HK1167695B - Method for producing solid carbon by reducing carbon oxides - Google Patents

Description

Method for reducing carbon oxides to solid carbon

RELATED APPLICATIONS

The present application claims priority from united states provisional patent application serial No. 61170199, filed 4/17/2009, entitled "method of reducing carbon oxides to produce solid carbon". The contents of this application are incorporated herein by reference in their entirety.

Background

In general, the present application relates to a catalytic conversion process that produces valuable solid carbon by reducing carbon oxides. Specifically, a method for producing solid carbon (e.g., buckminsterfullerene) by reducing a carbon-oxygen compound (e.g., carbon monoxide, carbon dioxide) as a carbon source with a reducing agent (e.g., hydrogen or hydrocarbon) in the presence of an existing catalyst. The process is useful for the commercial production of solid carbon products in a variety of forms and can catalytically convert the carbon oxides mentioned to solid carbon and water.

These processes produce solid carbon products from carbon oxides. The process of the present invention is used to produce solid carbon products such as buckminster fullerenes using carbon oxidation as the principal carbon source. Thus, the present process involves a process for converting carbon oxides (primarily carbon monoxide and carbon dioxide) to solid carbon and water by catalysis. The carbon oxides used in the process may be derived from the atmosphere, combustion gases, process off-gases, well natural gases, other natural and industrial feedstocks. The desired carbon oxides are obtained by separating the above feedstocks and collecting them therefrom.

Solid carbon has many commercial applications. These applications include long standing uses such as the use of carbon black and the use of carbon fibers as filler materials in tires, inks, and the like, the use of many various forms of graphite (e.g., the use of pyrolytic graphite as a heat shield), and the innovative emerging applications of buckminster fullerenes, including babbitt carbon spheres and cloth-based tubes. The production of solid carbon in its various forms, under the action of suitable catalysts, has previously generally involved a variety of hydrocarbons, mostly natural gas. The use of hydrocarbons as carbon sources has historically been due to the availability and low cost of abundance of hydrocarbons. The use of carbon oxides as a carbon source in the reduction reaction to produce solid carbon products is largely unutilized.

The process scheme uses 2 rich feedstocks, carbon oxides (e.g., carbon dioxide (CO)₂) And carbon monoxide (CO)) and a reductant. The reducing agent is preferably a hydrocarbon gas (e.g., natural gas, methane, etc.), hydrogen (H)₂) Or mixtures of the above. The hydrocarbon gas provides the dual function of both as an additional carbon source and as a reductant for the carbon-oxygen compound. The synthesis gas is mainly composed of carbon monoxide (CO) and hydrogen (H)₂) The composition, and therefore the gas of the mixed species, has both a carbon-oxygen compound and a reducing gas. It may be advantageous to use synthesis gas for all or part of the reaction gas mixture.

Carbon oxides, particularly carbon dioxide, are abundant gases that can be extracted from point source emissions (e.g., exhaust gases from hydrocarbon combustion), as well as from certain degassing processes. Carbon dioxide may also be extracted from the air. Point-source emissions tend to be an economical feedstock for carbon dioxide capture due to their higher concentration of carbon dioxide than the atmosphere. The direct availability of air can reduce costs that result from eliminating transportation costs by utilizing carbon dioxide from the local air to produce solid carbon products.

Carbon dioxide has an ever increasing availability and cheapness, and since carbon dioxide is a by-product of power generation and chemical processes, it is desirable to capture carbon dioxide and subsequent sequestration (typically via an injected formation) for the purpose of avoiding carbon dioxide emissions to the atmosphere. For example, carbon dioxide capture and sequestration is the basis for "green" coal fired power stations. In current practice, the capture and sequestration of carbon dioxide requires substantial expense. The carbon dioxide of interest to the process flow disclosed in this application is an economically valuable by-product rather than the disposal costs associated with non-valuable waste products.

The processes disclosed herein can be incorporated into power production and industrial processes for the sequestration of carbon oxides and the conversion thereof to valuable solid carbon products. For example, carbon oxides in combustion or process off-gases may be separated and collected as feedstock for the process. In some cases, these methods may be incorporated directly into the process flow without the need for separation and collection, for example, as an intermediate step in a multi-stage gas turbine power plant. The process is very suitable for oxyfuel combustion processes, with direct incorporation into the process.

Catalytic conversion processes can now be incorporated into the combustion process with fossil fuels. Many methods of combining catalytic conversion processes with various combustion processes and power production cycles will emerge in the art. These processes include adding a catalytic converter in two stages of the power production cycle, passing the combustion gas through the catalytic converter and converting at least a portion of the carbon oxides therein to solid carbon; or separating all or part of the carbon oxides from the gas from the combustion process and passing the separated gas to a catalytic reduction converter.

Combining the catalytic conversion process with the separation process may be beneficial because it will provide a carbon separation sequestration unit that is more economical than existing separation sequestration methods. The specific method of combining a catalytic converter with various separation processes using heat generated in the catalytic converter to provide at least some process heat for the separation process, and the equipment and costs associated with compression, liquefaction, and transportation, will be reduced as the catalytic converter may use lower pressure carbon oxides, and operating efficiency may be increased. For example, a separation process, such as amine absorption, may receive at least a portion of the heat required for the dissociation from the catalytic converter and provide low pressure carbon oxide gas to the catalytic converter.

There are also some limited number of ways in which carbon, oxygen and hydrogen can react. There is a spectrum of reactions involving these three elements, where the various equilibrium states have been named. Hydrocarbon cracking reactions in the range of hydrogen equilibrium states to carbon equilibrium states are favored for solid carbon production, typically cracking reactions in the presence of little or no oxygen. The Boudouard reaction, also known as carbon monoxide disproportionation, is a range of equilibrium states between carbon and oxygen that favors the production of solid carbon, usually with little or no hydrogen present. The Bosch reaction occurs in an equilibrium region that favors the production of solid carbon, where carbon, oxygen, and hydrogen are all present. Other equilibrium states favor the production of hydrocarbons or oxygenates (e.g., sabatier and Fischer-Tropsch processes) without the production of solid carbon products.

The relationship between the hydrocarbon cracking reaction, the Boudouard reaction and the bosch reaction can be understood by the C-H-O equilibrium diagram, as shown in FIG. 21. The C-H-O equilibrium diagram in FIG. 21 shows various known Carbon Nanotube (CNT) formation routes. The hydrocarbon cracking reaction is at the connection H₂And on the balance line of C: to the left of the component triangle. The reaction on this line is a conclusion that has been published by some researchers that confirms that the CNTs react at different points of this line. The use of hydrocarbon cracking reactions in the preparation of CNTs has been disclosed in a number of patents. The Boudouard reaction or the disproportionation of carbon monoxide is carried out in the presence of a catalyst in the linkage with O₂And on the balance line of C: the right side of the composition triangle. Equilibrium lines through the phase diagram at different temperatures represent the approximate region in which solid carbon will form. For any one temperature, solid carbon will form in the region above the corresponding equilibrium line, but not in the region below the equilibrium line.

The process of the invention, which is based primarily on the Bosch reaction, is based on the composition of a triangular intermediate region, which is an equilibrium state established between solid carbon and carbon, hydrogen and oxygen in different configurations. Some of the points in the intermediate zone disclosed herein are in fact highly advantageous for the production of CNTs and some other forms of solid carbon products, and the form of the solid carbon product can be selectively controlled by careful selection of the catalyst, reactant gases and reaction conditions. Thus, these processes open new avenues for producing valuable solid carbon products (e.g., CNTs).

The Ellingham diagram defines the enthalpy of equilibrium formation of solid carbon in a carbonaceous gas as a function of temperature. This diagram is well known in the art and is a very useful reference for understanding the scope of the equilibrium state.

The process of the present invention employs the Bosch reaction to produce valuable solid carbon products. Bosch reactionIs a reaction in which carbon dioxide is reduced by hydrogen to produce solid carbon and water. The variation of the Bosch reaction temperature reported in the literature ranges from 450 ℃ to more than 2000 ℃. In the case of a catalyst (e.g., iron) used, the reaction rate is generally increased and the reaction temperature is decreased.

Heretofore, the Bosch reaction was used for the purpose of recovering oxygen during respiration in a closed, isolated environment such as a submarine, airship, moon or mars base (see U.S. Pat. No. 4452627, Carbon dioxide conversion System for oxygen recovery, Birbarta et al; and U.S. Pat. No. 1735925, Process of production reduction products of Carbon dioxide reduction products, Jaeger). Typically, solid carbon refers to the particular graphite deposited on the solid catalyst bed or collection plate and is considered a detrimental action that contaminates the catalyst and must be removed. There has been little prior disclosure of the value of different forms of solid carbon produced by modification of this process, and little prior disclosure of solid carbon as the primary product required in these reactions.

The Boudouard reaction, also known as carbon monoxide disproportionation, proceeds in the following manner:

at least three aspects of the process of the present invention that differ from the Boudouard reaction are: i) carbon monoxide is not essential to the process, although it may serve as a carbon source; ii) reducing the carbon monoxide to form solid carbon and water using a separate reductant; and iii) carbon dioxide is not a reaction product.

A recent group of patents discloses the use of carbon monoxide as a carbon source to form carbon nanotubes. The production of solid carbon using carbon monoxide is by a disproportionation reaction or Boudouard reaction. Smalley (U.S. Pat. No. 6761870) discloses the use of a carbon monoxide disproportionation reaction in the presence of a catalyst to produce single-walled carbon nanotubes that are vapor phase nucleated and grown in high pressure CO.

Nasibulin et al inA Novel Hybrid Carbon MaterialA novel mixed carbon material (see Nature Nanotechnology Natural Nanotechnology 2, p. 156-161, 2006) discloses the preparation of so-called nanobuds in two different one-stop continuous processes, during which fullerenes are produced on iron-catalytic particles together with SWNTs (single-arm nanotubes) by carbon monoxide disproportionation. This is a representative carbon monoxide disproportionation application in the literature. Nasibulin inAn essential role of CO2 and H2O during single-walled CNT synthesis from carbon monoxideThe important roles of CO2 and H2O in the synthesis of single-walled carbon nanotubes by carbon monoxide (Chemical Physics Letters, prompter of Chemical Physics 417 (2005) pp.179-184) further reveal the important effects of carbon dioxide and water during the growth of carbon nanotubes, but are particularly pointed out at the above-mentioned about 15,000In ppm concentration, the presence of carbon dioxide inhibits the formation of carbon nanotubes.

Tennent, in U.S. Pat. No. 4663230 (carbon fiber, method of producing carbon fiber, and compositions containing carbon fiber), discloses and specifies the use of carbon oxides for carbon fiber production, although his reaction is specifically directed to the reaction between a carbon-containing compound and carbon over a catalyst specifically tailored for its invention, which is essentially carbon particles encapsulated by a suitable metal core. Tennent specifically claims "wherein the compound capable of reacting with carbon is CO₂，H₂Or H₂O。”

U.S. Pat. No. 6,333,016 to Resasco et alMethod of Producing NanotubesMethods for the production of nanotubes disclose the disproportionation of carbon monoxide over a variety of Co-Mo catalysts. They do not claim any relevance to the use and presence of a reducing agent in the reaction gas mixture.

In contrast, the method of the present invention is not limited to carbon monoxide as the carbon source gas. The process of the present invention uses a reducing agent other than a carbon oxygen compound. Meanwhile, the method of the invention relies on the mixing of the carbon oxygen compound and the reducing agent to produce valuable solid carbon products under the action of the existing catalyst.

Hydrocarbon cracking reactions are well known chemical reactions and have been used in commercial production to produce carbon black, various carbon nanotubes, and buckminster fullerene products. In some of the existing processes for inventing and producing various forms of solid carbon, the form of producing solid carbon is controlled by the temperature, pressure and catalyst applied to pyrolyze the hydrocarbons. For example, U.S. patent No. 2,796,331 to Kauffman et al discloses a process for producing various forms of carbon fibers from hydrocarbons under conditions of excess hydrogen action using hydrogen sulfide as a catalyst and discloses a method for collecting carbon fibers on a solid surface, and Kauffman also claims the use of coke oven gas as a hydrocarbon source.

Wiegand et al (U.S. patent No. 2,440,424) disclose an improved process for carbon black production involving rapid and thorough doping of hydrocarbon gases, natural gas, with high velocity, regulated quantities of highly turbulent explosive flames containing oxygen far in excess of the required complete combustion explosive gases. The explosive gas is used primarily to heat a secondary "make-up gas" for decomposing hydrocarbon gases, which is introduced into a heating chamber containing far more oxygen than is available, so that the hydrocarbon cracking reaction occurs rather than combustion.

Brownlee et al (U.S. patent No. 1478730) disclose a process for producing specified carbon blacks from hydrocarbon feedstocks and ultimately increasing the yield of carbon black particles produced by pyrolysis of hydrocarbons in a gas stream (without combustion) and separating the specified carbon blacks by rapidly cooling the gas prior to contacting the regular carbon blacks, wherein the carbon black particles are formed on furnace refractory materials and other curved surfaces in the combustion zone. Brownlee protects the designated carbon black as a valuable part of its invention.

Bourdeau et al (U.S. patent No. 3378345) disclose a method of growing pyrolytic graphite whiskers into elongated crystals perpendicular to a substrate using a hydrocarbon gas containing non-stoichiometric amounts of water or carbon dioxide or a mixture of both (the ratio of hydrocarbon gas to water or carbon dioxide is 50: 1). The reaction takes place at low pressure (0.1 to 20mm Hg) and the starting temperature is 700 ℃ and 1200 ℃ and at least gradually increases in temperature (3 ℃ per minute) to 1400 ℃.

Diefendorf (U.S. Pat. No. 3172774) discloses a deposition process for pyrolyzing graphite using hydrocarbon gases where the recombination conditions are low pressure (0.2-70mm Hg) and temperature is 1450-. Low pressure is an important condition that allows carbon to form on the surface of the composite condition, which first forms carbon black in the gas phase.

Huang et al (U.S. Pat. No. 20060269466) disclose the use of hydrocarbons as a carbon source for the production of carbon fiber materials.

Li et al (U.S. patent application No. 20080118426) disclose the use of pyrolysis of a hydrocarbon source gas to produce carbon nanotubes in various morphologies. Li does not indicate the type of hydrocarbon source gas, but hydrocarbon gas is implied in the cracking description at the reaction temperature illustrated.

Fujimaki et al (U.S. Pat. No. 4014980) disclose a method for producing graphite whiskers based on a reaction of "mixing one or more gasified compounds having a condensed polycyclic structure of two to five benzene rings with an inert gas containing a small amount of CO, CO2 or H2O". According to the process claimed in the patent, Fujimaki does not indicate the use of a reduction reaction, nor does it indicate the use of carbon oxides as the main carbon source for the production of graphite whiskers.

Hydrocarbon cracking is defined as the thermal decomposition reaction of hydrocarbons. The process of the present invention, which is a branch of the field of hydrocarbon cracking in the production of solid carbon products, uses carbon oxides as a carbon source to produce solid carbon in various forms. The process of the present invention can be used with hydrocarbon gases, with the gases being used as reducing agents on carbon oxide gases and the second benefit being to drive the carbon to a solid carbon product. The importance of carbon and oxygen compounds in the selective formation of the desired carbon product has not generally been mentioned or indicated in previous hydrocarbon cracking reactions.

The Bosch reaction has been studied extensively, and several patents have also disclosed the use of the reaction in environments where oxygen recovery from the respiration process is desirable or valuable, such as in submarine or spacecraft environments. The recovery is typically accomplished by passing the carbon dioxide laden gas through a carbon dioxide concentrator and then transporting the collected carbon dioxide to a carbon dioxide reduction system. A number of carbon dioxide reduction processes have been used, including chemical and electrochemical means.

Holmes et al "A Carbon Dioxide Reduction Unit Using Bosch Reaction and Expendable Catalyst CartridgesCarbon dioxide reduction Unit Using Bosch reaction and consumable catalytic core (Kangville general motors Co., Lanli research)Heartfelt research, 11 months 1970) has disclosed the use of the Bosch reaction for the recovery of oxygen from carbon dioxide.

Birbara et al (U.S. patent No. 4,452,676) disclose a method for recovering oxygen from carbon dioxide by combining carbon dioxide with hydrogen to form formaldehyde and water using the Sabatier reaction and subsequently pyrolyzing the formaldehyde while depositing the resulting solid carbon on a non-catalytic glass substrate. Formaldehyde is pyrolyzed on a stable glass surface heated to high temperatures of about 1000-. This will have the result that the storage problem of the carbon material is reduced due to its high density.

The U.S. national aerospace agency has sponsored research into the Bosch reaction to expect that the process will be applied at different times to restore the carbon dioxide of the expired air in the space ship to oxygen. This work has produced a series of reports, published papers and academic papers. The focus of this work is the water oxygen recovery production.

Selected documents relating to the U.S. national aerospace agency-sponsored Bosch reaction include:

·A carbon dioxide reduction unit using Bosch reactioncarbon dioxide reduction Unit Using Bosch reaction

·Methods of Water Production a survey of methods considered for the ISS including Bosch and Sabatier reactionsMeasurement of the Water production pathway involving Bosch and Sabatier reactions at International space stations, Oregon State University.

·Comparison of CO2 Reduction Process-Bosch and SabatierComparison of the carbon dioxide reduction Process- -Bosch and Sabatier reactions, SAE International, July 1985, Document Number 851343.

·Bunnel，C.T.，Boyda，R.B.，and Lee，M.G.，Optimization of the Bosch CO2 Reduction Process(Bosch) dioxideOptimization of carbon reduction Process, SAE Technical Paper Series No.911451, presented 21st International Conference on Environmental Systems, San Francisco, CA, July 15-18, 1991

·Davenport，R.J.；Schubert，F.H.；Shumar，J.W.；Steenson，T.S.，Evaluation and characterization of the methane-carbon dioxide decomposition reactionEvaluation and characterization of methane-carbon oxidative decomposition reaction, Access Number: 75N27071

·Noyes，G.P.，Carbon Dioxide Reduction Processes for Spacecraft ECLSS：A Comprehensive ReviewCarbon dioxide reduction process in spacecraft ECLSS: general evaluation, SAE Technical Paper Series No.881042, Society of Automotive Engineers, Warrendale, PA, 1988.

·Arlow，M.，and Traxler，G.，CO2 Processing and O2 Reclamation System Selection Process for Future European Space ProgrammesThe future European space program CO2 processing and O2 recovery systems selection procedures, SAE Technical Paper Series No.891548, Society of Automotive Engineers, Warrendale, PA, 1989.

·Optimization of the Bosch CO2 Reduction ProcessOptimization of the reduction Process of the Bosch reaction CO2 SAE International, July 1991, Document Number 911451.

·Garmirian，J.E.，″Carbon Deposition in a Bosch Process Using a Cobalt and Nickel CatalystCarbon deposition using cobalt and nickel catalysts during the Bosch reaction ", Disservation, MIT, March 1980.

·Garmirian，J.E.，Reid，R.C.，″Carbon Deposition in a Bosch Process Using Catalysts Other than Iron《Carbon deposit by using a catalyst other than iron in the Bosch reaction Process, Annual Report, NASA-AMES Grant No. NGR22-009,723, July 1, 1978.

·Garmirian，J.E.，Manning，M.P.，Reid，R.C.，″The use of nickel and cobalt catalysts in a Bosch reactorUse of Nickel and cobalt catalysts in Bosch reactors, 1980

·Heppner，D.B.；Hallick，T.M.；Clark，D.C.；Quattrone，P.D.， Bosch-An alternate CO2 reduction technologyBosch reaction- -symbiotic CO2 reduction technology, NTRS Access Number: 80A15256

·Heppner，D.B.；Wynveen，R.A.；Schubert，F.H.，Prototype Bosch CO2 reduction subsystem for the RLSE experimentTheory of the prototype Bosch reaction CO2 reduction system in RLSE experiments, NTRS access Number: 78N15693

·Heppner，D.B.；Hallic k，T.M.；Schubert，F.H.，Performance characterization of a Bosch CO sub 2 reduction subsystemPerformance characterization of the Bosch reaction CO daughter reduction system 2, NTRS access Number: 80N22987

·Holmes，R.F.；King，C.D.；Keller，E.E.，Bosch CO2 reduction system developmentDevelopment of the Bosch reaction CO2 reduction System, NTRS Access Number: 76N22910

·Holmes，R.F.；Kelle r，E.E.；King，C.D.，A carbon dioxide reduction unit using Bosch reaction and expendable catalyst cartridgesCarbon dioxide reduction units employing Bosch reactions and consumable catalytic cores, General Dynamics Corporation, 1970, NTRS access Number: 71N12333

·Holmes，R.F.，Automation of Bosch reaction for CO2 reductionAutomation of the Bosch reaction to facilitate the reduction of CO2, NTRS Access Number: 72B10666

·Holmes，R.F.；Keller，E.E.；King，C.D.，Bosch CO2 reduction unit research and developmentResearch and development of the CO2 reduction unit of the Bosch reaction NTRS Access Number: 72A39167

·Holmes，R.F.；King，C.D.；Keller，E.E.，Bosch CO2 reduction system developmentDevelopment of the Bosch reaction CO2 reduction System, NTRS Access Number: 75N33726

·King，C.D.；Holmes，R.F.，A mature Bosch CO2 reduction technologyMature Bosch carbon dioxide reduction technology, NTRS Access Number: 77A19465

·Kusner，R.E.，″Kinetics of the Iron Catalyzed Reverse Water-Gas Shift ReactionKinetics of iron catalyzing the Water gas Shift reaction PhD Thesis, Case Institute of Technology, Ohio (1962)

·Isakson，W.E.，Snacier，K.M.，Wentrcek，P.R.，Wise，H.，Wood，B.J.″Sulfur Poisoning of Catalysts"Sulfur poisoning of catalysts", SRI, for US ERDA, Contract No. E (36-2) -0060, SRI Project 4387, 1977

·Manning，M.P.，Garmirian，J.E.，Reid，R.C.，″Carbon Deposition Studies Using Nickel and Cobalt CatalystsResearch on carbon deposition using nickel and cobalt catalysts, Ind. Eng. chem. Process Des. Dev., 1982, 21, 404-

·Manning，M.P.；Reid，R.C.，Carbon dioxide reduction by the Bosch processCarbon dioxide reduction reaction by Bosch process, NTRS access Number: 75A40882

·Manning，M.P.，″An Investigation of the Bosch ProcessInvestigation of the Bosch reaction Process ", MIT Disservation (1976)

·Manning，M.P.；Reid，R.C.；Sophonpanich，C.，Carbon deposition in the Bosch process with ruthenium and ruthenium-iron alloy catalystsCarbon deposition using ruthenium and iron alloy ruthenium catalysts during the Bosch reaction, NTRS access Number: 83N28204

·Meissner，H.P.；Reid，R.C.，The Bosch process"Bosch reaction procedure", NTRS Access Number: 72A39168

·Minemoto，M.，Etoh，T.，Ida，H.，Hatano，S.，Kamishima，N.，and Kita，Y.，Study of Air Revitalization System for Space StationStudy of gas recovery System in space station, SAE Technical Paper Series No.891576, Society of Automotive Engineers, Warrendale, Pa, 1989.

·Otsuji，K.，Hanabusa，O.，Sawada，T.，Satoh，S.，and Minemoto，M.，″An Experimental Study of the Bosch and the Sabatier CO2 Reduction ProcessesExperimental studies on the reduction of carbon dihydrides in Bosch and Sabatier reactions, SAE Technical Paper Series No.871517, presented 17th society Conference on Environmental Systems, Seattle, WA, July 1987.

·Ruston，W.R.，Warzee，M.，Hennaut，J.Waty，J.，″The Solid Reaction Products of the Catalytic Decomposition of Carbon Monoxide on Iron at 550CSolid reaction products of catalytic decomposition by Carbon monoxide at 550 ℃ under the action of iron ", Carbon, 7, 47(1969)

·Ruston，W.R.，Warzee，M.，Hennaut，J.，Waty，J.，″Basic Studies on the Growth of Carbon Deposition from Carbon Monoxide on a Metal Catalyst《Fundamental studies on the growth of carbon by deposition of carbon monoxide on metal catalysts ", d.p. report 394, Atomic Energy inventory, Winfrith (1966).

·Sacco，A.，″An Investigation of the Reactions of Carbon Dioxide，Carbon Monoxide，Methane，Hydrogen，and Water over Iron，Iron Carbides，and Iron OxideInvestigation of the reaction of carbon dioxide, carbon monoxide, methane, hydrogen with water, iron-carbon compounds, and iron oxides, PhD Thesis, MIT (1977)

·Sophonpanich，C.，Manning，M.P.，and Reid，R.C.，″Utilization of Ruthenium and Ruthenium-Iron Alloys as Bosch Process CatalystsThe use of ruthenium and ruthenium-iron alloys as catalysts for the Bosch reaction process, SAE Technical Paper Series No.820875, Society of Automotive Engineers, Warrendale, PA, 1982.

·Schubert，F.H.；Clark，D.C.；Quattrone，P.D.，Integrated testing of an electrochemical depolarized CO2 concentrator/EDC/and a Bosch CO2 reduction subsystem/BRS/Electrochemical integration test of depolarized carbon dioxide concentrator (EDC) and Bosch carbon dioxide reduction system (BRS), NTRS access Number: 77A19483

·Schubert，F.H.；Wynveen，R.A.；Hallic k，T.M.，Integration of the electrochemical depolorized CO2 concentrator with the Bosch CO2 reduction subsystemElectrochemical integration of depolarized CO2 concentrator with Bosch carbon dioxide reduction System, NTRS Access Number: 76N22907

·Wagner，Robert C.；Carrasquillo，Robyn；Edwards，James；Holmes，Roy，Maturity of the Bosch CO2 reduction technology for Space Station applicationMaturity of the Bosch carbon dioxide reduction technology applied to space stations, NTRS access Number: 89A27804, SAE Technical Paper Series No.88099.

·Global Warming & Greenhouse Gases：Integrated-Technologies Remediation of Greenhouse Gas EffectsGlobal warming&Greenhouse gases: integrated technology for restoration of greenhouse gas effect.

·Walker，P.L.，Rakszawski，J.F.，and Imperial，G.R.，Carbon Formation from Carbon Monoxide-Hydrogen Mixtures over Iron CatalystsProperties of Carbon Formed from a mixture of Carbon monoxide and hydrogen over an iron catalyst, J.Phys.chem., 73, 133, (1959)

In these previous processes, the goal was to recover oxygen, and solid carbon was only considered a hazardous product and a disposal problem. Although the Bosch reaction is used in the process proposed in the present invention, unlike previous processes, the type and quality of solid carbon that can be produced is of interest in the process of the present invention, as well as the means to control the morphology of the solid carbon through the use of catalysts, gas mixtures and process variables (e.g., temperature, pressure and retention time) to ensure the production of solid carbon products of high economic value. The method of the present invention identifies and validates a range of solid carbon products, including carbon nanotubes, that can be produced by Bosch reaction control.

Disclosure of Invention

The disclosure herein provides a method and apparatus for the efficient, commercial scale production of solid carbon products in a variety of morphologies by a reduction process using carbon oxides as the primary carbon source, wherein the carbon oxides are reduced with a reducing agent in the presence of a catalyst to produce the desired solid carbon product. The type, purity and homogeneity of the solid carbon product are controlled by the reaction conditions (time, temperature, pressure, partial pressure of the reactants) and the catalyst (including size, formation method and catalyst shape).

The process of the present invention uses the Bosch reaction to produce solid carbon products, including carbon nanotubes, by reducing carbon dioxide using any of a variety of reducing gases, such as hydrogen or formaldehyde, in the presence of a catalyst under reaction conditions most suitable for the particular desired type of solid carbon. The catalytic conversion process may be integrated with a variety of separation techniques, as well as with a number of carbon dioxide generating processes.

One of the morphologies of solid carbon products of particular interest is single-walled carbon nanotubes. It is apparent that the catalyst used has a diameter about 1.2 to 1.6 times the diameter of the finally produced single-walled carbon nanotube, thereby producing a single-walled carbon nanotube. The catalyst may be in the form of catalyst nanoparticles of the desired size or in the form of solid catalyst (e.g., in the form of a stainless steel) in which the crystal grain size of the steel is of a size characteristic of the diameter of the desired carbon nanotubes. Catalyst nanoparticles may be formed in or near the reaction zone by injection of an aerosol, wherein the concentration of catalyst precursor in each aerosol particle is as large as the desired nanoparticle size for production, as the solute (if any) vaporizes and the catalyst precursor decomposes to produce catalyst nanoparticles. By selecting the catalyst and reaction conditions, the process can be tuned to produce a relatively specific morphology of carbon.

Carbon nanotubes are very valuable because they have unique material properties including strength, current carrying capacity, thermal conductivity, and electrical conductivity. The current heavy use of carbon nanotubes includes use as additives in resin composites. The research and development of carbon nanotube applications is very extensive in a variety of different applications or applications of interest. One impediment to the widespread use of carbon nanotubes is production costs. The inventive method can help to reduce this cost.

Drawings

Other features and advantages of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, in which:

FIG. 1 depicts a view of an exemplary experimental set-up as disclosed in the examples of the present application;

FIG. 2 depicts a side view of "forest-like" grown Carbon Nanotubes (CNTs) in the form of "pillows" on a substrate produced as a result of the experiment of example 1, conducted in accordance with one embodiment of the method of the present invention;

FIG. 3 depicts a top view at 700 magnification of pillow forest sheets of CNTs produced as a result of the experiment of example 1; FIG. 4 depicts a diagram of the pillow CNTs depicted in FIG. 3 at 18,000x magnification, including forest sheets;

FIG. 5 depicts a graph of elemental analysis of typical pillow-shaped CNTs grown by forest sheet growth;

FIG. 6 depicts a sample plot of CNTs produced as a result of the experiment of example 2 at 10,000x magnification;

FIG. 7 depicts the sample plot depicted in FIG. 6 at 100,000 magnification;

FIG. 8 depicts pictures of 3161 stainless steel wafer and CNT forest sheet growth, obtained from experiments performed in accordance with the experimental description of example 3;

figure 9 depicts an area image of forest-like sheet CNTs grown according to example 3 at 2,500x magnification;

FIG. 10 depicts an image of forest-like sheet CNTs grown at 10,000 magnification according to example 3;

FIG. 11 depicts photographs of steel wool samples from experiments according to example 4;

FIG. 12 depicts an image of particles of a powder at 800 magnification according to example 4;

FIG. 13 depicts an image of particles of a powder at 120,000 magnification, according to example 4;

FIG. 14 depicts photographs of surface-grown stainless steel wire samples of graphite plates tested according to example 5;

figure 15 depicts an image of a graphite plate at 7,000x magnification according to example 5;

figure 16 depicts an image of a graphite plate at 50,000x magnification according to example 5;

FIG. 17 depicts pictures of samples of stainless steel wafers of carbon nanotube "pillow" grown fibers tested according to example 6;

FIG. 18 depicts an image of a fiber at 778 magnification grown according to the "pillow" morphology as shown in example 6 as a substructure;

FIG. 19 depicts an image of a "pincushion" at 11,000 magnification according to example 6;

FIG. 20 depicts an image of a "pincushion" at 70,000 magnification according to example 6; and

FIG. 21 depicts a C-H-O equilibrium phase diagram.

The specific implementation mode is as follows:

the tbosc reaction uses hydrogen to reduce carbon oxides to give solid carbon and water. The reaction occurs at temperatures above about 650 c under the action of the catalyst. The reaction is slightly exothermic (thermal reaction) and starts stoichiometrically:

per gram of solid carbon (C)_(S)) About release 2.3X 10³J/g heat. The reaction is a reversible reaction that can be oxidized by water and carbon dioxide to form solid carbon (in an oxygen transfer reaction), so although the reaction temperature is above about 450 c, which is the desired temperature for producing solid carbon, if the temperature is too high, the reverse reaction will increase and the overall reaction rate will decrease (reaction equilibrium is shifted to the left).

In general terms, the process of the invention involves the creation of solid carbon, particularly carbon nanotubes of varying size or morphology, wherein the formation of the carbon oxides is accomplished by combusting a combustible mixture of primarily hydrocarbons and oxygen or by injecting the carbon oxides obtained from some other source, a carbon oxide and a reducing agent into a reaction zone that has been preheated to the desired reaction temperature. The reaction generally takes place in the presence of a catalyst, since the composition and size of the catalyst are important factors in controlling the formation of the final solid carbon. The reaction conditions (temperature, pressure and residence time of the reaction gas in the reaction zone) are controlled according to the desired characteristics of the solid carbon product. The reaction gas mixture is generally recycled, and during each cycle the reaction gas mixture is passed through the reactor and through a condenser to remove excess water and to control the partial pressure of water vapor in the reaction gas mixture.

Solid carbon in a plurality of different forms can be produced by the carbon-oxygen compound reduction process of the method. Some of the solid carbon forms that may be produced include:

graphite, including pyrolytic graphite;

graphene;

carbon black;

carbon fibers;

buckminster fullerenes, including babbitt carbon spheres, single-walled carbon nanotubes, and multi-walled carbon nanotubes.

Hydrogen is only one of the reducing agents suitable for the reduction reaction of the process of the invention. The hydrocarbon gas may be used in a reduction reaction to provide hydrogen and a portion of the carbon for the reduction reaction. The generally available reducing gas mixture of one or more hydrocarbon gases, such as that found in natural gas, may be an economical option in some applications. In one embodiment, the reducing gas comprises stoichiometric amounts of formaldehyde:

CO2+CH4←→2C(s)+2H2O

wherein the amount of heat released in the exothermic reaction is undetermined.

The reaction kinetics that favor the formation of the desired species of solid carbon can be established through the use of suitable catalysts. For example, it may be possible to accelerate the reaction and to operate the reaction at low temperatures by the action of elements of subgroup VIII (such as iron) or compounds containing elements of subgroup VIII (such as iron carbide). The catalyst formed by mixing these elements can be designed to produce the desired solid carbon morphology. With the use of a catalyst, the reaction is usually completed within 5 seconds of proceeding, and depending on the appropriate reaction conditions and catalyst reaction time, may be shortened to tenths of a second.

Typically, the solid carbon formed by the Bosch reaction is present in the form of graphite. According to the process of the present invention, the morphology of the solid carbon produced is controllable by the reaction conditions, the shifted catalyst and how the catalyst is contacted with hydrogen and carbon oxides. In one embodiment, the catalyst is formed in the reaction zone by chemical reaction of a catalyst precursor compound, such as ferrocene or some other metallocene, or the condensation of some other metal-containing precursor such as pentacarbonyl with the reaction product to form a catalyst, which serves to introduce the nanoparticles into the reaction gas or deposit them on the internal surfaces of the reaction zone.

The use of catalyst precursors to form catalysts in a reaction zone tends to result in catalysts of various particle sizes, which in turn results in a corresponding distribution of solid carbon sizes (e.g., pore size of carbon nanotubes). When the catalyst precursor is introduced into the reaction zone, some portion of the catalyst may form on the surface of the solid carbon product in the reaction zone. Additional solid carbon particles then tend to form on the catalyst surface. These phenomena result in branched morphologies, such as branched carbon nanometers.

In some cases, the catalyst on the surface of the solid carbon product forms a babbitt sphere that is a partial nanobud formed by the combination of the tubular structure. The introduction of additional catalyst precursor into the reactor at a later stage with the intention of forming the desired branched or bud-like morphology is a modification of the process of the present invention, and this modification is readily apparent to the skilled person.

The catalyst may be formed by a variety of catalyst precursors. These catalyst precursors decompose to form the desired catalyst. This decomposition may occur in a manner to form a catalyst that is subsequently introduced into the reaction zone. The optional catalyst precursor has a decomposition temperature below the reaction zone temperature and therefore decomposes to form catalyst particles when the procatalyst precursor is introduced into the reaction zone. The use of a catalyst precursor is a good way to control the size of the catalyst particles. Control of the catalyst particles or catalyst particle size is a factor in controlling the morphology and diameter of the carbon nanotubes grown on the catalyst.

The catalyst precursor contains a compound of a metal known to be effective in catalyzing the reaction. For example, some metals known as effective catalysts, such as metallocenes (e.g., ferrocenes), such as hydroxylates (e.g., cobalt carbonyls), such as oxides (e.g., iron oxide, also known as rust), and the like, can decompose at temperatures below the reaction temperature. There is a wide range of suitable compounds for those skilled in the art in selecting the catalyst precursor and producing the catalyst precursor mixture for decomposition to produce the desired catalyst.

It should be noted that the addition of small amounts of a substance (e.g., sulfur) to the reaction zone may tend to act as a catalyst precursor to accelerate the growth of carbon products on the catalyst. Such promoters may be introduced into the reactor in a wide variety of compounds. Such compounds should be selected to have a decomposition temperature below the reaction temperature. For example, if sulfur is selected as a promoter based on an iron catalyst, the sulfur will likely be introduced into the reaction zone as a thiophene gas, or as droplets of thiophene in a carrier gas.

The literature on the growth of buckminster fullerenes and carbon nanotubes contains many specific methods for forming suitable catalysts. For example, it is common knowledge in the art to describe the use of catalyst precursors, catalyst promoters, hot-wire processes, and the like. Specific suitable modifications of these standard methods will readily occur to those skilled in the art.

Nucleation of the catalyst may be promoted by the use of a pulsed laser, wherein the pulses are passed through the decomposed, or decomposing, catalyst precursor and the resulting catalyst vapor in the gas. The use of such a laser lamp promotes uniformity in the size of the catalyst nanoparticles produced.

The optimum reaction temperature is produced depending on the catalyst composition and the catalyst particle size. Small particle size catalysts tend to have optimal reaction temperatures that are significantly lower than the same catalyst materials of larger particle size. The skilled person may require experimentation to determine the optimum temperature for any particular catalyst and for any catalyst size. For example, the initial reaction temperature for an iron-based catalyst in the range of about 400 c to 800 c, depends on the particle size and composition and the desired solid carbon product. That is, graphite and amorphous solid carbon are generally formed at lower temperatures and carbon nanotubes are formed at higher temperatures.

Typically, the reaction is carried out over a wide range of pressures, from near vacuum to overpressure. Increasing pressure generally increases the reaction rate. However, here, it is unknown whether there is an upper limit of the pressurization favorable for the reaction.

In another embodiment, the morphology of the carbon produced is predominantly carbon nanotubes of relatively uniform diameter. The catalyst particle size, and hence the tube diameter, is controlled by physically dispersing and dispersing aerosol of pre-prepared catalyst precursor particles, such as Fe3O4 nanoparticles, into the reaction zone. Such dispersed catalyst particles may generate one of a reactant gas or a carrier gas that was previously injected into the reaction zone.

The carbon nanotubes grow from nucleation sites, which are the catalytic particles. The catalytic particles may be discrete iron nanoparticles deposited on a steel domain structure or steel wool, or on an inert substrate such as a quartz disk. The size of the carbon nanotubes will be proportional to the size of the nucleation sites. The ratio between the catalyst particle size and the carbon nanotube diameter is considered to be about 1.3 to 1.6. A possible theoretical basis relating particle size and pore size is proposed by Nasibulin et al in "Correlation of catalyst particles to single-walled carbon nanotube diameter", although Nasibulin predicts 1.6 to be higher than that observed in normal experiments.

Steel is a readily available catalyst in many different formulations comprising various metals, which are known to be effective catalysts for the Bosch reaction. In the process of the present invention, various grades of steel and stainless steel, as well as those prepared by various treatment methods and in various forms, are used as catalysts for solid carbon growth, particularly for solid carbon nanotube growth. Small particle size steels tend to produce smaller diameter carbon nanotubes. The particle size is a function of both the chemistry of the steel and the heat treatment process used to prepare the particles. Light steel often produces carbon nanotubes with diameters in excess of 100nm, while stainless steel (e.g., 304 steel or 316L steel) produces carbon nanotubes with diameters in the 20nm range.

Various forms of steel may be suitable catalysts in the growth of carbon nanotubes. For example, steel wool, steel plates, steel shot (as used for sandblasting) provide satisfactory growth rates and the same quality. The morphology of carbon nanotubes grown on steel is dependent on the chemical morphology of the steel and the manner in which it is processed. This may be due to any of a number of factors that are not currently well understood; but its generation is related to grain size and boundary shape of the metal, where the characteristic size of these technical features controls the characteristic diameter of the population of carbon nanotubes grown on the surface of these steel samples. Suitable experimentation may determine that the correct chemistry for the steel and the treatment of the steel to obtain the desired morphology of the carbon nanotubes and with a controlled diameter is readily available to those skilled in the art.

According to the disclosed method, rust on steel is considered to be a good catalyst in the production process of carbon nanotubes. Although the reaction mechanism is not clear at present, this mechanism exists because iron oxide, including rust, is an effective oxidant precursor. Upon heating the rusted sample, the iron oxide will decompose while the iron atoms will combine to form small iron particles as a catalyst for proper carbon nanotube growth.

When using solid catalysts, such as wafers of steel, carbon nanotubes appear to form a series of growth patterns. Although the mechanism is not fully understood, interaction of the reactive gases with exposed surface particles and the onset of carbon nanotube growth at the surface has occurred. As growth continues, entanglement of the clustered adjacent tubes occurs and lifting of the catalyst particles at the surface reveals a new layer of catalyst particles, with which the reaction gases can interact. By lifting off each layer of the surface, the carbon nanotubes become highly entangled in small pieces, which look like a "pillow" or a cocklebur at a magnification of 800 to 100. If a sample remains in the reaction zone, these layers will continue to grow and lift until the catalyst is consumed and eventually carbon nanotube "pillows" of various structures (e.g., forest turns, fibers, or columns) are formed. The observed separation of the pillows from the underlying catalyst substrate means that the fluidized bed reactor, where the pillows are washed from the substrate, introduced into the gas stream, and then captured from the gas mixture, may be an economical reactor for producing carbon nanotube pillows.

The pillow morphology, as depicted for example in fig. 3 and 18, is characterized by the presence of highly entangled clusters of carbon nanotubes, particularly clusters of carbon nanotubes having dimensions below 1 mm. Thus, as depicted in the figures, the carbon nanotube pillows exhibit a large amount of spherical or pillow-shaped cohesive mixture of nanotubes, with little difference in appearance from the lumpy periphery. These pillow morphologies can include many carbon nanotube wave morphologies of different diameters, lengths and types, often occurring in discrete units of forest morphology, columnar morphology, and filament growth on the substrate. Many different compositions of steel (e.g., light steel, 304 stainless steel, 316KL stainless steel) and many different forms (e.g., steel plate, steel wool, and steel shot) tend to produce carbon nanotube pillow shapes over a wide range of reaction temperatures of the reactive gas mixer.

The observed wavy morphology of carbon nanotubes is very easy to felt. For example, if a sample of carbon nanotube pillow shapes dispersed in an ethanol solution is gently agitated and the solution is then shaken, the wave shapes may cohesively interlock such that the boundaries of apparent growth of the pillow shapes merge together and form a more extensive coverage of structural pillow shapes may be particularly suitable for paper, felt, electrodes, etc. that form carbon nanotubes of different morphologies that may have been developed or are being developed. The potential applications of these pillow shapes will be readily apparent to those skilled in the art.

Various different reaction designs are possible for promoting the formation and collection of the desired solid carbon product. Particularly aerosol and fluidized bed reactor fluid wall reactors suitable for large scale continuous production of solid carbon products, have the advantage of providing for the introduction of various materials (catalyst, additional reactants) and minimizing or eliminating solid carbon products on the reaction walls.

The catalytic converter may utilize different designs known in the art.

● aerosol reactor, which produces catalyst in the gas phase from catalyst precursors or catalyst pre-made and selected for a specific size distribution, is mixed into a liquid or carrier gas solution and then sprayed into the reactor (e.g., by spraying). The catalyst may then remain distributed in the gas phase or precipitate on the surface of the solid in the reaction zone during the growth phase of the carbon product and subsequently transport the product out of the reaction zone;

● fluidized bed reactor, wherein catalyst or catalyst coated particles are introduced into the reactor and solid carbon grows on the surface of the particles. Catalyst coated particles are introduced into the reactor and particles of solid carbon grown on the surface. Whether the solid carbon is scrubbed in the reactor and carried out of the reactor in the reaction gas or the catalyst particles are collected while the solid carbon is removed from its surface;

● batch reactor, the catalyst is either a fixed solid surface (e.g., a piece of steel, or steel wool) or is mounted on a fixed solid surface (e.g., catalyst nanoparticles deposited on an inert substrate), and the solid carbon growing on the catalyst, catalyst and solid carbon are periodically purged from the reactor.

● continuous reactor in which a solid catalyst or catalyst mounted on a solid substrate is moved by a flowing gas stream, resulting in solid carbon product being collected, the solid surface being prepared and newly introduced into the reactor. The solid substrate may be a catalytic material (e.g., stainless steel plate) or a surface on which a catalyst is mounted. Suitable plates for solid surfaces include silicon wafers, plates, rollers, or spheres.

In one embodiment of the process of the present invention, a fluidized bed reactor is used which can be designed to retain the catalyst while allowing CNTs to be entrained in the gas stream and to be thrown out high above the desired size from the reaction zone due to drag on the forming particles. This control can be achieved by the size of the reactor, the gas flow rate, or a combination of size and flow rate, while allowing for a residence time in excess of the wash and the corresponding size of the solid carbon product (e.g., length of carbon nanotubes).

The catalytic converter may be designed as a batch or continuous reactor such that solid carbon is deposited on at least one solid surface, wherein the solid surface (on which the carbon is deposited) is designed as the object of production or component associated therewith, while the solid carbon product may comprise or consist entirely of pyrolytic graphite composition, or one or more types of babbitt fullerenes. The entire surface of the object produced need not be covered with carbon. The carbon deposition area on the solid surface may be selectively defined in one or more regions by masking, or by selective deposition of a catalyst or catalyst precursor to promote the production of solid carbon on certain portions of the solid surface.

The creation of such a method of collecting and separating solid carbon products from a gas stream or solid surface will readily occur to those skilled in the art, and will also include known methods of separating solids from a gas or liquid stream. These methods of separating solid carbon products from the gas phase include, but are not limited to, washing, centrifugation, electrostatic deposition, and filtration.

The separation of the solid product from the gas stream and the catalyst depends on the type of reaction utilized. For example, the solid carbon may be collected directly from the gas stream within an aerosol reactor or washed from a fluidized bed reactor using an electrophoretic or thermomigration collector or by various filtration methods. For solid catalysts or catalysts mounted on a solid surface, the solid carbon product may be discarded from the solid support material or else be ground away.

It may be advantageous in some cases to remove the product from the reaction gas mixture for cooling (e.g., to remove solid carbon from the reactor and pass it through a purge chamber in which the reaction gas is removed by an inert purge gas such as helium). Cleaning prior to cooling helps to reduce unwanted deposition or growth of solid carbon morphology on the desired solid carbon product during cooling.

In an aerosol or fluidized bed reactor, the residence time in the growth zone can be controlled by a number of forces (e.g., attractive, electromagnetic, or centrifugal forces) that oppose the movement of the gas stream. These effects control residence time against gas flow to the plate owner, thereby allowing the size of the solid carbon product to be controlled.

In another embodiment, electrospray is an efficient way to use an aerosol reaction, which directs a pre-formed catalyst, or catalyst precursor solution, into small droplets of individual particles. Electrospray separation helps to preserve the dispersed particles so that they do not aggregate or fuse. Electrospray also tends to control the carbon particles produced and to make them easier to collect from an aerosol using an electrostatic collector.

The catalyst in the aerosol reactor may be generated by spraying a catalyst precursor or a pre-formed catalyst carrier gas or fluid transported into the reaction zone. The catalyst or catalyst precursor can be prepared beforehand and mixed with the reaction gas before the catalytic conditioning process. Catalytic conditioning by heating an inert carrier gas promotes the growth of specific helices of single-walled carbon nanotubes, such as helium, which is well known to promote the growth of metallic characteristic helicities. In addition, one or more substances may be introduced into the reaction zone to modify the physical properties of the desired solid carbon product, either by incorporation in the solid carbon product or by deposition on the surface of the solid carbon product.

In many cases, the catalyst particles are removed from the surrounding matrix that is grown as carbon nanotubes, and thus the catalyst particles can be considered to be embedded into one of the ends of the nanotubes. The catalyst ends are shown in the scanning electron microscope images to be larger (e.g., 1.3 to 1.6 times diameter) than the tube ends from which they began to grow. This may be due to the catalyst surrounding the carbon shell, or an indicative fundamental relationship between the catalyst particle size and the carbon nanotubes from which it began to grow, or due to some other factor or even coincidence. In any event, one way to control the size of the carbon nanotubes appears to be by the size of the catalytic particles, including catalytic particles that are slightly larger than the desired nanometer size.

In practice, the catalyst particle size can be controlled by a number of ways including as domains in the metal matrix. For example, light steel wool typically produces larger diameter carbon nanotubes than 316L stainless steel. The size of the carbon nanotubes is adjusted by using nanoparticles of a pre-made desired size, or by spraying droplets of the catalyst precursor, either on the surface or in an aerosol in which the catalyst particles will crystallize (the size of the final particles can be controlled by adjusting the precursor concentration and the size of the sprayed droplets).

The physical properties of solid carbon materials can be substantially modified by the use of other materials on the surface of the solid carbon. Many different modification treatments and functional modifications of the resulting solid carbon are known in the art and are readily achievable by those skilled in the art. The process of the invention contemplates the addition of modifying agents such as ammonia, thiophene, nitrogen and excess hydrogen to the reaction gas, which, according to literature records, may lead to the desired modification of the physical properties of the solid carbon. At least a portion of these modification treatments and functional modifications may be performed in the reaction zone.

Many of these modifying agents may be applied during the reaction. These species may be introduced into the reduction reaction chamber in the vicinity of completion of the solid carbon formation reaction, for example by injection of a stream containing water in which the species, such as metal ions, are stored. These species may also be introduced as a component of the carrier gas, for example, it is well known that excess hydrogen is a significant product of the desired solid carbon product produced in the hydrogenation of carbon grids, and in some cases, of the semiconductor type.

One advantage of this process is its applicability to power generation, chemical engineering and manufacturing, where combustion of a primary hydrocarbon fuel feedstock is a source of a group of electrical power and various engineering heats. The resulting combustion gas comprising carbon oxides can be used as a carbon feedstock for producing a desired solid carbon product. The process of the present invention is scalable to many different modes of production, such that, for example, operating carbon-oxygen emissions can be scheduled by implementing equipment designed for the process, either by combustion processes for large coal-fired power plants or by internal combustion engine arrangements.

In another embodiment, the carbon oxides obtained from the feed gas mixture are formed by separation and collection from the feed mixture while the carbon oxide feed is being used in the reduction process. In one embodiment, the catalytic conversion process may be used as an intermediate step in a multi-stage power extraction process, wherein the first step cools the combustion gases to the reaction temperature of the reduction process in order to produce the desired solid carbon product. The cooled combustion gas may then be passed through a reduction process and subsequently through an additional power extraction stage at the temperature required for the reduction reaction.

Combining the process of the invention with a hydrocarbon combustion process due to electricity production has the additional advantage that the hydrogen necessary for the reduction process can be formed by electrolysis of water using a low power pad. The oxygen formed during electrolysis can be used as at least part of the combustible mixture in the combustion process.

When the disclosed method is to use a hydrocarbon in conjunction with a combustion or chemical process, a portion of the hydrocarbon in the process may be used as a reductant gas. This may include decomposing hydrocarbons to form hydrogen gas for supply as a reductant gas. Suitable methods for adapting the process of the present invention to the hydrocarbon feedstock available will be readily apparent to those skilled in the art.

The reduction process of the present invention results in the formation of solid carbon products and water. The water can then be concentrated and extracted by latent heat of phase change for heating purposes, or as part of a low voltage power extraction cycle. The selection of extracted water as a useful by-product and the advantageous use of the associated latent heat of phase change is readily achievable by those skilled in the art.

Examples

Although the embodiments herein described are intended to illustrate the methods of the present invention, it will be understood that these descriptions are made only for purposes of illustration and that variations within the spirit and scope of the invention will occur to those skilled in the art. The following examples are included as illustrations of the method of the present invention.

In the following sections, each example will be described in detail with additional information, while scanning electron microscope images of the products of each example will be included.

The experimental set-up used in all the examples is depicted in FIG. 1. The experimental apparatus comprises two quartz roasting furnaces 1 and 2 connected in series. This arrangement was made to enable separate tests to be performed on each furnace simultaneously, with the potential for different reaction temperatures and different catalysts, but with the same reaction gas mixture and pressure. This arrangement allows for more rapid testing while both furnaces are running simultaneously. However, only a single furnace requires efficient operation: the arrangement of the two roasting furnaces shown is premised on the convenience of the experiment. The sample was placed in one of the baking ovens. All tests were run in batch mode. The baking oven was passed for 1 to 2 hours to reach the desired temperature and cooled for 4 to 6 hours so that the sample could be transferred. Typically, only one furnace is operated for the experiment. All of the components depicted in FIG. 1, along with their associated piping, instrumentation and accessories, are collectively referred to as an "experimental setup" and will be described in the examples of experiments that follow.

The different components of the gases used in the examples are:

● carbon dioxide (CO)₂) Research grade, plex corporation

● methane (CH)₄) Research grade, plex corporation

● Nitrogen (N)₂) Standard grade, Plax Corp

● helium (He), research grade, France liquefied air Co

● Hydrogen (H)₂) Research grade, plex corporation

As shown in fig. 1, the gas is fed from the gas supply 6 to the mixing valve 7, where the gas is measured and distributed to the furnaces 1 and 2. The gas flows through the furnaces 1 and 2, is conveyed to a refrigerated condenser 4 (dew point temperature 38 ° f), then through a compressor 3 and back to the top of the furnace 1. If a particular experiment requires the removal of inert gas from the furnace, a vacuum pump 5 will be used to evacuate the experimental apparatus.

The temperature of the first roasting furnace 1 was measured by a type K thermocouple fixed in the furnace at about the center line thereof. The temperature of second furnace 2 was measured by a type K thermocouple fixed in the insulating ceramic bore of the furnace approximately at the center line of second furnace 2. The temperatures recorded are the measured temperatures shown on these thermocouples, which, although shown in the reaction zone, are not very accurate. Similar disadvantages will occur at the exact recorded reaction temperature for any particular experimental set-up in different regions of the reaction zone. However, the final record is for recording the measured temperature, and one skilled in the relevant art can produce similar results in a similar device by appropriate experimentation and modification of the temperature.

No attempt was made to measure and control the recirculation flow while the quality of the product and the reaction rate appeared to be independent of whether the high capacity compressor or low volume pump was used. These phenomena may be due to the fact that the flow rate in each case is above a critical threshold. Flow rate is an important factor in optimizing the design and operation of the production facility, but is not particularly important in the tests recorded herein, since the volume of the experimental set-up is much larger than the volume of catalyst and ultimately produced solid carbon product. Appropriate testing determines the optimum flow rate for a particular production design, which is readily determinable by one skilled in the art.

Through experiments, the gas in the experimental device suddenly begins to drop rapidly when the pressure rises along with the temperature. Once the pressure begins to drop, the temperature changes as the catalyst and gas mixture changes. Where a sudden drop in pressure may be indicative of the onset of solid carbon product formation. The pressure is then maintained by adding additional reactant gas to the reaction apparatus. Then within a short time the pressure will start to rise, at which time the addition of the marker reaction gas will stop. The pressure drop and the time of the drop appear to represent the onset and duration of carbon nanotube growth and the growth rate.

The start-up procedure follows one of two methods: heating in an inert gas (helium or nitrogen), or heating in air. The experimental set-up was evacuated and purged for about 5 minutes with heating in an inert gas, after which the vacuum pump 5 was turned off while the experimental set-up was filled with an inert gas to atmospheric pressure. The inert gas is then turned off and the furnace is opened to begin the heating cycle. In the case of heating in air, no cleaning is required at the start-up of the furnace. It is only necessary to open the furnace and reach the desired temperature.

When the furnace reached approximately the experimental set point temperature, the experimental setup was removed and the reaction gas mixture (typically a mixture of carbon dioxide and reducing gas) was purged for 5 minutes. The reaction gas in the experimental setup then reaches atmospheric pressure while the temperature continues to increase until the anti-experimental setup measured temperature reaches the selected experimental temperature

In the examples, the furnace is controlled for a fixed time (typically 1 hour) during which the furnace is shut down, cleaned and cooled. After the furnace was closed, the vacuum pump 5 was turned on, the reaction gas was evacuated and the experimental apparatus was purged with an inert gas (helium or nitrogen) for about 5 minutes, and then the vacuum pump 5 was turned off, the experimental apparatus was filled with an inert gas to atmospheric pressure, and then cooled.

In the experiments, there was no observed difference in the quality of the CNTs product based on inert gas purging and cooling. Further testing has shown that the properties of CNTs are modified by the cooled gas mixture and the rate of cooling. Continuous flow reaction apparatus according to the description herein in the examples is readily achievable by a person skilled in the art.

Example 1

For example 1, a sample of a light steel wafer with a large number of red rust spots present was used as a catalyst. A light steel wafer is placed at about the centerline of the furnace 1. The vacuum pump 5 was started and the experimental set-up was purged with helium for 5 minutes. After 5 minutes the vacuum pump 5 was turned off, the compressor 3 was turned on and the cryocondenser 4 was turned on while continuing to feed helium gas until the pressure reached 680T and the gas flow was turned off. The furnace 1 is then started.

When the temperature of the calciner 1 reaches the set point temperature of 680 c, the vacuum pump 5 is started and the reaction apparatus is purged for 5 minutes with the stoichiometrically mixed carbon dioxide and hydrogen reaction gas supplied by the gas supply means 6 controlled by the mixing valve 7. After 5 minutes the vacuum pump 5 was switched off. When the pressure of the reaction apparatus reached 760Torr, the supply of the reaction gas was stopped. Additional reactant gas is periodically added to maintain the reactor at a gauge pressure between 640Torr and 760 Torr. After 1 hour of test run the furnace 1 was shut off, the vacuum pump 5 was started and the experimental set-up was purged with helium gas for 5 minutes, wherein the helium gas was supplied through a gas supply 6 controlled by a mixing valve 7. Then, the vacuum pump 5 was turned off, and the introduction of the helium purge gas was continued until the gauge pressure in the reaction apparatus reached 740 Torr. The cooled furnace 1 is then removed.

The steel sample was removed after the furnace 1 was cooled. Shown in FIG. 2 is a photograph of the sample after removal; note the "forest" morphology of growth on the substrate. The forest morphology is composed of carbon nanotube "waves". Figure 3 shows an electron micrograph of the same sample at 700x magnification. Figure 4 shows an electron micrograph of the same sample at 18,000x magnification and shows details of a typical "pincushion". The size of CNTs (tens to hundreds of nanometers in diameter) indicates that they are most likely multi-walled nanotubes. Note that in the attached fig. 4, the catalyst can be seen at the growth tip of each carbon nanotube. The average diameter of the growth tips appears to be about 1.2 to 1.3 times the diameter of the carbon nanotubes with which they are associated. FIG. 5 depicts an elemental analysis of the CNTs of FIG. 4, indicating that the CNTs are composed of carbon and small amounts of iron and oxygen, possibly due to catalyst particles embedded at the growth tips of the CNTs.

Example 2

For example 2, a sample of quartz disks was moved to lay down on 304 stainless steel wafers, which served as catalysts. A 304 stainless steel catalyst wafer was placed in the furnace 1at about the centerline. The vacuum pump 5 was turned on and the experimental set-up was purged with helium for 5 minutes. After 5 minutes the vacuum pump 5 was turned off, the compressor 3 was turned on, the cryocondenser 4 was turned on and the helium gas was continued to be passed in until the pressure reached 680Torr, at which time the gas inflow was stopped. The furnace 1 is then opened.

When the temperature of the calciner 1 reaches the set point temperature of 680 c, the vacuum pump 5 is started and the reaction apparatus is purged for 5 minutes with the stoichiometrically mixed carbon dioxide and hydrogen reaction gases supplied through the gas supply means 6 controlled by the mixing valve 7. After 5 minutes the vacuum pump 5 was switched off. When the pressure of the reaction apparatus reached 760Torr, the supply of the reaction gas was stopped. 1. Additional reactant gas is periodically added to maintain the reactor at a gauge pressure of between 640 and 760 Torr. After 1 hour of test run the furnace 1 was shut off, the vacuum pump 5 was started and the experimental set-up was purged with helium gas for 5 minutes, wherein the helium gas was supplied through a gas supply 6 controlled by a mixing valve 7. Then, the vacuum pump 5 was turned off, and the introduction of the helium purge gas was continued until the gauge pressure in the reaction apparatus reached 740 Torr. The furnace 1 is then removed and cooled.

After cooling furnace 1, the steel sample was removed from furnace 1. The fiber mesh of CNTs is grown between quartz and wafers. Part of the CNT fiber mesh was adhered to the quartz and steel catalyst wafer surfaces. FIG. 6 shows an electron micrograph of the sample at 10,000 magnification, and FIG. 7 shows an electron micrograph of the sample at 100,000 magnification. The size of CNTs (tens to hundreds of nanometers in diameter) indicates that they may be multi-walled nanotubes.

Example 3

For example 3, 316L stainless steel wafers were used as catalysts. A 316L stainless steel wafer was placed in furnace 1at about the centerline. The compressor 3 was turned on, the cryocondenser 4 was turned on, the vacuum pump 5 was turned on, and a purge gas containing helium gas was introduced into the experimental apparatus, wherein the purge gas was supplied through the gas supply device 6 controlled by the mixing valve 7. After 5 minutes of cleaning, the vacuum pump 5 was turned off while continuing to introduce helium cleaning gas until the experimental apparatus reached a gauge pressure of 680Torr, and the flow of cleaning gas was turned off

When the temperature of the furnace 1 reaches 700 c, the vacuum pump 5 is started and the reaction gas, which is supplied by the gas supply means 6 controlled by the mixing valve 7, is passed through the reaction means with a stoichiometric mixture of carbon dioxide and hydrogen. After 5 minutes, the vacuum pump 5 was turned off while continuing to introduce the reaction gas until the experimental apparatus reached a gauge pressure of 730Torr, at which time the flow rate of the reaction gas was reduced to a low flow rate sufficient to maintain the pressure between 700Torr and 730 Torr. After the experimental set-up had run for 1 hour, the furnace 1 was closed and the vacuum pump 5 was started while the experimental set-up was purged with helium gas for 5 minutes, wherein the helium gas was supplied through a gas supply 6 controlled by a mixing valve 7. The vacuum pump 5 was then turned off while continuing to introduce helium gas until the gauge pressure in the experimental apparatus reached 760 Torr. The furnace 1 is then removed and cooled.

After cooling furnace 1, the steel sample was removed from furnace 1. After cooling furnace 1, the 316L stainless steel wafers were removed from furnace 1. Figure 8 is a photograph of a 316L stainless steel wafer. Note the solid carbon product, where carbon nanotubes are grown on only a portion of the wafer. The cause of this phenomenon is not clear. Fig. 9 depicts an image of a CNT forest-like area on a wafer at 2,500x magnification, and fig. 10 is an image of the same CNT forest-like area at 10,000x magnification. The resulting diameter of the tube shows that CNTs are more likely to be multi-walled.

Example 4

For example 4, a sample of light steel velvet was used as the catalyst. Light steel wool was placed in the furnace 1at about the center line and heated in air. The calciner 1 was started and the compressor 3 was turned on while the cryocondenser 4 was turned on, the vacuum pump 5 was started when the calciner 1 reached 645 c (i.e. before the calciner 1 reached the set point temperature of 700 c) and the stoichiometrically mixed carbon dioxide and hydrogen gas supplied by the gas supply means 6 controlled by the mixing valve 7 was passed to the experimental set-up for 5 minutes. After 5 minutes, the vacuum pump 5 was turned off while continuing to introduce gas until the experimental apparatus reached a gauge pressure of 530Torr, and the flow rate of the reaction gas was decreased to a flow rate sufficient to maintain the pressure at a low level between 500Torr and 530 Torr. After the experimental set-up had run for 1 hour, the furnace 1 was closed and the vacuum pump 5 was started while the experimental set-up was purged with helium gas for 5 minutes, wherein the helium gas was supplied through a gas supply 6 controlled by a mixing valve 7. The vacuum pump 5 was then turned off and helium gas was continued to be introduced until the gauge pressure in the experimental apparatus reached 760 Torr. The cooled furnace 1 is then removed.

After cooling the calciner 1 the steel wool is removed together with the solid carbon product. Figure 11 is a photograph of a steel wool sample. Note the powdery black band of the solid carbon product, which by sampling and SEM examination yields an ion image of the powder at 800x magnification as depicted in fig. 12. The particles are a "wave" of a multitude of wave forms including powdery black bands. FIG. 13 depicts the same "waveform" image at 120,000 magnification. This diameter indicates that the CNTs may be multi-walled.

Example 5

For example 5, sample No. 316 stainless steel wire was used as the catalyst. A 316 stainless steel wire was placed in furnace 1at about the centerline and heated in air. The furnace 1 is opened and the cryocondenser 4 is opened. The vacuum pump 5 was turned on and the reaction gas comprising stoichiometrically mixed carbon dioxide and hydrogen, supplied through the gas supply means 6 controlled by the mixing valve 7, was used to clean the experimental apparatus for 5 minutes. After 5 minutes, the vacuum pump 5 was turned off and the compressor 3 was turned on while continuing to introduce the reaction gas mixture until the gage pressure in the experimental apparatus reached 589Torr, and the inflow of the reaction gas was stopped. The experimental setup was run for 1 hour with the furnace 1 closed and the vacuum pump 5 turned on while the experimental setup was purged with helium gas for 5 minutes, where the helium gas was supplied through a gas supply 6 controlled by a mixing valve 7. The vacuum pump 5 was then turned off while continuing to introduce helium gas until the gauge pressure in the experimental apparatus reached 700 Torr. The cooled furnace 1 is then removed.

After cooling the furnace 1, the steel wire was removed from the furnace 1. Figure 14 is a photograph of a sample of steel wire with a solid carbon product grown on the surface on a graphite plate in this example. The images of the graphite sheet samples are the image of the graphite sheet at 7,000x magnification shown in figure 15 and the detailed image of the graphite sheet at 50,000x magnification shown in figure 16 produced by SEM.

Example 6

For example 6, 304 stainless steel wafers were used as catalysts. A sample of a quartz magnetic disk was placed on the upper surface of a steel wafer. A 304 stainless steel wafer was placed in the furnace 1at about the centerline along with the quartz disk. The vacuum pump 5 was turned on and the reaction gas comprising stoichiometrically mixed carbon dioxide and hydrogen, supplied through the gas supply means 6 controlled by the mixing valve 7, was used to clean the experimental apparatus for 5 minutes. After 5 minutes, the vacuum pump 5 was turned off, the compressor 3 was turned on, and the cooling condenser 4 was turned on while continuing to introduce helium gas until the pressure in the experimental apparatus reached 680Torr, and the inflow of the reaction gas was stopped. The cooled furnace 1 is then removed.

When the temperature of the roasting furnace 1 reached the set point temperature of 650 c, the vacuum pump 5 was started and the experimental set-up was purged for 5 minutes with the stoichiometrically mixed carbon dioxide and hydrogen reaction gas supplied through the gas supply means 6 controlled by the mixing valve 7. After 5 minutes the vacuum pump 5 was switched off. When the experimental set-up reached 730Torr gauge, the reaction gases were stopped. The reactor pressure was maintained between 640Torr and 760Torr by the periodic addition of additional reactant gas. After 1 hour of test run the furnace 1 was shut off, the vacuum pump 5 was started and the experimental set-up was purged with helium gas for 5 minutes, wherein the helium gas was supplied through a gas supply 6 controlled by a mixing valve 7. Then, the vacuum pump 5 was turned off, and the introduction of the helium purge gas was continued until the gauge pressure in the reaction apparatus reached 740 Torr. The cooled furnace 1 is then removed.

Figure 17 is a photograph of a sample grown on the surface of a graphite plate. The image of the graphite plate sample is an image of the graphite plate at 778x magnification as shown in figure 18 produced using SEM. The waveform shown in fig. 18 includes a fiber morphology. Fig. 19 shows an image of a waveform at 11000x magnification in which highly entangled carbon nanotube structures can be seen. FIG. 20 is a detailed view at 7000 magnification of some carbon nanotubes including the same waveform as shown in FIG. 19.

Thus, the present invention has technical advantages over the prior inventions. While embodiments of the method of the present invention have been described, various modifications and improvements will be apparent to those skilled in the art. Such alterations, modifications, and improvements are intended to be part of this disclosure, and are intended to be within the spirit and scope of the invention.

Claims (56)

1. A method of producing a solid carbon product, the method comprising:

mixing a first gaseous stream comprising carbon dioxide with a second gaseous stream comprising a gaseous reducing agent to form a gaseous reaction mixture;

injecting the gaseous reaction mixture into a reaction zone; and

reacting carbon dioxide with a gaseous reducing agent in a reaction zone in the presence of an iron-containing catalyst to form water and a solid carbon product; and is

Separating at least a portion of the water produced in the reaction zone from the reaction gas mixture during the reaction of the carbon dioxide with the gaseous reducing agent;

the reaction gas mixture was passed through a condenser to remove water produced in the reaction zone.

2. The method of claim 1, wherein reacting carbon dioxide with a gaseous reducing agent in the presence of an iron-containing catalyst in a reaction zone comprises forming single-walled carbon nanotubes, multi-walled carbon nanotubes, carbon nanotube fibers, graphite platelets, graphene, carbon black, amorphous carbon, or a combination thereof.

3. The method of claim 1, wherein reacting carbon dioxide with a gaseous reducing agent in a reaction zone comprises forming a carbon nanotube wave-shaped morphology produced by highly entangled agglomeration of carbon nanotubes.

4. The method of claim 1, further comprising:

circulating the reaction gas mixture from the reaction zone into a condensing zone to remove moisture from the reaction gas mixture to produce a dry cycle gas mixture; while the recycle gas mixture is recycled into the reaction zone.

5. The method of claim 4, further comprising mixing the dry recycle gas mixture with the reactant gas mixture to produce a gas mixture that is provided to the reaction zone.

6. The method of claim 1, further comprising heating the reaction gas mixture or the reaction zone prior to providing the reaction gas mixture to the reaction zone.

7. The method of claim 1, further comprising:

maintaining the reaction conditions in the reaction zone constant;

continuously flowing a stream of reactant gas into the reaction zone for a period of time;

removing at least a portion of the solid carbon product from the reaction zone.

8. The method of claim 1, wherein providing the gaseous reaction mixture to the reaction zone comprises controlling at least one of:

reaction gas mixture temperature;

the pressure of the reaction zone;

partial pressure of the reaction gas mixture;

reaction gas mixture composition;

the temperature in the reaction zone;

the residence time of the reaction gas mixture in the reaction zone;

the residence time of the solid carbon product in the reaction zone;

catalyst particle size;

the manner in which the catalyst is produced;

morphology of the catalyst.

9. The method of claim 1, further comprising separating a first gas stream comprising carbon dioxide from at least one of a mixed gas, atmospheric air, combustion gases, process off-gases, waste gases produced during Portland cement production, or well gases.

10. The method of claim 1, further comprising continuously transporting portions of the reactant gas mixture and solid carbon product from the reaction zone to a separation process for separating the solid carbon product from the reactant gas mixture.

11. The method of claim 10, further comprising transporting the separated solid carbon product to a purge chamber, purging the solid carbon product with an inert purge gas to remove residual reactant gas from the mixture, and cooling the solid carbon product.

12. The method of claim 1, further comprising: stopping the flow of reactant gas to the reaction zone; removing the reaction gas from the reaction zone; providing an inert gas to the reaction zone; cooling the solid carbon product in the reaction zone; and removing the solid carbon from the reaction zone.

13. The method of claim 1, further comprising passing the carbon nanotubes formed in the reaction zone through a growth and annealing zone.

14. The method of claim 1, further comprising cooling the solid carbon product.

15. The method of claim 14, wherein cooling the solid carbon product comprises replacing the reaction gas with an inert purge gas.

16. The method of claim 1, wherein the iron-containing catalyst comprises steel or is formed from the reduction of one or more oxides comprising steel constituents.

17. The method of claim 1, wherein the iron-containing catalyst comprises iron atoms resulting from decomposition of iron oxide.

18. The method of claim 1, wherein the iron-containing catalyst comprises iron oxide, or iron carbide.

19. The process of claim 1, wherein the iron-containing catalyst is provided to the reaction zone by a predetermined carrier gas.

20. The method of claim 19 wherein the carrier gas comprises a mixture of one or more inert gases and carbon dioxide.

21. The method of claim 1, further providing a catalyst precursor to the reaction zone.

22. The method of claim 21, wherein the catalyst precursor comprises at least one of a metal carbonyl, a metal oxide, an iron carbide, or a metallocene.

23. The method of claim 21, wherein the catalyst precursor decomposes when exposed to the reaction gas mixture at a temperature to form the catalyst.

24. The method of claim 21, wherein the concentration of the catalyst precursor in the reaction mixture is in the range of one part per million to one hundred parts per million.

25. The method of claim 21, further comprising providing an inoculant to the reaction zone, wherein the inoculant promotes formation of the catalyst precursor into the catalyst.

26. The method of claim 21, further comprising promoting nucleation of the catalyst from the catalyst precursor by providing a gaseous metal-containing compound or a pulsed laser.

27. The method of claim 1, further comprising adding a catalyst precursor to the reaction gas mixture.

28. The method of claim 27, wherein the catalyst precursor comprises at least one of a material selected from the group consisting of thiophene, heterocyclic sulfur, inorganic sulfides, volatile lead, and bismuth compounds.

29. The method of claim 1, wherein the second gas stream comprises hydrogen, or a hydrogen-containing synthesis gas.

30. The method of claim 1, wherein the second gas stream comprises at least one of hydrocarbon gas, natural gas, or methane.

31. The method of claim 1, wherein the first gas stream comprises carbon monoxide.

32. The method of claim 1, wherein the first gas stream consists essentially of carbon dioxide.

33. The method of claim 1, wherein the first gas stream comprises carbon monoxide, carbon dioxide, atmospheric air, combustion gases, process off-gases, waste gases produced during Portland cement production, or well gases.

34. The method of claim 1, further comprising controlling the temperature of the reaction gas in the reaction zone to be in the range of 450 ℃ to 2000 ℃.

35. The method of claim 1, further comprising controlling the temperature of the reaction gas mixture in the reaction zone to be in the range of 400 ℃ to 800 ℃.

36. The method of claim 1, further comprising controlling the temperature of the reaction gas mixture in the reaction zone to be 650 ℃.

37. The method of claim 1, further comprising controlling the temperature of the reaction gas mixture in the reaction zone to be 700 ℃.

38. The process of claim 1 further comprising controlling the temperature of the reaction gas mixture in the reaction zone to be in the range of 450 ℃ to 1500 ℃.

39. The method of claim 1, further comprising controlling the pressure in the reaction zone to be in the range of 640to 760 torr.

40. The method of claim 1, further comprising controlling the pressure in the reaction zone to be in the range of 700to 730 torr.

41. The method of claim 1, further comprising controlling the pressure of the reaction zone to 1 atm.

42. The method of claim 1, further comprising removing solid carbon product from the reaction gas mixture prior to cooling.

43. The process of claim 1, wherein the reaction zone comprises a fluidized bed reactor having catalyst particles comprising a reactor bed.

44. The method of claim 43, wherein the catalyst comprises preformed particles comprising a selected particle size for controlling the diameter of the carbon nanotubes.

45. The method of claim 1, wherein the reaction zone comprises an aerosol reactor.

46. The process of claim 45 wherein the catalyst is maintained in an aerosol spray to produce a solid carbon product as the catalyst particles pass through the reaction zone.

47. The method of claim 45, further comprising adhering a catalyst to one or more surfaces of the aerosol spray particles within the reaction zone.

48. The method of claim 1, wherein the reaction zone comprises at least one roaster.

49. The process of claim 1 wherein the reaction zone also comprises a batch reactor or a continuous reactor.

50. A composition of matter comprising carbon nanotube pillows formed from entangled agglomerated carbon nanotubes, wherein the carbon nanotubes are formed from the reaction of carbon dioxide and a gaseous reducing agent in the presence of an iron-containing catalyst.

51. A composition according to claim 50, wherein said pillows are formed by clumping together having a diameter generally less than 1 mm.

52. The composition of claim 50, wherein the pillow-like morphology comprises spherical or pillow-like agglomerated carbon nanotubes.

53. The composition of claim 50, wherein the pillow-like morphology comprises carbon nanotubes of varying diameters, varying lengths and varying morphologies.

54. A composition as claimed in claim 50, wherein the pillow shapes comprise agglomerates of carbon nanotubes.

55. A composition according to claim 50, wherein the pillow shape is readily bondable.

56. The composition of claim 50, wherein the pillow shape comprises characteristic growth boundaries configured to coalesce when the pillow shape is dispersed into the ethanol solution by gentle agitation, and then shaking the solution.