Equipment and method for large-scale production of granular materials

Abstract

An apparatus and method are provided that enable large-scale production of particulate materials, such as graphene particles. The apparatus includes an ignition assembly that includes an easily interchangeable electrode cartridge that can be configured to self-clean between combustion cycles to produce the particulate material. The method of producing the particulate material requires low energy input to initiate the combustion reaction, which is then self-sustaining until the reactants are exhausted.

Description

[0001] Related Applications

[0002] This application claims the benefit of U.S. Provisional Patent Application No. 63 / 039,087, filed on June 15, 2020, the disclosure of which is incorporated herein by reference in its entirety. Technical Field

[0003] The present invention generally relates to apparatuses and methods for the large-scale production of particulate materials, particularly carbon-containing particulate materials such as graphene. The particulate materials are produced during a combustion process in which the chemical energy contained in the reactants is sufficient to sustain the reaction responsible for generating the particulate materials. In one or more embodiments, the apparatus includes an ignition assembly that includes a pair of electrodes, each electrode being contained within a respective cartridge that is removable from the ignition assembly. The ignition assembly can also be configured to self-clean between reaction cycles. Background Art

[0004] Graphene is a two-dimensional monolayer of sp 2 hybrid-bonded carbon atoms with a hexagonal crystal structure. Graphene has several unique physical properties, including excellent mechanical strength, high intrinsic carrier mobility at room temperature, and electrical and thermal conductivities comparable to in-plane values of graphite. As a result, graphene has generated interest in many applications, including nanoelectronics and sensors, nanocomposites, batteries, supercapacitors, and hydrogen storage. However, one drawback that has hindered the widespread adoption of graphene in these fields is the inability to produce commercial-scale graphene in a cost-effective manner. Current graphene manufacturing processes are expensive, complex, energy-intensive, and often involve corrosive chemicals and catalysts.

[0005] U.S. Patent No. 9,440,857, the entire content of which is incorporated herein by reference, is directed to a method for producing graphene particles in a simple, controllable detonation process by detonating a carbon-containing material and an oxidizer within a reaction vessel. The desired amounts of reactants are loaded into the reaction vessel, and a spark is used to effect detonation of the materials. An aerosol containing graphene particles is produced. However, the described apparatus, while well-suited for producing graphene on a laboratory scale, is not efficient for producing graphene particles on a commercial scale and develops fouling on the spark generator after repeated detonation cycles.

[0006] Luong et al. describe a method for producing graphene by flash synthesis. "Gram-scale bottom-up flash graphene synthesis", Nature 577, 647-651 (2020). In flash synthesis, graphene is synthesized from solid carbon sources such as coal, petroleum coke, biochar, and carbon black by rapidly heating the carbon source to high temperatures using the high voltage of a capacitor bank discharge. Although the production of graphene particles has been reported to reach the gram scale, such a process is expected to be capital- and energy-intensive due to the rapid heating of the carbon source using a capacitor bank.

[0007] Accordingly, there is a need in the art for an apparatus and method for producing graphene that is economical and scalable, allowing for the production of graphene particles on a commercial scale. SUMMARY OF THE INVENTION

[0008] According to one embodiment of the present invention, there is provided an apparatus for producing particulate material by combustion of reactants. The apparatus includes a reaction chamber, a vacuum source operatively connected to the reaction chamber, and an ignition assembly. The reaction chamber is operatively connected to a carbonaceous material source and an oxidizer source. The vacuum source can be used to selectively evacuate at least a portion of the contents of the reaction chamber, particularly after the particulate material has been generated. The ignition assembly is configured to initiate the combustion of a quantity of carbonaceous material and a quantity of oxidizer fed into the reaction chamber from their respective sources. The ignition assembly includes a pair of electrodes that are operable to generate an ionization arc therebetween, each electrode being contained within a respective cartridge that is removably received within the ignition assembly.

[0009] According to another embodiment of the present invention, there is provided an electrical ignition assembly that can be used to initiate a combustion reaction in a reaction chamber. The ignition assembly includes a housing having an inlet port configured to be fluidly connected to one or more gaseous reactant material sources and an outlet port configured to be fluidly connected to the reaction chamber. The inlet port and the outlet port are connected by a passage. The ignition assembly further includes a pair of electrodes, each electrode having an electrode tip extending into the passage. Each electrode is contained within a respective cartridge that is removably received within the housing.

[0010] According to another embodiment of the present invention, a method for producing graphene particles is provided. The method includes introducing a mixture containing a carbonaceous material and an oxidizing agent into a reaction chamber. The carbonaceous material and the oxidizing agent are introduced into the reaction chamber through an ignition assembly including a pair of electrodes. An ionization arc is generated between the pair of electrodes within the ignition assembly to cause the carbonaceous material and the oxidizing agent to burn and generate a temperature of at least 3000 K within the reaction chamber, thereby generating an aerosol containing graphene particles. The aerosol is withdrawn from the reaction chamber using a vacuum source operatively connected to the reaction chamber. The graphene particles are recovered as graphene powder from the aerosol withdrawn from the reaction chamber.

[0011] Brief Description of the Drawings

[0012] Figure 1 is a schematic view of an exemplary apparatus for producing particulate material by burning reactants according to one or more embodiments of the present invention;

[0013] Figure 2 is a schematic view of an exemplary reaction chamber and ignition assembly according to one or more embodiments of the present invention;

[0014] Figure 3 is Figure 2 a perspective view of the ignition assembly of

[0015] Figure 4 is Figure 3 a cross-sectional view of the ignition assembly of

[0016] Figure 5 is a cross-sectional view of the ignition assembly depicting a pair of electrodes carried by the ignition assembly Figure 3 of

[0017] Figure 6 is Figure 5 an exploded view of one of the electrodes of

[0018] Figure 7 is a cross-sectional view of the ignition assembly depicting a pair of venturi structures for guiding the flow of a liquid introduced into the ignition assembly around the electrodes Figure 3 of

[0019] Although the drawings do not necessarily provide exact dimensions or tolerances of the illustrated components or structures, the relationships between the components of the structures shown in the drawings are drawn to scale.

[0020] Detailed Description of the Preferred Embodiment

[0021] See Figure 1, the figure depicts an apparatus 10 for producing particulate materials according to one or more embodiments of the present invention. The apparatus 10 generally includes a reaction chamber 12, a vacuum system 14 which includes a vacuum pump 16 and a vacuum ballast tank 18, a particle collector 20, and an ignition assembly 22. A carbonaceous material source 24 and an oxidant source 26 are operatively connected to the reaction chamber 12 via a gas manifold 28. In certain embodiments, a purge gas source 30, such as air, may also be connected to the reaction chamber 12 via the manifold 28. However, within the scope of the present invention, the oxidant source 26 can be used as a purge gas without the need for a separate purge gas source. The inlet of the vacuum pump 16 is connected to a three-way valve 38b. The valve 38b is also connected to the manifold 28 and the vacuum ballast tank 18. In this way, the vacuum pump 16 can be configured to evacuate the reaction chamber 12 when preparing to fill the reaction chamber with reactants, or to evacuate the ballast tank 18 during the reaction and collection cycles to accelerate the vacuum recovery of the tank 18. A filter 32a, such as a HEPA filter, can be placed between the pump 16 and the valve 38b to prevent fine particles from being drawn into the pump. Additionally, a filter 32b, also such as a HEPA filter, can be placed upstream of the ballast tank to capture any particles that may be entrained in the airflow from the particle collector 20. In an alternative embodiment, a second vacuum pump (not shown) can be used to continuously evacuate the ballast tank 18.

[0022] The mass of the carbonaceous material and the oxidant introduced into the manifold 28 can be monitored by mass meters 34, 36. It should be understood that multiple mass meters can be provided and operatively connected to other reactant sources so that the apparatus 10 can react more complex reactant mixtures rather than the simple binary mixture shown. Additionally, the flow rates of the reactants and the purge gas into and out of the manifold 28 can be controlled by a plurality of control valves 38a - e. The operation of the valves 38 can be controlled by a central electronic controller (not shown). The central controller can also include various sensors (not shown) placed throughout the apparatus 10 to monitor and record important process parameter data for providing quality control, traceability, record keeping, and monitoring of the mean time between failures (MTBF).

[0023] In certain embodiments, the carbonaceous material can include, but is not limited to, carbon-rich precursors, gases, gas mixtures, powders, aerosols, and other materials. In a preferred embodiment, the carbonaceous mixture contains hydrocarbon compounds, preferably saturated or unsaturated C 1 -C 12Hydrocarbon compounds. In certain embodiments, acetylene is a particularly preferred hydrocarbon material. The carbon-containing material can comprise a single material or compound, or a mixture of carbon-containing compounds. For example, acetylene can be the only carbon-containing compound in the reaction mixture, or the reaction mixture can comprise a mixture of hydrocarbon compounds. Additionally, the carbon-containing material does not need to be provided in gaseous form. The carbon-containing mixture can comprise solids or liquids that can be finely dispersed within the reaction vessel (e.g., an aerosol comprising fine solid particles (such as coal powder or petroleum coke) and / or droplets (such as liquid hydrocarbons)). In certain embodiments, the carbon-containing material should present as large a surface area as possible so that the combustion reaction can proceed rapidly and generate the heat required to achieve the desired reaction temperature.

[0024] The oxidizing agent can be any material capable of oxidizing the carbon-containing material in a combustion reaction. In one or more embodiments, the oxidizing agent comprises oxygen, which can be in its elemental form or combined with other elements. In certain embodiments, the oxidizing agent is selected from the group consisting of: O 2 、N 2 O, NO, and mixtures thereof. When the oxidizing agent comprises O 2 , O 2 can be provided in substantially pure form (i.e., 99% or higher), as air, or in combination with other inert materials.

[0025] The ratio of the oxidizing agent present in the reaction vessel prior to combustion to the carbon-containing material can contribute to the characteristics of the graphene particles formed after combustion of the reaction mixture. In certain embodiments, the molar ratio of the oxidizing agent to the carbon-containing material is about 1.5 or less. In certain embodiments, the ratio of the oxidizing agent to the carbon-containing material is from about 0.1 to about 1.5, from about 0.2 to about 1.2, from about 0.4 to about 1.0, or from about 0.6 to about 0.8.

[0026] Figure 2 An exemplary reaction chamber 12 is described, which is connected to an exemplary ignition assembly 22 via short pipe nipples 39, 40, and a pipe union 42. In certain embodiments, the ignition assembly 22 can be integrated with the reaction chamber 12 rather than provided as a separate module. As shown, the reaction chamber 12 is generally cylindrical and includes an inlet 44 configured to introduce reactants into the reaction chamber 12, and an outlet 46 through which particulate matter generated within the reaction chamber 12 is removed and conveyed to a particle collector 20. In certain embodiments, the construction of the reaction chamber 12 can withstand high temperatures and shock waves that may be generated by the combustion of the reactants. Additionally, the reaction chamber 12 can contain a catalyst or a consumable feedstock.

[0027] Figures 3 - 7The implementation manner of the ignition assembly 22 and its components are described in more detail. As shown in the figure, the ignition assembly 22 includes a housing 48 having an inlet 50 and an outlet 52. However, within the scope of the present invention, the ignition assembly 22 can also be integrated with the reaction chamber 12 instead of being provided as a separate module. A stub 54 is threadedly connected within the inlet 50 and connects the inlet to the gas manifold 28. A stub 39 is threadedly connected within the outlet 52. The inlet 50 and the outlet 52 are interconnected by a passage 56 extending through the housing 48. At least a pair of electrode cartridges 58 are removably received within ports 60 that extend through the circumferential housing sidewall 62. The cartridges 58 are preferably placed opposite to each other and include electrode tips 64 that extend into the passage 56. The distance between the electrode tips 64 is referred to as the arc gap. Also located within the housing 48 are one or more liquid diverter cartridges 66 received within ports 68 that also extend through the sidewall 62. In the illustrated implementation, the assembly 22 includes two opposing liquid diverter cartridges 66 that are approximately 90° in direction from each electrode cartridge 58.

[0028] Figure 6 The structure of an exemplary cartridge 58 made in accordance with the present invention is described. Each cartridge 58 includes electrical terminals 70 that can be connected to a power source (not shown) capable of providing the required voltage to generate an ionization arc between the electrode tips 64. The electrode tips 64 include the terminals of an elongated electrode 72 that is received within a bore 74 of a body 76. The electrode 72 is preferably a wire or thread formed of a metal or metal alloy such as copper, gold, silver, aluminum, nickel, iron, platinum, brass, or steel. The body 76 contains an insulating material that electrically isolates the electrode 72 from the rest of the cartridge 58. In one or more embodiments, the body 76 is also relatively non-porous and can contain, for example, glass or glazed ceramic. As described below, the non-porous nature of the body 76 helps to retard or prevent the penetration of graphene particles into the cartridge 58, which, given the high electrical conductivity of graphene, could cause an electrical short within the cartridge. In certain embodiments, the insulating material forming the body 76 and isolating the electrode 72 can have a porosity of less than 0.1, less than 0.01, or less than 0.001, as determined by any of several well-known methods for measuring the porosity of a material, such as the direct volume method, the optical method, the imbibition method, or the gas expansion method.

[0029] The body 76 is received within the bracket 78, and the body tube section 80 projects through the orifice 82. A plurality of washers or shims 84 (collectively) are located around the tube section 80 and within the bracket 78. The sleeve 86 also surrounds a portion of the body 76 and is itself received within the bracket 78. The O-ring 88 provides a seal between the sleeve 86 and the body 76. The washer 90 and nut 92 are threaded onto the long electrode 72 to maintain the sealing pressure and positional security of the O-ring 94 and the tip 64 against the body 76. The O-ring 94 provides a seal between the electrode tip 64 and the body 76. The O-rings 96, 98 provide a seal between the bracket 78 and the housing 48.

[0030] The ferrule 100 surrounds the distal portion of the electrode 72 and is received within the collar 102, which is configured to abut the sleeve 86. Preferably, the ferrule 100 comprises an electrically insulating material, which may be the same or different from the material forming the body 76. The collar 102 is threaded onto the bracket 78 to provide positional security for the components of the electrode assembly. Notably, the collar 102 holds the electrode tip 64 in a fixed position within the channel 56. The collar 102 and the bracket 78 may be fixed with a set screw 104. The nut 106 secures the ferrule 100 within the collar 102. The terminal 70 is connected to the distal end of the electrode 72. Bearings 108 and bushings 110 surround respective portions of the bracket 78, and set screws 112 may be used to secure the bushing 110 within the port 60.

[0031] The electrode cartridge 58 is also adjustable within its respective port 60 such that the desired arc gap can be fixed and maintained even during servicing of the ignition assembly 22 and replacement of the cartridge.

[0032] In one or more embodiments, the electrode 72 is configured to be movable within the ignition assembly. As explained in more detail below, being able to move the electrode 72 without completely removing it from the ignition assembly 22 can assist in cleaning the electrode tip 64. In one or more embodiments, the electrode 72 can be rotated by connecting an actuator (not shown, such as a servo motor or pneumatic piston) to the electrode itself or the cartridge 58. The actuator can be operated to rotate or index the electrode 72 by a number of degrees after each combustion reaction or after any predetermined number of combustion reactions. In other embodiments, the electrode 72 can be extended, retracted, and / or rotated within the ignition assembly 22 to provide cleaning or symmetric wear of the electrode.

[0033] In one or more embodiments, as shown, the ignition assembly 22 includes one or more, preferably two, fluid diverter boxes 66. As Figure 7As shown, the fluid diverter box 66 includes a Venturi structure 114 that extends into the channel 56. The Venturi structure 114 includes an inclined surface 116 that is configured to direct the fluid flowing through the channel 56 across the surface of the electrode tip 64 that is opposite to the direction of the fluid flowing through the ignition assembly (i.e., the surface of the electrode tip 64 facing the outlet 52). Thus, the Venturi structure 114 ensures that the purge gas flowing through the channel 56 substantially contacts the entire surface of the electrode tip 64, thereby removing the particles accumulated thereon, especially carbonaceous deposits.

[0034] In some embodiments, the cartridge 58 and / or the diverter box 66 are configured to be easily removable from the ignition assembly 22 and different cartridges and / or diverter boxes can be installed in their place. Thus, when repairing the ignition assembly 22, the downtime of the device 10 is very short. The self-cleaning function of the ignition assembly 22 and the feature of quickly replacing the cartridge 58 and / or the barrel 66 greatly facilitate the ability of the device 10 to produce particulate materials on a commercial scale.

[0035] As described above, the device 10 can be used to produce particulate materials, especially graphene particles, by a combustion reaction. The carbonaceous material and the oxidant enter the reaction chamber 12 through the manifold 28 and the ignition assembly 22. The carbonaceous material and the oxidant can be mixed upstream or inside the manifold 28 and then delivered to the reaction chamber 12. The pressure of the reaction mixture in the reaction chamber 12 before combustion can be changed to provide control over the reaction conditions and the reaction products formed. In some embodiments, the initial pressure of the reaction mixture in the reaction chamber 12 can be about 0.1 to about 3 atmospheres, about 0.5 to about 2 atmospheres, or about 1 atmosphere. The vacuum system 14 can be used to assist in filling the reactants into the reaction chamber 12. The vacuum system 14 can be used to evacuate the reaction chamber 12 before introducing the reactants. In some embodiments, the reaction chamber is evacuated to an absolute pressure of less than 0.2 atmospheres, less than 0.1 atmospheres, or less than 0.05 atmospheres. Evacuating creates a clean environment for the reaction and helps introduce the reactants into the reaction chamber without having to pump the reaction chamber when introducing the reactants.

[0036] Once the desired amounts of carbonaceous material and oxidizer are loaded into reaction chamber 12, an ionization arc is generated between the electrode pairs 72 within ignition assembly 22, thereby initiating the combustion of the carbonaceous compound and the oxidizer. After initiation, the combustion reaction is self-sustaining until the reactants present in reaction chamber 12 are depleted. It should be noted that in a preferred embodiment, the combustion reaction is a detonation reaction. However, within the scope of the present invention, the combustion reaction can also be a deflagration or burning reaction. As used herein, "detonation" is distinguished from a mere "deflagration" or "burning" of the carbonaceous material. Detonation generally involves a supersonic exothermic wavefront in a medium that accelerates and ultimately drives a shock front propagating ahead of it. Deflagration is typically described as a subsonic combustion propagated by heat conduction. Detonation reactions also typically have the characteristic of producing higher temperatures in the reactants and reaction products.

[0037] In one or more embodiments, the combustion reaction occurs at a temperature of at least 3000K, at least 3500K, or at least 4000K. In certain embodiments, the combustion reaction occurs at a temperature of from about 3000K to about 5000K, from about 3500K to about 4500K, or about 4000K. It has been found that the combustion of the carbonaceous material and the oxidizer at these temperatures favors the formation of highly ordered graphene particles rather than graphite soot. If necessary, an inert gas material (such as helium, neon, argon, or nitrogen) can be included in the reaction mixture to charge the reaction vessel to assist in temperature control during combustion. Additionally, in certain embodiments, particularly those in which the combustion reaction is a detonation, the combustion of the reaction mixture proceeds very rapidly. In certain embodiments, the duration of combustion is from about 5 to about 100 ms, from about 10 to about 75 ms, or from about 20 to about 50 ms.

[0038] In certain embodiments, the particulate material (e.g., graphene particles) produced by the combustion reaction is dispersed within reaction chamber 12 in the form of an aerosol. The particulate material may tend to immediately aggregate after formation into particles having an average particle size of from about 35 to about 250 nm, from about 50 to about 200 nm, or from about 75 to about 150 nm. In some embodiments, if allowed to continue under static conditions, the particles can aggregate to form a gel. The conditions and requirements for the particulate material to aggregate into a solid aerosol are described in U.S. Patent No. 7,691,909, which is incorporated herein by reference in its entirety. To form a gel, the particles must generally be retained in the reaction chamber and remain substantially undisturbed for a relatively long period of time. In one or more embodiments, it is preferred to remove the particles from the reaction vessel before they can fully aggregate and form an aerosol. Thus, in certain embodiments of the present invention, the particles are removed from the reaction vessel while still dispersed as an aerosol, and the formation of a gel is avoided.

[0039] Since the particulate material generated during the reaction is usually very fine, it often forms a coating on the surface of the device, especially on the electrode 72, which can lead to fouling. However, in one or more embodiments, the electrode cartridge 58 is configured to withstand the pressure generated within the device 10 during the combustion reaction and prevent the infiltration of fine particulate matter, thereby maintaining an electrically isolated system. As described above, embedding the electrode 72 in a non-porous material can prevent particles from entering the cartridge 58 to create a short circuit hazard. The electrode 72 can also be configured as a graphene coated to shed pressure.

[0040] As Figure 1 shown, the vacuum system 14 can be used to draw the aerosol out of the reaction chamber 12 and transport it to the particle collector 20. In one or more embodiments, the particle collector 20 can be any conventional device for separating fine particles from an air stream. For example, the particle collector 20 can include any type of dust collection device, such as an inertial separator (e.g., a settling chamber, a baffle chamber, or a centrifugal collector such as a cyclone separator), a fabric filtration device (such as a baghouse), a wet scrubber, or an electrostatic precipitator. The particulate material, especially graphene particles, can then be removed from the particle collector as a powder.

[0041] Within the scope of the present invention, the particle collector 20 is operatively connected to a plurality of parallel reaction chambers 12. The reaction cycles within each reaction chamber 12 can be staggered to ensure continuous production of particulate material and continuous collection of these materials within the particle collector 20.

[0042] During the discharge of the aerosol from the reaction chamber 12, a cleaning or flushing operation can be performed to remove carbon deposits on the inner surface of the ignition assembly 22, especially the electrode tip 64. The carbonaceous material from source 24 and the oxidant from source 26 stop flowing to the manifold 28, and the flushing gas from source 30 begins to flow. Alternatively, in embodiments where no separate flushing gas is provided, the flow of the carbonaceous material from source 24 is stopped, but the flow of the oxidant from source 26 (which now acts as a flushing gas) continues.

[0043] The flushing gas is directed through the manifold 28 to the ignition assembly 22 and the reaction chamber 12. As the flushing gas flows through the ignition assembly, its function is to remove carbonaceous particles, especially graphene particles, which may have deposited on the surface of the electrode tip 64 due to the generation of graphene aerosol within the reaction chamber 12 and the channel 56. The flushing gas resuspends the accumulated particles and carries them through the reaction chamber 12 into the particle collector 20. In certain embodiments, the vacuum conditions within the reaction chamber 12 are maintained by the vacuum system 14 to draw the resuspended graphene particles out of the ignition assembly 22 and into the particle collector 20.

[0044] As described above, as Figure 7 shown, the fluid diverter box 66 changes the flow direction of the purge gas through the channel 56 so that the purge gas flows over the surface of the electrode tip 64 in a direction opposite to the normal direction of flow through the ignition assembly 22. In this embodiment, without the diverter box 66, the surface of the electrode tip 64 facing the normal fluid flow direction through the ignition assembly 22 would effectively shield the opposing surface creating a dead zone where graphene particles could accumulate and remain undisturbed. However, the inclined surface 116 of the Venturi structure 114 introduces the purge gas into these dead zones and through the surface of the electrode tip 64 facing the ignition assembly outlet 52.

[0045] Also as described above, as an alternative to or in combination with the diverter box 66, the electrode box 58 can be configured to rotate so that the surface of the electrode tip 64 facing the outlet 52 changes periodically. Thereby, the ability of graphene particles to accumulate on any part of the surface of the electrode tip 64 is greatly reduced.

[0046] In certain embodiments, an ionization arc can be generated between a pair of electrode tips 64 when the purge gas passes through the ignition assembly 22. In the presence of the purge gas and the resuspended carbonaceous material, the generation of the arc or multiple successive arcs can vaporize the carbonaceous material, further ensuring the transport of these materials out of the ignition assembly 22. Additionally, one or more ionization arcs generated during the electrode cleaning process can be monitored by one or more sensors. Detection of the arc during this process can provide a high level of confidence that the next particle formation reaction will be successful when the carbonaceous material and oxidant are reloaded into the reaction chamber 12.

[0047] After the cleaning operation (purge gas passing through the ignition assembly 22), the reaction chamber 12 can be isolated from the vacuum system 14 and additional carbonaceous material and oxidant can be introduced into the reaction chamber 12. Now the reaction chamber is loaded with reactants and ready for the ignition assembly 22 to initiate the combustion of the reactants and produce a further quantity of particulate material, particularly graphene particles. The above steps can be repeated multiple times. It should be noted that in certain embodiments, the above cleaning operation does not need to be performed after every combustion reaction occurring within the reaction chamber 12. In such embodiments, a predetermined number of combustion and aerosol discharge cycles can be carried out before starting the cleaning cycle with the purge gas.

[0048] The following description provides an example of an operating mode of apparatus 10. At t = 0, the pressures in gas manifold 28 and reaction chamber 12 are 1 atmosphere, and particle collector 20 and vacuum ballast tank 18 have been evacuated and are at a pressure of approximately 0.1 atmosphere. Valves 38c and 38e are opened, and valve 38b is set to evacuate reaction chamber 12. Due to the large vacuum reservoir in the vacuum ballast system, opening valve 38e can quickly draw the pressure in gas manifold 28 and reaction chamber 12 down to approximately 1 / 3 atmosphere, causing valve 38e to close. Reaction chamber 12 and manifold 28 continue to be evacuated through valves 38b and 38c until gas manifold 28 and reaction chamber 12 reach approximately 0.1 atmosphere. At t = 0.5 to 5 seconds, valve 38b switches to draw air from ballast tank 18, and mass flow meters 34, 36 begin to accurately dispense reactant materials into reaction chamber 12 at a programmed rate and concentration. The calculated dispense amount typically refills reaction chamber 12 to 1 atmosphere within 15 to 50 seconds. Once all reactants have been dispensed, valves 38a and 38c are closed, and valve 38d is opened as a safety pressure release. Then, the control system can wait for a programmed delay, typically 1 second, before ignition assembly 22 initiates the reaction. After the control system detects a successful reaction, after an optional programmed delay (usually 0 seconds, but can be 1 or 2 seconds), valve 38e is opened, and the collection process begins by quickly pulling the reaction chamber back to approximately 1 / 3 atmosphere. After a few minutes, valve 38c is opened, thereby venting reaction chamber 12 to 1 atmosphere through valve 38d which is already open. This introduces a high-speed gas flow through gas manifold 28 and into reaction chamber 12. This gas flow pushes the graphene aerosol from reaction chamber 12 into particle collector 20, where the graphene is collected, for example, in a specially modified industrial bag filter. At the same time, the high-speed gas flow, propelled by electrodes 72 (and electrode tips 64) of the ignition system, in combination with a special spark sequence, effectively cleans the electrodes, thus preparing them for the next reaction. This programmable collection / cleaning period typically lasts 5 to 20 seconds, after which ignition assembly 22 is turned off, valve 38d is closed, valve 38a is opened, valve 38b switches the vacuum pump 16 to manifold 28, and reaction chamber 12 is quickly pulled back to approximately 1 / 3 atmosphere as valve 38c is opened and valve 38d is closed, and the cycle repeats. In some embodiments, the time required to complete one cycle is less than 120 seconds, preferably about 20 to about 100 seconds, about 30 to about 90 seconds, or about 35 to about 75 seconds.

Claims

1. An apparatus for producing particulate material by combustion of reactants, which comprises: a reaction chamber operatively connected to a carbonaceous material source and an oxidant source; a vacuum source operatively connected to the reaction chamber, which is operable to evacuate at least a portion of the contents of the reaction chamber; and an ignition assembly configured to initiate combustion of a quantity of carbonaceous material and a quantity of oxidant fed into the reaction chamber from their respective sources; the ignition assembly includes a first electrode contained in a first cartridge and a second electrode contained in a second cartridge, the first electrode and the second electrode being operable to generate an ionization arc therebetween, the first cartridge being removably received in a first port of the ignition assembly, and the second cartridge being removably received in a second port of the ignition assembly; the apparatus further includes one or more fluid diverters configured to direct or disrupt at least a portion of the fluid flowing through the ignition assembly to pass through a surface of the electrode that does not face the direction of the fluid flowing into the ignition assembly.

2. The apparatus according to claim 1, wherein the ignition assembly includes a housing having an inlet port configured to be fluidly connected to a carbonaceous material source and an oxidant source, and the housing further has an outlet port configured to be fluidly connected to the reaction chamber, the inlet port and the outlet port being connected by a passage through the housing.

3. The apparatus according to claim 1, wherein the one or more fluid diverters include one or more Venturi structures having an inclined surface protruding into the passage.

4. The apparatus according to claim 1, wherein the apparatus is operatively connected to a purge gas source, and the apparatus is configured to direct purge gas through the ignition assembly to remove carbon and / or carbonaceous compounds deposited on the electrodes due to the combustion of the carbonaceous material and the oxidant.

5. The apparatus according to claim 4, wherein the purge gas source is the same as the oxidant source.

6. The apparatus according to claim 4, wherein the purge gas contains air.

7. The apparatus according to claim 1, wherein the oxidant contains oxygen.

8. The apparatus according to claim 1, wherein the carbonaceous material contains one or more hydrocarbon compounds.

9. The apparatus according to claim 1, wherein the first electrode and the second electrode are selectively rotatable within the ignition assembly.

10. The apparatus according to claim 1, wherein the electrodes include a non-porous material surrounding an electrical conductor, the electrical conductor including an electrode tip that passes through the non-porous material and extends into a passage within the ignition assembly.

11. The apparatus according to claim 10, wherein the non-porous material contains glass or glazed ceramic.

12. The apparatus according to claim 1, wherein the vacuum source includes a vacuum pump and a gas ballast tank.

13. An electric ignition assembly operable to initiate a combustion reaction within a reaction chamber, which comprises: a housing having an inlet port configured to be fluidly connected to a gaseous reactant material source and an outlet port configured to be fluidly connected to the reaction chamber, the inlet port and the outlet port being connected by a passage; and A first electrode contained within a first cartridge and a second electrode contained within a second cartridge, each of the first and second electrodes having an electrode tip extending into the channel, the first cartridge being removably received within a first port of the housing and the second cartridge being removably received within a second port of the housing; The ignition assembly further includes one or more fluid diverters configured to direct at least a portion of the fluid flowing through the ignition assembly across a surface of the electrode that does not face the direction of the fluid flowing into the ignition assembly.

14. The electric ignition assembly of claim 13, wherein the one or more fluid diverters include one or more Venturi structures having an inclined surface that protrudes into the channel.

15. The electric ignition assembly of claim 13, wherein, The first and second electrodes are selectively rotatable within the ignition assembly.

16. The electric ignition assembly of claim 13, wherein the first and second electrodes comprise a non-porous material surrounding an electrical conductor, the electrical conductor including an electrode tip that passes through the non-porous material and extends into the channel within the ignition assembly.

17. The electric ignition assembly of claim 16, wherein the non-porous material comprises glass or glazed ceramic.

18. A method of producing graphene particles, which comprises: Introducing a mixture comprising a carbonaceous material and an oxidant into a reaction chamber, the carbonaceous material and the oxidant being introduced into the reaction chamber through an ignition assembly including a first electrode contained within a first cartridge and a second electrode contained within a second cartridge, the first cartridge being removably received within a first port of the ignition assembly and the second cartridge being removably received within a second port of the ignition assembly; Generating an ionization arc between the first and second electrodes within the ignition assembly so that the carbonaceous material and the oxidant combust and a temperature of at least 3000 K is generated within the reaction chamber to produce an aerosol comprising graphene particles; Withdrawing the aerosol from the reaction chamber using a vacuum source operatively connected to the reaction chamber; and Recovering the graphene particles as graphene powder from the aerosol withdrawn from the reaction chamber; wherein the method further comprises passing a purge gas through the ignition assembly while maintaining a vacuum within the reaction chamber; wherein the step of passing the purge gas through the ignition assembly includes passing at least a portion of the purge gas flowing through the ignition assembly across a surface of one or both of the electrodes that is opposite to the direction in which the carbonaceous material and the oxidant flow through the ignition assembly, thereby removing graphene particles accumulated on the surface.

19. The method of claim 18, wherein the composition of the purge gas is the same as that of the oxidant.

20. The method of claim 18, wherein the method further comprises generating an ionization arc between the first and second electrodes within the ignition assembly while the purge gas passes through the ignition assembly.

21. The method of claim 18, wherein after passing the purge gas through the ignition assembly, the method further comprises separating the reaction chamber from the vacuum source and introducing additional carbonaceous material and oxidant into the reaction chamber.

22. The method according to claim 18, wherein the step of combusting the carbonaceous material and the oxidizer is a detonation reaction.

23. The method according to claim 18, wherein the step of combusting the carbonaceous material and the oxidizer is a deflagration reaction.

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