Patent Description:
Continuous production of solid products from reactive gases typically entails reacting the reactive gases in the presence of a catalyst in such a way that the solid products are elutriated from the surface of the catalyst. The solid products are thus swept away from the catalyst and subsequently harvested in a suitable process or series of processes for removing particulates from reaction tail-gases. Reactors conventionally used for such continuous solid production include fluidized-bed reactors, fixed bed reactors, pulsed bed reactors, shaft kilns, etc. Particulate removal devices typically include cyclones, bag houses, electrostatic precipitators, scrubbers, etc..

Various morphologies and allotropes of carbon are used industrially, such as for fuel, as reducing agents and electrodes in metallurgical processes, as corrosion-resistant materials in furnaces and heat exchangers, as carbon electrodes, as fillers and colorants in plastics, rubbers and inks, and as strengtheners in many polymer formulations including tires and hoses. High-purity carbon in many allotropes and morphologies is a bulk commodity chemical widely used in industry. Carbon nanotubes (CNTs) may be particularly valuable.

CNTs may be used for various emerging applications because of their remarkable material properties. CNT use in various manufacturing processes potentially adds strength, toughness, impact resistance, electrical conductivity, and/or thermal conductivity to a product. Currently, CNTs are one of the more expensive allotropes of carbon, and the cost, availability, and quality limit broad industrial uses of this material. Methods for producing CNTs that reduce costs and improve availability and quality would therefore be useful.

CNTs may be produced in a variety of sizes and types. Background information on carbon nanotubes is included in <CIT>, There are two main classes of carbon nanotubes: singlewalled carbon nanotubes (SWNTs) and multi-walled carbon nanotubes (MWNTs). CNTs are typically produced using methods that form primarily SWNTs or primarily MWNTs of various lengths and diameters. One CNT manufacturing process, described in <CIT>, may produce a mixture of both MWNTs and SWNTs.

In <CIT>, a production apparatus for carbon nanotube production is described. This apparatus does not include a product separator comprising a water-gas conversion reactor configured to oxidize solid carbon to a carbon oxide and hydrogen by addition of water.

<CIT> describes a reactor system for making carbon nanotubes. Monitoring or controlling the temperature inside the reaction vessel is not described.

<CIT> discloses a device for producing nanocarbon. Nanocarbon is produced from a low hydrocarbon and oxygen, and part of the feed gas stream is combusted in order to generate heat. Carbon dioxide is removed from the reflux gas before the reflux gas is introduced back into the reactor.

In some embodiments, an apparatus for producing carbon nanoparticles by reducing carbon oxide compounds using a reducing agent includes a reactor configured to receive a dried recycle gas stream, a fresh feed gas stream comprising carbon oxide, and a gaseous reducing agent. The reactor includes at least one mixing means configured to mix the reagents to form a combined gaseous feed stream, a first heat exchanger configured to heat the combined gaseous feed stream to a first temperature, at least one heater configured to further heat the combined gaseous feed stream to a temperature higher than the first temperature, and a reaction vessel configured to receive the heated combined gaseous feed stream. The reactor further includes at least one control system feedback loop configured to monitor and control a reaction temperature in the reaction vessel and the at least one heater. The reaction vessel is configured to maintain predetermined reaction conditions of temperature and pressure, and has an output configured to deliver a tail gas stream to the first heat exchanger. The reaction vessel and other associated vessels and piping that may be subjected to metal dusting conditions in the course of normal service may be designed to prevent metal dusting such as, for example, by using high-chromium steel or a ceramic lining.

The system also includes a product separator configured to separate the tail gas stream into a products stream and the clean tail gas stream. The products stream includes carbon nanoparticles. The product separator is configured to pass the products stream through a cooling heat exchanger lock drum. The product separator comprises a water-gas conversion reactor configured to oxidize solid carbon to a carbon oxide and hydrogen by addition of water. The system also includes a water separation unit configured to receive the clean tail gas stream from the product separator. The water separation unit includes a second heat exchanger configured to transfer heat from the clean tail gas stream to the recycle gas stream, a first condenser configured to receive the clean tail gas stream and to cool the clean tail gas stream to condense water from the clean tail gas stream, and a second condenser to further cool the clean tail gas stream and form the dried recycle stream. A product receiving unit (e.g., a product packaging unit) is configured to receive the products stream from the cooling heat exchanger lock drum.

In some embodiments, product separator and water separator systems may be combined as a scrubber suitable for condensing at least a portion of the water vapor in the tail gas stream and for removing the solid carbon entrained in the tail gas stream. In such cases, the solid carbon becomes entrained in the water stream exiting the scrubber. The wet product may be subsequently removed from the water and dried to form a dry product that can then be transferred to a product-receiving unit, as described above.

The present disclosure describes a reactor, system, and method for the production of solid carbon products from reactive gases using a fixed plate reactor, a fluidized-bed reactor, or another type of reactor, along with separation equipment for solid carbon and water. The products are formed from the reactive gases in contact with a catalyst material. The reactor, system, and method reduce the capital and operating costs associated with production of solid carbon and water. By adjusting operating parameters of the system, a variety of carbon allotropes of various morphologies can be produced using the system. For example, the systems may be used to form carbon nanotubes (CNTs), buckminsterfullerenes, graphite, carbon nanofibers, graphene, diamond, and amorphous carbon including coke and carbon black. In particular, the methods and systems disclosed herein generally use carbon oxides and a reducing agent to form products and water in a wide variety of reactor designs including, but not limited to, fixed-plate reactors, aerosol reactors, shaft kiln reactors, fixed bed reactors, counter-flow bed reactors, or fluidized-bed reactors. The system may be scaled to various production capacities.

As used herein, the terms "product," "products," "solid products," "carbon products," and "solid carbon products" are synonymous and mean and include any dusty, friable, powdery, sandy, chunky, or porous material that may occur as solid granules or agglomerations of solid material, with or without voids. Such materials specifically include nanoparticles of various chemistries and morphologies including carbon nanotubes, carbon nanofibers, and nanodiamonds.

As used herein, the term "carbon oxide" means and includes carbon dioxide, carbon monoxide, and mixtures thereof. As used herein, the term "reducing agent" means and includes a material capable of reducing a carbon oxide. Reducing agents include, for example, hydrogen, a hydrocarbon gas such as methane, an alcohol such as ethyl alcohol, and mixtures thereof.

As used herein, the terms "catalyst" and "catalyst material" mean and include a material formulated to promote one or more reactions, resulting in the formation of a product. A portion of a catalyst may be removed from a surrounding portion of the catalyst during the reaction and contained in or adhered to the product. Thus, some of the catalyst may be physically removed during the reaction, and the catalyst may be continually replenished. The 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 for forming products include, for example, iron, nickel, cobalt, etc., or other elements of Groups <NUM> through <NUM> of the periodic table, and alloys and mixtures thereof. For example, catalysts may be selected from Groups <NUM> through <NUM> of the periodic table. Note that the periodic table may have various group numbering systems. As used herein, group <NUM> is the group including Be, group <NUM> is the group including Sc, group <NUM> is the group including Ti, group <NUM> is the group including V, group <NUM> is the group including Cr, group <NUM> is the group including Mn, group <NUM> is the group including Fe, group <NUM> is the group including Co, group <NUM> is the group including Ni, group <NUM> is the group including Cu, group <NUM> is the group including Zn, group <NUM> is the group including B, group <NUM> is the group including C, and group <NUM> is the group including N. In some embodiments, commercially available metals are used without special preparation. Catalysts may be granular, fibrous, particulate, zeolite, or in any other form compatible with the reactor design and catalyst-handling methods disclosed herein. For example, catalyst includes steel sand-blasting grit, steel wool, chopped steel wool, and similar materials.

<NUM> stainless steel appears to catalyze the formation of CNTs under a wide range of temperatures, pressures, and gas compositions. However, the rate of formation of CNTs on <NUM> stainless steel appears to be relatively low, such that <NUM> stainless steel may be used effectively as a construction material for process equipment, with minimal deposition on surfaces thereof in normal operations. <NUM> stainless steel, in contrast, appears to catalyze the formation of solid carbon at significantly higher rates than <NUM> stainless steel, but may also form various morphologies of carbon. Thus, <NUM> 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 <NUM>% or less by weight. For example, <NUM> stainless steel contains from about <NUM>% to about <NUM>% Cr by weight. Catalysts may also be selected to include Ni, such as in amounts of about <NUM>% or more by weight. For example, <NUM> stainless steel contains from about <NUM>% to about <NUM>% 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 conventional processes. Given the good results observed with <NUM> stainless steel, the Ni and/or Cr may have a synergistic effect with Fe.

Solid carbon is formed using a catalytic conversion reactor to reduce carbon oxides using a reducing agent in the presence of a catalyst. By adjusting operating parameters of the system (e.g., reaction gas mixture, type and form of the catalyst, temperature, or pressure), various carbon allotropes and morphologies can be produced.

Oxidation and subsequent reduction of the catalyst surface alter the grain structure and grain boundaries. Without being bound by any particular 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 <NUM> to about <NUM>,<NUM>, from about <NUM> to about <NUM>,<NUM>, or from about <NUM> to about <NUM>. The resulting grain size may range from about <NUM> to about <NUM>, from about <NUM> to about <NUM>, from about <NUM> to about <NUM>, or from about <NUM> to about <NUM>. 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. Without being bound to any particular 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 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 product (e.g., a CNT diameter). Catalyst powder may be formed in or near the reaction zone by injecting an aerosol solution such that upon evaporation or a carrier solvent, a selected particle size distribution results. Alternatively, powdered catalyst may be entrained in a carrier gas and delivered to the reactor. By selecting the catalyst and the reaction conditions, the process may be tuned to produce selected morphologies of 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).

In certain embodiments, a broad range of inexpensive and readily available catalysts, including steel-based catalysts, are described, without the need for activation of the catalyst before it is used in a reaction. Iron alloys, including steel, may contain various allotropes of iron, including alpha-iron (austenite), gamma-iron, and delta-iron. In some embodiments, reactions disclosed herein advantageously utilize an iron-based catalyst, wherein the iron is not in an alpha phase. In certain embodiments, a stainless steel containing iron primarily in the austenitic phase is used as a catalyst.

Catalysts, including an iron-based catalyst (e.g., steel, steel wool), may be used without a need for an additional solid support. In certain embodiments, reactions disclosed herein proceed without the need for a ceramic or metallic support for the catalyst. Omitting a solid support may simplify the setup of the reactor and reduce costs.

A reactor may be coupled with heating and cooling mechanisms to control the temperature of the reactor. For example, a reactor may be configured such that products and excess reactant are recycled through a cooling mechanism to condense water vapor. The products and/or excess reactant may then be reheated and recycled through the reactor. By removing some of the water vapor in the recycled gases, the morphology of formed may be controlled. Changing the partial pressure of water vapor changes the carbon activity of a mixture. The reactor may also be coupled to a carbon collector in which water and unreacted reactants are separated from the carbon products. The separated products are collected and removed from the system.

In certain embodiments hereof, the partial pressure of water in the reaction is regulated by various means, including recycling and condensation of water, to influence, for example, the structure or other aspects of the composition of products produced. The partial pressure of water appears to assist in obtaining certain desirable carbon allotropes.

The system typically includes various subsystems, such as a gas supply subsystem, a gas handling subsystem, a heating subsystem, a reactor subsystem, a product separation subsystem, a water separation subsystem, a water treatment subsystem, a product packaging subsystem, and a utilities subsystem. The subsystems may be arranged in many combinations, and may be replaced with other unit operations that perform similar or related functions. Various arrangements of these subsystems are described herein. The characterization of components of the system as distinct subsystems is for convenience of explanation only, and various other groupings of the unit operations described may be selected based on the principles disclosed herein.

The subsystems may be arranged to accommodate a variety of gas and product flows. In general, gas flows from the gas handling subsystem to the reactor subsystem. Recycled gas flows from the water removal subsystem to the gas handling subsystem, and water flows from the water removal subsystem to the water treatment subsystem. Other flows may be directed to accommodate selected design specifications. Product may be removed by a product removal subsystem either directly from the reactor (e.g., as in a shaft-kiln or counter-flow packed bed reactor) or from the tail gas stream exiting the reactor (e.g., as in a fluidized bed or pulsed bed reactor) prior to entering the water removal subsystem.

For example, <FIG> illustrates a simplified block flow diagram of a system <NUM> for producing solid carbon and water. <FIG> includes process flow lines indicating the movement of material through the system <NUM>. In the system <NUM>, reaction gases flow from a gas supply subsystem <NUM> to a gas handling subsystem <NUM>, then to a heating subsystem <NUM> on the way to a reactor subsystem <NUM>.

As further depicted by dashed lines in <FIG>, the gas supply subsystem <NUM> may optionally provide reaction gases at various points within the system <NUM>. For example, the gas supply subsystem <NUM> may supply gases directly to the heating subsystem <NUM>, where the reaction gases may mix with recycled gases from the gas handling subsystem <NUM>. Alternatively, the gas supply subsystem <NUM> may provide the reaction gases directly into the reactor subsystem <NUM>.

Products may be removed before cooling. In such embodiments, hot reaction gases with entrained products flow directly from the reactor subsystem <NUM> to the product removal subsystem <NUM>. After the products are removed, remaining hot gases pass to the heating subsystem <NUM>. The remaining hot gases are counter-flowed through one or more heat exchangers in the heating subsystem <NUM> to provide at least a portion of the heat required to bring the reaction gases to a predetermined reaction temperature. The resulting cooled gases flow to the water removal subsystem <NUM>. The water removal subsystem <NUM> separates water from the gases. The water passes to a water treatment subsystem <NUM>, and the remaining gases are recycled to the gas handling subsystem <NUM>. A utilities subsystem provides support to other subsystems, such as for cooling water, chilled glycol, an inert gas purge, a vent stack, and/or a flare.

An alternate system <NUM>' illustrating another way in which the subsystems may be combined, is depicted in <FIG>. The system <NUM>' has the same subsystems as system <NUM>, but the tail gases and products have different flow paths. Hot tail gases with entrained products flow from the reactor subsystem <NUM> directly to the heating subsystem <NUM>, where at least a portion of the heat in the hot tail gases is transferred to the reaction gases entering the reactor subsystem <NUM>. After the heat exchange, the cooled tail gases flow to the product removal subsystem <NUM>, where the product is removed. The remaining tail gases then flow to the water removal subsystem <NUM>.

The choice of flow paths for gases, liquids, and solids is a design choice. If pressurizing the reaction gases is required, the reaction gases may flow from the gas supply subsystem <NUM> to the gas handling subsystem <NUM>, and from there to the heating subsystem <NUM>. If compression is not desired (e.g., if the gas supply subsystem <NUM> provides reaction gases at sufficient pressure), the reaction gases may flow to the heating subsystem <NUM> or directly to the reactor subsystem <NUM>.

In some embodiments, the gas supply subsystem <NUM> provides a fresh feed gas stream of process gases, including at least one carbon oxide and at least one reducing agent. A portion of the carbon oxide fresh feed gas stream and a portion of the reducing agent fresh feed gas stream are added to the recirculating gas mixture separately or in combination.

Typically, adding the gases separately to the recirculating gas mixture just prior to the reactor subsystem <NUM> greatly reduces the risk of reaction during heating. However the fresh feed gas streams can be added at any point to the recirculating gas stream, including prior to the gas handling subsystem <NUM>. Depending on where the fresh feed streams are added, the fresh feed gas streams may be preheated to avoid lowering the temperature of the recirculating gas mixture below the capacity of the system <NUM> to maintain selected conditions. In one embodiment, hydrogen is added before the gas handling subsystem <NUM> without preheating and carbon oxide is preheated and added just before the reactor subsystem <NUM>. In another embodiment, the hydrogen and the carbon oxide are each preheated and added separately just before the reactor subsystem <NUM>.

The gas supply subsystem <NUM> may include means for storing a supply of reaction gases and means for regulating the pressures, temperatures, and flow rates of the gases. The gas supply subsystem <NUM> may also contain a control system feedback loop to monitor and control the flow rate of at least one of the fresh feed gases to maintain system pressure or reaction gas composition in the system <NUM>. An effective control system may use the system pressure (e.g., the inlet or outlet pressure of the compressor or process gas blower) to control the flow rate of fresh reducing agent and the reaction gas composition to control the carbon oxide flow rate. Parameters that may be controlled include the carbon activity and the oxygen potential of the reaction gas mixture in the reactor. The partial pressure of water is one factor that appears to affect the type and character (e.g., morphology) of solid carbon formed, as well as the kinetics of carbon formation.

Carbon activity (Ac) can be used as an indicator of whether solid carbon will form under particular reaction conditions (e.g., temperature, pressure, reactants, concentrations). Without being bound to any particular theory, it is believed that carbon activity is the 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 the reactants, divided by the partial pressure of gaseous tail gas constituents. For example, in the reaction, CO(g) + H<NUM>(g) # C(s) + H<NUM>O(g), with a reaction equilibrium constant of K, the carbon activity Ac is defined as K·(PCO·PH2/PH2O). Thus, Ac is directly proportional to the partial pressures of CO and H<NUM>, and inversely proportional to the partial pressure of H<NUM>O. Higher PH2O tends to inhibit CNT formation. The carbon activity of this reaction may also be expressed in terms of mole fractions and total pressure: Ac=K·PT(YCO·YH2/YH2O), where PT 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 and the carbon activity of the reaction gases in the reactor.

Similarly, oxygen potential can be used as an indicator of whether a catalyst material will oxidize under particular reaction conditions (e.g., temperature, pressure, reactants, and reactant concentrations). Oxidation of catalyst material may limit the ability of the catalyst material to subsequently catalyze reactions. Oxygen potential may be defined in terms of the equilibrium constant of the oxidation reaction. For example, iron metal may be oxidized to iron oxide: Fe + ½ O<NUM> <IMG> FeO. The equilibrium constant is defined as KFeO = exp[-ΔGFeO/(RgT)] = √(PO2/PT), where ΔGFeO is the Gibbs free energy of the oxidation reaction, Rg is the gas constant, T is the absolute temperature, PO2 is the partial pressure of oxygen, and PT is the total pressure. Using this equation, the partial pressure of oxygen that will initiate the oxidation of iron may be determined: PO2 > PT·KFeO<NUM>. The partial pressure of oxygen can be obtained from the equilibrium of one or more fast reactions involving oxygen, such as:
<CHM>
<MAT> or
<CHM>
<MAT> In these reactions, Ki is the equilibrium constant for the decomposition of gas i. The partial pressure of oxygen may be controlled by the partial pressures of other gases.

The gas handling subsystem <NUM> typically includes an air-handling device (e.g., a compressor or process gas blower) suitable for moving reaction gases through the system by providing motive power to flow the reaction gases at desired flow rates and pressures through the system <NUM>. The gas handling subsystem <NUM> also includes associated controls and components. The gas handling subsystem <NUM> circulates the gas mixtures through the system <NUM>. Various compressor types suitable to the service and capacity of the system <NUM> may be selected including reciprocating, scroll, screw, hooked-screw and centrifugal compressors, or process gas blowers. In one embodiment, discharge from the water removal subsystem <NUM> feeds a compressor of the gas handling subsystem <NUM>. The gas handling subsystem <NUM> typically discharges the reaction gas stream to the heating subsystem <NUM>. The gas handling subsystem <NUM> may also include a control system feedback loop to monitor and control the flow rate of the reaction gas stream.

The heating subsystem <NUM> typically includes one or more heat exchangers, wherein hot gases from the outlet of the reactor subsystem <NUM> are counter flowed with reaction gases flowing to the inlet of the reactor subsystem <NUM>. One or more heaters may provide additional heat to the reaction gases to reach a selected temperature prior to entering the reactor subsystem <NUM>. The reaction gas stream may be heated to reaction temperatures in the heating subsystem <NUM>. The flow of gases through the heating subsystem <NUM> may allow recovery of at least a portion of the process heat from the reaction tail gas stream. The reactor subsystem <NUM> may also contain one or more heaters to further heat the reaction gas feed stream to a selected temperature prior to entering a reaction vessel. The heating subsystem <NUM> may also include a control system feedback loop to monitor and control the temperature of the reaction gas stream.

The reactor subsystem <NUM> includes a reactor, such as a fluidized bed, a packed bed, a shaft kiln, or any other appropriate design. The reactor subsystem <NUM> also typically includes associated controls and components, such as features for catalyst flow. A reaction vessel receives the heated combined feed stream and catalyst. CNT and water formation occur within the reaction vessel as the reaction gas stream contacts the catalyst. The reaction vessel outputs a reactor tail gas stream that may contain the reaction products (e.g., water and CNTs or other carbon products) and unreacted gases. The reaction vessel may also include a control system feedback loop to monitor and control reaction conditions in the reaction vessel and/or the heaters.

Various reactor types and configurations may be used in the reactor subsystem <NUM>, including, plate, fixed-bed, fluidized-bed, pulsed fluid-bed, shaft-kiln, and rotating-bed reactors. In one embodiment, catalyst material is formed into a series of plates in a plate reactor. For example, the plates may be concentric steel tubes. In another embodiment, the catalyst material is in the form of small particles in a fixed-bed reactor, and the catalyst material and product are periodically removed from the reactor and agitated to remove the product from the catalyst particles. The catalyst material is separated for reuse, and the product is removed for packaging. In yet another embodiment, a pulsed fluid-bed reactor is used, wherein a bed of catalyst particles is maintained as a fixed bed and periodically fluidized by pulses of the reaction gases (e.g., a temporary increase in the flow rate of reaction gases) so that the product is elutriated and removed from the reactor.

The product removal subsystem <NUM> typically includes means for separating products from a gas stream. Such means may include one or more cyclones (single-stage or multi-stage), filters, electrostatic precipitators, bag houses, or various combinations of these separation devices. The product removal subsystem <NUM> may include any suitable device(s), such as one or more cyclones operating in series, to remove various fractions of solid carbon from the tail gas stream. The product removal subsystem <NUM> may also include associated controls and components. The product removal subsystem <NUM> removes the product from the reactor tail gas stream to form a products stream and a clean tail gas stream. In embodiments in which the reactor subsystem <NUM> includes a shaft-kiln reactor, the product and catalyst are removed from the bottom of the reactor through a lock hopper system. In such embodiments, the product removal subsystem <NUM> may include additional means to separate the residual catalyst from the solid carbon and to classify the residual catalyst and recycle all or portions thereof to the catalyst feed system for the reactor.

In some embodiments, a lock drum passes the products stream from the product removal subsystem <NUM> to a product packaging subsystem <NUM>, while a clean tail gas stream outlet passes the clean tail gas stream to the heating subsystem <NUM>, to a heat exchanger within the reactor subsystem <NUM>, or to the water removal subsystem <NUM>. The function of a lock drum is to isolate the reaction gases in the product removal subsystem <NUM> from the product packaging subsystem <NUM>. A lock drum typically includes means for purging the reaction gases and may include means for cooling of the product prior to transfer to the product packaging subsystem <NUM>. The product packaging subsystem <NUM> may include means for handling and transfer of materials, such as pneumatic transfer, screw conveyor, or other such means as are commonly used in the handling of powdered or granular products.

The product removal subsystem <NUM> may be configured to operate at substantially the same temperature as the reactor, such as in embodiments in which the tail gases flow from the reactor subsystem <NUM> directly to the product removal subsystem <NUM> (e.g., in system <NUM> of <FIG>). In such embodiments, materials and design of the lock hopper may be selected to withstand the expected temperatures of the products. In embodiments in which the tail gases are cooled before flowing to the product removal subsystem <NUM> (e.g., in system <NUM>' of <FIG>), materials and design of the lock hopper may be less robust. That is, cooling the tail gases may allow the lock hopper to be formed from a wider range of materials. Whether to cool the reactor tail gas prior to or after product separation may influence the available product-separation options because some separation techniques may require particular temperature ranges.

In some embodiments, the product removal subsystem <NUM> or the water removal subsystem <NUM> may include a water-gas conversion reactor capable of capturing solid carbon material that bypasses the product removal subsystem <NUM>. Water is injected into the water gas conversion reactor so that the water-gas reaction (i.e., C(s) + H<NUM>O → CO + H<NUM>) converts remaining solid carbon material back to carbon oxides and hydrogen. Oxidation of solid carbon may limit or prevent the fouling of downstream equipment, contamination of the water removed from the tail gas stream, or contamination of the vent gas streams.

In some embodiments, the water-gas conversion reactor may include a control system to regulate the flow of water based on the pressure drop across the water-gas reactor and the downstream water content of the clean tail gas stream. The water-gas conversion reactor may include filter materials selected to withstand the operating temperatures and water-gas reaction conditions (e.g., sintered metal or ceramic filters). In some embodiments, multiple filters may be employed, and reaction gases may alternate between the filters. In such embodiments, each filter may cycle between a filtering mode and a water-gas reaction mode. The filter may collect solid carbon in filtering mode. After a period of time, the filtering efficiency may decrease. The filter may then be switched to water-gas reaction mode. In the water gas reaction mode, the filter or a supplemental reaction gas stream (e.g., all or a portion of the clean tail gas stream) is heated to increase reaction rates of the water-gas reaction. After a period of time, the filter may be free of built-up solid carbon, and the filter may be switched back to filtering mode. If two or more filters are present, one may operate in filtering mode while another operates in water-gas reaction mode, allowing continuous operation of the filtering system.

The reaction gas mixtures and conditions of the system <NUM> are commonly associated with metal dusting (i.e., deposition of solid carbon on metal surfaces). Thus, the materials and components selected for the high temperature portions of the system <NUM> may be selected to avoid metal dusting. An advantage of adding water in the water-gas reactor in excess of that required for the water-gas reaction is that water tends to passivate or protect common grades of stainless steel (e.g., <NUM>, <NUM>, etc.) from metal dusting. Excess water may reduce the risk of metal dusting and may be used downstream or removed. For example, if the product removal subsystem <NUM> includes a water-gas conversion reactor operating with excess water, the clean tail gas leaving the product removal subsystem <NUM> may flow to the heating subsystem <NUM> (see <FIG>). After flowing through the heating subsystem <NUM> or a portion thereof, the clean tail gas stream may flow through additional heat exchangers to further cool the clean tail gas stream and through one or more filters to remove additional product. The clean tail gas stream then flows through one or more heat exchangers or condensers within the water removal subsystem <NUM>.

The water removal subsystem <NUM> typically includes means for condensing the water from the process gas stream after the product has been removed. The water removal subsystem <NUM> may include one or more condensers cooled by water, chilled brine, glycol, or air, as well as associated tanks, controls, and components. In some embodiments, the water removal subsystem <NUM> includes a two-stage condenser in which the first stage is water-cooled and the second stage is glycol- or brine-cooled to achieve a clean tail gas stream having a lower the dew point than is possible with water-cooling alone.

The water removal subsystem <NUM> may be operated to remove sufficient water and maintain a desired water concentration (e.g., partial pressure of water) in the dried gases exiting the water removal subsystem <NUM>. The water concentration influences the oxidation potential of reaction gases in the reactor. Therefore, controlling the water concentration may be important to control the deposition of the selected allotropes and morphologies of solid carbon and to avoid oxidation or fouling of the catalysts. The cooling medium (e.g., water, brine, glycol, air, etc.) for the condensers may be provided by a utilities subsystem.

The water removal subsystem <NUM> may have an output for condensed water and an output for the recycled gas stream. The recycled gas stream returns to the gas handling subsystem <NUM> for reuse or ventilation to a safe location. If the feed gases contain significant inert impurities, a purge stream may control the accumulation of the inert gases in the system <NUM>. The condensed water from the water removal subsystem <NUM> is transferred to the water treatment subsystem <NUM>.

The water treatment subsystem <NUM> typically includes one or more filters for minimizing product discharge in the water. The water treatment subsystem <NUM> may also include one or more aeration tanks, overflow tanks, and associated controls and components. The water treatment subsystem <NUM> may be operable to limit or minimize the release of reaction gases or product with the water. The water treatment subsystem <NUM> may contain a water tank and at least one filter to remove product impurities before discharging condensed water to a drain. The water treatment subsystem <NUM> may also include air sparging or other treatment of the water to remove dissolved reaction gases from the condensed water.

The product packaging subsystem <NUM> typically includes product storage and handling equipment to transfer product to containers in a manner that limits or minimizes worker and environmental contamination from airborne solid carbon particles. For example, the product packaging subsystem <NUM> may include an automated drum load-out station configured to operate with negative pressure, HEPA and ULPA filtration systems, and associated controls and components. The product packaging subsystem <NUM> may be physically proximate to the product removal subsystem <NUM> and may include a silo, a vent, and a conveyor belt to move product to enclosed load-out units. The product packaging subsystem <NUM> may be configured to load containers such as barrels. The product packaging subsystem <NUM> may also include a blower and filter to provide negative pressurization to load-out units and to remove impurities from air within the product packaging subsystem <NUM>. The product packaging subsystem <NUM> may also provide access to a product shipping area.

The utilities subsystem typically includes plant services for the operation of the system <NUM>. Such services may include plant air, cooling water supply, chilled brine or glycol supply, vent system (e.g., a stack and flare system), inert purge gas supply and handling, and associated controls and components. The utilities subsystem may provide a cyclic cooling water supply and return (e.g., a cooling tower) and a cyclic glycol supply and return (e.g., a chiller) for the condensers, and at least one vent or flare to release filtered gases.

The system <NUM> includes various control mechanisms. For example, the system <NUM> may include means to determine gas composition, reactor pressure, reactor temperature, and reaction gas flow rates. The system <NUM> may also include means to control such parameters, such as valves, heaters, etc. Controlling such parameters may allow an operator to select products of a given particular quality and morphology.

Gas composition within the system <NUM> may be controlled by providing the carbon oxide make-up gas stream at a rate selected to maintain a desired carbon activity in the tail gas streams and by providing the reducing agent make-up gas stream to maintain the pressure in the system <NUM>. Because the reducing agent is consumed in the reaction at a stoichiometric ratio with the carbon oxides, the pressure in the system falls as the reaction gases are consumed. The flow of the reducing gas may be controlled to maintain the pressure, and the carbon oxide stream may be controlled to maintain the carbon activity in the tail gas streams.

In some embodiments, the partial pressure of water vapor is controlled within the system <NUM>. Controlling water vapor partial pressure is useful to form a desired allotrope and morphology of solid carbon. Controlling water vapor partial pressure is also useful to maintain the catalyst in a condition for promoting reactions (e.g., by limiting oxidation of the catalyst). Control of the water vapor partial pressure may be achieved through various means, such as controlling the condensation temperature in the water removal subsystem <NUM>, which determines the partial pressure of water vapor in the dry gas leaving the condensers. Control of the water vapor partial pressure may also be achieved through the control of the carbon oxide make-up gas stream, which determines the rate of water formation in the reactor subsystem <NUM>. The reduction of the carbon oxide by the reducing agent in the reactor subsystem <NUM> results in the formation of water vapor in the reactor subsystem <NUM>.

The water vapor formed in the reactor subsystem <NUM> is believed to be an important contributor to the allotropes and morphologies of carbon formed. As the oxygen potential of the reaction gases in the reactor subsystem <NUM> increases, allotropes and morphologies of solid carbon having higher Gibbs free energies tend to preferentially oxidize in the water gas reaction. By controlling the oxygen potential of the reaction gases in the reactor subsystem <NUM>, the selectivity of the carbon allotropes and morphologies produced can be improved.

The allotropes and morphologies of carbon formed in the reactor subsystem <NUM> depend on the carbon activity, oxygen potential, temperature, pressure, and type of catalyst. Suitable conditions for various types of solid carbon can be readily determined by experiment.

Carbon activity may be controlled by heating components of the system <NUM> to operating conditions in the presence of pure hydrogen (e.g., a heated hydrogen stream). Once the system <NUM> is at operating temperature and pressure, the carbon oxide make-up gas stream is introduced. The flow of the carbon oxide make-up gas stream is controlled to maintain a selected reaction gas composition or tail gas composition. The reducing agent make-up gas stream may be similarly controlled to maintain the desired system pressure.

Thus, the pressure at any point in the system <NUM> may be used as the process control variable. For example, the compressor outlet pressure may be used as the process control variable to control the reducing agent make-up gas stream flow rate. In other words, the outlet pressure may be maintained at a constant value by changing other parameters. Many variations may also be used to control make-up gas flow, such as safety interlocks, positive feedback control of the carbon activity and oxygen potential by controlling the flow of the carbon oxide make-up gas stream, condenser temperature control in the water removal subsystem <NUM>, etc..

A relatively stable reaction pressure, which may be provided as described above, may be important because the deposition of products is typically a diffusion-limited process. Without being bound to a particular theory, higher pressure appears to correlate with a higher rate of carbon formation. Furthermore, the morphology of the solid carbon may vary with pressure. To maintain consistent carbon morphology, the carbon activity and oxygen potential may be adjusted to compensate for the increased pressure. The carbon activity and oxygen potential can be adjusted by a combination of changing the reaction gas mixture, changing the temperature of the reactor subsystem <NUM>, and changing the temperature of the condensers in the water removal subsystem <NUM>.

In some embodiments, start-up of the system <NUM> is performed under an atmosphere in which carbon formation is not possible in any of the equipment. For example, the start-up atmosphere may typically be an inert atmosphere such as nitrogen or argon, or a reducing atmosphere such as hydrogen. Start-up often includes a period during which the reactor is at a temperature of at least approximately <NUM> and in an atmosphere of flowing hydrogen or other reducing gas that reduces any metal oxides prior to introducing the reaction gases. The start-up may continue for a suitable time for catalyst reduction, which depends on the catalyst composition and physical form. The flow of reducing gases during the start-up process transports water vapor formed by the catalyst reduction to the water removal subsystem <NUM>, where the water vapor can be removed from the system <NUM>.

Thus, the process heater of the heating subsystem <NUM> may be divided into two sections: a first high-power start-up heater used for start-up heating only and a second lower-power operating heater for continuous operation. The start-up heater may be isolated from the system during normal operation or may be located in an otherwise cool section of the heating system where the carbon activity is sufficiently low that carbon will not deposit. The operating heater is typically located adjacent the reactor subsystem <NUM> so that the heated reaction gases flow directly into the reactor vessel from the operating heater.

The operating heater of the heating subsystem <NUM> can be simplified if direct combustion is used to bring the gases to reaction temperature. If oxygen is introduced into the recycle gas mixture, some of the gases may oxidize, releasing heat and forming CO, CO<NUM>, and water in various proportions depending on the composition of the recycle gas mixture. This direct combustion may provide sufficient energy to heat the reaction gases to the reaction temperature. The oxygen may be supplied from a water electrolysis device that generates both oxygen and hydrogen. Both of the generated gases may be subsequently used as feed gases to the process, with the water used for the direct-combustion heating and the hydrogen added as a reducing gas. Direct-combustion heating is described in International Patent Application No. <CIT>, titled "Direct-Combustion Heating,".

Reaction gas temperature can be controlled by the heating subsystem <NUM>. If all or a portion of the make-up gas stream is injected at the entrance to the reactor vessel, downstream of the operating heater, a make-up heater may be added to this make-up gas stream. The make-up heater can be controlled based on the mixed gas temperature of the make-up gas stream and the reaction gas stream. The make-up gas heater or heaters may use a portion of the hot tail gases to provide energy for the make-up gas heating.

Reaction gas flow rate control can be achieved through a variety of means. Generally, components of the system <NUM> may be protected from low-flow conditions by interlocking flow controls. For example, when low-flow conditions occur, the carbon oxide make-up gas stream may be terminated and the process heaters shut off.

<FIG> depicts one embodiment of a system <NUM> for production of solid carbon products. Aspects of this embodiment are shown in further detail in <FIG>. The system <NUM> typically includes a gas supply subsystem <NUM>, a gas handling subsystem <NUM>, a reactor subsystem <NUM>, a product separation subsystem <NUM>, a water separation subsystem <NUM>, a water treatment subsystem <NUM>, a product packaging subsystem <NUM>, and a utilities subsystem <NUM> (each shown in more detail in <FIG>). In <FIG>, solid arrows indicate the flow of materials (gas, liquid, etc.). In the system <NUM>, information also flows within and between various subsystems. The subsystems may be modified or combined, or may be added to additional subsystems as fitting desired production processes. The subsystems may be positioned to improve operating economics and to make efficient use of space in a process facility. The subsystems may also include various instruments or equipment, such as valves, transducers, flow meters, switches, controllers, computers, etc. The gases referenced in this description are for example only and may be substituted for, and/or added to other gases. The assignment of specific mechanics to specific subsystems within the system is also for example only.

As depicted in <FIG>, gas supply subsystem <NUM> includes at least a supply of liquefied carbon dioxide (CO<NUM>) or other carbon oxide <NUM> (e.g., a tank, pipe, etc.), and a supply of at least one reducing gas <NUM> such as methane (CH<NUM>) of any selected purity. When conditions such as pressure and temperature are appropriate, the carbon oxide <NUM> passes through a vaporizer <NUM>, which evaporates the carbon oxide <NUM> to form carbon oxide gas. The carbon oxide gas is split into two portions <NUM>, <NUM> that pass into the gas handling subsystem <NUM> (see <FIG>). One or more valves <NUM>, <NUM> may control the flow of gases. A reducing agent <NUM> is provided to subsequent processes through reducing gas stream <NUM>.

In the gas handling subsystem <NUM>, shown in <FIG>, one portion of the carbon oxide gas <NUM> is mixed with the reducing gas stream <NUM>. The combined gas stream may optionally be mixed with a recycle stream <NUM> containing dry tail gas supplied by the water separation subsystem <NUM> (see <FIG>). The combined gases may enter a first tank <NUM> before being compressed in a compressor or process gas blower <NUM>. The compressed gas is transferred to a second tank <NUM> for holding or further processing. The compressed gas from the second tank <NUM> is mixed with a portion <NUM> of the carbon oxide gas to form a combined feed gas stream <NUM> under conditions selected for particular reactions, such as temperature, pressure, concentration, and density. The conditions typically depend on the desired endproduct; for example, carbon nanotubes, graphite, and carbon black each form under different reaction conditions. The combined gas feed stream <NUM> is analyzed by at least one analyzer <NUM> to obtain information useful for controlling other components of the system <NUM> (e.g., concentration of reactants in the combined feed gas stream <NUM>, temperature, or pressure).

As shown in <FIG>, the combined gas feed stream <NUM> flows to the reaction subsystem <NUM> and to at least one heat exchanger <NUM> therein. The heat exchanger <NUM> is typically a counter-flow heat exchanger configured for gas-gas interchange, and the combined gas feed stream <NUM> receives heat from a warmer clean tail gas stream <NUM> from a cyclone <NUM> within the product separation subsystem <NUM> (see <FIG>). Multiple heat exchangers may be used to heat the combined gas feed stream; for example, two heat exchangers <NUM> are shown in <FIG>. The heat exchangers <NUM> typically include materials selected for the process temperatures and to be resistant to metal dusting corrosion. In some embodiments, a small amount of water is added to the gas flow streams before the first heat exchanger <NUM> to cause a deposit of metal oxide on surfaces of the heat exchangers <NUM> to limit or prevent metal dusting. The heat exchangers <NUM> cool the clean tail gas stream <NUM> to form a cooled clean tail gas stream <NUM>, which flows to the water separation subsystem <NUM> (see <FIG>).

Within the reaction subsystem <NUM>, the combined gas feed stream <NUM> flows to at least one heater <NUM> (e.g., an electric heater) to bring the reactants up to reaction conditions, then to a reactor <NUM>. The heater <NUM> receives reaction feedback information from the reactor <NUM> via one or more sensors. The reactor <NUM> may be lined with a ceramic material to mitigate metal dusting corrosion therein. The reactions that occur within the reactor <NUM> may be Bosch-type reactions at conditions that produce selected morphologies of solid carbon, such as those disclosed in <CIT>.

A reactor tail gas stream <NUM> flows from the reactor <NUM> to a cyclone <NUM> within the product separation subsystem <NUM> (<FIG>). The cyclone <NUM> and flow lines connecting the reactor <NUM> to the cyclone <NUM> may be ceramic-lined to limit or prevent metal dusting corrosion. The cyclone <NUM> separates the reactor tail gas stream <NUM> into a products stream <NUM>, such as CNTs, and the clean tail gas stream <NUM>. The products stream <NUM> includes particles smaller than a selected size. For example, the cyclone <NUM> may be configured to separate particles smaller than about <NUM> microns into the products stream <NUM>. The size of particles separated into the products stream <NUM> depends on operating conditions and particle properties (e.g., shape and density).

The products stream <NUM> passes through a cooling apparatus <NUM>. Some residual gases <NUM>, such as gases containing carbon oxides and potentially explosive reducing agents such as hydrogen and methane may pass through a filter <NUM> and vent to a safe location (e.g., a flare, an exhaust stack). After cooling, the products stream <NUM> is transferred to the product packaging subsystem <NUM> (see <FIG>).

After leaving the cyclone <NUM>, the clean tail gas stream <NUM> returns to the reaction subsystem <NUM> (<FIG>) wherein the at least one heat exchanger <NUM> transfers heat from the clean tail gas stream <NUM> to the combined feed gas stream <NUM>, as described above. Alternatively, the reactor tail gas stream <NUM> may be first passed through a heat exchanger <NUM> before the cyclone <NUM>. Metal dusting corrosion of the heat exchanger <NUM> may be reduced by injecting a small amount of water into the clean tail gas stream <NUM> before the heat exchanger <NUM>. The water causes a layer of metal oxide to form on internal surfaces of the heat exchanger <NUM>, protecting the heat exchanger <NUM> from metal dusting.

As shown in <FIG>, the cooled clean tail gas stream <NUM> flows to another heat exchanger <NUM> before entering a condenser <NUM> (e.g., a one-stage water-cooled condenser) in the water separation subsystem <NUM>. The cooled clean tail gas stream <NUM> passes through at least one filter <NUM>, where liquid water may be diverted into a holding tank <NUM>. After the clean tail gas stream <NUM> passes through the filter <NUM>, a portion <NUM> of the clean tail gas stream <NUM> may be safely vented, and the remainder of the clean tail gas stream <NUM> flows into a second condenser <NUM>.

The second condenser <NUM> may be a two-stage condenser, in which a first stage is water-cooled and a second stage is glycol-cooled. After passing through the two-stage condenser <NUM>, condensed water may be held in a holding tank <NUM> for a period of time before mixing with the output of the holding tank <NUM>. The condensed water <NUM> flows to the water treatment subsystem <NUM> (see <FIG>) for further processing. As water is collected in the holding tank <NUM>, recycled gases <NUM> flow back to the heat exchanger <NUM>, and finally to the tank <NUM> within the gas handling subsystem <NUM> (<FIG>). Cooling water and glycol for the condensers <NUM>, <NUM> may be supplied by the utilities subsystem <NUM> (see <FIG>). In such embodiments, cooling water <NUM>, <NUM> may flow to the first condenser <NUM> and a first set of coils of the second condenser <NUM>, respectively. The cooling water returns <NUM>, <NUM> flow back to the utilities subsystem <NUM>. Chilled glycol <NUM> flows to a second set of coils of the second condenser <NUM>, and glycol return <NUM> flows back to the utilities subsystem <NUM>.

Within the water treatment subsystem <NUM> (<FIG>), a tank <NUM> accumulates the condensed water <NUM> from the water separation subsystem <NUM>. The tank <NUM> may systematically release water to a pump <NUM>, such as through a valved port in or near the bottom of the tank <NUM>. The pump <NUM> directs the condensed water <NUM> through one or more filters <NUM> to form a purified water stream <NUM>. The purified water stream <NUM> then passes to storage, municipal waste, or another safe and permitted disposal means.

The product packaging subsystem <NUM>, shown in <FIG>, transfers the products stream <NUM> to a shipping package <NUM>, such as a barrel, box, or other container. The shipping package <NUM> may be selected to meet requirements for safe and effective transportation and delivery. The process of packaging may occur in a negative-pressure enclosure so that products do not contaminate workers or the workspace, for example, by flowing residual gases <NUM> through a fan or blower <NUM> and a HEPA/ULPA filter <NUM> before venting. After the products are packaged, shipping packages <NUM> may be moved to a shipping area <NUM>, such as a loading dock.

The utilities subsystem <NUM>, shown in <FIG>, may interact with and support other subsystems of the system <NUM>. For example, the utilities subsystem <NUM> may include a cooling tower <NUM> configured to supply cooling water to and receive cooling water returns from the water separation subsystem <NUM> (<FIG>). Heat is removed from the cooling water returns <NUM>, <NUM> in the cooling tower <NUM>. The cooling water <NUM>, <NUM> is recycled via a pump <NUM> back to the water separation subsystem <NUM>. A chiller <NUM> receives the glycol return <NUM> from the water separation subsystem <NUM>. A glycol pump <NUM> recycles the chilled glycol <NUM> to the water separation subsystem <NUM>. The utilities subsystem <NUM> may also include at least one flare or vent <NUM> designed for the safe venting of various process gases. For example, the vent <NUM> may be configured to receive the residual gases <NUM> from the product separation subsystem <NUM>, the portion of the tail gas stream <NUM> from the water separation subsystem <NUM>, and/or the residual gases <NUM> from the product packaging subsystem <NUM>. The utilities subsystem <NUM> may also include other operations, sensors, or controls, as necessary for the system <NUM> to function.

<FIG> depicts another system <NUM> for producing solid carbon products of various morphologies. The system <NUM> includes a gas supply subsystem <NUM>, a gas handling subsystem <NUM>, a fluidized-bed reaction subsystem <NUM>, a product separation and packaging subsystem <NUM>, a water treatment subsystem <NUM>, and a venting subsystem <NUM> (each shown in more detail in <FIG>). In the system <NUM>, solid arrows indicated the flow of materials (gas, liquid, etc.).

<FIG>, solid arrows indicate the flow of materials (gas, liquid, etc.). Information also flows within and between various subsystems. The subsystems may be modified or combined, or may be added to with additional subsystems as fitting desired production processes. The subsystems may be positioned to improve operating economics and to make efficient use of space in a process facility. The subsystems may also include various instruments or equipment, such as valves, transducers, flow meters, switches, controllers, computers, etc. The gases referenced in this description are for example only and may be substituted for, and/or added to other gases. The assignment of specific mechanics to specific subsystems within the system is also for example only.

As depicted in <FIG>, a supply of liquefied carbon oxide (e.g., CO, CO<NUM>) is provided from a source <NUM> (e.g., a tank, pipe, etc.) within the gas supply subsystem <NUM>. When conditions such as pressure and temperature are appropriate, the carbon oxide passes through a first vaporizer <NUM>, which evaporates the carbon oxide to form carbon oxide gas <NUM>. The gas supply subsystem <NUM> also includes a reducing agent source <NUM> of, for example, liquefied hydrogen (H<NUM>). When conditions such as pressure and temperature are appropriate, the liquid reducing agent passes through a second vaporizer <NUM>, which evaporates the liquid reducing agent to form reducing gas <NUM>.

Both the carbon oxide gas <NUM> and the reducing gas <NUM> flow to the gas handling subsystem <NUM>, shown in <FIG>, where they mix to form a combined fresh feed gas stream. The gas handling subsystem <NUM> includes a heat exchanger <NUM> configured to receive and cool a clean tail gas stream <NUM> from the product separation and packaging subsystem <NUM> (see <FIG>). The clean tail gas stream <NUM> passes through one or more filters <NUM> and/or condensers <NUM>. Condensed water <NUM> leaves the condensers <NUM> and flows to the water treatment subsystem <NUM> (see <FIG>). A portion of the resulting dried clean tail gas stream may form a vent gas <NUM> and flow to the venting subsystem <NUM> (see <FIG>), and another portion passes through a pump <NUM> and is mixed with the combined feed gas stream to form a reaction gas <NUM>. The reaction gas <NUM> receives heat from the clean tail gas stream <NUM> in the heat exchanger <NUM> before flowing to the fluidized-bed reaction subsystem <NUM> shown in <FIG>.

In the fluidized-bed reaction subsystem <NUM>, the reaction gas <NUM> stream passes through a heat exchanger <NUM> (e.g., a cross-flow gas-gas interchange heat exchanger) to extract heat from a tail gas stream <NUM>. Multiple heat exchangers may be utilized to achieve a selected amount of heat transfer. The heat exchanger <NUM> includes materials appropriate for the temperatures and conditions therein, such as materials resistant to metal dusting corrosion. A heater <NUM> provides additional heat to bring the reaction gas <NUM> to reaction conditions prior to flowing into the reaction vessel <NUM>. The reaction gas <NUM> flows into a reaction vessel <NUM>, wherein CNTs or other carbon products (e.g., nanodiamonds, graphite, carbon black, etc.) are formed. The reaction vessel <NUM> may be ceramic-lined to mitigate the effects of metal dusting corrosion. The reactions that occur within the reaction vessel <NUM> may be Bosch-type reactions at conditions that produce selected morphologies of solid carbon, such as those disclosed in <CIT>.

The tail gas stream <NUM> flows to the product separation and packaging subsystem <NUM>, as shown in <FIG>. The tail gas stream <NUM> enters a cyclone <NUM>, which separates the tail gas stream <NUM> into a products stream <NUM> and the clean tail gas stream <NUM>. The cyclone <NUM> and flow lines connecting the reaction vessel <NUM> to the cyclone <NUM> may be ceramic-lined to limit or prevent metal dusting corrosion.

The products stream <NUM> includes particles smaller than a selected size. For example, the cyclone <NUM> may be configured to separate particles smaller than about <NUM> microns into the products stream <NUM>. The size of particles separated into the products stream <NUM> depends on operating conditions and particle properties (e.g., shape and density). In some embodiments, the cyclone <NUM> may be configured to separate various morphologies of carbon formed in the reaction vessel <NUM>. In some embodiments, the heat exchanger <NUM> (<FIG>) may be within the product separation and packaging subsystem <NUM>, such that the clean tail gas stream <NUM> flows through the heat exchanger <NUM>.

The products stream <NUM> passes through a cooling apparatus <NUM>. Some residual gases <NUM>, such as gases containing carbon oxides and potentially explosive reducing agents (e.g., hydrogen, methane, hydrocarbon gases), may pass through a filter <NUM> and vent to a safe location (e.g., at the top of an exhaust stack).

After cooling, the products stream <NUM> may be packaged in a shipping container <NUM>. In the process of packaging, residual gases <NUM> may pass through a pump <NUM> and a filter <NUM> before venting. After the products are appropriately packaged for storage and shipping, the shipping containers <NUM> may be moved to a shipping area <NUM>, such as a loading dock.

The water treatment subsystem <NUM>, shown in <FIG>, receives the condensed water <NUM> from the gas handling subsystem <NUM> (see <FIG>). The condensed water <NUM> may pass through one or more filters <NUM> to form a purified water stream <NUM>. The purified water stream <NUM> may pass through one or more cooling devices <NUM> (e.g., a cooling tower) en route to storage, municipal waste, or safe run-off.

The venting subsystem <NUM>, shown in <FIG> may include at least one vent <NUM> in a safe location (e.g., at the top of an exhaust stack). For example, the vent <NUM> may be configured to receive the vent gases <NUM> from the gas handling subsystem <NUM> (<FIG>) and/or the residual gases <NUM>, <NUM> from the product separation and packaging subsystem <NUM> (<FIG>).

<FIG> depicts another system <NUM> for producing solid carbon products of various morphologies. The system <NUM> includes a gas supply subsystem <NUM>, a gas handling subsystem <NUM>, a reactor subsystem <NUM>, a product separation subsystem <NUM>, a water separation subsystem <NUM>, a water treatment subsystem <NUM>, a product packaging subsystem <NUM>, and a utilities subsystem <NUM> (each shown in more detail in <FIG>). In <FIG>, solid arrows indicate the flow of materials (gas, liquid, etc.). Information also flows within and between various subsystems. The subsystems may be modified or combined, or may be added to with additional subsystems as fitting desired production processes. The subsystems may be positioned to improve operating economics and to make efficient use of space in a process facility. The subsystems may also include various instruments or equipment, such as valves, transducers, flow meters, switches, controllers, computers, etc. The gases referenced in this description are for example only and may be substituted for, and/or added to other gases. The assignment of specific mechanics to specific subsystems within the system is also for example only.

As depicted in <FIG>, a supply of liquefied carbon oxide, for example carbon dioxide (CO<NUM>) or carbon monoxide (CO) is provided from a carbon oxide source <NUM> (e.g., a tank, pipeline, etc.) within the gas supply subsystem <NUM>. When conditions such as pressure and temperature are appropriate, the carbon oxide passes through a vaporizer <NUM>, which evaporates the carbon oxide to form carbon oxide gas. The carbon oxide gas is split into three portions <NUM>, <NUM>, <NUM>. A reducing gas source <NUM> (e.g., a tank, pipeline, etc.) provides reducing gas stream <NUM>, such as methane (CH<NUM>) of any selected purity. The carbon oxide and the reducing gas stream <NUM> typically flow from cryogenic storage tanks and may pass through heaters to vaporize the liquids. The reducing gas stream <NUM> may pass through at least one compressor or process gas blower <NUM> to achieve a selected pressure. The reducing gas stream <NUM> and one portion <NUM> of the carbon oxide gas are mixed and heated in a heater <NUM> to form a combined feed gas stream <NUM>. The combined feed gas stream <NUM> and one portion <NUM> of the carbon oxide gas flow to the gas handling subsystem <NUM> (see <FIG>), and the other portion <NUM> of the carbon oxide gas flows to the reactor subsystem <NUM> (see <FIG>). One or more valves <NUM>, <NUM> may control the flow of gases.

In the gas handling subsystem <NUM>, shown in <FIG>, the combined feed gas stream <NUM> is mixed with a recycle stream <NUM> containing carbon oxide gas supplied by the water separation subsystem <NUM> (see <FIG>). The gases may be combined before or within a first tank <NUM>, before being compressed in a compressor or process gas blower <NUM> to a suitable pressure to accommodate the pressure drop through the overall reactor system that the gas handling subsystem <NUM> is designed to support. The compressed gas is transferred to a second tank <NUM> for holding or further processing. The compressed gas mixes with the portion <NUM> of the carbon oxide gas from the gas supply subsystem <NUM> (<FIG>) to form a combined feed gas stream <NUM> under conditions such as temperature, pressure, concentration, and density selected for particular reactions. The conditions typically depend on the desired end product. The combined gas feed stream <NUM> is analyzed by at least one analyzer <NUM> to obtain information to control other components of the system <NUM>. The combined gas feed stream <NUM> flows to the reactor subsystem <NUM> (<FIG>).

As shown in <FIG>, the combined gas feed stream <NUM> flows to the reactor subsystem <NUM> and to at least one heat exchanger <NUM> therein. The heat exchanger <NUM> is typically a cross-flow heat exchanger configured for gas-gas interchange, and the combined gas feed stream <NUM> receives heat from a warmer clean tail gas stream <NUM> from a cyclone <NUM> within the product separation subsystem <NUM> (see <FIG>). Multiple heat exchangers may be used to heat the combined gas feed stream; for example, two heat exchangers <NUM> are shown in <FIG>. The heat exchangers <NUM> typically include materials selected for the process temperatures and to be resistant to metal dusting corrosion. In some embodiments, a small amount of water is added to one or more gas flow streams before the first heat exchanger <NUM> to cause a fine deposit of metal oxide on surfaces of the heat exchangers <NUM> to reduce or prevent metal dusting. The heat exchangers <NUM> cool the clean tail gas stream <NUM> to form a cooled clean tail gas stream <NUM>, which flows to the water separation subsystem <NUM> (see <FIG>).

The combined gas feed stream <NUM> flows to at least one heater <NUM> (e.g., an electric heater) to bring the reactants up to reaction conditions. A portion of the carbon oxide gas <NUM> from the gas supply subsystem <NUM> (<FIG>) is mixed with the combined gas feed stream <NUM> before the combined gas feed stream <NUM> flows to a reactor <NUM>. The heater <NUM> receives reaction feedback information from the reactor <NUM> via one or more sensors. The reactor <NUM> may be lined with a ceramic material to mitigate metal dusting corrosion therein. The reactions that occur within the reactor <NUM> may be Bosch-type reactions at conditions that produce selected morphologies of solid carbon, such as those disclosed in <CIT>.

In the reactor <NUM>, the combined gas feed stream <NUM> contacts catalyst material on a conveyor belt <NUM>. The reactor <NUM> has an input to receive catalyst material from at least one hopper <NUM> in communication with the reactor <NUM> and an output to release catalyst material into a tank <NUM>. The conveyor belt <NUM> moves catalyst material within the reactor <NUM>. Residual gases may flow from the tank <NUM> back to the reactor <NUM>, or may form a vent gas <NUM>. The hopper <NUM> may also release a vent gas <NUM>.

The clean tail gas stream <NUM> flows to the water separation subsystem <NUM> (<FIG>), to another heat exchanger <NUM> before entering a condenser <NUM> (e.g., a one-stage water-cooled condenser). The clean tail gas stream <NUM> passes through at least one filter <NUM>, where liquid water may be diverted into a holding tank <NUM>. After the clean tail gas stream <NUM> passes through the filter <NUM>, a portion <NUM> of the clean tail gas stream <NUM> may be safely vented, and the remainder of the clean tail gas stream <NUM> flows into a second condenser <NUM>.

The second condenser <NUM> may be a two-stage condenser, in which a first stage is water-cooled and a second stage is glycol-cooled. After passing through the two-stage condenser <NUM>, condensed water may be held in a holding tank <NUM> for a period of time before mixing with the output of the holding tank <NUM>. The condensed water <NUM> flows to the water treatment subsystem <NUM> (see <FIG>) for further processing. As water is collected in the holding tank <NUM>, recycled gases <NUM> flow back to the heat exchanger <NUM>, and finally to the tank <NUM> within the gas handling subsystem <NUM> (<FIG>). The condensers <NUM>, <NUM> in the water separation subsystem <NUM> may be supplied by the utilities subsystem <NUM> (see <FIG>). In such embodiments, cooling water <NUM>, <NUM> may flow to the first condenser <NUM> and a first set of coils of the second condenser <NUM>, respectively. The cooling water returns <NUM>, <NUM> flow back to the utilities subsystem <NUM>. Chilled glycol <NUM> flows to a second set of coils of the second condenser <NUM>, and glycol return <NUM> flows back to the utilities subsystem <NUM>.

Within the water treatment subsystem <NUM> (<FIG>), a tank <NUM> accumulates the condensed water <NUM> from the water separation subsystem <NUM>. The tank <NUM> may systematically release water to a pump <NUM>, such as through a port in or near the bottom of the tank <NUM>. The pump <NUM> directs the condensed water <NUM> through one or more filters <NUM> to form a purified water stream <NUM>. The purified water stream <NUM> then passes to storage, municipal waste, or a safe run-off.

The product packaging subsystem <NUM>, shown in <FIG>, transfers the products stream <NUM> to a shipping package <NUM>. In the process of packaging, the products stream <NUM> may flow to a hopper <NUM>, through a valve <NUM>, onto a conveyor belt <NUM>, and into the shipping package <NUM>. Residual gases <NUM> may pass through a pump <NUM> and filter <NUM> before venting. After the products are packaged, shipping packages <NUM> may be moved to a shipping area <NUM>.

Claim 1:
An apparatus for producing solid carbon by catalytically reducing carbon oxides using a reducing agent, comprising:
a reactor configured to receive a dried recycle gas, a fresh feed gas comprising at least one carbon oxide, and at least one reducing agent, the reactor comprising:
at least one mixing means configured to mix the dried recycle gas, the fresh feed gas, and the at least one reducing agent to form a combined feed gas;
at least one heat exchanger configured to heat the combined feed gas to a first temperature by recovering heat from at least one other higher-temperature process stream of the apparatus;
at least one heater configured to further heat the combined feed gas to a second temperature higher than the first temperature;
a reaction vessel configured to receive the heated combined feed gas, the reaction vessel further configured to maintain predetermined reaction conditions of temperature and pressure and to contain a catalyst; at least one discharge of raw tail gas comprising unreacted gases, reaction product gases, entrained solid carbon, and water; and
at least one control system feedback loop configured to monitor and control a reaction temperature in the reaction vessel and the at least one heater; and
a product separator configured to receive the raw tail gas from the reaction vessel and to separate the raw tail gas into a clean tail gas and a products stream comprising solid carbon, wherein the product separator is configured to pass the products stream through a cooling heat exchanger lock drum, wherein the product separator comprises a watergas conversion reactor configured to oxidize solid carbon to a carbon oxide and hydrogen by addition of water;
a water separation unit configured to receive the clean tail gas from the product separator and to remove at least a portion of the water in the clean tail gas to form a dried recycle gas, the water separation unit comprising:
a first condenser configured to receive the clean tail gas and to cool the clean tail gas to condense water from the clean tail gas; and
a water discharge system for removing the water from the apparatus; and
a product receiving unit configured to receive the products stream from the cooling heat exchanger lock drum.