WO2018098495A1 - Methods and systems for forming ammonia and solid carbon products - Google Patents

Abstract

Methods of concurrently forming ammonia and solid carbon products include reacting a first portion of natural gas in the presence of water to form hydrogen and at least one carbon oxide; separating the hydrogen from the at least one carbon oxide; reacting the hydrogen with nitrogen in the presence of a first catalyst to form a first tail gas comprising ammonia; and reacting a second portion of natural gas with the at least one carbon oxide in the presence of a second catalyst to form solid carbon and a second tail gas. Methods may also include removing sulfur from the natural gas source. A system for concurrently producing ammonia and solid carbon may include a conditioning unit, a methane reformer, a separator, a first reactor, and a second reactor.

Description

METHODS AND SYSTEMS FOR FORMING AMMONIA

AND SOLID CARBON PRODUCTS

PRIORITY CLAIM

This application claims the benefit of the filing date of United States Provisional Patent Application Serial No.

62/427,057, filed November 28, 2016, for "Methods and Systems for Forming Ammoma and Solid Carbon Products."

TECHNICAL FIELD

Embodiments of the present disclosure relate to methods and systems for concurrently forming ammoma and solid carbon products from a hydrocarbon, such as methane, and other materials, such as water and nitrogen.

BACKGROUND

U.S. Patent 8,679,444, issued March 25, 2014, and titled "Method for Producing Solid Carbon by Reducing Carbon Oxides," the disclosure of which is hereby incorporated herein in its entirety by this reference, discloses background information hereto. Additional information is disclosed in U.S. Patent 9,598,286, issued March 21, 2017, and titled "Methods and Systems for Forming Ammoma and Solid Carbon Products," the disclosure of which is incorporated herein in its entirety by this reference.

Ammoma is an important chemical having many applications, such as in the production of fertilizers, cleaners, explosives, etc. Ammoma is directly or indirectly used in a variety of chemical processes to produce various nitrogen- containing compounds, such as amines, aramid fibers, and pharmaceuticals. The production of ammoma is therefore a major worldwide industry. Ammoma is commonly produced by the Haber-Bosch process.

In the Haber-Bosch process, ammoma is synthesized by the reaction of hydrogen and nitrogen in the presence of a catalyst, such as iron, according to Reaction 1 :

3H₂(g) + N₂(g) 2NH₃(g) (1).

The rate of reaction of hydrogen and nitrogen in Reaction 1 is a function of the reaction conditions including the temperature, pressure, and presence of catalyst. Increasing the temperature increases the reaction rate, but also shifts the reaction equilibrium. The equilibrium constant K_eq, defined as the ratio of the product of the partial pressures of the product to the product of the partial pressures of the reactants, as shown in the equation

is also a function of temperature. However, because Reaction 1 consumes four moles of gas (nitrogen and hydrogen) to produce two moles of ammoma gas, the equilibrium conversion to ammoma gas increases with increased pressure. That is, at a given temperature, the fraction of molecules of ammoma present at equilibrium is higher at relatively high pressure than at relatively low pressure. Conventional production of ammoma by the Haber-Bosch process generally involves temperatures between about 300°C and about 550°C and pressures between about 5 MPa and about 35 MPa. Conventional production of ammoma is described in, for example, G. Ertl, "Primary Steps in Catalytic Synthesis of Ammoma," J. Vac. Sci. Technol. A 1(2), p. 1247-53 (1983).

The conditions conventionally used to form ammoma require high-pressure reaction vessels, pipes, valves, and other equipment. Equipment and machinery capable of operating at high pressures have high capital costs because stronger materials (e.g., thicker walls, exotic materials, etc.) are generally more expensive. Furthermore, heating and pressurizing reactants generally require heat exchangers, pumps, and compressors, such that energy consumption may play a significant role in production costs. Hydrogen used in Reaction 1 may be from any source, but is conventionally formed from methane, coal, or another hydrocarbon. The preparation of the feed gases is typically a multi-step process including steam reforming, shift conversion, carbon dioxide removal, and methanation, with associated apparatus and operating expenses. For example, a common synthesis route is to form hydrogen from methane. In such a process, the methane is reformed typically in a steam reformer, wherein methane reacts with water in the presence of a nickel catalyst to produce hydrogen and carbon monoxide:

CH₄ + H₂0→CO + 3H₂ (2),

which is referred to in the art as a "steam-reforming" reaction. Secondary reforming then takes place using oxygen to convert residual methane to carbon oxides, hydrogen, and water:

2CH₄ + 0₂→ 2CO + 4H₂ (3);

CH₄ + 20₂→ C0₂ + 2H₂0 (4).

Carbon monoxide may be converted to carbon dioxide to form additional hydrogen:

CO + H₂0→C0₂ + H₂ (5),

which is referred to in the art as the "water-gas shift reaction." Carbon dioxide is removed from the mixed gases and is typically discharged to the atmosphere. The gases are then passed through a methanator to convert residual carbon monoxide, a catalyst poison, to methane and water:

CO + 3H₂→CH₄ + H₂0 (6).

The overall result of Reactions 2-6 is that methane and steam are converted to carbon dioxide and hydrogen, with residual methane and steam available for recycle. Conventional preparation of hydrogen from hydrocarbons, such as described for the example of methane, for use in the Haber-Bosch process may be performed in a series of reactors, and may require separation or other treatment of some components of gas streams to form a suitably pure hydrogen stream.

Ammonia production as outlined above can result in significant releases of carbon dioxide to the atmosphere. Concerns with regard to, for example, anthropogenic greenhouse-gas emissions, make such emissions undesirable. Thus, it would be advantageous to provide a method of forming ammonia that minimizes or eliminates carbon dioxide emissions.

DISCLOSURE

Methods of concurrently forming ammonia and solid carbon products include reacting a first portion of natural gas in the presence of water to form hydrogen and at least one carbon oxide; separating the hydrogen from the at least one carbon oxide; reacting the hydrogen with nitrogen in the presence of a first catalyst to form a first tail gas comprising ammonia; and reacting a second portion of natural gas with the at least one carbon oxide in the presence of a second catalyst to form solid carbon and a second tail gas. The methods may also include removing sulfur from the natural gas. Carbon oxide(s) formed in the production of ammonia may be beneficially used to form solid carbon and water, which may each be valuable products. The formation of ammonia and solid carbon may provide advantages over forming either product alone .

In some embodiments, a system for concurrently producing ammonia and solid carbon includes a conditioning unit, a methane reformer, a separator, a first reactor, and a second reactor. The conditioning unit is configured to remove sulfur from a natural gas source to form a purified natural gas. The methane reformer is configured to react a first portion of the purified natural gas in the presence of water to form hydrogen and at least one carbon oxide. The separator is configured to separate the hydrogen from the at least one carbon oxide. The first reactor is configured to react the hydrogen with nitrogen in the presence of a first catalyst to form a first tail gas comprising ammonia. The second reactor is configured to react a second portion of the purified natural gas with the at least one carbon oxide in the presence of a second catalyst to form solid carbon and a second tail gas. The system may also include heating systems, refrigeration systems, compressors, etc. BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram depicting a system for forming ammonia and solid carbon products, and illustrates some embodiments of the method;

FIGS. 2-7 are charts graphically illustrating some data from Examples 1-22;

FIGS. 8-81 are scanning electron microscopy (SEM) images of some samples of carbon formed in Examples 1-22;

FIG. 82 is a chart graphically illustrating some data from Examples 23-26; and

FIGS. 83-90 are SEM images of some samples of carbon formed in Examples 23-26.

MODE(S) FOR CARRYING OUT THE INVENTION

This disclosure includes methods and systems for forming ammonia and solid carbon products from hydrocarbons in linked (e.g., parallel or series) processes. A hydrocarbon source is treated to remove sulfur-containing products and form a purified hydrocarbon gas. In an ammonia-synthesis process, a first portion of the hydrocarbon gas reacts with water in a wet-reforming reaction to form carbon monoxide and hydrogen. The carbon monoxide may further react with water to form carbon dioxide and hydrogen. The hydrogen, after removal of the carbon oxides, reacts with nitrogen to form ammonia. In a carbon-synthesis process, the carbon oxides from the ammonia-forming process react with a second portion of the hydrocarbon gas to form solid carbon and water. The solid carbon and the water may be used within the process or may be sold or otherwise used for another process or product. Thus, the methods disclosed herein may be used to beneficially use carbon oxides, a material that may be conventionally considered a waste, to form useful products.

As used herein, the term "carbon oxide" means and includes carbon monoxide, carbon dioxide, or any combination of carbon monoxide, carbon dioxide, and one or more other materials (e.g., nitrogen, argon, methane, oxygen, etc.).

As used herein, the term "catalyst" means and includes a material formulated to promote one or more reactions described herein. A portion of a catalyst may be removed from a surrounding portion of the catalyst during some reactions and contained in or adhered to a solid product, particularly for carbon products. Thus, some of the catalyst may be physically removed during the reaction, and the catalyst may need to be continually replenished. A portion of the catalyst may not therefore be considered a catalyst in the classical sense, but is nonetheless referred to herein and in the art as a "catalyst," if the reaction is not believed to alter chemical bonds of the material forming the catalyst. Particularly useful "catalysts" include iron, nickel, cobalt, etc., and alloys and mixtures thereof, as described herein and known to promote Haber-Bosch and carbon synthesis reaction chemistries.

As used herein, the term "solid carbon products" means and includes any material that comprises carbon and may include any material comprising at least one of one or more of carbon nanotubes and one or more carbon nanofibers. Solid carbon products may be useful in various applications, such as filters, reactors, electrical components (e.g., electrodes, wires, batteries), structures (e.g., beams, frames, pipes), fasteners, molded parts (e.g., gears, bushings, pistons, turbines, turbine blades, engine blocks), etc. Such solid carbon products may exhibit enhanced properties (e.g. , strength, electrical or thermal conductivity, specific surface area, porosity, etc.) with respect to conventional materials. This disclosure includes a new class of materials that contain a plurality of CNTs, a plurality of carbon nanofibers, or a combination thereof formed into solid shapes under pressure. When such solid shapes are sintered, covalent bonds form between at least some of the CNTs, the carbon nanofibers, or both forming solid shapes. This material has numerous useful properties.

FIG. 1 depicts a process flow diagram of one embodiment of a system 100 for forming ammonia and solid carbon products and a method that may be performed using the system 100. The system 100 is divided into several subsystems for illustration purposes. In particular, the system 100 includes a conditioning subsystem 104, a reforming subsystem 110, a separation subsystem 120, an ammonia synthesis subsystem 130, a carbon synthesis subsystem 140, and a separation subsystem 150. The subsystems are shown separately, but two or more of the subsystems may be combined into a single apparatus. The system 100 may also include other subsystems, such as for heating, cooling, pressurizing, or controlling the flow of materials.

As shown in FIG. 1, a source gas 102 containing a hydrocarbon enters the conditioning subsystem 104, which is configured to remove various impurities 106 to form a purified source gas 108. For example, the conditioning subsystem 104 may include a filter, an adsorption unit, a compressor and/or any other means to prepare the source gas 102 for reaction in subsequent operations. In some embodiments, the conditioning subsystem 104 is configured to remove impurities 106 that poison some catalysts, such as hydrogen sulfide, mercaptans, or chlorine. For example, the conditioning subsystem 104 may include activated carbon, on which the impurities 106 adsorb. The conditioning subsystem 104 may be a packed bed, a fluidized bed, or any other appropriate device.

The conditioning subsystem 104 may be configured to process a larger amount of the source gas 102 than a conditioning subsystem of a conventional ammonia-production system having an ammonia-production capacity similar to the system 100, because the conditioning subsystem 104 also provides a portion of the purified source gas 108 to the carbon synthesis subsystem 140. The source gas 102 may optionally include some carbon oxides or other gases. If present, the carbon oxides may be beneficially used in the same manner as carbon oxides formed in the system 100, and described in more detail below. The source gas 102 may be a well gas, a purified natural gas (e.g., as provided by a public utility) or another natural or industrial source of hydrocarbons.

The purified source gas 108 may be divided into two or more portions. As shown in FIG. 1, a first portion of the purified source gas 108 enters the reforming subsystem 110 and a second portion of the purified source gas 108 enters the carbon synthesis subsystem 140. The reforming subsystem 110 is also configured to receive water 112, and is operated at conditions that promote the formation of a reformed gas 114 through steam reforming. For example, if the purified source gas 108 includes methane, the reforming subsystem 110 may be operated to promote the reaction of methane with water to form carbon monoxide and hydrogen, as shown in Reaction 2, above. The carbon monoxide may be converted to carbon dioxide to form additional hydrogen in the water-gas shift reaction, as shown in Reaction 5, above.

The reforming subsystem 110 may be configured to operate in two or more stages. In some embodiments, a first stage of the reforming subsystem 110 produces a partially reformed gas having a lower concentration of hydrocarbons than the purified source gas 108. A second stage of the reforming subsystem 110 produces the reformed gas 114, having an even lower concentration of hydrocarbons. The reforming subsystem 110 may include any number of stages configured to produce a reformed gas 114 at any selected hydrocarbon concentration. The reforming subsystem 110 may be configured to operate at temperatures from about 700°C to about 1,100°C and at pressures from about 300 kPa to about 25 MPa. The reforming subsystem 110 may include one or more catalyst materials, such as silica-supported nickel. The reforming subsystem 110 may also include one or more heaters, such as a gas-fired heater configured to burn hydrocarbons in the presence of oxygen The purified source gas 108 may receive heat through walls of the heater(s) separating combustion products from the purified source gas 108. In some embodiments, the reforming subsystem 110 may include a direct-combustion heat source, in which combustion products are mixed with the purified source gas 108, and are combined to form the reformed gas 114. Direct-combustion heating is described, for example, in U.S. Patent Application Publication 2016/0039677, published February 11, 2016, titled "Direct Combustion Heating," the entire contents of which are incorporated herein by this reference. In some embodiments, heater(s) associated with the reforming subsystem 110 may be sized and configured to provide sufficient heat to meet the needs of subsequent operations, such as in the ammonia synthesis subsystem 130 and/or the carbon synthesis subsystem 140. If the heater(s) of the reforming subsystem 110 are large enough, the need to subsequently or separately heat gases may be reduced or eliminated. Operating conditions of the reforming subsystem 110 may be selected to form CO and/or C0₂ in various ratios. In some embodiments, the reforming subsystem 110 may operate at conditions that yield more CO and less C0₂ than reformers in conventional ammonia-production systems, because the CO can be profitably used in the carbon synthesis subsystem 140.

The reformed gas 114 may be separated in the separation subsystem 120 into hydrogen 122 and carbon oxides 124. Though referred to herein as "hydrogen" 122 and "carbon oxides" 124, a person having ordinary skill in the art will understand that these gases may include other materials as impurities, such as water, hydrocarbons, nitrogen, etc. Furthermore, the hydrogen 122 may include some amount of carbon oxides, and the carbon oxides 124 may include some amount of hydrogen. The separation subsystem 120 may be separate from the reforming subsystem 110, as shown in FIG. 1, or the separation subsystem 120 and the reforming subsystem 110 may be combined into a single subsystem. The separation subsystem 120 may include any appropriate means for separating carbon oxides 124 from hydrogen 122 that are known in the art and not described in detail herein, such as amine absorption or physical absorption in a solvent.

The hydrogen 122 enters the ammonia synthesis subsystem 130, which is configured to promote the formation of ammonia 134. Nitrogen 132 also enters the ammonia synthesis subsystem 130, and the nitrogen 132 reacts with the hydrogen 122, such as in the Haber-Bosch process (Reaction 1, above). Typically, the ammonia synthesis subsystem 130 may operate at temperatures from about 250°C to about 800°C, such as from about 300°C to about 550°C. The ammonia synthesis subsystem 130 may operate at pressures from about 10 MPa (about 1450 psi) to about 40 MPa (about 5,800 psi), such as at pressures from about 13.8 MPa (about 2000 psi) to about 34.5 MPa (about 5,000 psi). Because the ammonia synthesis subsystem 130 may operate at high pressures, the components of the ammonia synthesis subsystem 130 are typically designed to withstand such conditions. For example, reaction vessels, pipes, and associated equipment may be formed to have steel walls.

The ammonia synthesis subsystem 130 may be configured such that the nitrogen 132 and the hydrogen 122 react in the presence of a catalyst. Catalysts may lower the temperature and/or pressure required to form ammonia. Suitable catalysts may include, for example, iron or steel with or without minor amounts of oxides (e.g., K₂0, CaO, Si0₂, or Al₂0₃).

The ammonia 134 formed in the ammonia synthesis subsystem 130 is generally removed from the ammonia synthesis subsystem 130 in gaseous form (i.e., as anhydrous ammonia, NH₃), and may be liquefied for storage and transport. The ammonia 134 may be processed by conventional methods, stored, transported, or sold. For example, the ammonia 134 may be compressed for storage and transport in pressurized tanks. Optionally, ammonia may be absorbed in water to form aqueous ammonia (NH₄OH). Anhydrous and aqueous ammonia have industrial uses, and either may be sold as a commodity or processed to form another material. For example, anhydrous ammonia may be mixed with concentrated nitric acid to form ammonium nitrate (NH₄N0₃), which may be used as a fertilizer or as a component of explosives.

The carbon oxides 124 and the second portion of the purified source gas 108 enter the carbon synthesis subsystem 140. The carbon oxides 124 and the second portion of the purified source gas 108 may be compressed before entering the carbon synthesis subsystem 140 or within the carbon synthesis subsystem 140. That is, the carbon synthesis subsystem 140 may in some embodiments include one or more compressors. The carbon synthesis subsystem 140 may be structured and configured to promote reactions between the purified source gas 108 and the carbon oxides 124 to form a tail gas 142 containing solid carbon and water:

CH₄ + C0₂ <→ 2C + 2H₂0 (7) .

The carbon synthesis subsystem 140 includes one or more catalysts formulated to promote the formation of solid carbon. Some metals from Groups 2-15 of the periodic table, such as from groups 5-10, (e.g., nickel, molybdenum, chromium, cobalt, tungsten, iron, manganese, ruthenium, platinum, iridium, etc.) actinides, lanthanides, alloys thereof, and combinations thereof accelerate the reaction rate of Reaction 7 under certain conditions. For example, catalysts include iron, nickel, cobalt, molybdenum, tungsten, chromium, and alloys thereof. Note that the periodic table may have various group numbering systems. As used herein, group 2 is the group including Be, group 3 is the group including Sc, group 4 is the group including Ti, group 5 is the group including V, group 6 is the group including Cr, group 7 is the group including Mn, group 8 is the group including Fe, group 9 is the group including Co, group 10 is the group including Ni, group 11 is the group including Cu, group 12 is the group including Zn, group 13 is the group including B, group 14 is the group including C, and group 15 is the group including N. In some embodiments, commercially available metals are used without special preparation. Some suitable catalysts are described in U.S. Patent 8,679,444. Other catalysts are described in, for example, U.S. Patent Application Publication 2015/0078981, published March 19, 2015, titled "Methods for Using Metal Catalysts in Carbon Oxide Catalytic Converters," and U.S. Patent Application Publication 2015/0086468, published March 26, 2015, titled "Methods and Structures for Reducing Carbon Oxides with Non-Ferrous Catalysts," the disclosures of each of which are incorporated herein in their entirety by this reference. Some catalysts facilitate operations at lower temperatures and pressures. In some embodiments, steel (e.g., mild steel) may be used as a catalyst in the carbon synthesis subsystem 140.

While not intending to be bound by theory, the following may help to explain the results described herein. In the production of the solid carbon, nanoparticles of the catalyst (which may be referred to as "nanocatalyst") are formed and embedded in the solid carbon. These nanoparticles typically form greater than 0.4% by weight of the solid product. These nanoparticles may remain catalytically active in their solid carbon mounts. Without being bound to a particular theory, it is believed that the grain size and composition of the catalyst, as well as reaction conditions, determine the type and morphology of solid carbon formed.

304 stainless steel appears to catalyze the formation of solid carbon (e.g., carbon nanotubes (CNTs), carbon nanofibers (CNFs)), etc.) under a wide range of temperatures, pressures, and gas compositions. However, the rate of formation of CNTs on 304 stainless steel appears to be relatively low, such that 304 stainless steel may be used effectively as a construction material for process equipment, with minimal deposition on surfaces thereof in normal operations. 316L stainless steel, in contrast, appears to catalyze the formation of solid carbon at significantly higher rates than 304 stainless steel, but may also form various morphologies of carbon. Thus, 316L stainless steel may be used as a catalyst to achieve high reaction rates, but particular reaction conditions may be maintained to control product morphology. Catalysts may be selected to include Cr, such as in amounts of about 22% or less by weight. For example, 316L stainless steel contains from about 16% to about 18.5% Cr by weight. Catalysts may also be selected to include Ni, such as in amounts of about 8% or more by weight. For example, 316L stainless steel contains from about 10% to about 14% Ni by weight. Catalysts of these types of steel have iron in an austenitic phase, in contrast to alpha-phase iron used as a catalyst in some conventional processes. Given the good results observed with 316L stainless steel, the Ni and/or Cr may have a synergistic effect with Fe.

Oxidation and subsequent reduction of the catalyst surface alter the grain structure and grain boundaries of the catalyst. While not intending to be bound by theory, oxidation appears to alter the surface of the metal catalyst in the oxidized areas. Subsequent reduction may result in further alteration of the catalyst surface. Thus, the grain size and grain boundary of the catalyst may be controlled by oxidizing and reducing the catalyst surface and by controlling the exposure time of the catalyst surface to the reducing gas and the oxidizing gas. The oxidation and/or reduction temperatures may be in the range from about 500°C to about 1,200°C, from about 600°C to about 1,000°C, or from about 700°C to about 900°C. The resulting grain size may range from about 0.1 μπι to about 500 μηι, from about 0.2 μπι to about 100 μιτι, from about 0.5 μπι to about 10 μπι, or from about 1.0 μπι to about 2.0 μπι. In some embodiments, the catalyst may be an oxidized metal (e.g., rusted steel) that is reduced before or during a reaction forming solid carbon. While not intending to be bound by theory, it is believed that removal of oxides leaves voids or irregularities in the surface of the catalyst material, and increases the overall surface area of the catalyst material.

Catalysts may be in the form of nanoparticles or in the form of solid materials including, for example, steel or other bulk metals or as domains or grains and grain boundaries within a solid material. Catalysts may be selected to have a grain size related to a characteristic dimension of a desired diameter of the solid carbon product (e.g., a CNT diameter). Examples of suitable catalysts include elements of Groups 5-10 of the periodic table, actinides, lanthanides, alloys thereof, and combinations thereof. Catalysts may be deposited in the carbon synthesis subsystem 140 in the form of solids, beads, granules, powders, or aerosols.

Because a portion of the bulk catalyst is removed with every CNT, the catalyst in the catalytic converter may need to be replenished from time to time, based on the reactor properties (e.g., volume) and reaction conditions (e.g., temperature, pressure, etc.). Catalyst powder may be formed in or near the reaction zone by injecting an aerosol solution such that upon evaporation of a carrier solvent, a selected particle size distribution results. Alternatively, powdered or particulate catalyst may be entrained in the purified source gas 108 or the carbon oxides 124 delivered to the carbon synthesis subsystem 140.

By selecting the catalyst and the reaction conditions, the process may be "tuned" to produce selected morphologies of solid carbon product. In some embodiments, the catalyst may be formed over a substrate or support, such as an inert oxide that does not participate in the reactions. However, the substrate is not necessary; in other embodiments, the catalyst material is an unsupported material, such as a bulk metal or particles of metal not connected to another material (e.g., loose particles, shavings, or shot, such as may be used in a fluidized-bed reactor).

Carbon activity (A_c) can be used as an indicator of whether solid carbon will form under particular reaction conditions (e.g., temperature, pressure, reactants, concentrations). While not intending to be bound by theory, it is believed that carbon activity is a key metric for determining which allotrope of solid carbon is formed. Higher carbon activity tends to result in the formation of CNTs, lower carbon activity tends to result in the formation of graphitic forms.

Carbon activity for a reaction forming solid carbon from gaseous reactants can be defined as the reaction equilibrium constant times the partial pressure of gaseous products, divided by the partial pressure of reactants. For example, in the reaction, CH_4(g) + C0_2(g) ^ 2C_(S) + 2H₂0_(g), with a reaction equilibrium constant of K, the carbon activity A_c is defined as K-(P_mo ² Pco₂'Pc_Hd- Thus, A_c is directly proportional to the square of the partial pressure of H₂0, and inversely proportional to the partial pressures of CH₄ and C0₂. The carbon activity of this reaction may also be expressed in terms of mole fractions and total pressure:

where P_T is the total pressure and Y is the mole fraction of a species. Carbon activity generally varies with temperature because reaction equilibrium constants vary generally with temperature. Carbon activity also varies with total pressure for reactions in which a different number of moles of gas are produced than are consumed. Mixtures of solid carbon allotropes and morphologies thereof can be achieved by varying the catalyst(s) and the carbon activity of the reaction gases in the reactor

The reaction conditions, including the temperature and pressure in the reaction zone, the residence time of the reaction gases, and the grain size, grain boundary, and chemical composition of the catalyst(s) may be controlled to obtain solid carbon products having selected characteristics. In some embodiments, the purified source gas 108 and the carbon oxides 124 are recycled through the reaction zone and passed through a condenser with each cycle to remove excess water and to control the partial pressure of the water vapor in the carbon synthesis subsystem 140. Because the partial pressure of water vapor affects the carbon activity, water vapor appears to affect the type and character (e.g., morphology) of solid carbon formed, as well as the kinetics of carbon formation.

Reaction conditions of the carbon synthesis subsystem 140 (e.g., time, temperature, pressure, partial pressure of reactants, catalyst properties, etc.) may be optimized to produce a selected type, morphology, purity, homogeneity, etc. of the solid carbon 152. For example, conditions may be selected to promote the formation of CNTs. In some embodiments, the solid carbon 152 includes allotropes of carbon or morphologies thereof, including graphite, pyrolytic graphite, graphene, carbon black, fibrous carbon, buckminsterfullerenes, single-wall CNTs, or multi-wall CNTs. The carbon synthesis subsystem 140 may operate at any pressures including pressures of from near vacuum to about 30 MPa (300 bar), such as from about 100 kPa (1.0 bar) to about 1000 kPa (10 bar). In general, higher pressures correspond to faster reaction rates and a shift in equilibrium to the desired products. The carbon synthesis subsystem 140 may operate at temperatures of from about 550°C to about 1200°C, such as from about 650°C to about 800°C.

Though the carbon synthesis subsystem 140 is shown in FIG. 1 as a single unit, the carbon synthesis subsystem 140 may include two or more reaction vessels. For example, one reaction vessel may operate at conditions favorable to a first step of a reaction, and another reaction vessel may operate at conditions favorable to a second step of a reaction. The carbon synthesis subsystem 140 may include any number of reaction vessels or regions in which materials may react, depending on the particular reactions expected to occur. Each reaction vessel may be configured and operated to optimize a reaction step. For example, reaction vessels may operate at different temperatures or pressures from one another.

The tail gas 142 may enter the separation subsystem 150, which is configured to separate solids, liquids, and/or gases. The separation subsystem 150 may be configured to remove solid carbon 152 from water 154 and a recycle gas 156. The separation subsystem 150 may include any device operable to separate particulate matter from gases. For example, the separation subsystem 150 may include a cyclone, a scrubber, an elutriate r, a filter, an electrostatic precipitator, a bag house, a condenser, etc., or any combination thereof. The recycle gas 156 leaving the separation subsystem 150 may be gaseous, and may be substantially free of solids. For example, the recycle gas 156 may include less than about 1%, less than about 0.1%, or even less than about 0.05% solids by mass. Techniques for separation of solids from liquids and gases depend upon the type of equipment of the carbon synthesis subsystem 140 and the expected composition of the tail gas 142. The separation subsystem 150 may include two or more devices operated in series or parallel to provide selected purity (i.e., absence of solids) of the recycle gas 156. The recycle gas 156 may be recycled to another subsystem in the system 100, such as to the conditioning subsystem 104 or the carbon synthesis subsystem 140 (after optionally heating and/or compressing the recycle gas 156). In some embodiments, the recycle gas 156 or a portion thereof may be vented to the atmosphere, for example after appropriate treatment. The solid carbon 152 removed from the separation subsystem 150 may be sold as a commercial product, used in the production of another product, stored for long-term sequestration, etc.

A lock hopper system may be used to remove the solid carbon 152 from the carbon synthesis subsystem 140 or from the separation subsystem 150. The lock hopper system may also include a means for cooling the solid carbon 152 to a temperature below the oxidation temperature of the product in air prior to discharging. A lock hopper system or other separation means may control the release of gases to the atmosphere and may purge the solid carbon 152 of reaction gases prior to removal of the solid carbon 152 from the system 100. Other suitable means may used for removing the solid carbon 152 from the system 100 that conserve reaction gases and minimize worker and environmental exposure to the reaction gases.

In some embodiments, the water 154 leaving the separation subsystem 150 is used within the system 100. For example, the water 154 may be used as the water 112 or to process the ammonia 134 leaving the ammonia synthesis subsystem 130. In some embodiments, the water 154 and the ammonia 134 may each enter a scrubber operable to absorb the ammonia 134 in the water 154. The scrubber may include a spray nozzle, a packed tower, an aspirator, etc.. Any remaining gases may be processed as waste or recycled within the system 100.

In some embodiments, the carbon synthesis subsystem 140 may include two or more reactors configured to operate in series. Each reactor may be configured and operated to optimize formation of solid carbon and water, and water may be removed between the two reactors. Removal of water may promote reactions between the purified source gas 108 and the carbon oxides 124 (e.g., Reaction 7, above) by shifting the equilibrium. Appropriate separation equipment, compressors, heaters, coolers, etc. may be used between reactors, such as the separation subsystem 150 described herein.

The carbon synthesis subsystem 140 may be a batch reactor, a continuous-flow reactor, or a semi-continuous- flow reactor (e.g., configured to be operated for a period of time, then shut down for a period of time, such as to regenerate or replace the catalyst). In some embodiments, a solid catalyst or catalyst mounted on a solid substrate is moved through a flowing gas stream, the resulting solid carbon is harvested, and the solid surface is renewed and reintroduced to the carbon synthesis subsystem 140. The solid substrate may be the catalyst material (e.g., a solid piece of a chromium-, molybdenum-, cobalt-, iron-, or nickel-containing alloy or superalloy) or a surface on which the catalyst is mounted.

In one embodiment, the carbon synthesis subsystem 140 includes a fluidized-bed reactor designed to retain the catalyst while allowing the solid carbon to be entrained in the flow of the tail gas 142 and to be lofted out of the reaction zone upon reaching a desired size. The shape of the reactor and the gas flow rates influence the residence time of the elutriates and the corresponding size of the solid carbon (such as the length of CNTs or CNFs).

The carbon synthesis subsystem 140 may include one or more batch reactors in which the catalyst is either a fixed solid surface (e.g., the catalyst may be a steel plate) or is mounted on a fixed solid surface (e.g., catalyst nanoparticles deposited on an inert substrate). In such embodiments, solid carbon is grown on the catalyst, and the catalyst and solid carbon 152 are periodically removed from the carbon synthesis subsystem 140 (e.g., instead of or in addition to a distinct separation subsystem 150). Alternatively, the carbon synthesis subsystem 140 may include continuous reactors, wherein the solid carbon 152 is removed from the catalyst as the solid carbon 152 is formed.

Some reactant concentrations in the system 100 may be selected to be stoichiometric or near-stoichiometric. That is, the gases may include concentrations and flow rates of reactants (carbon oxide, nitrogen, methane, etc.) that, if fully reacted, would be entirely or almost entirely consumed. For example, the hydrogen 122 may be provided at a molecular flow rate of about three times the molecular flow rate of the nitrogen 132. This mixture, if fully reacted according to Reaction 1, would consume approximately all of the hydrogen 122 and the nitrogen 132 within the ammonia synthesis subsystem 130. Other mixtures may be selected to react according to particular reactions or to obtain a particular product. The compositions of gases in some subsystems may be in a ratio other than near stoichiometric. The compositions of gases may be selected based on economics, process controls, environmental regulations, etc. In some embodiments, inert gases are present in the system 100, such as argon. In such cases, appropriate venting may control the accumulation of inert gases in the process gas streams if the system recirculates significant portions of the gas.

FIGS. 2 and 3 illustrate the relationship between differing gas ratios on the rates of formation of solid carbon. FIGS. 2 and 3 were generated based on data collected in Examples 1-22, described below. FIG. 2 illustrates the highest rate of carbon formation observed at various H₂:CO ratios in the presence of S-70 carbon-steel shot, as determined in Examples 1-11, with each point on FIG. 2 corresponding to one of these Examples. FIG. 3 illustrates the highest rate of carbon formation observed at various H₂:(CO+C0₂) ratios in the presence of S-70 carbon-steel shot observed in Examples 12-22. FIG. 3 shows that, for the experimental conditions of Examples 12-22, H₂:(CO+C0₂) ratios of about 1.0 or less appear to yield higher rates of carbon formation than higher H₂:(CO+C0₂) ratios.

FIGS. 4 and 5 illustrate the relationship between BET surface area of carbon formed and the H₂:CO or

H₂:(CO+C0₂) ratios, respectively, in Examples 1-22. For the purposes of FIGS. 4 and 5, the solid carbon that had the highest growth rate was tested for each gas ratio. Specific surface area may be an indicator of the type of solid carbon formed because some morphologies, such as CNTs, have higher BET surface areas than others, such as amorphous carbon. FIG. 4 shows that, for the experimental conditions of Examples 1-11, H₂:CO ratios from about 0.7 to about 1.2 appear to yield carbon having higher BET surface areas than other H₂:CO ratios. FIG. 5 shows that, for the experimental conditions of Examples 12-22, H₂:(CO+C0₂) ratios of about 1.0 and higher appear to yield carbon having higher BET surface areas than lower H₂:(CO+C0₂) ratios.

FIG. 6 illustrates the relationship between temperature on the rates of formation of solid carbon for Examples 1-22. As shown in FIG. 6, under the conditions of Examples 1-22, the highest rates of formation may occur from about 500°C to about 750°C. FIG. 7 illustrates the relationship between the BET surface area and the rates of formation of solid carbon.

Heat may be recovered from the ammonia 134, the water 154, the recycle gas 156, or any other material within the system 100, such as by passing the water 154 and the source gas 102 through one or more heat exchangers. Such heat recovery may be an effective way to recover a portion of the process heat and help bring the reactants to reaction temperature. Any gas or liquid streams may be processed as known in the art for overall energy optimization. The tail gas 142 may be maintained above the dew point of the water vapor in the tail gas 142 prior to separation of the solid carbon 152 from the water 154 and the recycle gas 156 to limit or prevent the condensation of water in or on the solid carbon 152.

As described previously herein with respect to the reforming subsystem 110, the system 100 may include one or more heaters configured to provide the heating needs of the system 100. The system 100 may also include one or more refrigeration systems or condensers configured to provide the cooling needs of the system 100. For example, a single unit may provide refrigeration to condense methane from the reformed gas 114, ammonia 134 formed in the ammonia synthesis subsystem 130, and water 154 formed in the carbon synthesis subsystem 140.

In some embodiments, a portion of the solid carbon 152 formed in the carbon synthesis subsystem 140 may be used in the conditioning subsystem 104. For example, the solid carbon 152 may be used in the conditioning subsystem 104 to remove impurities 106, such as by adsorption. The solid carbon 152 may be processed to increase its specific surface area or to make it suitable for use in the conditioning subsystem 104 {e.g., pressed into pellets). In some embodiments, the solid carbon 152 may be used as formed in the carbon synthesis subsystem 140.

By combining the reforming subsystem 110 and the ammonia synthesis subsystem 130 with the carbon synthesis subsystem 140, carbon oxides formed in the reforming subsystem 110 may be beneficially used in the carbon synthesis subsystem 140. Furthermore, water formed in the carbon synthesis subsystem 140 may be beneficially used for recovery of ammonia 134 formed in the ammonia synthesis subsystem 130. Thus, the combined system 100 may have greater efficiencies than the ammonia synthesis subsystem 130 and the carbon synthesis subsystem 140 operating alone.

EXAMPLES

In each of Examples 1-22 below, catalyst samples were separately placed in quartz boats about 8.5 cm long and

1.5 cm wide, and the boats were inserted end-to-end into a quartz tube having an inner diameter of about 2.54 cm and a length of about 1.2 m. The quartz tube was then placed in a tube furnace. The quartz tube was purged with hydrogen gas to reduce the surface of the coupons before the tube furnace was heated to operating conditions. After the tube furnace reached operating conditions, reaction gases were introduced into the quartz tube (i.e., flowed continuously through the quartz tube) such that both the upper and lower surfaces of each coupon were exposed to reaction gas. The temperature, pressure, and gas composition were measured at each coupon. After the test, the samples were removed from the quartz tube. Weight changes and carbon formation were noted, carbon deposition rates were calculated, and some samples were tested for BET surface area and/or imaged using SEM (scanning electron microscopy), as indicated in the tables below. Note that reduction of catalysts and measurement errors may produce negative calculated carbon deposition rates, even when some solid carbon forms.

The catalyst used for Examples 1-22 was S-70 steel shot, which comprises carbon steel having from about 0.10% to about 0.15% C, from about 0.10% to about 0.25% Si, from about 1.20% to about 1.50% Mn, from about 0.05% to about 0.15% Al, up to about 0.035% P, and up to about 0.035% S, with the remainder Fe. S-70 shot has a particle size distribution such that all the material passes through a #40 sieve, and at least 90% of the material is retained by a #120 sieve.

Example 1: H,: CO ratio of 1.0

A reaction gas containing about 45% H₂, 45% CO, and 10% Ar was introduced into the quartz tube at about 310 kPa. The reaction gas had an H₂:CO ratio of about 1.0. The gases flowed over the shot for about 30 minutes at 1200 seem (standard cubic centimeters per minute). Methane, carbon dioxide, and water were also formed in the quartz tube.

Table 1 : Solid Carbon Formation with an H₂:CO ratio of 1.0

Sample # 1 2 3 4 5 6

Temperature (°C) 325.2 490.0 536.9 575.1 615.3 645.5

Deposition rate (g/cm²/hr) 0.135 1.000 18.210 7.500 3.475 1.414

Surface Area (m²/g) 69.086 202.924 215.355 196.472 132.051

SEM image FIG. 8 FIG. 9 FIG. 10 FIG. 11 FIG. 12

Mole fraction H₂ 0.447 0.438 0.431 0.423 0.415 0.407

Mole fraction CH₄ 0.001 0.007 0.011 0.015 0.020 0.025

Mole fraction C0₂ 0.003 0.011 0.017 0.025 0.032 0.040

Mole fraction CO 0.446 0.431 0.421 0.407 0.394 0.381

Mole fraction H₂0 0.002 0.010 0.016 0.023 0.030 0.037

Mole fraction Ar 0.101 0.103 0.104 0.106 0.108 0.110 Sample # 7 8 9 10 11 12

Temperature (°C) 670.6 698.7 740.7 793.6 658.4 467.2

Deposition rate (g/cm²/hr) 0.706 -0.340 -0.192 -0.559 -0.348 -0.245

Surface Area (m²/g) 78.487 42.285 28.917

SEM image FIG. 13 FIG. 14 FIG. 15 FIG. 16 FIG. 17

Mole fraction H₂ 0.398 0.390 0.380 0.369 0.355 0.349

Mole fraction CH₄ 0.030 0.035 0.041 0.047 0.055 0.059

Mole fraction C0₂ 0.048 0.056 0.065 0.075 0.087 0.093

Mole fraction CO 0.365 0.352 0.336 0.318 0.296 0.286

Mole fraction H₂0 0.046 0.053 0.062 0.072 0.083 0.089

Mole fraction Ar 0.112 0.114 0.117 0.119 0.123 0.124

Example 2: H,:CO ratio of 0.6

Twelve samples of S-70 shot were placed in quartz boats in a quartz tube as described above. A reaction gas containing about 36.75% H₂, 61.32% CO, and 1.93% Ar was introduced into the quartz tube at about 310 kPa. The reaction gas had an H₂:CO ratio of about 0.6. The gases flowed over the shot for about 30 minutes at 1200 seem. Methane, carbon dioxide, and water were also formed in the quartz tube. After the test, approximately 1.126 g of water was collected.

Table 2: Solid Carbon Formation with an H₂:CO ratio of 0.6

Example 3: H,:CO ratio of 0.7

Twelve samples of S-70 shot were placed in quartz boats in a quartz tube as described above. A reaction gas containing about 40.27% H₂, 57.61% CO, and 2.12% Ar was introduced into the quartz tube at about 310 kPa. The reaction gas had an H₂:CO ratio of about 0.7. The gases flowed over the shot for about 30 minutes at 1200 seem. Methane, carbon dioxide, and water were also formed in the quartz tube. After the test, approximately 1.127 g of water was collected.

Table 3 : Solid Carbon Formation with an H₂:CO ratio of 0.7

Example 4: H,:CO ratio of 0.8

Twelve samples of S-70 shot were placed in quartz boats in a quartz tube as described above. A reaction gas containing about 43.40% H₂, 54.32% CO, and 2.28% Ar was introduced into the quartz tube at about 310 kPa. The reaction gas had an H₂:CO ratio of about 0.8. The gases flowed over the shot for about 30 minutes at 1200 seem. Methane, carbon dioxide, and water were also formed in the quartz tube. After the test, approximately 0.814 g of water was collected.

Table 4 : Solid Carbon Formation with an H₂ : CO ratio of 0.8

Sample # 1 2 3 4 5 6

Temperature (°C) 232.302 454.337 523.562 566.927 598.773 635.658

Deposition rate (g/cm²/hr) 0.140 0.000 16.513 15.300 5.845 1.982

Surface Area (m²/g) 211.840 219.911 197.470 156.819

SEM image FIG. 36 FIG. 37 FIG. 38 FIG. 39 FIG. 40

Mole fraction H₂ 0.4319 0.4227 0.4155 0.4065 0.3971 0.3870

Mole fraction CH₄ 0.0007 0.0065 0.0111 0.0167 0.0227 0.0290

Mole fraction C0₂ 0.0016 0.0122 0.0206 0.0310 0.0419 0.0535

Mole fraction CO 0.5419 0.5266 0.5145 0.4994 0.4836 0.4667

Mole fraction H₂0 0.0010 0.0085 0.0145 0.0220 0.0298 0.0381

Mole fraction Ar 0.0229 0.0234 0.0239 0.0244 0.0250 0.0256 Sample # 7 8 9 10 11 12

Temperature (°C) 658.180 681.776 721.115 770.607 799.983 521.404

Deposition rate (g/cm²/hr) 0.796 0.174 -0.262 -0.889 -0.330 1.109

Surface Area (m²/g) 108.131

SEM image FIG. 41 FIG. 42 FIG. 43

Mole fraction H₂ 0.3764 0.3663 0.3538 0.3413 0.3282 0.3114

Mole fraction CH₄ 0.0357 0.0421 0.0500 0.0579 0.0661 0.0767

Mole fraction C0₂ 0.0657 0.0774 0.0919 0.1064 0.1215 0.1409

Mole fraction CO 0.4490 0.4320 0.4111 0.3900 0.3681 0.3399

Mole fraction H₂0 0.0469 0.0553 0.0656 0.0760 0.0868 0.1008

Mole fraction Ar 0.0263 0.0269 0.0277 0.0284 0.0292 0.0303

Example 5: H,:CO ratio of 0.9

Twelve samples of S-70 shot were placed in quartz boats in a quartz tube as described above. A reaction gas containing about 46.15% H₂, 51.42% CO, and 2.43% Ar was introduced into the quartz tube at about 310 kPa. The reaction gas had an H₂:CO ratio of about 0.9. The gases flowed over the shot for about 30 minutes at 1200 seem. Methane, carbon dioxide, and water were also formed in the quartz tube. After the test, approximately 0.716 g of water was collected.

Table 5 : Solid Carbon Formation with an H₂ : CO ratio of 0.9

Example 6: H,: CO ratio of 1.0

Twelve samples of S-70 shot were placed in quartz boats in a quartz tube as described above. A reaction gas containing about 48.69% H₂, 48.75% CO, and 2.56% Ar was introduced into the quartz tube at about 310 kPa. The reaction gas had an H₂:CO ratio of about 1.0. The gases flowed over the shot for about 33 minutes at 1200 seem. Methane, carbon dioxide, and water were also formed in the quartz tube. After the test, approximately 0.28 g of water was collected.

Table 6: Solid Carbon Formation with an H₂:CO ratio of 1.0

Example 7: H?: CO ratio of 1.1

Twelve samples of S-70 shot were placed in quartz boats in a quartz tube as described above. A reaction gas containing about 50.98% H₂, 46.33% CO, and 2.68% Ar was introduced into the quartz tube at about 310 kPa. The reaction gas had an H₂:CO ratio of about 1.1. The gases flowed over the shot for about 33 minutes at 1200 seem. Methane, carbon dioxide, and water were also formed in the quartz tube. After the test, approximately 0.72 g of water was collected.

Table 7 : Solid Carbon Formation with an H₂ : CO ratio of 1.1

Sample # 1 2 3 4 5 6

Temperature (°C) 319.498 477.632 540.239 584.586 608.378 640.956

Deposition rate (g/cm²/hr) 0.048 0.535 20.135 9.740 3.481 1.336

Surface Area (m²/g) 190.989 216.314 192.042 143.338

SEM image FIG. 63 FIG. 64 FIG. 65 FIG. 66 FIG. 67

Mole fraction H₂ 0.5061 0.4978 0.4901 0.4817 0.4728 0.4638

Mole fraction CH₄ 0.0018 0.0071 0.0122 0.0177 0.0235 0.0294

Mole fraction C0₂ 0.0033 0.0108 0.0177 0.0254 0.0334 0.0416

Mole fraction CO 0.4594 0.4468 0.4349 0.4220 0.4084 0.3945

Mole fraction H₂0 0.0024 0.0099 0.0169 0.0246 0.0326 0.0409

Mole fraction Ar 0.0270 0.0276 0.0281 0.0287 0.0293 0.0299 Sample # 7 8 9 10 11 12

Temperature (°C) 681.755 733.803 792.002 793.277 706.177 515.097

Deposition rate (g/cm²/hr) 0.630 0.482 -0.240 -0.306 0.081 1.071

Surface Area (m²/g) 68.523 163.674

SEM image FIG. 68 FIG. 69 FIG. 70 FIG. 71

Mole fraction H₂ 0.4543 0.4454 0.4346 0.4228 0.4105 0.4021

Mole fraction CH₄ 0.0356 0.0414 0.0485 0.0562 0.0642 0.0697

Mole fraction C0₂ 0.0501 0.0582 0.0679 0.0786 0.0897 0.0973

Mole fraction CO 0.3801 0.3663 0.3498 0.3318 0.3129 0.2999

Mole fraction H₂0 0.0494 0.0576 0.0674 0.0780 0.0892 0.0969

Mole fraction Ar 0.0305 0.0311 0.0318 0.0326 0.0335 0.0340

Example 8: H,: CO ratio of 1.2

Twelve samples of S-70 shot were placed in quartz boats in a quartz tube as described above. A reaction gas containing about 52.96% H₂, 44.25% CO, and 2.79% Ar was introduced into the quartz tube at about 310 kPa. The reaction gas had an H₂:CO ratio of about 1.2. The gases flowed over the shot for about 30 minutes at 1200 seem. Methane, carbon dioxide, and water were also formed in the quartz tube. After the test, no liquid water was collected.

Table 8: Solid Carbon Formation with an H₂:CO ratio of 1.2

Example 9: H,: CO ratio of 1.3

Twelve samples of S-70 shot were placed in quartz boats in a quartz tube as described above. A reaction gas containing about 54.93% H₂, 42.25% CO, and 2.82% Ar was introduced into the quartz tube at about 310 kPa. The reaction gas had an H₂:CO ratio of about 1.3. The gases flowed over the shot for about 30 minutes at 1200 seem. Methane, carbon dioxide, and water were also formed in the quartz tube. After the test, approximately 1.301 g of liquid water was collected. Table 9 : Solid Carbon Formation with an H₂ : CO ratio of 1.3

Example 10: H,: CO ratio of 1.4

Twelve samples of S-70 shot were placed in quartz boats in a quartz tube as described above. A reaction gas containing about 56.53% H₂, 40.50% CO, and 2.98% Ar was introduced into the quartz tube at about 310 kPa. The reaction gas had an H₂:CO ratio of about 1.4. The gases flowed over the shot for about 30 minutes at 1200 seem. Methane, carbon dioxide, and water were also formed in the quartz tube. After the test, approximately 1.291 g of liquid water was collected.

Table 10: Solid Carbon Formation with an H₂:CO ratio of 1.4

Sample # 1 2 3 4 5 6

Temperature (°C) 219.247 442.198 526.660 568.270 600.624 637.408

Deposition rate (g/cm²/hr) 0.000 0.059 13.426 9.010 2.902 1.011

Surface Area (m²/g) 170.963 202.636 156.619 112.280

SEM image

Mole fraction H₂ 0.5637 0.5548 0.5460 0.5367 0.5270 0.5172

Mole fraction CH₄ 0.0006 0.0074 0.0141 0.0212 0.0286 0.0361

Mole fraction C0₂ 0.0006 0.0067 0.0127 0.0190 0.0256 0.0323

Mole fraction CO 0.4049 0.3932 0.3816 0.3693 0.3566 0.3437

Mole fraction H₂0 0.0006 0.0078 0.0150 0.0225 0.0303 0.0383

Mole fraction Ar 0.0295 0.0301 0.0306 0.0312 0.0318 0.0324 Sample # 7 8 9 10 11 12

Temperature (°C) 659.041 684.198 722.030 774.816 796.155 525.324

Deposition rate (g/cm²/hr) 0.423 0.120 -0.192 -0.426 -0.226 0.607

Surface Area (m²/g)

SEM image

Mole fraction H₂ 0.5066 0.4963 0.4848 0.4724 0.4594 0.4458

Mole fraction CH₄ 0.0443 0.0521 0.0609 0.0704 0.0803 0.0907

Mole fraction C0₂ 0.0395 0.0465 0.0543 0.0627 0.0715 0.0807

Mole fraction CO 0.3297 0.3161 0.3010 0.2847 0.2676 0.2498

Mole fraction H₂0 0.0469 0.0552 0.0645 0.0746 0.0851 0.0961

Mole fraction Ar 0.0331 0.0338 0.0345 0.0353 0.0361 0.0369

Example 11: H,: CO ratio of 1.5

Twelve samples of S-70 shot were placed in quartz boats in a quartz tube as described above. A reaction gas containing about 58.13% H₂, 38.81% CO, and 3.06% Ar was introduced into the quartz tube at about 310 kPa. The reaction gas had an H₂:CO ratio of about 1.5. The gases flowed over the shot for about 30 minutes at 1200 seem. Methane, carbon dioxide, and water were also formed in the quartz tube. After the test, approximately 1.973 g of liquid water was collected.

Table 11 : Solid Carbon Formation with an H₂ : CO ratio of 1.5

Example 12: H,:(CO+CO?) ratio of 0.6

Twelve samples of S-70 shot were placed in quartz boats in a quartz tube as described above. A reaction gas containing about 36.73% H₂, 51.33% CO, 10.00% C0₂, and 1.93% Ar was introduced into the quartz tube at about 310 kPa. The reaction gas had an H₂:(CO+C0₂) ratio of about 0.6. The gases flowed over the shot for about 30 minutes at 1200 seem. Methane, carbon dioxide, and water were also formed in the quartz tube. After the test, approximately 1.322 g of liquid water was collected.

Table 12 : Solid Carbon Formation with an H₂ : (CO+C0₂) ratio of 0.6

Example 13: H,:(CO+CO,) ratio of 0.7

Twelve samples of S-70 shot were placed in quartz boats in a quartz tube as described above. A reaction gas containing about 40.27% H₂, 47.61% CO, 10.00% C0₂, and 2.12% Ar was introduced into the quartz tube at about 317 kPa. The reaction gas had an H₂:(CO+C0₂) ratio of about 0.7. The gases flowed over the shot for about 30 minutes at 1200 seem. Methane, carbon dioxide, and water were also formed in the quartz tube. After the test, approximately 0.961 g of liquid water was collected.

Table 13 : Solid Carbon Formation with an H₂ : (CO+C0₂) ratio of 0.7

Sample # 1 2 3 4 5 6

Temperature (°C) 273.013 471.137 534.113 578.873 604.176 636.591

Deposition rate (g/cm²/hr) -0.275 0.426 16.870 11.192 3.480 1.476

Surface Area (m²/g) 180.022 229.136 227.403 154.036

SEM image

Mole fraction H₂ 0.4017 0.3946 0.3889 0.3823 0.3756 0.3688

Mole fraction CH₄ 0.0004 0.0037 0.0063 0.0094 0.0125 0.0156

Mole fraction C0₂ 0.1010 0.1076 0.1129 0.1189 0.1251 0.1313

Mole fraction CO 0.4753 0.4688 0.4635 0.4575 0.4514 0.4452

Mole fraction H₂0 0.0004 0.0038 0.0066 0.0097 0.0129 0.0161

Mole fraction Ar 0.0211 0.0215 0.0218 0.0222 0.0226 0.0230 Sample # 7 8 9 10 11 12

Temperature (°C) 675.742 734.772 794.487 792.794 703.585 598.358

Deposition rate (g/cm²/hr) 0.653 -0.260 -0.257 -0.358 0.021 1.020

Surface Area (m²/g) 71.928 168.492

SEM image

Mole fraction H₂ 0.3616 0.3543 0.3462 0.3383 0.3291 0.3237

Mole fraction CH₄ 0.0190 0.0223 0.0261 0.0297 0.0340 0.0364

Mole fraction C0₂ 0.1379 0.1446 0.1521 0.1594 0.1678 0.1727

Mole fraction CO 0.4385 0.4319 0.4244 0.4172 0.4088 0.4039

Mole fraction H₂0 0.0196 0.0231 0.0270 0.0307 0.0351 0.0377

Mole fraction Ar 0.0234 0.0238 0.0243 0.0247 0.0252 0.0255

Example 14: H,:(CO+CO,) ratio of 0.8

Twelve samples of S-70 shot were placed in quartz boats in a quartz tube as described above. A reaction gas containing about 43.40% H₂, 44.32% CO, 10.00% C0₂, and 2.28% Ar was introduced into the quartz tube at about 310 kPa. The reaction gas had an H₂:(CO+C0₂) ratio of about 0.8. The gases flowed over the shot for about 30 minutes at 1200 seem. Methane, carbon dioxide, and water were also formed in the quartz tube. After the test, approximately 1.08 g of liquid water was collected.

Table 14: Solid Carbon Formation with an H₂:(CO+C0₂) ratio of 0.8

Example 15: H,:(CO+CO?) ratio of 0.9

Twelve samples of S-70 shot were placed in quartz boats in a quartz tube as described above. A reaction gas containing about 46.15% H₂, 41.42% CO, 10.00% C0₂, and 2.43% Ar was introduced into the quartz tube at about 321 kPa. The reaction gas had an H₂:(CO+C0₂) ratio of about 0.9. The gases flowed over the shot for about 30 minutes at 1200 seem. Methane, carbon dioxide, and water were also formed in the quartz tube. After the test, approximately 1.788 g of liquid water was collected.

Table 15: Solid Carbon Formation with an H₂:(CO+C0₂) ratio of 0.9

Example 16: H,:(CO+CO?) ratio of 1.0

Twelve samples of S-70 shot were placed in quartz boats in a quartz tube as described above. A reaction gas containing about 48.69% H₂, 38.75% CO, 10.00% C0₂, and 2.56% Ar was introduced into the quartz tube at about 324 kPa. The reaction gas had an H₂:(CO+C0₂) ratio of about 1.0. The gases flowed over the shot for about 30 minutes at 1200 seem. Methane, carbon dioxide, and water were also formed in the quartz tube. After the test, approximately 1.666 g of liquid water was collected.

Table 16 : Solid Carbon Formation with an H₂ : (CO+C0₂) ratio of 1.0

Sample # 1 2 3 4 5 6

Temperature (°C) 319.997 474.485 533.438 571.639 610.075 644.531

Deposition rate (g/cm²/hr) 0.000 0.698 15.124 6.717 1.611 0.473

Surface Area (m²/g) 175.647 184.116 158.326 86.995

SEM image

Mole fraction H₂ 0.4866 0.4781 0.4696 0.4608 0.4517 0.4424

Mole fraction CH₄ 0.0010 0.0047 0.0083 0.0121 0.0161 0.0201

Mole fraction C0₂ 0.0934 0.0973 0.1013 0.1053 0.1095 0.1138

Mole fraction CO 0.3917 0.3862 0.3808 0.3751 0.3693 0.3634

Mole fraction H₂0 0.0016 0.0075 0.0134 0.0195 0.0258 0.0322

Mole fraction Ar 0.0258 0.0262 0.0267 0.0271 0.0276 0.0281 Sample # 7 8 9 10 11 12

Temperature (°C) 668.604 700.197 728.734 778.557 786.652 548.539

Deposition rate (g/cm²/hr) -0.037 -0.617 -0.571 -0.579 -0.429 0.324

Surface Area (m²/g) 146.486

SEM image

Mole fraction H₂ 0.4327 0.4226 0.4146 0.4036 0.3925 0.3815

Mole fraction CH₄ 0.0243 0.0286 0.0321 0.0368 0.0417 0.0464

Mole fraction C0₂ 0.1183 0.1230 0.1267 0.1318 0.1369 0.1420

Mole fraction CO 0.3572 0.3507 0.3456 0.3386 0.3314 0.3244

Mole fraction H₂0 0.0389 0.0459 0.0515 0.0591 0.0668 0.0744

Mole fraction Ar 0.0286 0.0291 0.0296 0.0301 0.0307 0.0313

Example 17: H,:(CO+CO,) ratio of 1.1

Twelve samples of S-70 shot were placed in quartz boats in a quartz tube as described above. A reaction gas containing about 50.95% H₂, 36.37% CO, 10.00% C0₂, and 2.68% Ar was introduced into the quartz tube at about 310 kPa. The reaction gas had an H₂:(CO+C0₂) ratio of about 1.1. The gases flowed over the shot for about 30 minutes at 1200 seem. Methane, carbon dioxide, and water were also formed in the quartz tube. After the test, approximately 1.503 g of liquid water was collected.

Table 17 : Solid Carbon Formation with an H₂ : (CO+C0₂) ratio of 1.1

Example 18: H,:(CO+CO,) ratio of 1.2

Twelve samples of S-70 shot were placed in quartz boats in a quartz tube as described above. A reaction gas containing about 52.99% H₂, 34.22% CO, 10.00% C0₂, and 2.79% Ar was introduced into the quartz tube at about 310 kPa. The reaction gas had an H₂:(CO+C0₂) ratio of about 1.2. The gases flowed over the shot for about 30 minutes at 1200 seem. Methane, carbon dioxide, and water were also formed in the quartz tube. After the test, approximately 1.426 g of liquid water was collected.

Table 18 : Solid Carbon Formation with an H₂ : (CO+C0₂) ratio of 1.2

Example 19: H,:(CO+CO?) ratio of 1.3

Twelve samples of S-70 shot were placed in quartz boats in a quartz tube as described above. A reaction gas containing about 54.86% H₂, 32.25% CO, 10.00% C0₂, and 2.89% Ar was introduced into the quartz tube at about 317 kPa. The reaction gas had an H₂:(CO+C0₂) ratio of about 1.3. The gases flowed over the shot for about 30 minutes at 1200 seem. Methane, carbon dioxide, and water were also formed in the quartz tube. After the test, approximately 3.53 g of liquid water was collected.

Table 19: Solid Carbon Formation with an H₂:(CO+C0₂) ratio of 1.3

Sample # 1 2 3 4 5 6

Temperature (°C) 252.146 451.619 522.938 565.951 601.038 638.622

Deposition rate (g/cm²/hr) -0.038 0.345 8.631 4.349 0.973 0.383

Surface Area (m²/g) 171.959 170.946 153.428 76.332

SEM image

Mole fraction H₂ 0.5501 0.5403 0.5303 0.5199 0.5091 0.4983

Mole fraction CH₄ 0.0004 0.0046 0.0089 0.0134 0.0180 0.0227

Mole fraction C0₂ 0.0934 0.0953 0.0972 0.0991 0.1012 0.1032

Mole fraction CO 0.3265 0.3225 0.3185 0.3143 0.3099 0.3056

Mole fraction H₂0 0.0006 0.0080 0.0154 0.0232 0.0311 0.0392

Mole fraction Ar 0.0290 0.0294 0.0298 0.0302 0.0306 0.0311 Sample # 7 8 9 10 11 12

Temperature (°C) 658.402 685.346 724.087 770.985 790.827 561.693

Deposition rate (g/cm²/hr) 0.000 -0.081 -0.298 -0.574 0.083 0.224

Surface Area (m²/g)

SEM image

Mole fraction H₂ 0.4867 0.4750 0.4624 0.4513 0.4371 0.4247

Mole fraction CH₄ 0.0276 0.0327 0.0381 0.0429 0.0490 0.0543

Mole fraction C0₂ 0.1054 0.1076 0.1100 0.1121 0.1148 0.1171

Mole fraction CO 0.3009 0.2961 0.2911 0.2866 0.2808 0.2758

Mole fraction H₂0 0.0478 0.0566 0.0659 0.0742 0.0848 0.0940

Mole fraction Ar 0.0316 0.0320 0.0325 0.0330 0.0336 0.0341

Example 20: H,:(CO+CO,) ratio of 1.4

Twelve samples of S-70 shot were placed in quartz boats in a quartz tube as described above. A reaction gas containing about 56.57% H₂, 30.46% CO, 10.00% C0₂, and 2.98% Ar was introduced into the quartz tube at about 324 kPa. The reaction gas had an H₂:(CO+C0₂) ratio of about 1.4. The gases flowed over the shot for about 30 minutes at 1200 seem. Methane, carbon dioxide, and water were also formed in the quartz tube. After the test, approximately 2.24 g of liquid water was collected.

Table 20 : Solid Carbon Formation with an H₂ : (CO+C0₂) ratio of 1.4

Example 21: H,:(CO+CO,) ratio of 1.5

Twelve samples of S-70 shot were placed in quartz boats in a quartz tube as described above. A reaction gas containing about 58.31% H₂, 28.81% CO, 10.00% C0₂, and 3.06% Ar was introduced into the quartz tube at about 324 kPa. The reaction gas had an H₂:(CO+C0₂) ratio of about 1.5. The gases flowed over the shot for about 30 minutes at 1200 seem. Methane, carbon dioxide, and water were also formed in the quartz tube. After the test, approximately 0.698 g of liquid water was collected.

Table 21 : Solid Carbon Formation with an H₂ : (CO+C0₂) ratio of 1.5

Example 22: H,:(CO+CO?) ratio of 0.6

Twelve samples of S-70 shot were placed in quartz boats in a quartz tube as described above. A reaction gas containing about 36.75% H₂, 41.32% CO, 20.00% C0₂, and 1.93% Ar was introduced into the quartz tube at about 303 kPa. The reaction gas had an H₂:(CO+C0₂) ratio of about 0.6. The gases flowed over the shot for about 30 minutes at 1200 seem. Methane, carbon dioxide, and water were also formed in the quartz tube. After the test, approximately 1.449 g of liquid water was collected.

Table 22 : Solid Carbon Formation with an H₂ : (CO+C0₂) ratio of 0.6

Sample # 1 2 3 4 5 6

Temperature (°C) 233.911 444.571 523.062 572.481 602.130 628.944

Deposition rate (g/cm²/hr) 0.248 0.291 11.204 7.706 2.519 0.938

Surface Area (m²/g) 165.619 184.272 203.133 110.785

SEM image

Mole fraction H₂ 0.3683 0.3603 0.3520 0.3436 0.3354 0.3269

Mole fraction CH₄ 0.0001 0.0020 0.0039 0.0059 0.0078 0.0098

Mole fraction C0₂ 0.1952 0.1970 0.1989 0.2008 0.2027 0.2047

Mole fraction CO 0.4164 0.4138 0.4110 0.4082 0.4055 0.4026

Mole fraction H₂0 0.0004 0.0071 0.0142 0.0212 0.0282 0.0354

Mole fraction Ar 0.0196 0.0198 0.0200 0.0202 0.0204 0.0206 Sample # 7 8 9 10 11 12

Temperature (°C) 667.465 716.074 779.188 799.738 759.567 568.100

Deposition rate (g/cm²/hr) 0.485 2.455 -0.168 -0.324 -0.509 1.046

Surface Area (m²/g) 155.518

SEM image

Mole fraction H₂ 0.3176 0.3087 0.2996 0.2905 0.2795 0.2709

Mole fraction CH₄ 0.0120 0.0141 0.0162 0.0184 0.0209 0.0230

Mole fraction C0₂ 0.2068 0.2088 0.2109 0.2130 0.2155 0.2175

Mole fraction CO 0.3995 0.3966 0.3935 0.3905 0.3869 0.3840

Mole fraction H₂0 0.0432 0.0508 0.0584 0.0661 0.0754 0.0827

Mole fraction Ar 0.0208 0.0210 0.0213 0.0215 0.0218 0.0220

In each of Examples 23-26 below, catalyst samples (S-70 steel shot) were placed in quartz boats in a tube furnace as in Examples 1-22. Reaction gases having about 43.4% H₂, 54.32% CO, and 2.28% Ar (i.e., an H₂:CO ratio of about 0.8) were provided for 30 minutes at 1200 seem and at various pressures indicated below. The highest reaction rates observed in each test are shown graphically in FIG. 82.

Example 23: H,:CO ratio of 0.8, 310 kPa

The reaction gases having an H₂:CO ratio of about 0.8 were provided at about 310 kPa. Methane, carbon dioxide, and water were formed in the quartz tube. After the test, approximately 0.814 g of liquid water was collected.

Table 23: Solid Carbon Formation with an H₂:CO ratio of 0.8

Example 24: H?:CO ratio of 0.8.4.0 lYIPa

The reaction gases having an H₂:CO ratio of about 0.8 were provided at about 4.0 MPa. Methane, carbon dioxide, and water were formed in the quartz tube. After the test, approximately 3.351 g of liquid water was collected. Table 24 : Solid Carbon Formation with an H₂ : CO ratio of 0.8

Example 25: H,:CO ratio of 0.8, 4.0 MPa

The reaction gases having an H₂:CO ratio of about 0.8 were provided at about 4.0 MPa. Methane, carbon dioxide, and water were formed in the quartz tube. After the test, approximately 1.64 g of liquid water was collected.

Table 25: Solid Carbon Formation with an H₂:CO ratio of 0.8

Sample # 1 2 3 4 5 6

Temperature (°C) 313.265 468.511 542.571 575.048 599.731 634.527

Deposition rate (g/cm²/hr) 0.062 1.017 25.928 12.426 5.835 2.045

Surface Area (m²/g) 66.608 199.783 239.199 242.729 262.067

SEM image

Mole fraction H₂ 0.4243 0.4049 0.3850 0.3627 0.3396 0.3132

Mole fraction CH₄ 0.0045 0.0185 0.0329 0.0490 0.0657 0.0848

Mole fraction C0₂ 0.0047 0.0191 0.0340 0.0507 0.0680 0.0877

Mole fraction CO 0.5412 0.5231 0.5043 0.4834 0.4617 0.4369

Mole fraction H₂0 0.0027 0.0109 0.0195 0.0290 0.0390 0.0503

Mole fraction Ar 0.0227 0.0235 0.0243 0.0252 0.0261 0.0272 Sample # 7 8 9 10 11 12

Temperature (°C) 676.676 737.616 791.559 792.169 695.472 390.589

Deposition rate (g/cm²/hr) 0.819 0.213 0.000 0.000 2.656 0.000

Surface Area (m²/g) 143.119 58.311 225.696

SEM image

Mole fraction H₂ 0.2861 0.2556 0.2221 0.1854 0.1397 0.1012

Mole fraction CH₄ 0.1043 0.1264 0.1506 0.1771 0.2101 0.2380

Mole fraction C0₂ 0.1079 0.1308 0.1558 0.1832 0.2174 0.2462

Mole fraction CO 0.4115 0.3828 0.3513 0.3168 0.2739 0.2377

Mole fraction H₂0 0.0619 0.0750 0.0893 0.1051 0.1247 0.1412

Mole fraction Ar 0.0283 0.0295 0.0308 0.0323 0.0341 0.0357

Example 26: H,:CO ratio of 0.8, 4.0 MPa

The reaction gases having an H₂:CO ratio of about 0.8 were provided at about 2.1 MPa. Methane, carbon dioxide, and water were formed in the quartz tube. After the test, approximately 1.751 g of liquid water was collected.

Table 26 : Solid Carbon Formation with an H₂ : CO ratio of 0.8

Sample # 7 8 9 10 11 12

Temperature (°C) 667.094 698.874 738.544 786.457 755.830 560.527

Deposition rate (g/cm²/hr) 0.738 0.262 0.220 0.084 0.923 0.292

Surface Area (m²/g) 97.891 61.952 112.426

SEM image

Mole fraction H₂ 0.3130 0.2889 0.2636 0.2369 0.2073 0.1838

Mole fraction CH₄ 0.0920 0.1105 0.1301 0.1506 0.1735 0.1915

Mole fraction C0₂ 0.0802 0.0964 0.1135 0.1314 0.1513 0.1671

Mole fraction CO 0.4214 0.3965 0.3702 0.3425 0.3118 0.2875

Mole fraction H₂0 0.0663 0.0797 0.0938 0.1086 0.1251 0.1381

Mole fraction Ar 0.0270 0.0279 0.0289 0.0299 0.0311 0.0320

Claims

What is claimed is: L A method of concurrently forming ammonia and solid carbon, the method comprising:

reacting a first portion of natural gas in the presence of water to form hydrogen and at least one carbon oxide;

separating the hydrogen from the at least one carbon oxide;

reacting the hydrogen with nitrogen in the presence of a first catalyst to form a first tail gas comprising ammonia; and reacting a second portion of natural gas with the at least one carbon oxide in the presence of a second catalyst to form solid carbon and a second tail gas.

2. The method of claim 1, wherein the at least one carbon oxide comprises carbon monoxide, and further comprising converting the carbon monoxide to carbon dioxide.

3. The method of claim 2, wherein converting carbon monoxide to carbon dioxide comprises reacting the carbon monoxide with water to form hydrogen and carbon dioxide.

4. The method of any of claims 1 through 3, wherein reacting a second portion of natural gas with the at least one carbon oxide comprises forming at least one of graphite, graphene, carbon black, fibrous carbon, buckminsterfuUerene, single-wall carbon nanotubes, multi-wall carbon nanotubes, carbon platelets, and nanodiamonds.

5. The method of claim 4, wherein reacting a second portion of natural gas with the at least one carbon oxide comprises forming a plurality of carbon nanotubes.

6. The method of any of claims 1 through 3, wherein reacting the hydrogen with nitrogen comprises reacting the hydrogen with nitrogen in the presence of a catalyst comprising iron.

7. The method of claim 6, wherein reacting the hydrogen with nitrogen comprises reacting the hydrogen with nitrogen in the presence of a catalyst comprising steel.

8. The method of any of claims 1 through 3, wherein reacting the hydrogen with nitrogen comprises reacting the hydrogen with nitrogen in the presence of a catalyst comprising a plurality of nanoparticles, wherein each nanoparticle is mounted on a carbon nanofiber.

9. The method of any of claims 1 through 3, wherein reacting the hydrogen with nitrogen comprises reacting the hydrogen with nitrogen in the presence of a catalyst at a temperature of between about 250°C and about 800°C.

10. The method of any of claims 1 through 3, wherein reacting the hydrogen with nitrogen comprises reacting the hydrogen with nitrogen in the presence of a first catalyst at a pressure of between about 10,000 kPa and about 40,000 kPa.

11. The method of any of claims 1 through 3, wherein reacting a second portion of the natural gas with the at least one carbon oxide comprises reacting the second portion of natural gas with the at least one carbon oxide in the presence of a catalyst comprising iron.

12. The method of claim 11, wherein reacting a second portion of the natural gas with the at least one carbon oxide comprises reacting the second portion of the natural gas with the at least one carbon oxide in the presence of a catalyst comprising steel.

13. The method of any of claims 1 through 3, wherein reacting a second portion of the natural gas with the at least one carbon oxide comprises reacting the second portion of the natural gas with the at least one carbon oxide in the presence of a catalyst at a temperature of between about 400°C and about 1000°C.

14. The method of any of claims 1 through 3, wherein reacting a second portion of the natural gas with the at least one carbon oxide comprises reacting the second portion of the natural gas with the at least one carbon oxide in the presence of a catalyst at a pressure of about 6.2 MPa or less.

15. The method of any of claims 1 through 3, further comprising controlling a concentration of water in contact with at least one of the first catalyst and the second catalyst to limit oxidation of at least one of the first catalyst and the second catalyst.

16. The method of any of claims 1 through 3, further comprising controlling a concentration of water in contact with the second catalyst to promote formation of a selected alio trope and morphology of the solid carbon.

17. The method of any of claims 1 through 3, further comprising recovering ammonia from the first tail gas.

18. The method of claim 17, wherein recovering ammonia from the first tail gas comprises:

exposing the first tail gas to an aqueous liquid;

absorbing at least a portion of the ammonia in the aqueous liquid; and

separating the first tail gas from the aqueous liquid.

19. The method of any of claims 1 through 3, wherein reacting a second portion of natural gas with the at least one carbon oxide comprises forming water as steam.

20. The method of claim 19, further comprising:

condensing at least a portion of the steam to form liquid water;

absorbing at least a portion of the ammonia in the liquid water; and

separating the absorbed ammonia from the liquid water.

21. The method of any of claims 1 through 3, wherein:

reacting a second portion of the natural gas with the at least one carbon oxide comprises forming the solid carbon in a reactor; and

further comprising removing the solid carbon from the reactor.

22. The method of any of claims 1 through 3, further comprising purifying the first tail gas.

23. The method of any of claims 1 through 3, further comprising purifying the second tail gas.

24. The method of any of claims 1 through 3, further comprising separating the solid carbon from the second tail gas.

25. The method of any of claims 1 through 3, further comprising recycling at least one of the first tail gas and the second tail gas.

26. The method of any of claims 1 through 3, wherein reacting a first portion of natural gas in the presence of water comprises reacting a synthesis gas in the presence of a third catalyst.

27. The method of any of claims 1 through 3, wherein a molar ratio of the hydrogen to the nitrogen is in a range from about 30: 1 to about 1:3.

28. The method of any of claims 1 through 3, further comprising removing sulfur from a natural gas source to form a purified natural gas.

29. The method of any of claims 1 through 3, wherein the natural gas is substantially free of sulfur.

30. A system for concurrently producing ammonia and solid carbon, the system comprising:

a conditioning unit configured to remove sulfur from a natural gas source to form a purified natural gas;

a methane reformer configured to react a first portion of the purified natural gas in the presence of water to form hydrogen and at least one carbon oxide;

a separator configured to separate the hydrogen from the at least one carbon oxide;

a first reactor configured to react the hydrogen with nitrogen in the presence of a first catalyst to form a first tail gas comprising ammonia; and

a second reactor configured to react a second portion of the purified natural gas with the at least one carbon oxide in the presence of a second catalyst to form solid carbon and a second tail gas.

31. The system of claim 30, further comprising a heater configured to provide thermal energy to at least one gas selected from the group consisting of the natural gas source, the purified natural gas, the hydrogen, the at least one carbon oxide, and the nitrogen.

32. The system of claim 30, further comprising a refrigeration system configured to remove thermal energy from at least one gas selected from the group consisting of the at least one carbon oxide, the first tail gas, and the second tail gas.

33. The system of any of claims 30 through 33, wherein the conditioning unit comprises solid carbon.

34. The system of any of claims 30 through 33, further comprising at least one compressor configured to pressurize at least one gas selected from the group consisting of the natural gas source, the purified natural gas, the hydrogen, the at least one carbon oxide, and the nitrogen.