Pre-catalysts are usually organometallic iron sources such as ferrocene together with / without a promoter such as thiophene. The components flow through the reactor under laminar flow conditions. The temperature profile in the FC-CVD process is parabolic where the temperature begins at approximately 400 °C, reaches a maximum of approximately 1300 °C, and ends at approximately 300 °C. The residence time in the high temperature zone is in the range of a couple of seconds. Some of the bottlenecks in this process includes evaporation of the catalyst in the high temperature zone, and condensation of active catalyst particles downstream which alters the size distribution of the nanoparticles formed in the front end of the reactor. The high temperature zone, which is necessary for hydrocarbon conversion, creates adverse and hard-to-control process conditions for catalyst generation. Additionally, the high temperature zone requires the whole reactor to be made of a material that can sustain such high temperatures and therefore increases the capital cost of the reactor.SUMMARY

[0005] Disclosed herein is an example method for forming carbon nanotubes comprising: volatilizing a metal in a plasma to form an active catalyst; introducing a hydrocarbon stream comprising methane into a hydrocarbon conversion unit and converting at least a portion of the methane into carbon reactant comprising ethylene, acety lene, or a combination thereof; introducing the active catalyst and the carbon reactant into a floating catalyst chemical vapor deposition reactor, yvherein the floating catalyst chemical vapor deposition reactor is operated at 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.

[0006] Further disclosed herein is a reaction system for forming carbon nanotubes comprising: a catalyst generation unit comprising: 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 volatizes the metal alloy to form an active catalyst; a hydrocarbon source comprising methane; a hydrocarbon conversion unit, wherein the hydrocarbon conversion unit is configured to take as input the hydrocarbon source and convert at least a portion of the methane into carbon reactant comprising ethylene, acetylene, or a combination thereof; and a floating catalyst chemical vapor deposition reactor comprising: a reaction zone; and an inlet for the active catalyst and the carbon reactant, wherein the floating catalyst chemical vapor deposition reactor is fluidicalty coupled to the catalyst generation unit and the hydrocarbon conversion unit such that the active catalyst and the carbon reactant are contacted in the reaction zone.

[0007] These and other features and attributes of the disclosed methods and systems of the present disclosure and their advantageous applications and / or uses will be apparent from the detailed description which follows.BRIEF DESCRIPTION OF THE DRAWINGS

[0008] To assist those of ordinary skill in the relevant art in making and using the subject matter hereof, reference is made to the appended drawings, wherein:

[0009] FIG. 1 is an illustrative depiction of an FC-CVD process for production of carbon nanotubes in accordance with certain embodiments of the present disclosure.

[0010] FIG. 2 is an illustrative depiction of an FC-CVD process for production of carbon nanotubes in accordance with certain embodiments of the present disclosure.

[0011] FIG. 3 A is an illustrative depiction of a plasma torch configuration for a hydrocarbon conversion reactor.

[0012] FIG. 3B is an illustrative depiction of an arc plasma configuration for a hydrocarbon conversion reactor.

[0013] FIG. 3C is an illustrative depiction of a configuration for a hydrocarbon conversion reactor.DETAILED DESCRIPTION

[0014] Disclosed herein are systems and methods for production of carbon nano-scale structures, such as carbon nanotubes or carbon nanofiber, and. more particularly, disclosed are systems and methods for production of carbon nano-scale structures using plasma generated active catalyst and a carbon reactant.Definitions

[0015] The words and phrases used herein should be understood and interpreted to have a meaning consistent with the understanding of those words and phrases by those skilled in the relevant art. No special definition of a term or phrase, i.e., a definition that is different from the ordinary' and customary' meaning as understood by those skilled in the art, is intended to be implied by consistent usage of the term or phrase herein. To the extent that a term or phrase is intended to have a special meaning, i.e., a meaning other than the broadest meaning understood by skilled artisans, such a special or clarifying definition will be expressly set forth in the specification in a definitional manner that provides the special or clarifying definition for the term or phrase.

[0016] For example, the following discussion contains a non-exhaustive list of definitions of several specific terms used in this disclosure (other terms may be defined or clarified in a definitional manner elsewhere herein). These definitions are intended to clarify the meanings of the terms used herein. It is believed that the terms are used in a manner consistent with their ordinary meaning, but the definitions are nonetheless specified here for clarity.

[0017] Carbon fibers, nanofibers, and nanotubes are allotropes of carbon that have a cylindrical nanostructure. The walls of the carbon nanotubes are formed from sheets of carbon in a graphene structure. As used herein, nanotubes include single wall nanotubes and multiple wall nanotubes of any length. The term “carbon nanotubes’' as used herein and in the claims, includes other fullerene allotropes of carbon, such as carbon fibers, carbon nanofibers, and other carbon nanostructures.FC-CVD Process

[0018] As discussed above, there are several challenges with scaling up floating catalyst chemical vapor deposition (FC-CVD) processes for producing carbon nanotubes. Conventional FC-CVD processes for producing carbon nanotubes include forming an active catalyst in-situ within an FC- CVD reactor by thermal decomposition of a pre-catalyst to form the active catalyst. Commonlyused pre-catalysts include compounds such as thiophene or elemental sulfur together with organometallic compounds containing iron, cobalt, and / or nickel metal and cyclopentadiene or carbon monoxides as ligands with some specific examples including Fe(CO)5 and ferrocene. The metal in the pre-catalyst is converted to the active metal catalyst. Conventional FC-CVD reactors involve a mixing of hydrocarbon decomposition, pre-catalyst decomposition, active catalyst nucleation, growth and agglomeration dynamics of catalyst nanoparticles along with the growth of CNTs on active catalyst particles. However, efficient formation of carbon nanotubes at the product end of the reactor is facilitated by having a substantially laminar flow with little or no mixing. In smaller scale conventional FC-CVD reactors the initial mixing of reactants can be achieved in a variety of manners, so that the flow is well-mixed even though the amount of turbulence in the flow is reduced or minimized. In other words, reactants can be well-mixed in a small-scale reactor while maintaining a Reynolds number below 1,000, or even below 500. By contrast, in a relatively larger scale reactor, creating a well-mixed flow at the beginning of the reactor will result in a turbulent gas flow with a Reynolds number greater than 5,000. Thus, for larger scale conventional FC-CVD reactors, a means for reducing the Reynolds number of the flow to roughly 500 or less, and preferably to about 10, is required as the flow reaches the product end of the reactor.

[0019] Attempting to scale up a conventional reactor for carbon nanotube production can present a variety of challenges. First, as the reactor diameter is increased, it becomes increasingly difficult, if not physically impossible, to transfer sufficient heat through the reactor walls to maintain the temperatures needed for thermally decomposing the pre-catalyst to form active catalyst. Additionally, the temperature of thermal decomposition for a particular pre-catalyst and the reaction temperature needed to produce carbon nanotubes may be substantially different, necessitating additional quench gases and process steps leading to more complicated reactor design. For example, attempting to cool the gas flows in the reactor after forming the active catalyst may result in the catalyst surface temperature becoming too cool to effectively catalyze carbon nanotube formation. Furthermore, as the pre-catalyst decomposes, the iron (or other metal) from the catalyst precursors tends to deposit on the walls of the reactor. This can result in 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 a temperature typically between 700° C. and 1000° C, the resulting metal has a higher phase stability as an atom deposited on a surface, as opposed to remaining in the gas phase. As a result, when a pre-catalyst is heated through the temperature range 700° C.-10000C, deposition of metal on exposed surfaces can occur. Thisdeposition of metal can continue until the temperature is above 1000° C., where metal atoms have a higher phase stability in the gas phase. In a conventional FC-CVD reactor, a substantial deposition of metal may be deposited on the reactor walls and thereby reduce or minimize the amount of activated catalyst that is formed.

[0020] In embodiments, methods for producing carbon nanotubes disclosed herein comprise three sub-processes. The first sub-process includes producing the active catalyst in a catalyst generation unit, the second sub-process includes producing 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 presently disclosed methods is that by separating the reactions, the process parameters such as temperature, pressure, and residence time for each of the sub processes can be optimized.

[0021] FIG. 1 is an illustrative depiction of an FC-CVD process 100 in accordance with certain embodiments of the present disclosure. In FIG. 1, a hydrocarbon feed 102 is introduced into hydrocarbon conversion unit 104. In hydrocarbon conversion unit 104, the hydrocarbons in hydrocarbon feed 102 are converted to a form suitable for forming carbon nanotubes, referred to herein as carbon reactants. A pre-catalyst 110 is introduced into a catalyst generation unit 112. In catalyst generation unit 112 the pre-catalyst is transformed into active catalyst. An active catalyst stream 114 and carbon reactant stream 106 are introduced into FC-CVD reactor 108 where the carbon reactant and active catalyst are reacted to form carbon nanotubes. A product carbon nanotube stream 116 is withdrawn from FC-CVD reactor 108.

[0022] A reactor system for carbon nanotube formation performs at least three types of reactions. In the hydrocarbon conversion unit, hydrocarbon is converted to a carbon reactant. Carbon reactants include, but are not limited to, C2 hydrocarbons such as ethylene and / or acetylene as well as hydrogen which are precursors for carbon nanotube formation. Reaction 1 is a generalized unbalanced reaction showing transformation of methane to ethylene, acetylene, and hydrogen.Reaction 1CH4C2H2+ C2H4+ H2

[0023] There are several suitable methods for converting the hydrocarbon to carbon reactant, including conversion of methane in a plasma torch followed by quenching to preserve C2 selectivity over coke and endothermic cracking in reverse flow reactor units, for example.

[0024] In the catalyst generation unit, a metal or metal alloy is converted to an active catalyst. In embodiments, the metal or metal alloy is evaporated by plasma volatilization to form a volatilized metal which is cooled and condensed to nanometer sized active catalyst. In further embodiments, the metal or metal alloy is ablated by the plasma to form the active catalyst. Reaction 2 is ageneralized reaction of a metal alloy (MA) with heat generated from plasma to form an active catalyst (MA*).Reaction 2 ti+PlasmaMA - > MA*

[0025] In the FC-CVD reactor carbon nanotubes are formed by contacting the carbon reactants produced in the hydrocarbon conversion unit with the active catalyst from the catalyst generation unit. Reaction 3 is a generalized reaction of carbon reactants C2H2and C2 / / 4formed in the hydrocarbon conversion unit with the active catalyst (MA*) from the catalyst generation unit to form carbon nanotubes.Reaction 3

[0026] It is noted that the term "catalyst" is used to describe the active catalyst (MA*) because it facilitates the formation of the carbon nanotubes. However, it is understood that at least a portion of the active catalyst is consumed during the carbon nanotube formation process, as at least part 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. Without being limited by theory, it is believed that the active catalyst promotes the formation and diffusion of carbon intermediate species through the catalyst particle which lead to carbon nanotube grow th as well as providing a surface for the nucleation of the carbon nanotubes.

[0027] The methods disclosed herein have several advantages over previous methods of producing carbon nanotubes, including that the conditions for each reaction are independent. The temperature, pressure, and residence times are independently optimized for the hydrocarbon conversion unit, the catalyst generation unit, and the FC-CVD reactor. The disclosed methods have higher utilization of the active catalyst as compared to conventional FC-CVD processes thereby requiring less catalyst per unit of carbon nanotube produced. The active catalyst produced by the methods disclosed herein allows for increased rate of carbon nanotube production by reducing reactor residence time and facilitating reactor scale-up with more efficient use of reactor volume. The active catalyst produced by the methods disclosed herein also has less tendency to deposit on reactor walls. Additionally, the plasma volatilization step allows for fine control of catalyst morphology and particle size, thus giving additional process control variables to affect the physical properties of the carbon nanotubes produced and to control coke formation.

[0028] Another advantage of the presently disclosed methods includes that a less expensive carbon source, such as methane, can be utilized to produce carbon reactants. The carbon reactantsare more susceptible to produce carbon nanotubes than the conventional FC-CVD methods using methane or other lighter hydrocarbons are pyrolyzed to produce carbon intermediate (C2+) which is then reacted with an active catalyst to form carbon nanotubes.

[0029] Another advantage of the presently disclosed systems and methods for production of carbon nanotubes includes that the carbon reactants and active catalyst can be well mixed before introduction into the FC-CVD reactor. It is desirable to have a well-mixed flow of activated catalyst and carbon reactants into the FC-CVD reactor such that the formation of carbon nanotubes is increased.Hydrocarbon Conversion Unit

[0030] In the hydrocarbon conversion unit, a hydrocarbon feed is introduced into a hydrocarbon conversion reactor and is converted to a carbon reactant. In embodiments, the hydrocarbon for forming the carbon reactant includes Cl -CIO hydrocarbon alkanes, alkenes, alkynes, aromatics, and / or naphthenes. Some specific examples of hydrocarbons include methane, ethane, ethylene, acetylene, propane, propylene, butane, butadiene, benzene, and combinations thereof. Alternatively, or in addition, the hydrocarbon sources include hydrocarbons from refinery streams such as an ethane steam cracker effluent and / or fluidized catalytic cracker (FCC) off gas. In further embodiments, the hydrocarbon includes a Cl -CIO alcohol. In embodiments, the hydrocarbon feed is converted to carbon reactants including, but not limited to, C2 hydrocarbons such as ethylene and / or acetylene as well as hydrogen which are precursors for carbon nanotube formation.

[0031] In embodiments, the hydrocarbon conversion unit includes plasma for heating the hydrocarbon to reaction temperature. In 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 a combination thereof. In further embodiments, the hydrocarbon can be heated by joule heating, flash joule heating, pulsed joule heating, electro fluidic heating, fired heating, electric arc heating, and combinations thereof.

[0032] In embodiments, the temperature of the plasma ranges from 4,000 K - 7,000 K or any suitable temperature to heat the hydrocarbon to reaction temperature. Alternatively, from 4,000 K -5.000 K, 5,000 K - 6.000 K, 6.000 K. - 7.000 K, or any ranges therebetween.

[0033] In embodiments where the hydrocarbon conversion unit comprises plasma, the hydrocarbon conversion unit can be operated at any suitable pressure for converting the hydrocarbons to carbon reactant, such as a pressure in a range of 0.5 bar gauge to 3 bar gauge. Alternatively, from 0.5 bar gauge to 1 bar gauge, from 1 bar gauge to 2 bar gauge, from 2 bar gauge to 3 bar gauge, or any ranges therebetween.

[0034] In embodiments where the hydrocarbon conversion unit comprises plasma, the hydrocarbon conversion unit can be operated at any suitable residence time for converting the hydrocarbons to carbon reactant, such as a residence time in a range of 1 millisecond to 100 milliseconds. Alternatively, from 1 millisecond to 10 milliseconds, 10 milliseconds to 50 milliseconds, 50 milliseconds to 100 milliseconds, or any ranges therebetween with efficient quenching to stop a majority of the reaction products as C2 intermediates.

[0035] Reaction heat to the system can be supplied by plasma generated using a plasma torch in either a plasma jet or an arc discharge configuration. Plasma torches and arc discharges convert electrical energy into thermal energy', and they offer a pathway to reduce the CO2 footprint of the carbon nanotube production process. Plasma torches can be operated by direct current (DC) and alternating cunent (AC), or any of the previously discussed plasma sources, to convert electricity into thermal heat. Both the high energy thermal plasma and microwave plasma torches can provide the needed reaction heat and the plasma velocity enables the short residence time in the hydrocarbon conversion step.

[0036] The hydrocarbon conversion unit can further comprise a quenching system configured to cool the product carbon reactant produced in the plasma. A quenching system can include a heat exchanger, quench tower, or any other suitable equipment for quickly cooling the carbon reactant to preserve the formed C2 selectivity' and to prevent amorphous carbon formation.

[0037] FIG. 3A is an illustrative depiction of a plasma torch configuration for a hydrocarbon conversion reactor. In FIG. 3A, hydrocarbon conversion reactor 300 includes a plurality of plasma torches 302 each producing plasma 304. In the operation of hydrocarbon conversion reactor 300, the plurality7of plasma torches 302 can each be individually controlled, such as by adjusting the power of the torch or turning the torch on / off. A hydrocarbon 320 is introduced into hydrocarbon conversion reactor 300 which contacts plasma 304 and converts the hydrocarbon 320 to carbon reactant 322 which is withdrawn from hydrocarbon conversion reactor 300.

[0038] FIG. 3B is an illustrative depiction of an arc plasma configuration for a hydrocarbon conversion reactor. In FIG. 3B, hydrocarbon conversion reactor 306 includes a plurality of plasma electrodes 308 which produce an arc plasma 310. In the operation of hydrocarbon conversion reactor 306, the plurality of plasma electrodes 308 can each be individually controlled, such as by adjusting the power of the electrode or turning the electrodes on / off. A hydrocarbon 320 is introduced into hydrocarbon conversion reactor 306 which contacts arc plasma 310 and converts the hydrocarbon 320 to carbon reactant 322 which is withdrawn from hydrocarbon conversion reactor 306.

[0039] FIG. 3C is an illustrative depiction of a configuration for a hydrocarbon conversion reactor. Scaling up production can include using a plurality of hydrocarbon conversion reactors 312 in parallel. A hydrocarbon 320 is introduced into each of the hydrocarbon conversion reactors 312 where the hydrocarbon is converted into carbon reactant 322 which is withdrawn from each hydrocarbon conversion reactor 312.

[0040] In further embodiments, the hydrocarbon conversion unit includes a reverse flow reactor, configured to convert the hydrocarbon to carbon reactant. The reverse flow reactor operates by alternating endothermic cracking reactions over a short residence time, followed by burning up the deposited coke to provide reaction heat needed for cracking in a subsequent cycle. A suitable reverse flow reactor is disclosed in U.S. Patent No. 9,809,506 to Hershkowitz et. al., incorporated by reference in its entirety.

[0041] In embodiments, a reverse flow’ reactor includes (i) at least one thermal mass and (ii) having a first zone, a second zone, and a reaction zone intermediate to the first and second zones. The hydrocarbon feed can be passed from the first zone to the second zone of the reactor, with heat being transferred from thermal mass located proximate to the first zone to the pyrolysis feed as the pyrolysis feed is passed through the reactor. The hydrocarbon feed can be passed proximate to the thermal mass at a peak pyrolysis temperature in the reaction zone in the range of from 850° C. to 1200° C., at a hydrocarbon partial pressure 48 kPa absolue, to convert ^10.0 wt. % of the hydrocarbon in the hydrocarbon feed into a carbon reactant product. The carbon reactant product can comprise C2 unsaturates having an ethylene: acetylene molar ratio ^1: 1. The process can be quenched by transferring heat from the pyrolysis product to thermal mass located proximate to the second zone to cool the carbon reactant product to a temperature below7the peak pyrolysis temperature. The thermal mass proximate to the first zone and the thermal mass proximate to the second zone can be regions of the same thermal mass or, alternatively, they can be separate thermal masses.

[0042] The reactor can be a reverse- flow reactor, with the hydrocarbon feed being passed to the reverse-flow reactor during a first time interval to produce the pyrolysis product. During a second time interval, a provided combustion feed comprising hydrocarbon fuel and oxidant can be passed to the reverse-flow reactor. Heat can be transferred from the second zone to the combustion feed, and the heated combustion feed can be exothermally reacted, typically proximate to 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. Thermal mass located in the zones receives, stores, and releases the transferred heat.

[0043] In certain aspects, the hydrocarbon feed has a residence time in the reverse-flow reactor of ^1.0 second, less than ^0.500 second, or less than ^0.100 second. Alternatively or in addition, the hydrocarbon feed can be passed through the reverse-flow reactor at a total gas residence time above 800° C. in the reaction zone of thermal mass of ^0.0500 second.

[0044] In other aspects, the hydrocarbon of the hydrocarbon feed can comprise ^50 wt. % ethane, based on total weight of the hydrocarbon in the hydrocarbon feed. The carbon reactant product can include unreacted hydrocarbon from the hydrocarbon feed. The pyrolysis feed can also comprise diluent, and the pyrolysis product can comprise unreacted diluent.

[0045] In other aspects, hydrocarbon feed can be passed through the reverse-flow reactor at a peak pyrolysis temperature in the range of from 900° C. to 1100° C. and a hydrocarbon partial pressure ^137 kPa absolute. In these or in alternative aspects, the hydrocarbon feed can be passed through the reverse-flow reactor at a total gas residence time in the reverse-flow reactor of ^0.75 seconds to convert ^50.0 wt. % of the pyrolysis feed's hydrocarbon to C2 unsaturates.

[0046] In embodiments, the reverse flow reactor is operated by providing a hydrocarbon feed comprises ethane and / or C3+ hydrocarbon, providing a reverse flow' reactor including at least one thermal mass, and having a first zone, a second zone, and a reaction zone intermediate to the first and second zones; passing the hydrocarbon feed from the first zone to the second zone of the reactor; transferring heat in the first zone from the thermal mass to the hydrocarbon feed as the pyrolysis feed is passed proximate to the thermal mass; passing the pyrolysis feed proximate to the thermal mass in the reaction zone to expose the pyrolysis feed to a peak pyrolysis temperature in the range of from 850° C. to 1200° C., at a hydrocarbon partial pressure ^48 kPa absolute, to convert i l 0.0 wt. % of the hydrocarbon in the hydrocarbon feed into a carbon reactant comprising C2 unsaturates, wherein the C2 unsaturates, and transferring heat in the second zone from pyrolysis product to the thermal mass to cool the pyrolysis product to a temperature below the peak pyrolysis temperature.Catalyst Generation Unit

[0047] In the catalyst generation unit, a metal or metal alloy is converted to an active catalyst byplasma volatilization. The volatilization of metal and / or metal alloy can be carried out by any suitable plasma. In 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 a combination thereof. In various embodiments, the plasma generator produces plasma by a variety of means. For example, plasma is produced by arc discharge betw een two electrodes and metal and / or metal alloy is fed into the resulting plasma. Alternatively, or in addition, the metal and / ormetal alloy can compose the electrodes themselves to be ablated off. Alternatively, or in addition, metal and / or metal alloy is fed into a plasma torch sustained by a microwave plasma generator. In embodiments, the temperature of the plasma ranges from 4,000 K - 7,000 K or any suitable temperature to volatilize the metal alloy. Alternatively, from 4,000 K -5,000 K, 5,000 K - 6,000 K, 6,000 K - 7,000 K, or any ranges therebetween.

[0048] 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 includes one or more of the metals in an amount of 1 wt.% to 99 wt.%, or any values therebetween. Some specific examples of suitable metal alloys include iron / nickel alloy compositions containing 10 wt.% - 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.% - 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.% - 25 wt.% cobalt, 10 wt.% - 25 wt.% manganese, with the balance comprising iron and trace impurities, if present. Another specific example of a suitable metal alloy includes iron / molybdemim alloy compositions containing 10 wt.% - 25 wt.% molybdenum with the balance comprising iron and trace impurities, if present.

[0049] In embodiments, the metal and / or metal alloy is disposed on a catalyst support, including, but not limited to activated carbon, alumina, zeolites, silica, and / or titanium dioxide. In embodiments, the metal alloy is disposed on the support in an amount of 1 wt.% to 99 wt.% by total weight of the metal alloy and support. Alternatively, from 1 wt.% to 10 wt.%, 10 wt.% to 20 wt.%, 20 wt.% to 50 wt.%, 50 wt.% to 99 wt.%, or any ranges therebetween.

[0050] In embodiments, the metal and / or metal alloy is introduced into the plasma by any suitable means. In embodiments, the metal and / or metal alloy is introduced into the plasma in a liquid or solid form. In embodiments, the metal and / or metal alloy is in a powder form, granular form, as an electrode within the plasma, as a solid piece such as a bar or wire, or combinations thereof. In further embodiments the metal and / or metal alloy is introduced into the plasma in a liquid form such as a molten metal form.

[0051] The plasma volatilization of the metal alloy forms the active catalyst (MA*) as a nanoparticle catalyst in an aerosol state. In 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*). In embodiments, the active catalyst (MA*) has a particle size in a range of 1 nm to 50 nm. Alternatively, in a range of1 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 ranges therebetween. In embodiments, the plasma volatilization of the metal alloy forms an aerosol with a metal alloy concentration suitable for forming carbon nanotubes such as a concentration of metal alloy in a range of 1,000 pg / m3to 100,000 pg / m3. Alternatively, 1,000 pg / m3to 5,000 pg / m3, 5,000 pg / m3to 10,000 pg / m3, 10,000 pg / m3to 100,000 pg / m3, or any ranges therebetween.

[0052] In embodiments a carrier gas is utilized with the plasma to carry the active catalyst (MA*) particles. Carrier gases include, without limitation, noble gasses such as argon, as well as nitrogen, helium and / or hydrogen, for example.FC-CVD Reactor

[0053] In embodiments, the carbon reactant and active catalyst are contacted in a reaction zone within an FC-CVD reactor, wherein the reaction zone is operated at conditions to form carbon nanotubes from the carbon reactant on the active catalyst. In embodiments, a feed to an FC-CVD reactor includes an active catalyst (MA*) and a carbon reactant. In further embodiments, a feed to an FC-CVD reactor includes the carbon reactant and hydrogen in an amount of 1 : 1 to 1 :50 mole ratio of carbon reactant to hydrogen. Alternatively, the feed to an FC-CVD reactor includes the carbon reactant and hydrogen in an amount of 1:1 to 1: 10, in an amount of 1 : 10 to 1 :25, in an amount of 1:25 to 1:50, or any ranges therebetween. In further embodiments a feed to the FC- CVD further includes an inert co-feed including argon, nitrogen, and / or helium, for example. In embodiments where a co-feed is used the feed to the FC-CVD reactor includes the carbon reactant and the inert co-feed in an amount of 1 :3 to 1 : 10 mole ratio of carbon reactant to co-feed.

[0054] Optionally, when a hydrogen containing gas is used, the hydrogen containing gas can also include CO so that the hydrogen containing gas corresponds to a synthesis gas. Synthesis gas can also optionally contain water and I or CO2.

[0055] In embodiments, a feed to an 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 reactant introduced into the reactor.

[0056] One or more of the components of the feed to the FC-CVD reactor can be heated prior to introduction into the FC-CVD reactor. One option for heating the gas flow can be to use multiple heating stages. For example, an initial heating stage can correspond to a furnace used for heating reactors, such as the type of furnace used in a steam cracking reaction system. Conventional furnaces can be used to heat one or more of the components of the FC-CVD feed to a temperature of 1000 °C or higher. Additional heating to further increase the temperature to 1100 °C or more, or 1200 °C or more, can be provided by a variety' of methods. One option can be to use electric heating to heat the walls of the conduit containing the gas flow. Although the reactor is of largesize, the conduit for heating the gas flow prior to entering the reactor can be sized appropriately to allow for efficient heat transfer. Other options can include induction heating or plasma heating. Still another option can be to include electric heating elements within the gas flow.

[0057] In some embodiments, the carbon reactant and active catalyst (MA*) is mixed prior to introduction into the FC-CVD reactor and / or be mixed in the reactor by introducing the feed components into the FC-CVD. In other embodiments, at least one of the carbon reactants and the active catalyst (MA*) are introduced into the reactor at a downstream location in the reactor relative to the direction of flow. Introducing different portions of the gas flow at different locations within the reactor can assist with managing the reaction profile in the reactor. For example, by adding a portion of the active catalyst or carbon reactant at a downstream location in the reactor, the amount of reactants available in each part of the reactor can be controlled, to further reduce the likelihood of early carbon nanotube formation and / or early deposition of carbon on the surfaces of the reactor.

[0058] The systems and methods for production of carbon nanotubes disclosed herein allow for thorough mixing of the carbon reactant and active catalyst. The plasma generated active catalyst allows for turbulent flow production of carbon nano-scale structures where 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 a range of 5,000 to 20,000. Alternatively, the flow through the FC-CVD reactor has a Reynolds number in a range of 5,000 to 8,000, 5,000 to 10.000, 5,000 to 15,000, or 5,000 to 20,000.

[0059] In embodiments the velocity of the gas within the reactor can be relatively high. The velocity within the reactor can determine the residence time of the reactants within the pyrolysis zone. By using a high velocity in combination with a low concentration of hydrocarbons in the total flow and a temperature greater than 1000 °C. a high level of conversion can be achieved while having a low residence time. Having a low residence time in the pyrolysis zone of the reactor can reduce or minimize carbon deposition on surfaces in the reactor prior to the products reaching the zone for carbon nanotube formation. In embodiments, the average residence time for 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 ranges therebetween.

[0060] In embodiments, the FC-CVD reactor is operated at a temperature in a range of 800 °C to 1600 °C. Alternatively, from 800 °C to 1000 °C, 1000 °C to 1200 °C, 1200 °C to 1600 °C, or any ranges therebetween. In embodiments, the FC-CVD reactor is operated at a gauge pressure in a range of 50 kPa to 200 kPa. In embodiments, the FC-CVD reactor is operated at gauge pressureof atmospheric pressure (101.325 kPa). Alternatively, at a gauge pressure in a range of 50 kPa to 100 kPa, 100 kPa to 150 kPa, 150 kPa to 200 kPa. or any ranges therebetween.Example Configuration

[0061] FIG. 2 is an illustrative depiction of an FC-CVD process 200 in accordance with certain embodiments of the present disclosure. While only elements necessary' to understand the principal operation FC-CVD process 200 are shown in FIG. 2, one of ordinary’ skill in the art will readily appreciate that additional elements and / or steps can be integrated into FIG. 2 without detracting from the disclosed embodiments. FC-CVD process 200 begins with introducing carrier gas stream 202 into plasma 204. In plasma 204, a metal alloy is volatilized by plasma to form a metal aerosol. The metal alloy can be of any form such as a powder form, granular form, as an electrode within the plasma, as a solid piece such as a bar or wire or introduced as a metal solution in aqueous carrier. The carrier gas combines with the metal aerosol to form activated catalyst stream 238. In embodiments, activated catalyst stream 238 is combined with recycle stream 222 and carbon reactant stream 234 to form reactor feed stream 212. Hydrocarbon stream 224 contains the carbon reactant for producing carbon nanotubes. Hydrocarbon stream 224 is introduced into hydrocarbon conversion unit 226 where the hydrocarbon components of hydrocarbon stream 224 are reacted to form carbon reactant stream 234. In embodiments, a portion of the carbon reactant stream can be split into stream 228 and introduced into FC-CVD reactor 206 at one or more points along the FC-CVD reactor 206. In FC-CVD reactor 206 the components introduced into FC-CVD reactor are reacted to from carbon nanotubes. The carbon nanotubes can be removed from FC-CVD reactor 206 via stream 230 to collection unit 210. Collection unit 210 may include a spool type collection unit or any other type of collection suitable for collecting carbon nanotubes to produce product nanotube stream 232. A reactor effluent stream 214 is withdrawn from FC-CVD reactor 206 which may include unreacted components of feeds to FC-CVD reactor 206 which is introduced into separation unit 208. Separation unit 208 includes equipment to separate the components of the reactor effluent stream 214 into recycle stream 218 and waste stream 216. Recycle stream 218 may include the components of the reactor effluent stream 214 such as hydrogen, carrier gas, unreacted carbon reactant, and other components useful to react to form further carbon nanotube product. Recycle stream 218 may be heated in heat exchanger 220 and may optionally7be split into recycle stream 222 for combining with activated catalyst stream 238 and recycle stream 236 for introduction into FC-CVD reactor 206.Additional Embodiments

[0062] Accordingly, the present disclosure may provide systems and methods for production of carbon nano-scale structures, such as carbon nanotubes or carbon nanofiber, and, moreparticularly, disclosed are systems and methods for production of carbon nano-scale structures using plasma generated active catalyst and a carbon reactant. The methods and systems may include any of the various features disclosed herein, including one or more of the following embodiments.

[0063] Embodiment 1. A method for forming carbon nanotubes comprising: volatilizing a metal in a plasma to form an active catalyst; introducing a hydrocarbon stream comprising methane into a hydrocarbon conversion unit and converting at least a portion of the methane into 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 at 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.

[0064] Embodiment 2. The method of embodiment 1 wherein the metal comprises a metal alloy comprises at least two metals selected from the group consisting of iron, nickel, cobalt, manganese, tungsten, molybdenum, and combinations thereof.

[0065] Embodiment 3. The method of any of embodiments 1-2 wherein the metal comprises an elemental metal selected from the group consisting of iron, nickel, cobalt, manganese, tungsten, and molybdenum.

[0066] Embodiment 4. The method of any of embodiments 1-3 wherein the active catalyst comprises nanoparticles having a size in a range of about I nm to about 50 nm.

[0067] Embodiment 5. The method of any of embodiments 1-4 wherein the hydrocarbon conversion unit comprises 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 hydrocarbons in the hydrocarbon stream are reacted to form the carbon reactant.

[0068] Embodiment 6. The method of any of embodiments 1-5 further comprising quenching the carbon reactant after contacting the second plasma.

[0069] Embodiment 7. The method of any of embodiments 1-6 wherein the second plasma is generated by at least one generator selected from the group consisting of a DC plasma generator, an RF plasma generator, a micro wave plasma generator, an inductively coupled plasma generator, an arc plasma generator, and combinations thereof.

[0070] Embodiment 8. The method of any of embodiments 1-7 wherein the hydrocarbon conversion unit comprises a reverse flow reactor wherein the reverse flow reactor comprises afirst zone, a second zone, and a reaction zone intermediate to the first and second zones, and wherein the method further comprises: passing the hydrocarbon stream from the first zone to the second zone of the reverse flow reactor; transferring heat in the first zone from the thermal mass to the hydrocarbon stream as the hydrocarbon stream is passed proximate to the thermal mass; passing the hydrocarbon stream proximate to the thermal mass in the reaction zone to expose the hydrocarbon stream to a peak pyrolysis temperature in the range of from about 850° C. to about 1200° C., at a hydrocarbon partial pressure =248 kPa absolute, to form the carbon reactant; and transferring heat in the second zone from carbon reactant to the thermal mass to cool the carbon reactant to a temperature below the peak pyrolysis temperature.

[0071] Embodiment 9. The method of any of embodiments 1-8 wherein the metal is introduced into the plasma as a powder, as granular form, as an electrode within the plasma, as a bar. as a wire, or a combination thereof.

[0072] Embodiment 10. The method of any of embodiments 1-9 wherein the metal is introduced into the plasma in a molten metal form and / or dissolved into a carrier fluid as a metal solution.

[0073] Embodiment 11. The method of any of embodiments 1-10 further comprising introducing a carrier gas into the plasma and w herein a feed to the floating catalyst chemical vapor deposition reactor includes the activated metal catalyst suspended in the carrier gas.

[0074] Embodiment 12. The method of any of embodiments 1-11 wherein the carrier gas comprises at least one gas selected from the group consisting of a noble gas, hydrogen helium, and combinations thereof.

[0075] Embodiment 13. The method of any of embodiments 1-12 wherein a feed to the floating catalyst chemical vapor deposition reactor comprises the carbon reactant in an amount of about 1 vol.% to about 10 vol.% of the feed, a hydrogen co-feed in an amount of about 20 vol.% to about 50 vol.%. of the feed, and a earner gas in an amount of about 50 vol.% to about 80 vol.% of the feed.

[0076] Embodiment 14. The method of any of embodiments 1-13 wherein the active catalyst and the carbon reactant turbulently flow through the floating catalyst chemical vapor deposition reactor.

[0077] Embodiment 15. The method of any of embodiments 1-14 wherein a Reynolds number of the active catalyst and carbon source flowing through the floating catalyst chemical vapor deposition reactor is in a range of about 5,000 to about 20,000.

[0078] Embodiment 16. A reaction system for forming carbon nanotubes comprising: a catalyst generation unit comprising: 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 volatizes the metalalloy to form an active catalyst; a hydrocarbon source comprising methane; a hydrocarbon conversion unit, wherein the hydrocarbon conversion unit is configured to take as input the hydrocarbon source and convert at least a portion of the methane into carbon reactant comprising ethylene, acetylene, or a combination thereof; and a floating catalyst chemical vapor deposition reactor comprising: a reaction zone; and an inlet for the active catalyst and the carbon reactant, wherein the floating catalyst chemical vapor deposition reactor is fluidically coupled to the catalyst generation unit and the hydrocarbon conversion unit such that the active catalyst and the carbon reactant are contacted in the reaction zone.

[0079] Embodiment 17. The reaction system of embodiment 16 wherein the hydrocarbon conversion unit comprises 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 hydrocarbons in the hydrocarbon source are reacted to form the carbon reactant.

[0080] Embodiment 18. The reaction system of any of embodiments 1-17 wherein the plasma generator is at least one selected from the group consisting of a DC plasma generator, an RF plasma generator, a microwave plasma generator, an inductively coupled plasma generator, an arc plasma generator, and combinations thereof.

[0081] Embodiment 19. The reaction system of any of embodiments 1-18 wherein the hydrocarbon conversion unit comprises a reverse flow reactor wherein the reverse flow reactor comprises a first zone, a second zone, and a reaction zone intermediate to the first and second zones.

[0082] Embodiment 20. The reaction system of any of embodiments 1-19 wherein the reverse flow reactor is configured to: pass the hydrocarbon source from the first zone to the second zone of the reverse flow reactor; transfer heat in the first zone from the thermal mass to the hydrocarbon source as the hydrocarbon source is passed proximate to the thermal mass; pass the hydrocarbon stream proximate to the thermal mass in the reaction zone to expose the hydrocarbon stream to a peak pyrolysis temperature; and transfer heat in the second zone from carbon reactant to the thermal mass to cool the carbon reactant to a temperature below the peak pyrolysis temperature.

[0083] While the disclosure has been described with respect to a number of embodiments and examples, those skilled in the art, having benefit of this disclosure, will appreciate that other embodiments can be devised which do not depart from the scope and spirit of the disclosure as disclosed herein. Although individual embodiments are discussed, the present disclosure covers all combinations of all those embodiments.

[0084] While compositions, methods, and processes are described herein in terms of "comprising." "containing." “having,’" or “including” various components or steps, the compositions and methods can also “consist essentially of’ or “consist of’ the various components and steps. The phrases, unless otherwise specified, “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, so long as such steps, elements, or materials, do not affect the basic and novel characteristics of the disclosure, additionally, they do not exclude impurities and variances normally associated with the elements and materials used.

[0085] All numerical values within the detailed description are modified by “about” the indicated value, and take into account experimental error and variations that would be expected by a person having ordinary skill in the art.

[0086] As used in the disclosure and in the claims which follow, the phrases a, an, and any grammatical variations mean one or more. A reference to a step, an element, a material, etc. encompasses one step, one element, and one material as well as one or more steps, one or more elements, and one or more materials.

[0087] Many alterations, modifications, and variations will be apparent to those skilled in the art in light of the foregoing description without departing from the spirit or scope of the present disclosure and that when numerical lower limits and numerical upper limits are listed herein, ranges from any lower limit to any upper limit are contemplated.

Claims

CLAIMS;1. A method for forming carbon nanotubes comprising: volatilizing a metal in a plasma to form an active catalyst; introducing a hydrocarbon stream comprising methane into a hydrocarbon conversion unit and converting at least a portion of the methane into 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 at 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.

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

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

4. The method of claim 1 wherein the active catalyst comprises nanoparticles having a size in a range of about 1 nm to about 50 nm.

5. The method of claim 1 wherein the hydrocarbon conversion unit comprises 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 hydrocarbons in the hydrocarbon stream are reacted to form the carbon reactant.

6. The method of claim 5 further comprising quenching the carbon reactant after contacting the second plasma.

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

8. The method of claim 1 wherein the hydrocarbon conversion unit comprises a reverse flow reactor wherein the reverse flow reactor comprises a first zone, a second zone, and a reaction zone intermediate to the first and second zones, and wherein the method further comprises: passing the hydrocarbon stream from the first zone to the second zone of the reverse flow reactor; transferring heat in the first zone from the thermal mass to the hydrocarbon stream as the hydrocarbon stream is passed proximate to the thermal mass; passing the hydrocarbon stream proximate to the thermal mass in the reaction zone to expose the hydrocarbon stream to a peak pyrolysis temperature in the range of from about 850° C. to about 1200° C., at a hydrocarbon partial pressure ^48 kPa absolute, to form the carbon reactant; and transferring heat in the second zone from carbon reactant to the thermal mass to cool the carbon reactant 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 granular form, as an electrode within the plasma, as a bar, as a wire, or a combination thereof.

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

11. The method of claim 1 further comprising introducing a carrier gas into the plasma and wherein a feed to the floating catalyst chemical vapor deposition reactor includes the 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 the group consisting of a noble gas, hydrogen helium, and combinations thereof.

13. The method of claim 1 wherein a feed to the floating catalyst chemical vapor deposition reactor comprises the carbon reactant in an amount of about 1 vol.% to about 10 vol.% of the feed, a hydrogen co-feed in an amount of about 20 vol.% to about 50 vol.%. of the feed, and a carrier gas in an amount of about 50 vol.% to about 80 vol.% of the feed.

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

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

16. A reaction system for forming carbon nanotubes comprising: a catalyst generation unit comprising: 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 volatizes the metal alloy to form an active catalyst; a hydrocarbon source comprising methane; a hydrocarbon conversion unit, wherein the hydrocarbon conversion unit is configured to take as input the hydrocarbon source and convert at least a portion of the methane into carbon reactant comprising ethylene, acetylene, or a combination thereof; and a floating catalyst chemical vapor deposition reactor comprising: a reaction zone; and an inlet for the active catalyst and the carbon reactant, wherein the floating catalyst chemical vapor deposition reactor is fluidically coupled to the catalyst generation unit and the hydrocarbon conversion unit such that the active catalyst and the carbon reactant are contacted in the reaction zone.

17. The reaction system of claim 1 wherein the hydrocarbon conversion unit comprises 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 hydrocarbons in the hydrocarbon source are reacted to form the carbon reactant.

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

19. The reaction system of claim 16 wherein the hydrocarbon conversion unit comprises a reverse flow reactor wherein the reverse flow reactor comprises a first zone, a second zone, and a reaction zone intermediate to the first and second zones.

20. The reaction system of claim 19 wherein the reverse flow reactor is configured to: pass the hydrocarbon source from the first zone to the second zone of the reverse flow reactor; transfer heat in the first zone from the thermal mass to the hydrocarbon source as the hydrocarbon source is passed proximate to the thermal mass; pass the hydrocarbon stream proximate to the thermal mass in the reaction zone to expose the hydrocarbon stream to a peak pyrolysis temperature; and transfer heat in the second zone from carbon reactant to the thermal mass to cool the carbon reactant to a temperature below the peak pyrolysis temperature.

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