Reactor and associated method for converting gaseous carbon-containing reactants into solid carbon products - Patents.com

Abstract

The reaction assembly has an elongated vessel defining a reaction chamber. A planar support within the reaction chamber has a surface for supporting a solid catalyst. The planar support is mounted transversely to the elongated axis of the vessel and forms a series of spaced apart barriers. A conduit introduces gas between successive barriers through an opening such that gas flow through the conduit causes the gas to flow along the support surface. By selecting an appropriate metal nanoparticle catalyst that can be seeded onto the support surface, the reaction assembly can be used to produce carbon nanofibers from carbon monoxide and hydrogen, which can then be removed by injecting a fluid.

Description

[Technical field]

[0001] The present invention generally relates to an apparatus, method and process for producing a solid product, such as carbon nanofibers (CNF), from gaseous reactants using a solid catalyst. In particular, the disclosure relates to the design of a reactor that supports a solid catalyst, and to processes for providing active catalytic sites for a reaction, growing carbon nanofibers on the active sites, recovering the carbon nanofibers, preparing the substrate for the next replenishment, and reinjecting or reactivating the catalyst on the substrate in the reactor. [Background technology]

[0002] There is an increasing demand for lightweight materials, including carbon, to increase energy efficiency and reduce greenhouse gases. Carbon material additives have applications in over 40 areas, including composites, batteries, plastics, and coatings. Carbon materials have a wide range of physical properties and are well known as multifunctional materials; that is, they can have a combination of multiple useful physical properties, such as mechanical strength, low density, low or high electrical conductivity, low or high thermal conductivity, electromagnetic properties, corrosion resistance, and UV resistance. Carbon can be found in a variety of allotropes, including amorphous carbon, graphite, graphene, diamond, fullerenes, carbon nanoforms, carbon nanofibers, fibers, and nanotubes.

[0003] The production of carbon materials is generally divided into two categories: catalytic and non-catalytic.

[0004] Non-catalytic formation of carbon materials (pyrolysis, peeling, wet spinning, etc.) requires a lot of energy and results in high CO2 emissions. For example, wet spinning of polyacrylonitrile (PAN) to produce carbon fiber requires heating at 1800-3000°C. The Japan Carbon Fiber Industry Association pointed out in its LCA report that carbon fiber production emits 20 tons of carbon dioxide per ton of carbon fiber. Catalytic formation of carbon allows the reduction of energy, control of the desired morphology, and production with increased purity of a particular morphology. However, catalytic processes have low production rates, so they are often carried out in batch or semi-batch processes.

[0005] The decomposition of carbon-containing gases on metal surfaces and the formation of carbon fibers (CFs) has been known as a catastrophic corrosion mechanism in metallurgy for decades before CFs were used in advanced applications. Carbon nucleates and grows inside the reactor walls, causing the metal surface to fracture and the channels to become clogged; this phenomenon is well studied as metal dusting and carburization. In general, catalytic carbon production is divided into two categories: fixed bed and continuous.

[0006] Carbon production using fixed bed catalysts occurs in two steps: (1) The catalyst is placed on a support and enters a heating zone before the carbon-containing gas flows. (2) CF is grown on a support and the process is discontinuous.

[0007] In continuous catalytic carbon production, a carbon-containing gas and a catalyst are injected together into a heated zone. The catalyst can be introduced to the support either in the form of already reduced iron or as an iron precursor that is reduced before or during CF production. This process can be modified to produce carbon fibers of various sizes, from micro to nano size.

[0008] Carbon nanofibers (CNFs) are fibers with dimensions in one direction (usually diameter) less than 100 nm. For decades, CNF growth has been viewed as a nuisance in many catalytic processes such as steam cracking and reforming, but they are gaining great interest and increasing value in advanced applications.

[0009] In existing systems, carbon nanofiber production is often performed as a batch or semi-batch process. This means that the reactor vessel must be cooled and opened, and the carbon-containing cartridge must be physically removed. To restart the process, catalyst must be replenished on the substrate surface. These challenges make carbon nanofiber production expensive and inefficient.

[0010] For example, U.S. Patent No. 9,096,435 discloses a system in which the catalyst is supported on a substrate or in a vessel located in the center of a heated zone, with a carbon-containing gas flowing over the substrate. The reactant gas enters the reactor through a single passage on one side of the vessel and exits on the other side of the vessel. The catalyst flow rate and loading define the space velocity and residence time for carbon growth, which determines the growth rate. The process is often a semi-continuous process with non-steady-state conditions. As the product (carbon) accumulates on the substrate, the partial pressures of the reactants change throughout the reactor.

[0011] US Patent No. 7,077,999 discloses a monolith for imparting swirl to a gas flow, which comprises alternating flat and corrugated strips defining gas flow channels. The strips are attached to a carrier at an angle. The corrugations of the corrugated strips may be oblique. The carrier defines a cylindrical shell for the strips, which extend from the carrier to a central region. The strips are curved, typically having a substantially involute shape, substantially filling the space between the central region and the shell. Due to the attachment angle between the strips and the carrier, the gas flow channels are oriented in different directions at different locations on the outlet face of the monolith. This structure therefore imparts swirl to the gas flowing through the monolith.

[0012] US Patent Application Publication No. 2019 / 0262792 discloses a reactor apparatus for use in solid carbon production, comprising a reactor shell defining a reactor inlet and a reactor outlet. Concentric cylinders or substantially parallel plates of catalytic material are disposed within the reactor shell and are configured and adapted to expose at least one contact surface to a gaseous reactant. Another apparatus includes a removable cartridge including a plurality of substantially parallel plates of catalytic material disposed within the reactor shell.

[0013] U.S. Patent Application Publication No. 2022 / 0089442 (published March 24, 2022) discloses a process and apparatus for producing carbon nanofibers. The process includes two stages. The first stage involves oxidizing light hydrocarbons to a mixture of hydrogen and carbon monoxide using carbon dioxide or water, or oxygen, or a combination thereof. The second stage involves converting the produced hydrogen and carbon monoxide to carbon nanofibers and steam. U.S. Patent Application Publication No. 2022 / 0089442 is incorporated herein by reference in its entirety. Summary of the Invention

[0014] According to the present invention, there is provided a reaction assembly comprising: The entrance and The exit, an elongate vessel defining a reaction chamber in fluid communication with the inlet and the outlet; one or more planar support(s) within the reaction chamber, the one or more planar support(s) having a surface for supporting a solid catalyst, the one or more planar support(s) mounted transversely to the elongated axis of the vessel and forming a series of spaced apart barriers along the elongated axis of the vessel; a conduit disposed within the reaction chamber and connected to the inlet or outlet, the conduit having a conduit opening disposed between successive barriers such that gas flow from the inlet to the outlet causes the gas to flow through the conduit and the gas to flow through the reaction chamber along the support surface between the successive barriers; A reaction assembly is provided comprising:

[0015] The conduit may be coaxial with the elongated vessel (eg, along the centre of the elongated vessel).

[0016] The vessel may have a uniform cross-section over the axial extent of a series of spaced apart barriers.

[0017] The support surface may form a heat exchanger. The support surface may be thermally conductive.

[0018] The support surface may be connected to the conduit and in thermal communication with the conduit.

[0019] There may be a gap between each of the spaced apart barriers and the elongated container, which allows gas to flow along the length of the elongated container. For example, the gap may provide a line of sight along the edge of the container, allowing unimpeded passage of gas. The gap may be less than 20% of the diameter of the elongated container (e.g., measured perpendicular to the elongated axis). The gap may be at least 5% of the diameter of the elongated container (e.g., measured perpendicular to the elongated axis). The gap may extend over at least 270° of the circumference of each of the spaced apart barriers. The gap may extend over the entire circumference of each of the spaced apart barriers.

[0020] Each reaction subchamber may be open. An open subchamber may not have reaction assembly components arranged to impede gas flow between the conduit and the outer wall of the elongated vessel (in a direction parallel to the support surface around at least 270° for the conduit for at least 80% of the distance between the barriers). It will be understood that a reaction assembly component may comprise one or more conduits, a wall of the elongated vessel, but not contain a solid product produced by a reaction occurring within the reaction chamber.

[0021] The reaction subchambers may be separated by two barriers and a wall of an elongated vessel. The gap may or may not be within the reaction subchamber. In some embodiments, the gap allows gas to pass from between the two barriers in one reaction subchamber to between the two barriers in another reaction subchamber. This can help control the pressure within the vessel. In other embodiments, a barrier (e.g., an elongated vessel with an inner wall and an annular conduit) can prevent gas from passing from between the two barriers in one reaction subchamber to between the two barriers in another reaction subchamber.

[0022] The conduit may be connected to or function as a thermometer used to probe the temperature along the assembly.

[0023] The container may be provided with a drainage exit for removing liquid.

[0024] The support surfaces may be spaced at least 1 mm apart. The support surfaces may be spaced at most 3 cm apart.

[0025] The pressure in the reaction chamber may be between 1 and 20 atmospheres. The temperature in the reaction chamber may be between 450 and 580° C. The pressure in the reaction chamber may be between 2 and 20 atmospheres.

[0026] The catalyst may be configured to catalyze a reaction that converts the gaseous reactants into a solid product.

[0027] According to a further aspect, there is provided a method of producing carbon nanofibers using the reaction assembly described herein, the method comprising: The method includes injecting gaseous reactants into a reaction chamber through a plurality of inlets such that a flow of the gaseous reactants passes over a solid catalyst, and removing gas from a plurality of outlets, the solid catalyst configured to convert the gaseous reactants into products, the products including carbon nanofibers.

[0028] The reactants may include hydrogen and carbon monoxide. The reactants may also include carbon dioxide, steam, and / or light hydrocarbons (e.g., methane, ethane, propane, and / or butane). The reactants may include a mixture obtained from a first reactor of the system described in US Patent Application Publication No. 2022 / 0089442. This reactor is configured to convert an oxidation stream (e.g., CO2, steam, oxygen, or a combination thereof) and light hydrocarbons (e.g., C1-C4) to produce an intermediate stream including CO and H2 (e.g., in a volume ratio close to 1:1). The resulting mixture may also include unreacted portions of the reactants (CO2, steam, and / or unreacted light hydrocarbons).

[0029] A fluid containing catalyst particles may be injected into the assembly through one or more inlets to populate the substrate with fresh nuclei and promote the growth of CNFs.

[0030] The catalyst particles may comprise one or more of the Group VIII metals, Fe, Ru, Os, Hs, Ni, Cu, Zn, Co and Mo.

[0031] The method may include annealing and reducing the catalyst particles to form a lower oxidation state of each active site.

[0032] The method may include forming a passive layer on the inner surface of the outer vessel prior to injecting the fluid carrying the catalyst particles into the reaction chamber. The metal bodies and substrates may be passivated or coated with one or more inert materials, such as ceramics, to avoid their participation in the desired chemical reaction (i.e., to avoid the formation of solid products on the surfaces of the metal bodies and substrates rather than on the intended support surfaces).

[0033] The method may include injecting one or more of the following gases into the reaction chamber: steam, an inert gas, carbon dioxide, a hydrocarbon, and a reducing gas.

[0034] The method may include harvesting the carbon nanofibers by flowing a fluid through the reaction chamber to detach the carbon nanofibers from the support surface, and separating the carbon nanofibers from the fluid outside the reaction chamber.

[0035] The method may include introducing an oxidant into the reaction chamber and increasing the temperature in the reaction chamber prior to collecting the carbon nanofibers.

[0036] The method may include injecting the fluids into the reaction chamber at different rates to promote mixing.

[0037] The method may include injecting catalyst particles into the reaction chamber in a seeding stage such that the catalyst particles adhere to the support surface. In some embodiments, the catalyst particles may be activated by exposure to particular environmental conditions (e.g., pressure and / or temperature) and / or reactants (e.g., oxidants or reductants). In some embodiments, the deposited catalyst particles do not require activation.

[0038] The method may include flowing a fluid through the chamber in a harvesting stage to detach the grown carbon nanofibers from the catalyst support surface and remove the detached carbon nanofibers from the reaction chamber. In other embodiments, harvesting may be accomplished by other means such as, for example, mechanical removal using a harvesting blade to cut or shear the carbon nanofibers from the support surface.

[0039] According to a further aspect, there is provided a method of producing carbon nanofibers, the method comprising the steps of: a seeding stage, which involves injecting catalyst fine particles into the reaction chamber, allowing them to adhere to the support surface, and then activating them; a growth stage, in which gaseous reactants are converted into carbon nanofibers by flowing them through a reaction chamber and over a catalytic support; a harvesting stage, in which the grown carbon nanofibers are detached from the catalyst support surface by flowing a fluid through the reaction chamber and the detached carbon nanofibers are removed from the reaction chamber; This includes cycling between two or more of the following:

[0040] This multi-stage cycle may be used in conjunction with any reaction vessel that contains a support surface for growing carbon fibers.

[0041] In some embodiments, the fluids injected into the reaction vessel at each stage may be carried by conduits dedicated to that stage (e.g., harvest conduits, reactant conduits, and seeding conduits), while in other embodiments, multiple stages may use the same conduits (e.g., a common conduit used for both the seeding stage and the harvest stage).

[0042] According to a further aspect, there is provided a method of producing carbon nanofibers using the reaction assembly described herein, the method comprising: a seeding step in which catalyst particles are injected into the reaction chamber, attached to the support surface, and then activated; a growth stage, in which gaseous reactants are converted into carbon nanofibers by flowing them through a reaction chamber and over a catalytic support; a recovery step in which the grown carbon nanofibers are detached from the catalyst support surface by flowing a fluid through the reaction chamber and the detached carbon nanofibers are removed from the reaction chamber; This includes cycling between

[0043] The conditions within the reaction chamber may be conditions that promote the production of solid carbon. The reaction to produce solid carbon may occur at a temperature of about 500° C. (e.g., between 300 and 800° C.). The reaction to produce solid carbon may occur at a pressure of about 10 atmospheres (e.g., between 5 and 20 atmospheres, or between 6 and 10 atmospheres).

[0044] In the context of the present disclosure, the planar support may be comprised of a single sheet of material. The planar support may have a support surface for the solid catalyst on one or both sides. The planar support may be formed of a thermally conductive material (e.g., may have a metal body). These features may improve heat transfer through the planar support (e.g., including along and across the support surface). This may help ensure that heat is distributed evenly within the reaction chamber.

[0045] In the context of this disclosure, a barrier can be considered to be a structure that blocks a line of sight parallel to the elongated axis along the elongated container. A barrier can be transverse (e.g., perpendicular) to the elongated axis. A barrier can be formed from a single planar support (e.g., a single circular support can be a single barrier). In some cases, a single support can form multiple barriers if it curves to block the line of sight along the elongated container multiple times. For example, a single helical support that curves around the elongated axis can be considered to form multiple barriers. In such cases, each portion of the helical support that blocks 360° around the helical axis can be considered a single barrier even if it is not structurally distinct from the next barrier.

[0046] Planar supports in the context of this disclosure include supports that extend in two dimensions to form a plane, but have a limited thickness (e.g., with respect to the extended dimension). Planar supports may have a thickness (e.g., perpendicular to the surface of the support) of less than 5 mm. Planar supports may be flat (i.e., not curved or bent) or curved or bent. Planar supports may be constructed from solid impermeable materials or permeable materials such as foams or meshes. Planar supports may have a rough support surface. Planar supports are typically rigid.

[0047] The planar support can be directly connected to the conduit (e.g., attached to the conduit). This connection can prevent gas from passing between the conduit and the planar support (e.g., a sealed connection around the conduit). The planar support or barrier can extend around the conduit over an angular range (e.g., 180° or more, up to 360°).

[0048] The conduit may extend into the body of the reaction chamber and be attached to the walls of the reaction chamber at only one or both ends (i.e., not along the length of the conduit). That is, at least the portion of the length of the conduit that is within the reaction chamber may be spaced from the wall of the elongated vessel. The conduit may be considered a flow path for transporting a fluid. The conduit may be in the form of a tube or a pipe.

[0049] The reactor may comprise an elongated vessel, possibly with a circular cross section, having one or more inner perforated vessels or conduits, typically with annular or circular cross section. A circular cross section vessel may allow for a more even distribution of heat throughout the reaction chamber.

[0050] An elongated container may have a length that is at least twice its lateral dimension (eg, height and / or width).

[0051] The elongated container may be tiltable. The elongated container may be configured to operate in an inclined configuration with the elongated axis at least 5° and / or up to 45° from the horizontal.

[0052] The barriers may be aligned vertically during operation (e.g., less than 30° or less than 5° to vertical). During operation, the reactants may be converted to solid products such as carbon nanofibers. The upright or vertical orientation of the barriers can reduce the forces of liquid flowing over the surfaces of the solid catalyst and the growing solid product. It can also ensure that the surface on which the solid product grows is consistent (e.g., rather than having a surface that faces significantly upwards and a surface that faces significantly downwards).

[0053] The reaction assembly may have at least 10 barriers spaced along the length of the elongated vessel.

[0054] The perforated inner tube or conduit may be coaxial with the elongated vessel or may be parallel to the elongated vessel. Placing the conduit centrally within the elongated vessel means that gas can pass from the central conduit in any direction. For a given catalyst support surface area, this allows for a minimum distance between where reactants are injected and the edge of the catalyst support surface. For example, in an embodiment where the inlet is located towards the bottom of the catalyst support surface, the reactant gas must travel a long distance to reach the top. This embodiment can still be used to promote reactions, but may result in non-uniform concentrations of reactants at various points on the catalyst surface, leading to less uniform growth. In other embodiments, the conduit may be located off-center within the reaction chamber. In other embodiments, the conduit may be located at an angle to the elongated axis within the reaction chamber. The conduit may be located in alignment (e.g., parallel) with the elongated axis within the reaction chamber.

[0055] The perforated vessel or conduit can be used to inject reactant fluids in gas or liquid form, or a combination thereof.

[0056] The perforations or openings in the inner tube or conduit may be adjusted to maintain the partial pressures of the reactants uniform throughout the interior of the reactor (e.g., within 10% pressure).

[0057] The size, number, shape and distribution of the openings can be configured or adjusted to provide uniform (less than 0.5%-10% difference) linear fluid velocity throughout the outer vessel in planar (xy) and vertical directions.

[0058] The perforations, holes or openings may be distributed in the conduit as a plurality of perforations distributed in three dimensions. Some of them may be in the same plane (xy) with the distance between the holes adjusted to 0.1 mm to 9999 mm (e.g., in the range of 0.1 mm to 50 mm). Some of the perforations are in separate xy planes with the distance between the planes adjusted to 0.1 mm to 9999 mm (e.g., in the range of 0.1 mm to 50 mm).

[0059] The planar supports may have a spacing along the elongate axis between 0.1 mm and 9999 mm (eg, in the range of 0.1 mm to 50 mm).

[0060] The spacing between the barriers may be the same as the distribution of perforations along the elongate axis.

[0061] The walls or barriers may act as heat exchangers: they are thermally conductive if the support surface comprises a metal.

[0062] The planar support also functions as a substrate upon which a catalyst can be supported.

[0063] Cultivating the substrate can begin with heat treating the metal substrate to create a non-active oxide layer texture with an uneven surface to increase the surface area for the seeding process. The surface texture can be alumina whiskers.

[0064] The substrate may also contain catalytic seeds for carbon growth.

[0065] The catalyst seeds can be transported via a fluid, liquid or gas, or a combination thereof, and spread through one or more perforated reservoirs on the substrate. The fluid can flow under pressures ranging from atmospheric to less than 100 atmospheres (e.g., 0.0001 atmosphere to 15 atmospheres).

[0066] During seeding, one or more perforated vessels can carry liquid and other perforated vessels can carry hot gas selected from steam, inert gases (N2, He, Ar, etc.), or hydrocarbons (CO2, C1, C2, C3, etc.), or reducing gases (CO, H2, etc.), and combinations thereof.

[0067] Prior to seeding, a passivation layer may be formed on the inner surface of the outer vessel. A passivation layer may be formed on the outer or inner surface of the perforated vessel to prevent seed deposition and carbon growth on undesired surfaces. Passivation may be performed on the outer or inner surface of the perforated vessel in the same or different manner. Passivation may be performed by surface treatment (such as fine polishing) or surface oxidation to minimize physical anchoring. Passivation may be performed by depositing another layer, such as a paraffin wax layer, to reduce the wettability of the surface and the seed fluid.

[0068] The catalytic seeds may be precursors comprising Group VIII metals, including Fe, Ni, Cu, Zn, Co, and Mo, and combinations thereof.

[0069] The support may have catalytic nanoparticles (nP). The distance between adjacent nanoparticles may be approximately the same as the diameter of the nanoparticles. That is, the average closest distance between adjacent nanoparticles may be 0.1 to 10 times the average diameter of the nanoparticles.

[0070] The support surface may include a non-active layer for carbon formation that holds well-distributed active nanoparticles such as Fe, Ni, Mg, Cr, Cu, Zn, Mo, Co, and Mn. The non-active layer is generally composed of oxide materials such as alumina, chromia, zirconia, silica, or combinations thereof. In some embodiments, this non-active layer is composed of alumina and zirconia whiskers that are 3D textured and form a rough surface. The terracing function is to provide a physical barrier between the nanoparticles (nP), separating the active metals and preventing them from sintering and grain growth during heat treatment and reaction. Carbon nanofibers grow on active sites that include nanoparticles of metals Fe, Ni, Mg, Cr, Cu, Zn, Mo, Co, and Mn, and combinations thereof. The whiskers may include alumina. The whiskers may include zirconia.

[0071] The alumina whiskers act like a cage, ensuring that the active metal is deposited in a well-distributed manner, while avoiding the nanoparticles from moving too far at temperatures where they would sinter (agglomerate) (the Tammann temperature). The alumina whiskers may be in the form of plates with at least one expanded dimension of 0.5-10 μm and at least one thickness dimension of 10-500 nm. These whiskers form a cage of less than about 0.2-10 μm, restricting the deposited catalyst nanoparticles from moving across the bulk surface.

[0072] The Tammann temperature (for bulk diffusion) can be considered to be the temperature at which the atoms or molecules of a solid have acquired enough energy that their bulk mobility becomes appreciable (e.g., allowing sintering). The Tammann temperature is typically about half the melting point in Kelvin. The surface diffusion temperature can be considered to be the temperature at which atoms or molecules can move on a surface.

[0073] Terracing of the active metals keeps the CNFs separate and can also suppress entanglement effects to elongate the CNFs. In some embodiments, the nanoparticle size varies below 10 nm or below 20 nm, below 35 nm or below 50 nm. In some embodiments, the nanoparticles are below 100 nm. These upper limits may correspond to the largest dimension of the nanoparticles (e.g., as measured by scanning electron microscopy or other imaging). The nanoparticles may have a Dv10 greater than 1 nm and / or a Dv90 less than 100 nm, where D is the largest dimension of the nanoparticle and the size is based on the volume distribution. Terracing and whiskers on the support surface generally add a third dimension to broaden the diffusion of the catalyst nanoparticles and increase the loading relative to more planar support structures. An example is the surface area of ​​a disk compared to the surface area after whiskers have been developed.

[0074] The substrate may include an iron-aluminum (e.g., FeCrAl) alloy. The alloy may include at least 1% aluminum by number. The substrate may include Aluchrom™, Kanthal AF™, Kanthal APM™, Nisshin Steel Ugine Savoie 12178™.

[0075] The use of FeCrAl can be advantageous for several reasons. The support may be heat treated to form alumina whiskers, which can be used to restrict the movement of the deposited nanoparticles. This allows the catalyst to selectively produce nanofibers, as the size and distribution of the catalyst nanoparticles is controlled. Since the support is also metallic, this allows the support to be bent into shapes (e.g., corrugated to increase surface area). The support may be thermally conductive. This may be important when used in conjunction with exothermic reactions, i.e., to distribute heat quickly to prevent the formation of hot spots and to transfer heat from one reactor to another. The support may be magnetic to facilitate the loading of nP (nanoparticles) (providing a physical bond prior to heat treatment and chemical bond formation).

[0076] The reaction assembly may include a cooler for removing heat from the support surface (e.g., during carbon nanofiber production). The cooler may include a heat exchanger, cooling fins, and / or a refrigeration unit (e.g., with a heat pump). The reaction assembly may include a heater for heating the support surface (e.g., during catalyst seeding or preparation). The heater and / or cooler may be connected to a component in thermal communication with the support surface.

[0077] The support may be corrugated or roughened to increase the surface area.

[0078] The nanoparticles may have a diameter of 10 to 150 nm.

[0079] The support may include a metal substrate.

[0080] The precursors containing the seeds for carbon growth may be annealed and reduced to form lower oxidation state active sites prior to reactant flow.

[0081] A reaction that forms carbon nanofibers can be considered selective if greater than 60% by weight of the carbon formed is in the form of carbon nanofibers (eg, not graphite or amorphous carbon).

[0082] This reactor design can be used to form solid carbon with other carbon-containing molecules such as hydrocarbons, C1, C2, C3, C4, ethylene, benzene, etc. This reactor design can also be used for other gas-to-solid carbon reactions (e.g., pyrolysis).

[0083] Unless otherwise stated, ratios given in this disclosure are to be interpreted as number ratios, for example, an H2:CO ratio of 0.5 means that there are 2 carbon monoxide molecules for every hydrogen molecule.

[0084] After a sufficient amount of time has passed to allow for carbon nanofiber growth, the harvesting process is initiated with one or more fluids entering the vessel through one or more conduits.

[0085] One or more conduits can carry fluids at different velocities to provide the energy (momentum) that detaches the CNFs from the alumina whisker substrate. One perforated tube can carry liquid and the other can carry gas to improve the turbulent mixing process. One or more conduits can be equipped with a specially designed orifice (i.e., nozzle) to spray the recovery fluid onto the planar substrate. The recovery fluid can be a gas (air, inert gas, etc.) or a liquid (water, alcohol, polyol, amide, phospholipid, oligosaccharide, polysaccharide, monosaccharide, etc.) or combinations thereof. The fluid is selected based on its fluid properties (e.g., to facilitate efficient recovery without damaging the product) and to avoid leaving behind any residue that may adversely affect the reaction in the reactor or the product quality.

[0086] After mixing for a period of time, the fluid containing the CNFs can be discharged from the vessel, and this process can be repeated until sufficient CNFs are recovered or removed from the vessel (e.g., greater than 50% by weight of the CNFs).

[0087] The outer container may include a drain for removing high concentrations of liquid. During collection, the container may be angled to facilitate drainage with the aid of gravity. The container may have a convex shape.

[0088] Prior to recovering the CNFs, a combination of oxidizing agents and elevated temperatures can be used to remove the amorphous carbon and / or partially oxidize the surface of the carbon nanomaterials.

[0089] Prior to recovery, the surface of the carbon may be functionalized with groups such as hydroxyl, carboxyl, or phenyl groups.

[0090] During the recovery period, the temperature may be increased to speed up and intensify mixing.

[0091] After a particular recovery cycle, the temperature may be increased again to remove unrecovered carbon from the reactor.

[0092] With respect to repeating the process of cultivating, seeding, planting, and harvesting carbon nanofibers, any step may be repeated after single or multiple operations.

[0093] The present disclosure also relates to reactor designs for seeding active sites on a microscopically roughened substrate, growing carbon nanofibers on the activated seeds, harvesting the carbon nanofibers, preparing the substrate for subsequent replenishment, and reinjecting or reactivating the seeds on the substrate within the reactor.

[0094] The diameter of the CNFs may be from 10 nm to 200 nm, and the length may be from 1 μm to tens of μm (e.g., up to 100 μm). The CNFs thus produced may have a solid core composed of graphene layers that may be aligned parallel, perpendicular, or at an angle to the fiber axis. Air-core fibers, called carbon nanotubes, are made of one or more coaxially wound graphene layers. The CNFs produced may have one or more of the morphologies described above, in very different proportions. After recovery, the substrate may need to be reloaded with catalyst nanoparticles. Various objects, features and advantages of the present invention will become apparent from the following description of specific embodiments of the invention, as illustrated in the accompanying drawings. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of various embodiments of the invention. Like reference numbers refer to like elements. [Brief description of the drawings]

[0095] [Figure 1] 1a and 1b are a cross-sectional view and a perspective cutaway view, respectively, of a first embodiment of a reaction assembly. [Diagram 2] 2a and 2b are a cross-sectional view and a perspective cutaway view, respectively, of a second embodiment of a reaction assembly. [Diagram 3] FIG. 3 is a cross-sectional view of a third embodiment of a reaction assembly. [Figure 4] FIG. 4 is a flow diagram illustrating how carbon nanofibers can be grown according to a further embodiment of the present disclosure. [Diagram 5] 5a and 5b are a cross-sectional view and a perspective cutaway view, respectively, of a fourth embodiment of a reaction assembly. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0096] <Introduction> Various aspects of the invention are described below with reference to the drawings. For ease of illustration, the components depicted in the drawings are not necessarily drawn to scale. Instead, emphasis is placed on highlighting the various contributions of the components to the functionality of the various aspects of the invention. In the course of this description, several possible alternative features are introduced. It will be understood that such alternative features can be substituted in various combinations to realize different embodiments of the invention, according to the knowledge and judgment of those skilled in the art.

[0097] One problem the inventors have identified with existing reactor systems is that the partial pressure of the reactants is generally higher near the reactant inlet and gradually decreases through the catalyst bed toward the reactor outlet. This phenomenon results in uneven flow distribution and pressure differentials across the reactor, resulting in less exposure of gas to fresh catalyst and, in severe cases, clogging of the reactor at the inlet to the catalyst bed. Furthermore, catalyst supports in the form of monoliths, honeycombs, or foams have limited space for carbon growth, and as carbon accumulates within the structure, it becomes compacted and difficult to recover.

[0098] As mentioned above, these issues have traditionally been addressed by increasing reactor size, excessive flow rates, and low amounts of catalyst, all of which can lead to reduced process efficiency and yield.

[0099] To address process inefficiencies, we propose new reactor designs that help with one or more of the following: ·Enhancing mass and heat transfer in the carbon production process; · Maintaining uniform distribution of reaction gases throughout the reactor; · Providing a method for recovering product and replenishing catalyst in the reactor.

[0100] The reactor design uses distributed openings and barriers to control the flow of reactant gases over the solid catalyst. The spaces between successive barriers act as small chambers (subchambers or reaction modules) that can provide uniform velocities of reactants. During the growth stage, where gaseous reactants are converted to solid products, more uniform flow is obtained across the catalyst surface. This configuration also helps provide uniform and efficient heat transfer, including adiabatic and / or isowall heat transfer during operation.

[0101] The reaction converts gases to solids, and pressure drops occur due to density differences between reactants and products. Spatially distributed inlets mean that partial pressures are more uniform across the catalyst support surface in smaller sub-chamber reaction zones. By manipulating the nozzle size, distance, distribution, and clearance space (the gap between the disk and the outer body), laminar flow can be created in all module sections. Carbon growth in all sections does not result in blockage of gas passages, as typically occurs in reactors with only one inlet. The clearance gap also allows for recycling of gas from one module to the other, which can maximize conversion.

[0102] This operation can be performed automatically, so the production system consists of a set of alternating reactor assemblies, some of which perform CNF growth and others serve for CNF recovery and restart by cutting the fibers and re-impregnating and activating the support surface to restart CNF growth. The catalysts impregnated on the support surfaces of these reactor assemblies allow the production of high quality carbon nanofibers at temperatures in the range of 400-690°C, more preferably in the range of 450-580°C.

[0103] <Chemical reaction> In terms of chemical reactions, the device can be used to catalytically convert gaseous CO (carbon monoxide) and hydrogen into solid carbon in the form of carbon nanofibers and water (steam and / or liquid water) according to the following reaction: 2CO+2H2→2C+2H2O, ΔΗ° 298 =-264kJ

[0104] The reactant can be obtained, for example, from the dry reforming of methane (DRM). The water produced in the high temperature reaction leaves the reactor in the form of steam.

[0105] As described further below, the H2-CO blend is flowed into a reaction chamber containing nanoparticles of Fe, Ni, Mg, Cr, Cu, Zn, Mo, Co, and Mn, and combinations thereof, which catalyze the growth of carbon fibers from the H2-CO mixture, thereby producing a solid CNF material.

[0106] It will be appreciated that under industrial conditions, these reactions are mostly carried out irreversibly, nevertheless, aspects of this technology relate to how to reprocess and recycle unreacted reactants to improve efficiency, which is conventional knowledge in chemical process design.

[0107] The H2:CO ratio can be configured to be at least 0.3 (e.g., at least 0.7 or 0.8). The H2:CO ratio can be configured to be up to 1.3 (e.g., up to 1.2 or 1.05). Changing the H2 / CO ratio to a higher value can result in undesirable carbon types and mechanisms (Boudouard reactions are undesirable), and changing the H2 / CO ratio to a lower value can waste hydrogen.

[0108] High CO or H2 deficiency can lead to high deposition rates of C via the Boudouard reaction, leading to extensive graphitization and the formation of carbon black and carbon fibers instead of nanofibers, reducing selectivity to more valuable products, i.e., the reaction is primarily to amorphous forms, or to fibers and graphite depending on T and residence time. Thus, an important aspect of the present invention is to ensure that the temperature and flow rate across the catalyst surface are consistent across the catalyst support surface. Otherwise, some parts of the catalyst support surface may favor conditions for the production of carbon nanofibers, while other parts may favor conditions for the production of other undesirable forms of carbon, such as amorphous forms.

[0109] A high percentage of CO favors a process with low selectivity towards carbon nanofibers. A high percentage of H2 slows down carbonization and typically favors graphitization and fiber formation, especially at high T (high T is needed to accelerate the reaction rate, considering the low partial pressure of CO). Furthermore, low CO partial pressure reduces the mobility of adsorbed C (due to the decomposition of CO at the surface of the nanoparticles), which reduces the diffusion rate of C through the nanoparticles, a key factor required to build nanofibers. Thus, graphene / graphite tends to be produced (rather than carbon nanofibers) with a higher percentage of H2.

[0110] The energy balance is exothermic, resulting in energy production. This heat needs to be distributed evenly within the reaction chamber. The design also facilitates heat removal through the support surface and conduits. This can help maintain a desired temperature within the reaction chamber and allows excess heat to be used elsewhere (e.g., to provide heat for endothermic precursor reactions).

[0111] The H2 / CO ratio, as well as other process and catalyst conditions, are adjusted to maximize the decomposition of the syngas into high purity carbon nanofibers and greatly reduce the likelihood of the Bosch, Boudouard, and methane-forming reactions taught in the prior art. The non-selective nature of these reactions generally results in the formation of a large assortment of different allotropes of the carbon solid products.

[0112] To react carbon monoxide with hydrogen to form carbon nanofibers (CNFs), the reaction is carried out using a supported catalyst, which in this embodiment is a nanoparticle immobilized on the parallel-walled alumina whiskers described above.

[0113] The oxide whiskers on the catalyst support surface make the support surface non-uniform, thereby allowing for high and well-distributed loading of catalyst nanoparticles. Transition metal nanoparticles have a high tendency to migrate at high temperatures (60% of Tamman temperature; in Kelvin), forming necks with adjacent particles, sintering, and ultimately forming larger particles. By providing a textured surface for the nanoparticles, it may be easier to control the distance of the active nanoparticles and / or the diameter of the carbon nanofibers.

[0114] The whisker layer can be formed directly on a suitable metal substrate, which can make the support layer more malleable and may also improve thermal conductivity from the whiskers.

[0115] Terracing or texturing the substrate adds additional dimensions to the substrate, helping to anchor the catalyst nanoparticles to the substrate site at the nanometer level. This is an advantage over growing CNFs on flat surfaces or stainless steel wool, which can reduce selectivity for carbon nanofiber growth and produce a wide variety of carbon morphologies, including graphite, microfibers, and amorphous carbon, which are less valuable than CNFs.

[0116] The chemical bond between alumina and catalytic nanoparticles modifies the reduction profile of the catalytic nanoparticles and keeps the size of the active sites in the nano range.

[0117] The support may be formed of an iron alloy containing 5 wt.% Al. In some embodiments, the support may contain less than 10 wt.% Al. The active catalyst may be Fe, Ni, Mg, Mn, Co, Cr, W, Ti, and Zn, or combinations thereof.

[0118] The support may be heat treated at temperatures between 700-1000°C for 5-48 hours to form Al2O3 whiskers on the surface and to make the support surface non-uniform, maximizing retention of catalyst particles on the support. This heat treatment may be considered a cultivation step that prepares the support surface to accept catalyst particles.

[0119] In some embodiments, the catalyst precursor deposited on the support is heat treated and reduced with CO, H2, or a combination thereof (diluted with inert gases, Ar, He, and N2) at a temperature of 500-800° C. for 2-48 hours. This is part of the seeding step.

[0120] According to another embodiment, the supported catalyst is designed to allow carbon-containing gases (CO, CO2 and C1-C4 light hydrocarbons) to easily pass through the reactor hot zone and supported catalyst for a significant period of time until the structuring elements are fully loaded with CNFs and can be recovered from the produced CNF material.

[0121] <Embodiment of linked sub-chambers> 1a and 1b show an embodiment of a reaction assembly 100, Entrance 101 and Exit 102; an elongated vessel 103 defining a reaction chamber 110 in fluid communication with an inlet 101 and an outlet 102; one or more planar supports 104a-f within the reaction chamber, the one or more planar supports having a surface for supporting a solid catalyst, the one or more planar supports being mounted transversely to the elongated axis 111 of the vessel and forming a series of spaced apart barriers along the elongated axis 111 of the vessel; A conduit 105 disposed within the reaction chamber 110 and connected to an inlet or outlet, the conduit having conduit openings (e.g., openings 108cd, 108de) disposed between successive barriers such that gas flow from the inlet 101 to the outlet 102 causes the gas to flow through the conduit 105 and the gas to flow through the reaction chamber 110 along the support surface between the successive barriers.

[0122] In this case, the reaction assembly 100 comprises a plurality of planar supports 104a-f, each of which is a circular vane spaced apart along a centrally located conduit 105. In this case, the conduit 105 is coaxial with an outer elongated vessel 103. In this case, the planar supports are attached to the conduit, which passes through the planar supports.

[0123] Each planar support 104a-f forms a corresponding spaced barrier. Each spatial region between each pair of consecutive or adjacent barriers can be considered as a subchamber 107aa, ab, bc, cd, de, ef and ff. The subchamber lettering is based on the lettering of the two bounding planar supports / barriers. For example, subchamber 107ab is located between planar supports or barriers 104a and 104b. The double-lettered subchambers form a subchamber together with the end of the container. For example, subchamber 107ff is located between planar support or barrier 104f and the end of container 103.

[0124] In this case, conduit 105 is connected to inlet 101. As reactants are injected into the conduit through inlet 101, gases are introduced into each of the sub-chambers 107aa-ff between successive planar supports through a series of conduit openings (e.g., perforations, holes, or nozzles) provided along the length of the conduit.

[0125] In this case, the planar supports 104a-f have a diameter smaller than the inner diameter of the elongated vessel 103. This means that there is a gap between the outer edge of the planar supports 104a-f and the inner surface of the wall of the elongated vessel 103. This allows any gas that is not converted to solid or gas in one subchamber to flow through the gap into the next subchamber and eventually out of the vessel through the outlet 102. In this embodiment, since the supports 104a-f are directly connected to the periphery of the conduit 105, the gas passing from the conduit opening to the outlet must flow radially along the support surface of the planar supports 104a-f on which the solid catalyst is attached.

[0126] The solid catalyst in this case is configured to promote the conversion of gaseous reactants to solid products. It will be appreciated that the conversion of gaseous reactants to solid or liquid products involves significant density changes. Thus, as the reactant gas moves across the catalyst, the reaction itself reduces the pressure in the vessel. In this embodiment, this is compensated for by providing various paths throughout the reaction chamber 110. Openings such as 108cd and 108de along the conduits (not all openings are labeled for clarity) allow the reactant gas to be introduced into the reaction chamber at various points along the length of the elongated vessel. This means that the reactants can be evenly distributed across the catalyst surface. In this case, at least one conduit opening is located between each pair of adjacent supports. In addition, there is also a conduit opening between the support 104f closest to the inlet 101. At the distal end of the conduit away from the inlet, the conduit is closed, and there are no conduit openings between the support furthest from the inlet 104a and the end of the vessel 103.

[0127] In this case, the vessel 103 has a uniform cross-section across the barriers 104a-f along the length of the elongated axis. Simulations of this configuration show that this results in consistent pressure in each sub-chamber. The first sub-chamber 107ff receives gas only from the conduit 105. Subsequent sub-chambers 107ab-ef, in this embodiment, receive progressively less gas from the conduit, but also receive unreacted gas from the previous sub-chamber, which serves to compensate for pressure differences, as shown by the arrows showing the flow of gas within the reaction assembly.

[0128] In the case of non-uniform production of solid products in the reaction chamber, distributing the openings along the length of the conduit means that blocking or dragging effects due to non-uniform growth can be mitigated. For example, if rapid solid growth occurs initially in the second sub-chamber because it receives more reactant gas flow, this can cause gas flow restriction through the second sub-chamber. However, instead of blocking the flow throughout the assembly, the reactant gas flow is automatically adjusted to be redirected through the other sub-chambers that have less resistance (i.e. less blocking or less drag). This accelerates solid production in the sub-chambers where solid production is less advanced and promotes uniform growth across the entire catalyst surface.

[0129] In this case, the surface is fitted with nanocatalysts for converting the gaseous reactants 116, hydrogen and carbon monoxide, into carbon and steam in the form of carbon nanotubes 115. This configuration ensures that the partial pressure of the reactants remains constant throughout the reaction vessel, allowing the carbon nanotubes to be grown uniformly across the support surface.

[0130] To facilitate the growth of carbon nanofibers, the support surfaces are spaced at least 1 mm apart (e.g., perpendicular to the support surfaces), allowing the carbon nanofibers to grow without creating a matrix that restricts the flow of reactant gases through the subchamber.

[0131] The support surface is thermally conductive and constitutes the heat-transfer inner wall in contact with the central gas sparging tube, forming a robust heat exchanger. The reaction of converting hydrogen and carbon monoxide to carbon and water is an exothermic reaction, and therefore inherently generates heat. Because the support surface is formed from a single sheet, the heat generated by the reaction can be easily distributed throughout the reaction vessel. In this embodiment, the support surface is connected to the conduits, which are all thermally conductive, as described above. Thus, in this case, heat is removed from the support surface by conduction through the central conduit. The central conduit may also be the location within which precursor reactions take place (e.g., dry reforming of light hydrocarbons with CO2 to CO and H2). In this way, heat from the carbonization section can be transferred to the dry reforming reactor, which can capture excess heat of carbonization for the internal endothermic process. Additionally, if necessary, in this embodiment, heat can be provided to the support surface by heating the central conduit. The temperature of the surface can also be measured using a thermocouple or other thermometer attached to the conduit.

[0132] The vessel in this case includes a drain outlet 106 for removing the liquid (and entrained solids). By elevating the reactant conduit above the bottom of the vessel, these non-gaseous components can fall below the reactant conduit and not interfere with the fluids being introduced into the reaction chamber. This embodiment is also configured to slope to direct the liquid to the drain outlet. It will be appreciated that other embodiments may be configured with a sloped bottom. The drain outlet can also be used when recovering solid products.

[0133] During recovery, after the reaction in the reactor is complete, a liquid containing water may be injected into the reactor. The reaction may continue in a parallel reactor while the CNF product is recovered and the catalyst is prepared for the next run.

[0134] Multiple Conduit Embodiments 2a and 2b show an embodiment of a reaction assembly, Entrance 201 and A plurality of outlets 202a,b; an elongated vessel 203 defining a reaction chamber 210 in fluid communication with an inlet and an outlet; one or more planar supports 204a-f within the reaction chamber, the one or more planar supports having a surface for supporting a solid catalyst, the one or more planar supports being mounted transversely to the elongated axis 211 of the vessel and forming a series of spaced apart barriers along the elongated axis 211 of the vessel; and a conduit 205 disposed within the reaction chamber and connected to the inlet or outlet, the conduit having a conduit opening disposed between successive barriers such that gas flow from the inlet to the outlet causes the gas to flow through the conduit and the gas to flow through the reaction chamber along the support surface between the successive barriers.

[0135] As in the previous embodiment, the reaction assembly includes a plurality of planar supports, each of which is a circular vane spaced apart along a central conduit, which in this case is coaxial with the outer vessel. Each planar support 204a-f defines a corresponding spaced apart barrier. The spatial regions between each pair of successive or adjacent barriers can be considered sub-chambers 207aa, ab, bc, cd, de, ef and ff.

[0136] Unlike the previous embodiment, this embodiment has an inlet conduit 205 for injecting reactant gases into the reaction chamber and multiple outlet conduits 225a,b for removing gases from the reaction chamber. In this case, the inlet conduit 205 and outlet conduits 225a,b are provided with multiple openings 208cd,de spatially distributed between adjacent barriers along the length of the reaction chamber 210. This allows for more uniform flow of gas within each sub-chamber.

[0137] Conduits 225a,b are also used for the seeding and harvesting stages. They can be used to carry reactants, nanocatalyst-containing fluids, and / or harvesting fluids. Their main purpose is to provide access to the surface of the disk.

[0138] It will be appreciated that the addition of outlet conduits allows gases to be taken directly from each sub-chamber, meaning that less gas passes from sub-chamber to sub-chamber compared to the previous embodiment, which helps ensure that the relative concentrations of reactants are the same in each sub-chamber.

[0139] As previously described, the reactor is configured to grow carbon nanofibers 215 as reactants 216 pass over a solid catalyst mounted on a support.

[0140] It will be appreciated that in other embodiments, one or more outlet conduits may be provided, hi other embodiments, the support surface may be connected to one or more outlet conduits.

[0141] As in the previous embodiment, the vessel in this case is provided with a drain outlet 206 for removing the liquid (and any entrained solids). By elevating the conduit above the bottom of the vessel, these non-gaseous components can fall below the reactant conduit and not interfere with the gas being introduced into the reaction chamber. The drain outlet can also be used to collect solid products.

[0142] <Embodiment of a sealed sub-chamber> FIG. 3 shows a further embodiment of a reaction assembly; Entrance 301 and An exit 302; an elongated vessel 303 defining a reaction chamber in fluid communication with an inlet and an outlet; one or more planar supports 304a-f within the reaction chamber, the one or more planar supports having a surface for supporting a solid catalyst, the one or more planar supports being mounted transversely to the elongated axis 311 of the vessel and forming a series of spaced apart barriers along the elongated axis 311 of the vessel; a conduit 305 disposed within the reaction chamber and connected to the inlet or outlet, the conduit having conduit openings 308cd, 308de disposed between successive barriers such that gas flow from the inlet to the outlet causes the gas to flow through the conduit and the gas to flow through the reaction chamber along the support surface between the successive barriers;

[0143] As in the previous embodiment, the reaction assembly comprises a plurality of planar supports, each of which is a circular vane spaced apart along a central conduit. In this case, the conduit is coaxial with the outer vessel. Each planar support forms a corresponding spaced apart barrier. The spatial regions between each pair of successive or adjacent barriers can be considered sub-chambers 307aa, ab, bc, cd, de, ef and ff. In this embodiment, the reaction chamber is comprised of a series of individual sub-chambers, with fluid flow between the sub-chambers being impeded by the barriers.

[0144] Unlike the previous embodiment, this embodiment has an inlet conduit 305 for injecting the reaction gas into the reaction chamber and an annular outlet conduit 325 surrounding the reaction chamber. That is, the elongated vessel in this case has a hollow wall, an inner wall forming the outside of the reaction chamber, and an outer wall forming the outside of the vessel. Openings in the inner wall located between successive supports allow gas to be removed from each subchamber and directed to the outlet 302. The inner wall helps to direct the gas exiting each reaction chamber to the outlet without entering the other reaction chamber on the way. It will be appreciated that in embodiments without this inner wall (such as the embodiments of Figures 1a, 2a and 5a), gas may exit one reaction subchamber and flow into another subchamber (e.g., a subchamber closer to the outlet). This may help to maintain a consistent pressure throughout the elongated vessel.

[0145] Additionally, the bottom surface of the lower wall slopes towards a drain 306 for removing liquid (and entrained solids) from the reaction chamber. It will be appreciated that the drain may be sealable or may include a liquid trap so that venting gases can be directed to an outlet rather than being exhausted through the drain. In this embodiment, the drain 306 is located at the same end of the vessel as the gas outlet 302, such that airflow towards the outlet directs liquid towards the drain. The drain may also be used when recovering solid products.

[0146] As previously described, the reactor is configured to grow carbon nanofibers 315 as reactants 316 pass over a solid catalyst mounted on a support.

[0147] <Process Cycle> As shown in FIG. 4 , the reactor assemblies described herein can be useful for facilitating a cyclic process of dispersing solid catalyst or seeding particles onto a support surface (seeding 432), converting gaseous reactants to solid products (growth 434), and recovering the solid products (recovery 431), without the need to open the reaction vessel and / or remove the support surface from the vessel.

[0148] Each process can be performed with fluids passing through the reaction vessel. These fluids can include gases, liquids, and / or particulate solids entrained in gases or liquids. Additionally, the processes can be performed while exposing the reaction vessel to different environmental conditions. Changing the environmental conditions can include one or more of changing the pressure, tilting the reaction assembly, and subjecting the reaction assembly to mechanical or ultrasonic forces.

[0149] Seeding involves injecting catalyst using a fluid containing particles through a nozzle. The nozzle may be an opening of one or more of the conduits described above or may be a separate nozzle. The nozzles are spatially distributed in the vessel, allowing the catalyst to be spread evenly over the support surface without the need to disassemble the reactor. Typically, there is at least one nozzle for injecting catalyst between each pair of adjacent barriers. In some embodiments, there are multiple conduits, one or more of which are used to inject the dispersed catalyst and one or more other conduits are used to introduce hot gas into the reaction chamber to anneal the catalyst and form chemical bonds with the substrate.

[0150] Seeding may include a cultivation step to prepare the substrate to receive the catalyst seeds. Cultivation may involve heat treating the metal substrate to form a non-active oxide layer texture with an uneven surface to increase the surface area for the seeding process. The surface texture may include alumina whiskers. Cultivation may include heating to remove residues of products of previous reactions (e.g., removing previously grown carbon nanofibers that were not removed in the harvesting stage). Cultivation may or may not be part of the seeding stage in each cycle.

[0151] The nozzle diameter, number and distribution can be manipulated in combination with the properties of the fluid containing the seeding particles to produce optimal coating efficiency and reduce waste in the catalyst preparation.

[0152] During seeding, a flow of gas can be maintained in the reaction chamber through one or more of the other conduits (i.e., the conduits not being used for seeding the particle carriers) to keep the catalyst particles away from the openings of the conduits and prevent the conduits from becoming blocked by the catalyst particles themselves or by solid products that may grow on such catalyst particles.

[0153] Depending on the nature of the catalyst, seeding may also include an activation step. Catalysts can be activated by changing the properties of the catalyst precursor to form an active catalyst. Activation can be achieved by changing the physical structure of the catalyst precursor (e.g., by heating to control particle size or to anneal the precursor) or by chemically modifying the catalyst precursor (e.g., by reacting with a reducing agent to change the oxidation state of the precursor to form an activated catalyst).

[0154] Seeding may also include controlling which surfaces in the reaction chamber should not be seeded. For example, in some embodiments, the walls of the vessel and the exterior surfaces of the conduits can be treated to prevent the catalyst particles injected during the seeding step from adhering to them. This ensures that the production of solid products is limited to the support surface.

[0155] The growth of solid products has been described. Growth involves injecting gaseous reactants into a reaction vessel such that the reactants pass over a solid catalyst mounted on a support surface. The catalyst promotes the conversion of the gaseous reactants into a solid product (e.g., carbon nanofibers) and possibly other products (e.g., gaseous products such as water vapor, or liquid products such as liquid water).

[0156] The growth may also include a finishing step to treat the grown nanofibers in situ before harvesting them. Finishing may include removing amorphous carbon or partially oxidizing the surface of the carbon nanomaterial. This may include injecting an oxidizing agent into the reaction chamber and / or increasing the temperature.

[0157] The finishing may include functionalizing the surface of the carbon prior to recovery, for example with groups such as hydroxyl, carboxyl, phenyl, etc.

[0158] Recovery is accomplished by creating sufficient physical forces to detach the solids from the surface and deagglomerate the particles.

[0159] This can occur by providing energy input in a localized form (shock wave effect, microjet effect, cavitation, friction, shear, thermal effect, etc.) The design of perforations and disks (module zones) allows spreading the liquid over a larger area, infiltrating the cavities and macroporous parts with the fluid, and loosening the soft aggregates.

[0160] A combination of liquid and gas can be flowed into the outer vessel through several perforated inlet lines. This can help to enhance the local physical forces for particle deagglomeration and dispersion within the liquid. For example, the liquid and gas mixture can form bubbles, which can be used to detach the carbon nanofibers from the solid catalyst. The liquid for collection can be a wide variety of solutions, including water-based, hydrocarbon-based, and alcohol-based. A combination of ultrasonic forces, natural resonance forces, and vibrations can be used to improve mixing.

[0161] Once the mixture of solids and liquids is removed from the vessel, the liquid and solids can be separated (eg, by filtration evaporation and / or cyclone separation) to obtain a dry solid product.

[0162] The growth stage and / or harvesting of the solid particles may cause parts of the solid catalyst to detach from the support surface. For example, in the production of carbon nanofibers, the carbon nanofibers may grow away from the catalyst particles, or they may grow between the catalyst particles and the support surface. In the latter case, the catalyst is attached to the free ends of the carbon nanofibers, so that harvesting the solid nanofiber product also removes the catalyst particles. Similarly, the forces generated during the harvesting stage to remove the solid product may also remove parts of the solid catalyst. This means that the catalyst may need to be reseeded periodically.

[0163] It will be appreciated that reseeding may or may not be necessary after each harvesting step. For example, depending on how quickly reseeding can be performed, it may be more efficient to perform a growth and harvest cycle before reseeding, even though the effectiveness of the reaction may decrease as the catalyst is gradually removed from the support surface. If catalyst is found to be exhausted in a particular process, a reseeding step may be scheduled every N growth and harvest cycles, where N is an integer.

[0164] Figures 5a and 5b show an embodiment of a reaction assembly 500 with an additional collection conduit. This embodiment is similar to the embodiment of Figure 1a, Entrance 501 and An exit 502; an elongated vessel 503 defining a reaction chamber in fluid communication with an inlet and an outlet; one or more planar supports (e.g., supports 504a) within the reaction chamber, the one or more planar supports having a surface for supporting a solid catalyst and mounted transversely to the elongated axis of the vessel, forming a series of spaced apart barriers along the elongated axis of the vessel; a reactant conduit 505 disposed within the reaction chamber and connected to an inlet or outlet, the conduit having a conduit opening disposed between successive barriers such that gas flow from the inlet to the outlet causes the gas to flow through the conduit and the gas to flow through the reaction chamber along the support surface between the successive barriers;

[0165] In this case, there are additional collection conduits 591a-b configured to carry a collection fluid (e.g., liquid). In this case, each collection conduit is disposed adjacent an outer wall of the elongated vessel. The collection conduits include a nozzle configured to inject the collection fluid along the support surface of the barrier (and / or slightly towards the support surface (e.g., to impinge on the support surface at an angle of less than 30°)) to shear the generated carbon nanofibers (e.g., towards the root of the generated carbon nanofibers adjacent the support surface). In this case, the nozzle is directional, preferentially directing the flow of fluid in a direction along the plane of the support surface.

[0166] In this embodiment, each support surface is associated with a respective directional nozzle located near that support surface, which ensures that the liquid is directed at the base of the growing nanofibers and helps shear the nanofibers from the support while reducing damage to the nanofibers.

[0167] The nanofibers are removed from the vessel along with the recovery fluid at drain 506, after which the nanofibers can be separated from the recovery fluid.

[0168] It will be appreciated that in other embodiments there may be only one recovery fluid conduit, or more than one. When using a liquid recovery fluid, one or more recovery conduits may be positioned toward the top of the vessel during recovery. This configuration allows liquid to be injected downwards so that the flow direction in the vessel coincides with gravity.

[0169] In some embodiments, the collection conduit may be the same as the reactant conduit. In some embodiments, the collection conduit may be used to seed the catalyst in a seeding stage. This may be advantageous when the nozzle is aimed along the support surface.

[0170] <Other options> The reactor may comprise one or more helical support surfaces having a helical axis aligned (e.g., coaxial) with the elongated axis of the vessel. In this embodiment, each helix may be considered as a single support forming multiple barriers along the length of the elongated vessel. One or both sides of the support may form a support surface for the solid catalyst. In helical embodiments, gas may travel between adjacent barriers around the helical axis. Again, the openings are distributed along the length of the conduit to facilitate injecting and withdrawing gas streams into and from the helix at different locations along the helical axis.

[0171] In the above embodiment, during the growth phase, reactants are introduced through conduits at the center and move towards the periphery of the vessel, in other embodiments the direction of gas flow may be reversed, with gas flowing from the periphery towards the center of the vessel and the remaining gas being removed from the vessel through a central conduit.

[0172] While the invention has been described and illustrated with respect to preferred embodiments and its preferred uses, it is not so limited, as will be understood by those skilled in the art that modifications and variations can be made which are within the full intended scope of the invention.

Claims

1. A reaction assembly comprising: The entrance and The exit, an elongated vessel defining a reaction chamber in fluid communication with an inlet and an outlet; one or more planar supports within the reaction chamber, the one or more planar supports having a surface for supporting a solid catalyst, the one or more planar supports being mounted transversely to the elongated axis of the vessel and forming a series of spaced apart barriers along the elongated axis of the vessel; a conduit disposed within the reaction chamber and connected to the inlet or outlet, the conduit having a conduit opening disposed between successive barriers such that gas flow from the inlet to the outlet causes the gas to flow through the conduit and the gas to flow through the reaction chamber along the support surface between the successive barriers; The reaction assembly comprising:

2. 10. The reaction assembly of claim 1, wherein the conduit is coaxial with the elongated vessel.

3. 3. The reaction assembly of claim 1 or 2, wherein the vessel has a uniform cross-section over the axial extent of the series of spaced apart barriers.

4. A reaction assembly according to any one of claims 1 to 3, wherein the support surface is connected to a conduit and is in thermal communication with the conduit, the support surface forming a heat exchanger.

5. 5. The reaction assembly of claim 1, wherein there is a gap between an outer edge of each of the spaced apart barriers and an inner surface of the wall of the elongated vessel, the gap allowing gas to flow along the length of the elongated vessel.

6. A reaction assembly according to any one of claims 1 to 5, wherein the vessel is provided with a drain outlet for removing liquid.

7. A reaction assembly according to any preceding claim, wherein the support surfaces are spaced apart by at least 1 mm.

8. The reaction assembly of any one of claims 1 to 7, wherein the solid catalyst is configured to catalyze a reaction that converts a gaseous reactant into a solid product.

9. The reaction assembly of any one of claims 1 to 8, wherein the solid catalyst is configured to catalyze a reaction that converts gaseous hydrogen and carbon monoxide into carbon nanofibers and water.

10. A reaction assembly according to any one of claims 1 to 9, wherein the catalyst is distributed on both sides of the barrier.

11. A reaction assembly according to any one of claims 1 to 10, wherein in operation the barriers are vertically aligned.

12. 12. The reaction assembly of claim 1, wherein the solid catalyst comprises catalyst particles comprising one or more of the Group VIII metals, Fe, Ni, Cu, Zn, Co and Mo.

13. 13. The reaction assembly of any one of claims 1 to 12, wherein the reaction assembly is configured to maintain a temperature in a reaction chamber between 450 and 580°C.

14. A method for producing carbon nanofibers using a reaction assembly according to any one of claims 1 to 13, comprising the steps of: injecting gaseous reactants into a reaction chamber through an inlet such that a flow of the gaseous reactants passes over a solid catalyst; and removing the gases through an outlet; The method of any of the above, wherein the solid catalyst is configured to convert the gaseous reactants into products, the products comprising carbon nanofibers.

15. 15. The method of claim 14, wherein the reactants comprise hydrogen and carbon monoxide.

16. 16. The method of claim 14 or 15, wherein the method comprises injecting a fluid containing catalyst particles into the assembly via one or more inlets to present at the surface prior to injecting the gaseous reactant.

17. 17. The method of claim 16, wherein the catalyst particles comprise one or more of the Group VIII metals, Fe, Ni, Cu, Zn, Co, and Mo.

18. 20. The method of claim 17, wherein the method comprises annealing and reducing the catalyst particles to form a lower oxidation state of each active site.

19. The method according to any one of claims 16 to 18, wherein the method comprises forming a passivation layer on the inner surface of the outer vessel before injecting the fluid carrying the catalyst particles into the reaction chamber.

20. 21. The method of any one of claims 14 to 20, wherein the method comprises injecting one or more of the following gases into the reaction chamber: steam, inert gas, carbon dioxide, hydrocarbon and reducing gas.

21. The method according to any one of claims 14 to 20, wherein the temperature in the reaction chamber is between 450 and 580°C.

22. The method according to any one of claims 14 to 21, wherein the pressure in the reaction chamber is between 1 and 20 atmospheres.

23. The method further comprising: collecting the carbon nanofibers by flowing a fluid through the reaction chamber to detach the carbon nanofibers from the support surface; Separating the carbon nanofibers from the fluid outside the reaction chamber; and The method according to any one of claims 14 to 21, comprising:

24. 24. The method of claim 23, wherein the method includes introducing an oxidant into the reaction chamber and increasing the temperature in the reaction chamber prior to collecting the carbon nanofibers.

25. 25. The method of claim 23 or 24, wherein the fluid comprises one or more of a gas, air, an inert gas, a liquid, water, an alcohol, a polyol, an amide, a phospholipid, an oligosaccharide, a polysaccharide, and a monosaccharide.

26. 26. The method of claim 24 or 25, wherein the method comprises injecting the fluids into the reaction chamber at different rates to promote mixing.

27. 24. The method of any one of claims 20 to 23, wherein fluid is injected into the vessel via one or more directional nozzles, each directional nozzle positioned adjacent the planar support and configured to inject fluid in a direction along a surface of the planar support.

28. A method according to any one of claims 14 to 27, wherein the method comprises injecting catalyst particles into the reaction chamber in a seeding step such that the catalyst particles adhere to the support surface.

29. 29. The method of any one of claims 14 to 28, wherein the method comprises flowing a fluid through the reaction chamber in a recovery step to detach the grown carbon nanofibers from the catalyst support surface and remove the detached carbon nanofibers from the reaction chamber.

30. A method for producing carbon nanofibers using a reaction assembly according to any one of claims 1 to 13, the method comprising the steps of: a seeding step, which involves injecting catalyst particles into the reaction chamber, allowing them to adhere to the support surface, and then activating them; a growth stage in which gaseous reactants are converted into carbon nanofibers by flowing them through a reaction chamber and over a catalytic support; a recovery step in which the grown carbon nanofibers are detached from the catalyst support surface by flowing a fluid through the reaction chamber and the detached carbon nanofibers are removed from the reaction chamber; The method as described above, comprising cycling between

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