Systems and methods for treating gases

Abstract

To provide systems and methods for processing gases.SOLUTION: The present invention provides a system for transforming a hydrocarbon-containing inflow gas into outflow gas products, where the system includes specified components.SELECTED DRAWING: None

Description

[Technical Field]

[0001] Related Applications This application claims the benefit of U.S. Provisional Patent Application No. 62 / 721,863, filed August 23, 2018, U.S. Provisional Patent Application No. 62 / 736,206, filed September 25, 2018, and U.S. Provisional Patent Application No. 62 / 793,763, filed January 17, 2019, the entire teachings of each of which are incorporated herein by reference.

[0002] The present invention relates to a system and method for treating gases. [Background technology]

[0003] background Acetylene can be used as a chemical precursor or feedstock for industrial combustion applications such as welding and metal cutting. Commercial production of acetylene has been occurring since the early 20th century. The original method for producing acetylene used coal as a feedstock through a process involving a calcium carbide intermediate. In the later 20th century, other methods were developed that primarily used heat-based processes such as thermal cracking or electric arc furnaces.

[0004] Acetylene produced from coal involves a three-step process: first, heating coal to produce high-carbon coke; second, further heating the coke in the presence of calcium oxide to produce calcium carbide; and third, reacting the calcium carbide with water to produce acetylene and calcium hydroxide. The first two steps require very high temperatures, while the last step is exothermic. This method for forming acetylene is still used commercially, especially in China, where coal is readily available.

[0005] However, this process introduces impurities from the coal and lime feedstocks into the final product, resulting in contaminated acetylene with impurities such as phosphine, arsine, and hydrogen sulfate. All of these species can contaminate catalysts for subsequent chemical reactions and therefore need to be scrubbed from the acetylene product before it can be used commercially. Chemical-grade acetylene used for further chemical processing must be >99.6% pure CH with <25 ppm phosphine / arsine / HS. Industrial-grade acetylene burned for welding and metal-cutting applications can tolerate more impurities (>98.0% pure CH, <500 ppm phosphine / arsine / HS). Therefore, coal-derived acetylene production is limited to the formation of industrial-grade acetylene in the United States; furthermore, even when coal-derived acetylene is used solely for welding and metal-cutting, the presence of potentially harmful contaminants raises concerns.

[0006] Alternatively, acetylene can be prepared from hydrocarbons by partial oxidation, for example, by a process developed by BASF, as described in U.S. Patent No. 5,629,999. In this process, hydrocarbon feedstock and oxygen are preheated and then reacted in a combustion chamber, causing the produced gas to reach temperatures >1500°C. The combustion reaction is quenched with water to achieve rapid cooling, resulting in a gaseous mixture of acetylene, hydrogen, carbon monoxide, water vapor, and by-products (referred to as "cleavage gas"). This method of acetylene production yields approximately 7.5% acetylene, along with significant amounts of hydrogen (57%), carbon monoxide (26%), and methane (5.2%). One of the by-products is soot, which must be removed from the cutting gas if it is to be further processed. Other by-products include higher-order hydrocarbons, including alkanes, alkenes, alkynes, and aromatics. Removing impurities from the cutting gas and recovering the acetylene it contains presents significant engineering challenges.

[0007] In addition to production problems, acetylene is difficult to handle and transport. It is highly explosive. When transported through pipelines, acetylene is maintained at low pressure and can only be transported short distances. For industrial purposes, acetylene is pumped into tanks at high pressure and dissolved in a solvent, such as dimethylformamide, N-methyl-2-pyrrolidone, or acetone. When an acetylene cylinder is opened, the dissolved gas evaporates and flows through a connecting hose to a welding or cutting torch. However, a certain amount of acetylene remains dissolved in the solvent and is returned to the manufacturer in this state, so not all of the acetylene in the cylinder is usable. With the rise of the petrochemical industry in the mid-20th century, acetylene continues to be used industrially (i.e., for welding, metal cutting, etc.), but it has been displaced as a precursor in chemical reactions and replaced with other feedstocks (e.g., ethylene) derived directly from petroleum rather than coal. However, as oil becomes more expensive and natural gas becomes cheaper, interest in acetylene as a platform for further chemical processing to replace petroleum-derived feedstocks is increasing.

[0008] Furthermore, the abundance of natural gas has led to the search for more ways to use this material without combustion, reduce its greenhouse gas effect, and avoid converting it to another greenhouse gas, CO2, through simple combustion. The growing demand for non-hydrocarbon sources of fuel supports the use of natural gas as a feedstock for producing hydrogen, which can then be used as a power source. Conventional technologies already exist for extracting hydrogen gas from the methane in natural gas. For example, steam reforming can produce hydrogen gas and carbon monoxide; the hydrogen produced by the steam reforming process can then be used in pure form for other applications, such as hydrogen fuel cells or gas turbines, where the hydrogen combines with oxygen to form water without emitting greenhouse gases. Other processes, such as partial oxidation, can produce hydrogen-containing synthesis gas, a combustible mixture that can be used as fuel. However, conventional technologies for producing hydrogen from methane have drawbacks. Steam reforming is performed at high temperatures, is energy-intensive, and requires expensive materials that can withstand harsh reaction conditions. Steam reforming uses a catalyst to carry out the conversion of methane to hydrogen, but the catalyst is vulnerable to poisoning by common pollutants. Partial oxidation is a less efficient technique than steam reforming for producing hydrogen, tends to form soot, and has limited hydrogen yield.

[0009] In addition to natural gas, other mixed gas sources, such as oceanic clathrates, coal mine gas, and biogas, also contain methane gas. Biogas is a naturally occurring mixed gas source produced by the anaerobic decomposition of organic waste materials in various man-made environments, such as landfills, manure holding ponds, and waste facilities, as well as in natural environments, such as peat bogs and melting permafrost. Anaerobic bacteria occurring in such environments digest the organic material, which accumulates in the environment and produces a gas mixture composed primarily of carbon dioxide and methane. Because methane is potentially flammable, biogas with a high methane content can be hazardous, as can be found in landfill-derived gas mixtures. Furthermore, methane is a potential greenhouse gas. Currently, biogas collected from organic decomposition (e.g., landfills, waste facilities, storage ponds, etc., or natural areas containing decaying organic material) can be purified to remove CO2 and other trace gases, resulting in concentrated methane for energy production. However, simply burning methane-rich biogas produces another greenhouse gas, CO. It is desirable to identify uses for biogas or other mixed gas sources that can utilize their energy potential without burning them, thereby reducing the greenhouse gas effect of methane while avoiding its conversion to another greenhouse gas, CO.

[0010] Thus, there is a need in the art for processes that use mixed gas sources, such as natural gas or biogas, and / or more refined hydrocarbon feedstocks (e.g., methane, ethane, propane, and butane, and combinations thereof) to form higher-value products. For those processes intended to produce acetylene, it would be advantageous to use mixed gas sources, such as natural gas or biogas, and / or more refined hydrocarbon feedstocks (e.g., methane, ethane, propane, and butane) as feedstocks to take advantage of the abundance of these feedstock materials while avoiding the limitations of other mixed gas conversion processes or hydrocarbon combustion processes. At the same time, there is a need in the art for processes that can produce acetylene in a convenient, economical manner using mixed gas sources, such as natural gas or biogas, and / or more refined hydrocarbon feedstocks. It would be particularly advantageous to produce acetylene with minimal impurities so that the acetylene can be used safely and substantially without further processing. Additionally, there is a further need in the art to provide alternative fuels, such as hydrogen, in a scalable and efficient manner. It is desirable to carry out these processes in a practical and environmentally responsible manner.

[0011] Acetylene also has utility as a fuel for various industrial applications, such as metal cutting. This application represents a large market comparable in size to acetylene's various petrochemical uses. Currently, acetylene's primary industrial use is as a fuel for oxyacetylene torches used to cut steel; in addition to cutting, acetylene is used in some welding, carburizing, and heat treating of steel. Oxyacetylene torches burn at a higher flame temperature (3,500 °C) than other oxy-fuel torches, such as oxyhydrogen (3,000 °C) and oxypropane (2,500 °C) torches, and oxyacetylene produces a smaller, more precise flame cone. These characteristics allow for higher quality and more precise cuts than comparable oxy-fuel cutting methods. Additionally, combustion of acetylene requires a smaller stoichiometric ratio of oxygen than other fuels, such as propane, and oxyacetylene torches consume less oxygen than other oxy-fuel torches, resulting in lower oxygen operating costs. Finally, the lower flame temperatures and higher oxygen requirements of other hydrocarbon fuel types, such as oxypropane torches, create a higher risk of incomplete combustion and the production of dangerous carbon monoxide in the working environment. For the aforementioned reasons, oxyacetylene cutting is the industry standard for cutting steel.

[0012] However, as previously noted, there are limitations to the production and transportation of acetylene. Therefore, obtaining acetylene for industrial cutting is costly and logistically difficult. First, acetylene used as torch fuel must be transported and stored in small metal cylinders due to the risk of explosion. To reduce the risk of explosion, the acetylene in the cylinder is dissolved in acetone, lowering its partial pressure and therefore the likelihood of explosion. Because acetone is present in the cylinder along with the acetylene, the acetylene can be withdrawn only at a low flow rate (e.g., not exceeding 1 / 7 of the vessel volume per hour), reducing the chance that acetone will be withdrawn into the bleed line along with the acetylene. Acetone in the gas supply can reduce the flame temperature and the quality of the cutting process. Even with a low bleed rate, the acetylene in the cylinder can be rapidly depleted; once depleted, the cylinder cannot be refilled on-site due to the risk of another explosion without expensive safety infrastructure and specialized skills. Due to the small size of the cylinders, they cannot be scaled up sufficiently for larger operations but instead must be connected in parallel by manifolding, adding to the complexity of the project. Also, due to the risk of explosion, the cylinders require several safety precautions when transported, adding cost and logistical challenges. [Prior art documents] [Patent documents]

[0013] [Patent Document 1] U.S. Patent No. 5,824,834 Summary of the Invention [Problem to be solved by the invention]

[0014] There remains a need in the art for a more streamlined, safer method of obtaining acetylene. It is desirable to avoid the need for acetone-containing cylinders as storage vessels for acetylene gas used in metalworking. For example, it would be useful to have acetylene fuel available on demand and when needed, avoiding the volume and flow rate constraints of cylinder storage. It would also be advantageous for acetylene to be produced close to the site of its use to avoid cylinder-specific difficulties associated with transportation. [Means for solving the problem]

[0015] overview In embodiments, a gas processing system for converting a hydrocarbon-containing inlet gas into an outlet gas product includes a gas delivery subsystem, a plasma reaction chamber, and a microwave subsystem, wherein the gas delivery subsystem is in fluid communication with the plasma reaction chamber and directs the hydrocarbon-containing inlet gas to the plasma reaction chamber, and the microwave subsystem directs microwave energy to the plasma reaction chamber to energize the hydrocarbon-containing inlet gas, thereby forming a plasma within the plasma reaction chamber, and the plasma results in conversion of hydrocarbons in the hydrocarbon-containing inlet gas into an outlet gas product comprising acetylene and hydrogen. In embodiments, the hydrocarbon-containing inlet gas can be derived from a mixed gas source, which can be natural gas or biogas; in embodiments, the hydrocarbon-containing inlet gas includes a gas selected from the group consisting of methane, ethane, propane, and butane, and the hydrocarbon-containing inlet gas can consist essentially of methane. In embodiments, the gas delivery subsystem includes a delivery conduit and a gas injector, the delivery conduit being in fluid communication with the gas injector, the delivery conduit delivering one or more gases to the gas injector, and the gas injector delivering the one or more gases to the plasma reaction chamber. The delivery conduit may include a feed gas delivery circuit that delivers a hydrocarbon-containing inlet gas to the gas injector, and the hydrocarbon-containing inlet gas may include or consist essentially of methane. In embodiments, the delivery conduit includes an additional gas delivery circuit that delivers an additional gas to the gas injector, and the additional gas may be hydrogen. In embodiments, the additional gas delivery circuit is an auxiliary gas delivery circuit that delivers an auxiliary gas to the gas injector, or the additional gas delivery circuit is a recycle gas delivery circuit that delivers a recycled gas to the gas injector. The recycled gas may include hydrogen, or the recycled gas may include a hydrogen-rich reactant gas that may consist essentially of hydrogen, or the recycled gas may consist essentially of a hydrogen-rich reactant gas.

[0016] In embodiments, the delivery conduit delivers each of the one or more gases to the gas injector through a separate path. In embodiments, the gas injector includes an injector body portion including two or more coaxially aligned separate gas feeds, where a first gas feed conveys a hydrocarbon-containing inlet gas to the plasma reaction chamber through a first set of one or more nozzles, and a second gas feed conveys an additional gas to the plasma reaction chamber through a second set of one or more nozzles. In embodiments, at least one of the one or more nozzles is oriented at an angle to the longitudinal axis of the plasma reaction chamber or at an angle to the lateral axis of the plasma reaction chamber. In embodiments, at least one of the one or more nozzles is oriented at an angle to the longitudinal axis or the lateral axis of the injector body portion. The combined gas flow from the first set of nozzles and the second set of nozzles generates a vortex flow within the plasma reaction chamber. In some embodiments, the plasma reaction chamber is disposed within an elongated reactor tube having a proximal end and a distal end, the elongated reactor tube being sized to interact with a microwave subsystem. The elongated reactor tube may be a quartz tube. The plasma reactor chamber may be disposed approximately in the center of the elongated reactor tube. In some embodiments, the gas injector conveys the hydrocarbon-containing inlet gas and the additional gas to the proximal portion of the elongated reactor tube, and the hydrocarbon-containing inlet gas and the additional gas flow distally from the proximal portion toward the plasma reaction chamber. The gas injector may be disposed centrally within the proximal portion, with the first set of one or more nozzles and the second set of one or more nozzles oriented circumferentially; alternatively, the gas injector is disposed peripherally within the proximal portion, with the first set of one or more nozzles and the second set of one or more nozzles oriented centrally. In embodiments, the microwave subsystem includes an applicator for directing microwave energy to a plasma reaction chamber, the plasma reaction chamber being disposed in a region of the elongated reactor tube that passes through and perpendicularly intersects the applicator. The applicator may be a single-arm applicator.In embodiments, the microwave subsystem further includes a power source, a magnetron, and a waveguide, where the power source energizes the magnetron to generate microwave energy, which is conveyed by the waveguide to an applicator, which directs the microwave energy to the reaction chamber within the elongated reactor tube, thereby forming a plasma within the plasma reaction chamber. The magnetron can generate L-band microwave energy. In embodiments, the plasma within the plasma reaction chamber generates effluent gaseous products, which flow distally within the plasma reaction chamber toward the distal end of the elongated reactor tube. The effluent products emerge from the distal end of the elongated reactor tube and enter an efficient separation and disposal subsystem. In embodiments, the effluent separation and disposable subsystem may include a solids filter and cold trap, and / or may include an adsorption column, and / or may include a pressure swing adsorption system adapted to remove non-hydrogen components from the effluent stream, and / or may include a temperature swing adsorption system adapted to remove higher acetylenes from the effluent stream, and / or may include an absorption column capable of absorbing acetylene, and / or may include a concentrated acid in an amount sufficient to oxidize higher hydrocarbons, and / or may include a catalyst suitable for converting higher hydrocarbons to derivative compounds separable from the effluent stream, and / or may include a condenser, and / or may include a gas separation membrane array capable of separating hydrogen from the effluent stream, and / or may include a hydrogen separation subsystem, which may be in fluid communication with a recycle gas delivery circuit, wherein hydrogen collected by the hydrogen separation subsystem is recycled to the recycle gas delivery circuit, and / or may include an acetylene separation subsystem. In embodiments, the system further includes a vacuum subsystem that maintains a first reduced pressure environment for effluent products passing through one or more components of the effluent separation and disposable subsystem. The vacuum subsystem may create a second reduced pressure environment within the extended reactor tube, and / or the vacuum subsystem may create a third reduced pressure environment for the gas delivery subsystem.In embodiments, the vacuum subsystem generates first, second, and third reduced pressure environments; in embodiments, the first, second, and third reduced pressure environments are in the range of about 30 to about 120 Torr. In embodiments, at least one of the reduced pressure environments is about 50 to about 100 Torr or about 60 to about 80 Torr. In embodiments, the first, second, and third reduced pressure environments are substantially similar. In embodiments, the system further includes a cooling subsystem. The cooling subsystem may include at least one of a water cooling subsystem and a gas cooling subsystem. In embodiments, the gas cooling subsystem includes a nitrogen-based cooling circuit, which may include one or more enclosures for components of the system, the one or more enclosures being sealed sufficiently to contain nitrogen gas around the components and exclude oxygen from the enclosures. In embodiments, the system includes a data management and safety subsystem.

[0017] Further disclosed herein is a method for treating a hydrocarbon-containing inlet gas to produce acetylene gas, the method comprising: providing the hydrocarbon-containing inlet gas; injecting the hydrocarbon-containing inlet gas into a reaction chamber; energizing the hydrocarbon-containing inlet gas in the reaction chamber with microwave energy to generate a plasma; forming gaseous products in the plasma, wherein one of the gaseous products is acetylene gas; and flowing the gaseous products out of the reaction chamber. In embodiments, the hydrocarbon-containing inlet gas is derived from a mixed gas source; the mixed gas source can be natural gas or biogas. In embodiments, the hydrocarbon-containing inlet gas comprises a gas selected from the group consisting of methane, ethane, propane, and butane, and the gas can consist essentially of methane. In some implementations, the method further comprises providing one or more additional gases simultaneously with providing the hydrocarbon-containing inlet gas, wherein the one or more additional gases can be selected from the group consisting of hydrogen, nitrogen, and a recycle gas. In embodiments, the recycle gas comprises a hydrogen-rich reactant gas, which can consist essentially of hydrogen. In some implementations, the method further comprises separating acetylene gas from the gaseous products after flowing the gaseous products out of the reaction chamber. In some implementations, the method further comprises recycling at least one of the gaseous products. In embodiments, at least one gaseous product can comprise or consist essentially of hydrogen gas.

[0018] Also disclosed herein is a method for converting a hydrocarbon-containing inlet gas to an effluent gas, the method comprising providing a hydrocarbon-containing inlet gas, directing the hydrocarbon-containing inlet gas to a gas treatment system described above, and using the gas treatment system described above to treat the hydrocarbon-containing inlet gas and convert the inlet gas to an effluent gas, wherein the effluent gas comprises acetylene. In an embodiment, the hydrocarbon-containing inlet gas is from a mixed gas source, which can be natural gas or biogas. In an embodiment, the effluent gas further comprises hydrogen.

[0019] Further disclosed herein is a metal cutting system, the system comprising the gas handling system described above and a storage system for containing the effluent gas product produced by the system; and an apparatus for metal cutting in fluid communication with the storage system, wherein the apparatus withdraws the effluent gas product from the storage system and ignites the gas product for use in metal cutting. In an embodiment, the apparatus is an acetylene torch or an oxyacetylene torch. In an embodiment, the metal cutting system further comprises a hydrogen separation system in fluid communication with the gas handling system described above, wherein the effluent gas flows to the hydrogen separation system, which separates the effluent gas into two product streams, one of which is an acetylene-rich gas; and the apparatus for metal cutting uses the acetylene-rich gas stored in the storage system as fuel for metal cutting.

[0020] That is, the gist of the present invention relates to the following. Item 1 1. A system for converting a hydrocarbon-containing inlet gas into a product outlet gas, the system comprising: including a gas delivery subsystem, a plasma reaction chamber, and a microwave subsystem; a gas delivery subsystem in fluid communication with the plasma reaction chamber for directing a hydrocarbon-containing inlet gas to the plasma reaction chamber; a microwave subsystem directing microwave energy to the plasma reaction chamber to impart energy to the hydrocarbon-containing inlet gas, thereby forming a plasma in the plasma reaction chamber, the plasma effecting conversion of hydrocarbons in the hydrocarbon-containing inlet gas to effluent gas products, the effluent gas products comprising acetylene and hydrogen. Section 2 2. The system of paragraph 1, wherein the hydrocarbon-containing inlet gas is derived from a mixed gas source. Section 3 3. The system of paragraph 2, wherein the mixed gas source is natural gas. Section 4 3. The system of paragraph 2, wherein the mixed gas source is biogas. Section 5 2. The system of paragraph 1, wherein the hydrocarbon-containing inlet gas comprises a gas selected from the group consisting of methane, ethane, propane, and butane. Section 6 6. The system of paragraph 5, wherein the hydrocarbon-containing inlet gas consists essentially of methane. Section 7 Item 1. The system of item 1, wherein the gas delivery subsystem comprises a delivery conduit and a gas injector, the delivery conduit being in fluid communication with the gas injector, the delivery conduit delivering one or more gases to the gas injector, and the gas injector delivering the one or more gases to the plasma reaction chamber. Section 8 8. The system of paragraph 7, wherein the delivery conduit comprises a supply gas delivery circuit that delivers the hydrocarbon-containing inlet gas to the gas injector. Section 9 9. The system of paragraph 8, wherein the hydrocarbon-containing inlet gas comprises methane. Item 10 10. The system of paragraph 9, wherein the hydrocarbon-containing inlet gas consists essentially of methane. Section 11 9. The system of paragraph 8, wherein the delivery conduit comprises a further gas carrying circuit that delivers further gas to the gas injector. Section 12 12. The system of paragraph 11, wherein the further gas is hydrogen. Item 13 12. The system of paragraph 11, wherein the further gas delivery circuit is an auxiliary gas delivery circuit that delivers an auxiliary gas to the gas insufflator. Item 14 12. The system of paragraph 11, wherein the further delivery circuit is a recycled gas delivery circuit that delivers recycled gas to the gas injector. Item 15 15. The system of paragraph 14, wherein the recycled gas comprises a hydrogen-rich reactant gas. Item 16 16. The system of paragraph 15, wherein the hydrogen-rich reactant gas consists essentially of hydrogen. Item 17 17. The system of paragraph 16, wherein the recycle gas consists essentially of hydrogen-rich reactant gas. Section 18 8. The system of paragraph 7, wherein the delivery conduit delivers each of the one or more gases to the gas injector through a separate pathway. Section 19 8. The system of paragraph 7, wherein the gas injector includes an injector body portion including two or more coaxially aligned separate gas feed bodies, a first gas feed body delivering a hydrocarbon-containing inlet gas to the plasma reaction chamber through a first set of one or more nozzles, and a second gas feed body delivering an additional gas to the plasma reaction chamber through a second set of one or more nozzles. Section 20 20. The system of paragraph 19, wherein at least one of the one or more nozzles is oriented at an angle to the longitudinal axis of the plasma reaction chamber or at an angle to the transverse axis of the plasma reaction chamber. Section 21 20. The system of paragraph 19, wherein at least one of the one or more nozzles is oriented at an angle relative to a longitudinal or lateral axis of the injector body. Section 22 20. The system of paragraph 19, wherein the combined gas flow from the first set of nozzles and the second set of nozzles creates a vortex flow within the plasma reaction chamber. Section 23 15. The system of paragraph 14, wherein the plasma reaction chamber is disposed within an elongated reactor tube having a proximal end and a distal end, the elongated reactor tube being dimensionally suitable for interaction with a microwave subsystem. Section 24 24. The system of paragraph 23, wherein the elongated reactor tube is a quartz tube. Section 25 24. The system of paragraph 23, wherein the plasma reaction chamber is located approximately midway along the elongated reactor tube. Section 26 24. The system of paragraph 23, wherein the gas injector delivers the hydrocarbon-containing inlet gas and the additional gas to a proximal portion of the elongated reactor tube, and the hydrocarbon-containing inlet gas and the additional gas flow distally from the proximal portion toward the plasma reaction chamber. Section 27 27. The system of paragraph 26, wherein the gas injector is centrally located in the proximal portion and the first set of one or more nozzles and the second set of one or more nozzles are oriented peripherally. Section 28 27. The system of paragraph 26, wherein the gas injector is peripherally disposed within the proximal portion, and the first set of one or more nozzles and the second set of one or more nozzles are centrally oriented. Section 29 24. The system of paragraph 23, wherein the microwave subsystem includes an applicator for directing microwave energy to the plasma reaction chamber, the plasma reaction chamber being disposed in a region of the elongated reactor tube that passes through and perpendicularly intersects the applicator. Item 30 30. The system of paragraph 29, wherein the applicator is a single-arm applicator. Item 31 30. The system of paragraph 29, wherein the microwave subsystem further comprises a power source, a magnetron, and a waveguide, wherein the power source energizes the magnetron to produce microwave energy, the microwave energy is conveyed by the waveguide to an applicator, and the applicator directs the microwave energy to a reaction chamber within the elongated reactor tube, thereby forming a plasma within the plasma reaction chamber. Section 32 32. The system of paragraph 31, wherein the magnetron produces L-band microwave energy. Item 33 32. The system of paragraph 31, wherein the plasma within the plasma reaction chamber produces effluent gaseous products that flow distally within the plasma reaction chamber toward the distal end of the elongated reactor tube. Section 34 34. The system of paragraph 33, wherein the effluent gaseous product emerges from the distal end of the elongated reactor tube and enters an effluent separation and disposal sub-system. Item 35 35. The system of paragraph 34, wherein the effluent separation and disposal sub-system comprises a solids filter and a cold trap. Section 36 35. The system of paragraph 34, wherein the effluent separation and disposable subsystem comprises an adsorption column. Section 37 35. The system of paragraph 34, wherein the effluent separation and disposal subsystem comprises a pressure swing adsorption system adapted to remove non-hydrogen components from the effluent stream. Section 38 35. The system of paragraph 34, wherein the effluent separation and disposal system comprises a temperature swing adsorption system adapted to remove higher acetylenes from the effluent stream. Item 39 35. The system of paragraph 34, wherein the effluent separation and disposable subsystem comprises an absorption column. Section 40 40. The system of paragraph 39, wherein the absorption column absorbs acetylene. Section 41 35. The system of paragraph 34, wherein the effluent separation and disposal subsystem contains concentrated acid in an amount sufficient to oxidize higher-order hydrocarbons. Section 42 35. The system of paragraph 34, wherein the effluent separation and disposal subsystem comprises a catalyst suitable for converting higher hydrocarbons to derivative compounds that can be separated from the effluent stream. Section 43 35. The system of paragraph 34, wherein the effluent separation and disposal subsystem comprises a condenser. Section 44 35. The system of paragraph 34, wherein the effluent separation and disposable subsystem comprises a gas separation membrane array. Section 45 35. The system of paragraph 34, wherein the gas separation membrane array separates hydrogen from the effluent stream. Section 46 35. The system of paragraph 34, wherein the effluent separation and disposal subsystem comprises a hydrogen separation subsystem. Section 47 47. The system of paragraph 46, wherein the hydrogen separation subsystem is in fluid communication with the recycle gas delivery circuit, and wherein hydrogen collected by the hydrogen separation subsystem is recycled to the recycle gas delivery circuit. Section 48 35. The system of paragraph 34, wherein the effluent separation and disposal subsystem comprises an acetylene separation subsystem. Section 49 35. The system of paragraph 34, further comprising a vacuum subsystem that creates a first reduced pressure environment for effluent products passing through one or more components of the waste separation and disposable subsystem. Item 50 50. The system of paragraph 49, wherein the vacuum sub-system creates a second reduced pressure environment within the extended reactor tube. Section 51 51. The system of paragraph 50, wherein the vacuum subsystem creates a third reduced pressure environment for the gas delivery subsystem. Section 52 52. The system of paragraph 51, wherein the vacuum sub-system generates first, second and third reduced pressure environments. Section 53 53. The system of paragraph 52, wherein the first, second, and third reduced pressure environments are within the range of about 30 to about 120 Torr. Section 54 54. The system of paragraph 53, wherein at least one of the reduced pressure environments is from about 50 to about 100 Torr. Section 55 55. The system of paragraph 54, wherein at least one of the reduced pressure environments is about 60 to about 80 Torr. Section 56 53. The system of paragraph 52, wherein the first, second and third reduced pressure environments are substantially similar. Section 57 2. The system of paragraph 1, further comprising a cooling subsystem. Section 58 58. The system of paragraph 57, wherein the cooling subsystem comprises at least one of a water cooling subsystem and a gas cooling subsystem. Section 59 59. The system of paragraph 58, wherein the gas cooling subsystem comprises a nitrogen-based cooling circuit. Item 60 60. The system of paragraph 59, wherein the nitrogen-based cooling circuit includes one or more enclosures for components of the system, the one or more enclosures being sealed sufficiently to contain nitrogen gas around the components and exclude oxygen from the components. Section 61 2. The system of paragraph 1, further comprising a data management and safety subsystem. Section 62 1. A method for treating a hydrocarbon-containing inlet gas to produce acetylene gas, comprising: providing a hydrocarbon-containing inlet gas; injecting a hydrocarbon-containing inlet gas into a reaction chamber; energizing a hydrocarbon-containing inlet gas within the reaction chamber with microwave energy to form a plasma; forming gaseous products within the plasma, wherein one of the gaseous products is acetylene gas; and flowing the gaseous product out of the reaction chamber. A method comprising: Section 63 63. The method of paragraph 62, wherein the hydrocarbon-containing inlet gas is derived from a mixed gas source. Section 64 64. The method of paragraph 63, wherein the mixed gas source is natural gas. Section 65 Item 64. The method of paragraph 63, wherein the mixed gas source is biogas. Section 66 63. The method of paragraph 62, wherein the hydrocarbon-containing inlet gas comprises a gas selected from the group consisting of methane, ethane, propane, and butane. Section 67 67. The method of paragraph 66, wherein the hydrocarbon-containing inlet gas consists essentially of methane. Section 68 63. The method of paragraph 62, further comprising providing one or more additional gases simultaneously with providing the hydrocarbon-containing inlet gas. Section 69 70. The method of paragraph 68, wherein the one or more additional gases are selected from the group consisting of hydrogen, nitrogen and recycled gases. Section 70 70. The method of paragraph 69, wherein the recycle gas comprises a hydrogen-rich reactant gas. Section 71 71. The method of paragraph 70, wherein the hydrogen-rich reactant gas consists essentially of hydrogen. Section 72 63. The method of claim 62, further comprising separating acetylene gas from the gas product after the step of flowing the gas product out of the reaction chamber. Section 73 63. The method of paragraph 62, further comprising recycling at least one of the gaseous products. Section 74 74. The method of paragraph 73, wherein the at least one gas product comprises hydrogen gas. Section 75 74. The method of paragraph 73, wherein at least one gaseous product consists essentially of hydrogen gas. Section 76 1. A method for converting a hydrocarbon-containing inlet gas to an outlet gas, comprising: providing a hydrocarbon-containing inlet gas; Directing a hydrocarbon-containing inlet gas to the system described in paragraph 1; and Item 1. Treating a hydrocarbon-containing inlet gas using the system of item 1 to convert the inlet gas to an effluent gas, wherein the effluent gas comprises acetylene. A method comprising: Section 77 77. The method of paragraph 76, wherein the hydrocarbon-containing inlet gas is derived from a mixed gas source. Section 78 78. The method of paragraph 77, wherein the mixed gas source is natural gas. Section 79 78. The method of paragraph 77, wherein the mixed gas source is biogas. Section 80 77. The method of paragraph 76, wherein the effluent gas comprises hydrogen gas. Section 81 The system according to item 1; a storage system for containing the effluent gas product produced by the system of paragraph 1; and Apparatus for cutting metal in fluid communication with a storage system wherein the device withdraws effluent gas products from a storage system and ignites the effluent gas products for use in cutting metal. Section 82 82. The metal cutting system of paragraph 81, wherein the device is an acetylene torch or an oxyacetylene torch. Section 83 82. The metal cutting system of claim 81, further comprising a hydrogen separation system in fluid communication with the system of claim 1, wherein the effluent gas flows to the hydrogen separation system, the hydrogen separation system separates the effluent gas into two product streams, one product stream being an acetylene-rich gas, and the apparatus for metal cutting uses the acetylene-rich gas stored in the storage system as a fuel for metal cutting. [Effects of the Invention]

[0021] The present invention may provide a system and method for treating gases. [Brief explanation of the drawings]

[0022] BRIEF DESCRIPTION OF THE DRAWINGS [Figure 1] FIG. 1 is a schematic diagram showing the various chemical reactions involved in the conversion of methane to hydrogen, carbon, and hydrocarbon products. [Figure 2] FIG. 2 shows a schematic diagram of a plasma-based hydrocarbon treatment system and its component subsystems. [Figure 3] FIG. 3 shows a schematic representation of the gas delivery subsystem. [Figure 4A] FIG. 4A illustrates an embodiment of a gas injector. [Figure 4B] FIG. 4B illustrates an embodiment of a gas injector. [Figure 5] FIG. 5 illustrates an embodiment of the microwave subsystem. [Figure 6] FIG. 6 illustrates an embodiment of the microwave subsystem. [Figure 7] FIG. 7 illustrates an embodiment of the microwave subsystem. [Figure 8] FIG. 8 is a schematic diagram showing a vacuum sub-system integrated with other sub-systems of a plasma-based hydrocarbon treatment system. [Figure 9] FIG. 9 is a block diagram of a plasma-based hydrocarbon treatment system and associated sub-systems. [Figure 10] FIG. 10 is a schematic diagram of the reaction chamber and its components. [Figure 11A] FIG. 11A is a schematic diagram of a gas injector in cross section. [Figure 11B] FIG. 11B is a schematic diagram of a gas injector in cross section. [Figure 12] FIG. 12 is a schematic diagram of the microwave subsystem. [Figure 13] FIG. 13 is a block diagram of a small scale system for gas processing. [Figure 14] FIG. 14 is a block diagram of a small scale system for gas processing. DETAILED DESCRIPTION OF THE INVENTION

[0023] Detailed Description Disclosed herein in more detail are systems and methods for converting C1-C4 hydrocarbons, including unsaturated hydrocarbons and saturated hydrocarbons such as methane (e.g., derived from mixed gas sources such as natural gas or biogas), to hydrogen, acetylene, and other carbon-based products. In embodiments, these systems and methods use non-thermal plasma generated by microwave energy to carry out these conversions. In embodiments, the systems and methods disclosed herein can be optimized (“tuned”) to maximize the efficient production of acetylene or hydrogen as products that can be isolated for further commercialization; in other embodiments, these systems and methods can be tuned to produce combinations of these gases for specific industrial purposes.

[0024] 1. Overview a. Non-thermal plasma Plasma, the fourth state of matter, is an ionized gas: any gas can be transformed into a plasma by applying sufficient energy to it, generating a significant density of charged species, namely electrons and ions. Plasma possesses some of the properties of gases, but unlike ordinary gases, these are due to the properties of the charged species present in the plasma state, because plasma responds to both electric and magnetic fields. Despite these properties, plasma is electrically neutral, a characteristic termed quasi-neutrality. In addition to ions and free electrons from precursor gases present in the plasma, plasma contains uncharged neutral gas species and precursor molecules that can enter into other chemical reactions. Some weakly ionized gases do not necessarily meet all the requirements of a plasma, but they can still possess many plasma-like properties that affect their behavior. For example, many high-pressure plasmas used in industrial applications fall into this category.

[0025] One of the fundamental properties of plasma is its temperature. Plasmas are used in chemical and industrial applications because they can produce temperatures much higher than those obtainable in traditional chemical engineering processes. In a plasma, energy is transferred to electrons, which then transfer energy to heavier particles through collisions. The electrons have a higher temperature than the heavier particles, and an equilibrium temperature is reached that reflects the collision frequency and radiation processes of the various particles in the plasma. The electron temperature (T) is close to that of the translational temperature (T) of the heavier particles. e ) are defined as thermal plasmas, with gas temperatures greater than 3,000 K. In contrast, in nonthermal plasmas, high-energy electrons can coexist with species with substantially lower temperatures. Therefore, the translational temperature T of a nonthermal plasma is proportional to the plasma's electron temperature T. e can be significantly lower than T e can approach 11,600 K in industrial plasmas or even higher temperatures in other types of plasmas.

[0026] The energy landscape of a plasma is more complex when the plasma contains molecules (such as H2, N2, or CH4) instead of just atoms. These molecules have the ability to store energy in various rotational and vibrational motions and therefore have rotational and vibrational temperatures associated with them. These temperatures for such plasmas generally lie between the translational and electronic temperatures of the plasma, and these temperatures can affect the behavior of the plasma and its associated chemistry. The technology disclosed herein is based on the ability of nonthermal plasmas to transfer a large portion of the electrical input energy to energetic electrons in the constituent feed gases rather than heating the gas itself. Electron collisions, ionization, dissociation, and excitation produce charged atomic and molecular species (e.g., electrons, ions, radicals) that can participate in chemical reactions.

[0027] Methane is particularly resistant to chemical transformations due to its stability: the cleavage of a C-H bond in methane requires 1664 kJ mol -1Using the techniques described below, non-thermal plasmas can be generated and utilized to break bonds in C1-C4 hydrocarbons, including methane bonds, to produce acetylene and molecular hydrogen with high efficiency and selectivity.

[0028] b. Microwave plasma generation In embodiments, the plasma used in these systems and methods is a microwave plasma formed by directing microwave energy at a methane-containing feed gas, as described in more detail below. While methane is used as an exemplary embodiment in this description, it is understood that other short-chain alkanes (e.g., ethane, propane, butane) may also be used as feed gases, either as single gas feed gases or in combination with each other or methane.

[0029] The microwave plasma process described herein is a gas-phase process that uses gaseous reactant precursors to form desired gaseous products. Due to the very fast oscillation frequency of the electric field relative to the molecular and electronic collision frequency, microwave-generated plasmas are often in a highly non-equilibrium state, meaning that the electronic and vibrational temperatures can be significantly higher than the gas temperature. In embodiments, collisions between charged species (electrons, ions) and uncharged species (molecules, atoms, particles) in microwave plasma transfer energy; this microwave-energized plasma supports a highly reactive chemical environment due to the energy contained in the plasma's free electrons. Due to the high degree of ionization of the precursor gas, the chemical dissociation and ionization of intermediates, and the high vibrational and excitational energy in the plasma, the desired chemical reactions described below proceed rapidly and efficiently.

[0030] Without being bound by theory, it is understood that microwave irradiation works to generate plasma from gaseous precursors as follows: When a precursor gas (e.g., methane) is subjected to microwave irradiation that meets or exceeds the dielectric strength of such gas, free electrons in the microwave field region (provided from background irradiation or other sources) can acquire sufficient energy from the microwave electric field during collisions with neutral molecules and ionize other atoms or molecules. The secondary ionized electrons are then accelerated in a direction governed by the electric field of the microwave irradiation, and they also gain energy until they cause another ionization event. This process of ionization progresses through the microwave field region until a steady state is reached. The final number of electrons in the plasma is primarily determined by the plasma's electron loss processes, such as diffusion, recombination, and attachment.

[0031] The systems and methods disclosed herein use C1-C4 hydrocarbons, such as methane, as reactant precursor gases that are subjected to microwave irradiation. Methane can be used to illustrate reactant precursor gases suitable for use in these systems and methods.

[0032] The above-mentioned ionization of methane in plasma initiated by collisions with energized electrons results in CH x The primary initiation reaction is the cleavage of the C-H bond in methane, resulting in the formation of CH, CH, CH, H, and C. These radicals can recombine to form the following radicals: CH3* + CH3* → C2H6 CH2* + CH2* → C2H4 CH* + CH* → C2H2 CH3* + CH* → C2H4 CH3* + CH2* → C2H4+ H* CH3* + CH* → C2H4 CH3* + CH* → C2H2+ H2 CH2* + CH* → C2H2+ H* A two-carbon fragment exemplified by:

[0033] Methane can also be bonded to various radicals to form the following formula: CH4+ CH3* → C2H6+ H* CH4+ CH2* → C2H6 CH4+ CH2* → C2H4+ 2H* / H2CH4+ CH* → C2H4 CH4+ CH* → C2H2+ H* + H2 A two-carbon fragment exemplified by:

[0034] In addition to the illustrated reaction to form two-carbon fragments and hydrogen, higher hydrocarbons can be formed by recombination of the plasma-generated radicals with each other and with the precursor gas. As used herein, the term "higher hydrocarbon" refers to any hydrocarbon having three or more carbon atoms, including aromatics, whether saturated or unsaturated.

[0035] Additionally, complete dehydrogenation of methane can occur, resulting in the formation of elemental carbon and hydrogen gases. Representative reactions are shown in Figure 1. As shown in Figure 1, some exemplary reactions that result in hydrocarbons are shown within the dotted line, and the elemental products (hydrogen and carbon) are shown outside the dotted line.

[0036] In embodiments, parameters can be optimized to maximize acetylene formation. In other embodiments, parameters can be optimized to maximize hydrogen formation. For example, as a general principle, if the feed gas entering the plasma reaction chamber contains less hydrogen compared to the hydrocarbon input, the output will be more hydrogen formed, potentially in combination with more carbon solids. Following this principle, to maximize hydrogen formation, a pure hydrocarbon feed can be used, producing more of the desired hydrogen in addition to a certain amount of carbon solids. Factors that influence product selectivity (e.g., allowing preferential formation of acetylene over other species, or allowing preferential formation of hydrogen over hydrocarbon products) include, but are not limited to, the identity of the reactant precursor gas, the addition of other gases to the system, the flow rate of any gases entering the system, the temperature and pressure within the reactor system, the amount and flow geometry of microwave power used to generate the plasma, the energy density within the reaction zone, the configuration of the electric field around the plasma, and the geometry and dimensions of the reactor vessel. In embodiments, static electric and magnetic fields can be used to influence plasma behavior and therefore product selectivity.

[0037] c. Precursor gas For the systems and methods disclosed herein, C1-C4 alkane hydrocarbons (e.g., methane, ethane, propane, and butane) or other hydrocarbon gases may be used as precursor gases, alone or in combination with other gases. In embodiments of these systems and methods, methane is the primary precursor gas. In embodiments, methane may be combined with hydrogen and / or nitrogen upon entering the plasma reaction chamber to form a single gas mixture that is energized to a plasma state. In embodiments, methane enters the plasma reaction chamber through its own set of nozzles, and other gases (such as hydrogen and / or nitrogen) are added to the plasma reaction chamber separately through a different set (or sets) of nozzles. Methane can be used in a pure state, or methane can be introduced into the system as a component of a commercially available gas stream.

[0038] Mixed gas sources such as natural gas or biogas are particularly advantageous sources of this precursor gas. As used herein, the term "biogas" refers to the mixed gas produced by the anaerobic decomposition of organic waste materials in various natural or man-made environments; the term "biogas" includes all such natural or man-made environments in which such gas-producing anaerobic decomposition can occur, such as landfills, manure ponds, municipal waste sites, sewage treatment plants, agricultural waste sites, permafrost spoil, etc. Biogas collected or recovered from these sites can be treated or upgraded to increase its methane content and remove impurities, making it particularly suitable as a precursor gas for the systems and methods disclosed herein.

[0039] Biogas, derived from feedstocks such as municipal waste, agricultural waste, plant material, sewage, fertilizer, food waste, or other natural or man-made organic sources, is typically formed in a closed system through anaerobic digestion or fermentation of organic material. The first stage of this process is hydrolysis, in which insoluble organic polymers are broken down into sugars and amino acids, which serve as substrates for the activity of anaerobic acidogenic bacteria. In the second stage, these bacteria convert the sugars and amino acids into carbon dioxide, hydrogen, ammonia, and organic acids; the acidogenic bacteria further convert the organic acids into acetic acid, ammonia, and carbon dioxide. In the third stage, another population of anaerobic bacteria, methanogenic microorganisms, convert these fermentation products into methane and carbon dioxide. Biogas, which contains a mixture of methane and carbon dioxide along with gaseous by-products such as hydrogen sulfide, can be collected and treated to remove carbon dioxide and undesirable gaseous products, leaving a gaseous mixture with a high concentration of methane suitable for energy generation or further processing. The methane in biogas can be concentrated using the process of biogas upgrading, resulting in a product with performance characteristics similar to fossil-fuel derived natural gas.

[0040] Biogas upgrading can involve processes such as water washing, adsorption, membrane separation, and amine gas treatment. The upgrading process can be advantageously carried out to remove oxygen from the biogas before using it as a gas source. Oxygen in the feed gas can make the feed gas vulnerable to combustion; furthermore, oxygen can corrode equipment used in the plasma-based hydrocarbon treatment systems disclosed herein. Furthermore, under certain circumstances, oxygen removal may be necessary to meet regulatory standards or other purity requirements. Several oxygen removal techniques are suitable for use with biogas. For example, oxygen can react with reduced metal species, oxidizing the metal and consuming oxygen. The oxidized metal species can then be regenerated back to their active form by passing a hydrogen- or carbon monoxide-containing stream over the metal species to reduce them, producing water or carbon dioxide, respectively. Metal species such as palladium or nickel can be used to catalytically combust oxygen at temperatures >500°F with hydrocarbon species mixed with O2. As an alternative approach, solid impurity scavengers can be used in a disposable manner to trap oxygen. For example, Fe2S3 can react with 3 molar equivalents of molecular oxygen to form rust and elemental sulfur. As yet another approach, oxygen can be separated from other gases by molecular sieves such as 5A or 13X molecular sieves, similar to technology found in air separation units (ASUs). Other upgrading processes for biogas are available to those skilled in the art using no more than routine experimentation. Upgraded biogas can reach purity and quality similar to natural gas in US pipelines and can be used for the same purposes.

[0041] When extracted from the ground, natural gas is primarily methane, making it a useful source of precursor gas for these systems and processes. Typically, natural gas also contains higher hydrocarbons such as ethane, propane, butane, and pentane, in addition to non-hydrocarbon impurities. The following table (Table 1) shows an exemplary composition of natural gas. [Table 1]

[0042] Natural gas is typically processed to remove most of the non-methane components before making it available for commercial or residential use, so that when it reaches consumers, it is nearly pure methane. As an example, commercially available natural gas may contain about 96% methane. While an extensive system of pipelines exists in the United States to transport natural gas to consumer markets after removing its impurities, much natural gas is found in areas far from these markets and from pipeline infrastructure (often referred to as remote or "stranded" natural gas). In embodiments, the systems and methods disclosed herein can be used in situ, for example, at stranded natural gas sites, to convert natural gas to acetylene and other useful products; thus, these systems and methods provide an economical way to utilize this stranded natural gas as a resource.

[0043] 2. Systems and Subsystems In embodiments, the plasma-based hydrocarbon processing system disclosed herein may include six subsystems: 1) gas delivery subsystem, 2) microwave subsystem, 3) vacuum subsystem, 4) refrigeration subsystem, 5) effluent separation and disposal subsystem, and 6) data management and safety subsystem. These subsystems are described in more detail below. The integration of these subsystems is shown schematically in Figure 2. Desired outputs from these subsystems and methods may include high methane conversion and high acetylene selectivity and / or high hydrogen selectivity.

[0044] As shown schematically in FIG. 2, plasma-based hydrocarbon processing system 200 provides for the conversion of one or more inlet gases 202, 204, and 208 to a mixture of gaseous products contained in an effluent stream 212 resulting from a plasma reaction chamber 214, where the plasma reaction chamber contains a plasma generated by a microwave subsystem 218. In the embodiment shown, hydrocarbon inlet gas 202, e.g., methane, enters plasma reaction chamber 214 separately from a hydrogen-containing inlet gas 208 produced from recycling a certain fraction of effluent stream 212. An optional auxiliary gas 204, such as nitrogen, may be introduced separately as shown or may be mixed with one or both of the other inlet gases 202 and 208. The various inlet gas streams and their direction to plasma reaction chamber 214 are contained in gas delivery subsystem 210, which is responsible for producing the appropriate ratios of inlet gases and controlling their flow rates. Once the inlet gas enters the plasma reaction chamber 214, it is energized by microwaves generated by microwave subsystem 218, thereby creating a plasma state within the plasma reaction chamber 214. The effluent stream 212 carries effluent (or "produced") gaseous products including acetylene, hydrogen, and a mixture of unreacted methane and higher hydrocarbons. Carbon solids may be entrained in the effluent gas stream 212. The effluent separation and disposal subsystem 220 allows for the separation of waste components from the effluent stream 212 so that they may be disposed of, and further allows for the separation of desired components into a separate stream, if desired, for further commercialization or reintroduction into the plasma reaction chamber 214 as the inlet gas 208. For example, acetylene 224 may be separated from the effluent stream 212 in the separation / disposal subsystem 220, and the acetylene may be used commercially. In embodiments, for example, the acetylene may be further purified for use in chemical reactions. In other embodiments, the acetylene may be further processed to either form other compounds or to form elemental carbon for other uses or disposal. In embodiments, the carbon solids entrained in effluent gas stream 212 may be removed by separation / disposal subsystem 220 as another product or waste material 222.In the embodiment shown, a recycle stream 228, primarily hydrogen, emerges from the separation / disposal subsystem and is recycled back to the plasma reaction chamber 214 as inlet gas 208. In other embodiments, some or all of the hydrogen produced by the reactor can be separated from the effluent stream 212 and separately commercialized. In still other embodiments, separation of the effluent stream 212 components proceeds differently: for example, carbon can be separated overall, and the mixed hydrogen and hydrocarbon gas stream is separated for commercialization or other uses. The separation / disposal subsystem can be configured to separate single gases or gas mixtures according to specific gas processing goals. As shown schematically in FIG. 2, a vacuum subsystem 230 surrounds certain system components to maintain them at low pressure. A cooling subsystem (not shown) provides appropriate cooling to each system component.

[0045] In embodiments, several system parameters, including input gas flow rate (SLM), input pressure, and power per converted hydrocarbon (e.g., methane), can be modified to optimize hydrocarbon (e.g., methane) conversion rate and acetylene or hydrogen selectivity. Table 2 shows the effect of varying these parameters. A useful metric for comparing results of different system parameters is efficiency, calculated as energy used per molecule of methane converted (eV / CH4). This metric is easily applied to both industrial applications, such as production cost per kg of product, and scientific applications, such as comparisons to bond strength and calculations of thermodynamic efficiency. [Table 2]

[0046] a. Gas Delivery Subsystem In embodiments, a gas delivery subsystem is constructed to direct inlet gases to the plasma reaction chamber. The gas delivery subsystem includes two components: a delivery conduit and a gas injector. Included in the description of this subsystem is a further description of: (i) the gas supplied to the reactor (inlet gas); (ii) a delivery conduit for transporting the inlet gases to the plasma reaction chamber, where the delivery conduit includes one or more separate circuits (or "transport circuits") for gas flow, which may include a main supply gas transport circuit, a secondary gas transport circuit for additional gases in addition to the main supply gas, and / or a recycle gas transport circuit for allowing the return of one or more produced gases (e.g., hydrogen) to be used as inlet gases for subsequent reactions; and (iii) a gas injector assembly in fluid communication with the delivery conduit and its component transport circuit, which introduces the component inlet gases into the plasma reaction chamber itself.

[0047] i. Inlet gas The inlet gases can include various combinations of precursor reactant gases, such as C1-C4 alkane hydrocarbons. The precursor reactant gases provide hydrogen or carbon for further reaction in the plasma. In embodiments, the inlet gases are methane and hydrogen, with nitrogen optionally combined with the methane. In some embodiments, methane and hydrogen are reactants. The ratios of the reactant gases, along with the optional nitrogen additive, can be empirically varied to optimize the product profile and yield.

[0048] The inlet gas used by the plasma-based hydrocarbon processing system can be supplied directly from a supply tank, a supply line, and / or via a recycle. As used herein, the term "inlet gas" refers to any gas added to the plasma reaction chamber where the plasma is formed. The inlet gas can be a reactant gas, such as methane or hydrogen, which is converted into various products by the plasma state, as described in FIG. 1. The inlet gas can also be a supplementary added gas, such as nitrogen. The inlet gas can be supplied from an external gas source, referred to as a "feed line," or from an internal system recycle, where gases produced by the system are reintroduced, in whole or in part, into the plasma reaction chamber for subsequent reaction.

[0049] Inlet gas entering the system via an external gas source or supply line can originate from a gas reservoir such as a storage tank, or from an externally located flowing gas line, such as a mixed gas supply line (e.g., a natural gas line or a biogas line). In embodiments, the inlet gas comprises solely (or substantially solely) the reactants methane and hydrogen, with no further gaseous additives intentionally added. The methane in the inlet gas can be obtained as a component of a more complex flowing gas mixture, such as natural gas or biogas. In embodiments, methane and optionally nitrogen are supplied from a supply line (i.e., a storage tank or flowing gas line), while hydrogen can be supplied from a storage tank or recycled from the product stream and directed back to the reactor.

[0050] The recycle gas stream used for in-situ recycle is the exhaust (i.e., effluent gas) from the plasma reaction chamber, optionally separated into various component gases, some or all of which gas(es) are reintroduced into the plasma reaction chamber. In embodiments, the hydrogen in the effluent gas product stream is separated from the other gases and recycled in purified form. In embodiments, the hydrocarbon inlet gas is introduced into the plasma reaction chamber via a flowing gas supply line, e.g., a natural gas line or a biogas line, while hydrogen is introduced into the plasma reaction chamber separately from the hydrocarbon inlet; this hydrogen can be derived in whole or in part from the recycle gas stream.

[0051] In embodiments, the recycled gas may comprise a hydrogen-rich reactant gas, where hydrogen is the major component, with some hydrocarbons also present that may react. The hydrogen-rich reactant gas may consist essentially of hydrogen, i.e., about 95% or more hydrogen, or about 96% or more hydrogen, or about 97% or more hydrogen, or about 98% or more hydrogen, or about 99% or more hydrogen. In embodiments, the hydrogen-rich reactant gas comprises about 90% or more recycled gas, or about 91% or more recycled gas, or about 92% or more recycled gas, or about 93% or more recycled gas, or about 94% or more recycled gas. In embodiments, the recycled gas consists essentially of the hydrogen-rich reactant gas, i.e., the hydrogen-rich reactant gas comprises about 95% or more recycled gas, or about 96% or more recycled gas, or about 97% or more recycled gas, or about 98% or more recycled gas, or about 99% or more recycled gas. In embodiments, the recycled gas comprises a non-reactant gas, such as nitrogen, in addition to the hydrogen-rich reactant gas. In embodiments, the remainder of the recycle gas, excluding the hydrogen-rich reactant gas, is nitrogen. In other embodiments, nitrogen is added as a separate auxiliary gas independent of its presence or absence in the recycle gas. The volumes of hydrogen and nitrogen used in the system can be expressed relative to the total methane flow. For example, the following inlet gas feed ratios can be used: methane:hydrogen:nitrogen, 1:0 to 3:0.1; in other embodiments, the following inlet gas feed ratios can be used: methane:hydrogen:nitrogen, 1:1 to 2:0.1. In embodiments, similar ratios of methane and hydrogen can be used in the absence of nitrogen. In one embodiment, a methane flow of 300 to 400 SLM (about 11 to 14 SCFM) to the reactor can be used. In one embodiment, a methane flow of about 380 SLM (13.4 SCFM) can be used. In embodiments, these flows are appropriate for a reactor power of 100 kW.

[0052] In embodiments, the amount of hydrogen entering the reactor can be varied to select for more or less acetylene production. Increasing the amount of hydrogen entering the reactor increases the amount of this gas available to react with methane, thereby improving conversion selectivity for acetylene production and reducing the amount of undesirable soot buildup. In embodiments, increasing the amount of hydrogen entering the reactor reduces the amount of ethylene in the effluent relative to acetylene.

[0053] In embodiments, hydrogen is provided from a hydrogen cylinder. In other embodiments, hydrogen can be provided by recycling hydrogen produced by the entire system: i.e., hydrogen produced from a C1-C4 hydrocarbon feedstock, such as methane, in the plasma reaction can be reused as a reactant. In some embodiments, a recycle gas delivery circuit that delivers hydrogen back to the system as an inlet gas can be combined with another inlet source of hydrogen, for example, from a hydrogen supply tank, to regulate this hydrogen input. This approach can be advantageous at certain points during the production cycle, such as at the start of the system when recycled hydrogen has not yet been produced, or to maintain hydrogen inlet at a constant level regardless of fluctuations in the hydrogen produced during recycle.

[0054] In one embodiment, the gas delivery subsystem can be pre-charged, for example, at the start of the system, to balance the gas mixture and to coordinate the gas flow with microwave energy. First, the system can be evacuated and set at a near-vacuum pressure. Second, the system can be charged from an external source of hydrogen, either back-charged with hydrogen introduced into the recycled gas transport circuit, or front-filled from a separate hydrogen inlet line. Third, C1-C4 hydrocarbons (e.g., methane) or C1-C4 hydrocarbon / nitrogen mixtures can be added as inlet gases, with the flow measured by a flow meter. Using a system pre-charged with the appropriate gases in this manner, the reactor can be energized and the inlet gas can be processed. As the inlet gas is processed in the plasma reaction chamber, hydrogen is produced in the outlet gas product stream along with other gas products. Hydrogen captured from the outlet gas product stream can then be recycled to the system, simultaneously reducing the external hydrogen input. Balancing the external and internal hydrogen inputs (from the external supply line and from the recycle) can facilitate a smooth start-up procedure for the overall system.

[0055] In embodiments, methane is the primary component of the hydrocarbon-containing inlet gas for the plasma-based hydrocarbon gas treatment described in these systems and methods. In embodiments, methane can be introduced from a gas cylinder, a pipeline, or from an inlet gas mixture (e.g., natural gas or biogas) as previously described. A series of compressors can be used so that methane is introduced at a precise pressure, e.g., a feed pressure of at least about 2 atm. When natural gas or biogas is used to provide the methane feed gas, the amount of available methane can be monitored, e.g., using a benchtop gas chromatograph, and impurities in the natural gas can be identified and removed. For example, if the natural gas or biogas feed contains sulfur, the sulfur can affect the purity of the acetylene product stream; such impurities must be removed prior to treatment. Various impurities commonly found in natural gas or biogas (e.g., carbon dioxide, mercaptans, hydrogen sulfide, etc.) can be removed by a series of pre-scrubbers, where the type of scrubber selected depends on the impurities to be removed.

[0056] Desirably, the methane-containing gas mixture can contain a high concentration of methane such that it is substantially free of impurities or other gases. Natural gas derived directly from a natural source without commercial processing can contain about 90% or more methane. However, commercially available processed natural gas or equivalently processed biogas can be substantially free of non-methane gases and impurities. Hydrocarbon-containing inlet gases from such sources are considered to consist essentially of methane, and this term refers to inlet gases containing about 95% or more methane. Such gases consisting essentially of methane can contain, for example, about 95% or more methane, or about 96% or more methane, or about 97% or more methane, or about 98% or more methane, or about 99% or more methane. Gases provided from natural sources, such as in-situ natural gas (found in mining wells prior to treatment) or biogas, may contain lower amounts of methane, but have higher concentrations of methane because they can be pre-treated for use as hydrocarbon-containing inlet gases; in embodiments, such pre-treated gases consist essentially of methane when used as hydrocarbon-containing inlet gases for these systems and methods.

[0057] In embodiments, other auxiliary gases may be used as components of the inlet gas stream or as additives to the gas stream, such as nitrogen, carbon dioxide, and / or other reactive or inert gases. In one embodiment, nitrogen may optionally be used as a component of the inlet feed gas; nitrogen may also be used as a seal gas for the vacuum pump described below. In one embodiment, the inlet feed gas contains about 10% nitrogen, although this amount may be varied or adjusted to optimize the efficiency and selectivity of acetylene production; in other embodiments, nitrogen may be present in an amount from about 0% to about 10%, either intentionally added or present externally, for example, as a trace component found externally in the feed gas. In other embodiments, no additional nitrogen is included. In addition to using nitrogen as an inlet gas component, nitrogen in gaseous and liquid form may be used as part of a refrigeration subsystem to cool various components and provide a nitrogen "buffer" around the reactor, as described below. Carbon dioxide can be included as a separate component of the inlet gas or can be mixed with the reactor effluent to serve as an internal standard for gas chromatography analysis of the reactor effluent. In one embodiment, carbon dioxide is added to the effluent in an amount 30% of the methane feed to achieve good accuracy in downstream gas chromatography measurements. In addition to the reactant gases, other auxiliary gases can be used as inlet gases, such as helium and argon for gas chromatography.

[0058] ii. Gas delivery conduit The gas delivery conduit carries various inlet gases (including reactant gases, additive or auxiliary gases, and recycle gases) to the gas injector; the gas injector delivers the various inlet gases to the plasma reaction chamber. The gas delivery conduit contains transport circuits specialized for specific gas streams: the feed gas is transported within the feed gas transport circuit, additional gases are transported by one or more additional gas transport circuits, and the recycle gas(es) are transported by one or more recycle gas transport circuits. In embodiments, these systems and methods use a hydrocarbon-bearing inlet stream, such as a methane stream or a mixed gas stream (e.g., natural gas or biogas), as the main gas feed, and the main gas feed is transported by the feed gas transport circuit. In embodiments, additional gas streams in addition to the main gas feed can also pass through the gas delivery conduit, adding an inert gas such as nitrogen and / or adding a reactant such as hydrogen as a separate stream via their designated transport circuits. Further, in embodiments, a recycle gas stream may be added to the mixture through a recycle gas delivery circuit, as described in more detail below; the recycle gas stream may contain hydrogen as a major component, along with small amounts of unreacted methane and other hydrocarbon components. In embodiments, each delivery circuit is in fluid communication with a gas injector assembly and delivers its gas separately to the gas injector assembly, for example, through specialized nozzles, valves, or conduits.

[0059] A schematic diagram of an embodiment of a gas delivery subsystem 300 in accordance with these systems and methods is shown in Figure 3. As shown in this figure, a hydrocarbon-bearing inlet gas stream 302 is combined with a hydrogen-bearing inlet gas stream 304 and an optional auxiliary gas stream 308 to enter a plasma reaction chamber 310. In the embodiment shown, the three gas streams enter through a gas injector 312 (described in more detail below), which disperses the various flows in a direction and velocity such that a vortex-like intermingling 314 of the three separate flows occurs in the plasma reaction chamber 310. The mixed gases in the vortex-like intermingling 314 enter a reaction region 318 of the plasma reaction chamber 310, where they are energized by microwave energy generated in a microwave subsystem 322 to form a plasma 320 within the reaction region 318 of the plasma reaction chamber 310. In the embodiment shown, input gases 302, 304, and 308 each enter gas injector 312 as separate streams through separate inlets, and each enters plasma reaction chamber 310 from the gas injector through its own outlet. The flow direction, flow velocity, and flow rate from each outlet are oriented such that it creates vortex mixing 314 of the gases within plasma reaction chamber 310.

[0060] The inlet gas can be introduced into the plasma reaction chamber in a constant or variable flow pattern, in a continuous or discontinuous flow pattern, and in any combination of these patterns. In embodiments, the variable flow pattern can be regular or irregular in its variability, and the pattern can include intermittent pulses or surges of flow superimposed on an underlying waveform that describes the flow pattern. A sinusoidal flow pattern is an example of a variable flow pattern, as are stepped or "boxcar" flow patterns that use square waves to delineate different amounts of flow. In embodiments, these variable flow patterns are discontinuous because they can include periods of no flow. In embodiments, the gas can be introduced through all inlets simultaneously, or the gas can be introduced through different inlets at different times. The gas can be introduced at different flow rates and with different flow patterns at each inlet. For example, the feed gas can be introduced continuously with a constant flow pattern, while one or more auxiliary gas streams can be introduced discretely, i.e., discontinuously. Or, for example, the feed gas can be introduced discontinuously (i.e., with interruptions in its flow) and one or more auxiliary gases can be introduced variably and / or discontinuously, such that the auxiliary gas flows and the feed gas does not. Or, as another example, the feed gas can be introduced continuously in a continuous flow pattern, while one or more auxiliary gases can be introduced continuously but with a different flow pattern than the feed gas. Other combinations of continuous / discontinuous patterning and flow pattern variability can be designed to achieve specific gas treatment goals, such as to reduce soot formation in the plasma reaction chamber or to increase acetylene selectivity or to allow for intermittent cleaning of the interior of the reaction tubes.

[0061] As previously described, gases energized into a plasma state undergo a spectrum of reactions such that the hydrocarbon feed gas is converted to other hydrocarbons and hydrogen. Figure 3 shows an effluent stream 324 resulting from plasma 320, which includes the desired hydrocarbon product(s), certain extraneous hydrocarbon products, and hydrogen gas. The components of effluent stream 324 are separated from one another by effluent separation / disposal system 328, previously described.

[0062] iii. Gas injector The gas injectors introduce various inlet gas streams into the plasma reaction chamber through multiple inlets. In embodiments, gas injectors containing flow channels for various inlet gas streams can be printed out from high-temperature resin. The gas injectors can be deployed within the reactor or positioned in fluid communication with the reactor at various distances from the plasma reaction chamber within the reactor, where the term "plasma reaction chamber" refers to the region within the reactor where microwave energy encounters the feed gas streams. In one embodiment, the gas injectors can be positioned at the proximal end of the reactor, allowing for antegrade gas flow from proximal to distal along the longitudinal axis of the reactor. In other embodiments, the gas injectors can be positioned at the distal end of the reactor or at any other location along the longitudinal axis of the reactor. In embodiments, the gas injectors are positioned centrally within the reactor tube, with gas flow directed circumferentially. In other embodiments, the gas injectors are positioned circumferentially within the reactor tube, with gas flow directed centrally. The gas flow exiting the nozzles can be directed at any angle along the long axis of the tube, so that the gas can flow axially proximally or distally. The nozzles can be aligned to produce symmetric or asymmetric vortex flows.

[0063] In embodiments, the inlet gas flow can be directed by a gas injector to create a helical or vortical gas flow, which helps mix the various gas streams. The gas injector is configured to provide a separate nozzle or port for each inlet gas stream as it enters the reactor. The vortical flow can result from a gas injector device centrally located within the reactor having two or more nozzles or ports, where each inlet gas is delivered separately through its own subset of one or more nozzles or ports. In one embodiment, these centrally located nozzles or ports within the reactor can be oriented toward the periphery and angled to create a desired gas flow pattern. In other embodiments, the vortical flow can be generated by gas flowing into the reactor through a gas injector having two or more nozzles or ports aligned along the periphery of the reactor, where each inlet gas is delivered separately through its own separate subset of two or more nozzles or ports. In embodiments, the vortical flow acts to confine the plasma toward the interior region of the reactor. As will be appreciated by those skilled in the art, additional vortex flow configurations, such as reverse vortex flow, may also be used.

[0064] Figures 4A and 4B show embodiments of gas injectors compatible with these systems and methods. Figure 4A shows a cross-section of the proximal portion of the reaction chamber 402 of a plasma reactor 400, in which the gas injector 404 is centrally located; the proximal location of the cross-section shown in Figure 4A is indicated by line A in Figure 3. This gas injector 404 shown in Figure 4A encloses two coaxial but separate gas flows: a central gas flow 408 and a secondary gas flow 410. The central gas flow 408 contains a primary feed gas, which may include one gas, e.g., methane, as the primary reactant. The secondary gas flow 410 contains a separate and different gas, e.g., an additional or supplemental gas, such as hydrogen; this gas may also be a recycled gas, such as hydrogen. Alternatively, the central gas flow 408 may contain an additional gas, while the secondary gas flow contains the primary feed gas. In other embodiments (not shown), the recycled gas flow can be maintained in a separate coaxial chamber separate from the flow channel for the auxiliary gas, with each flow channel having its own set of one or more gas nozzles entering the plasma reaction chamber 402. For the injector design shown in Figure 4A, central gas flow 408 exits gas injector 404 through the center of central gas nozzle 412, which is directed distally and is seen here only in cross section, while secondary gas flow 410 exits gas injector 404 through peripherally directed gas nozzles 412a and 412b. As shown in this figure, secondary gas nozzles 412a and 412b are oriented at an angle such that secondary gas flows 414a and 414b enter plasma reaction chamber 402 and form a gas vortex within reactor 400.

[0065] FIG. 4B shows a longitudinal cross-section of an embodiment of a gas injector 450 incorporating the principles illustrated in FIG. 4A. The gas injector 450 shown in FIG. 4B illustrates a coaxial alignment of a central gas flow 452 surrounded by a secondary gas flow 454. The gas injector 450 is centrally positioned within a reactor (not shown in this figure), and gas flows from the central gas flow 452 and the secondary gas flow 454 exit the gas injector 450 and flow into the reactor. The second gas nozzles 458a and 458b can be aligned at an angle (shown in FIG. 4A) such that the secondary gas exiting these nozzles is directed to generate a vortex flow. Similarly, the gas exiting the first gas nozzle 460 can be directed to generate or contribute to a vortex flow. In embodiments, the vortex flow created within reactor 400 by gas injector 450 allows for mixing of the gases, which in turn can optimize the exposure of the gas flow to the plasma.

[0066] b. Microwave sub-system In an embodiment, the microwave subsystem includes various components used to generate, direct, and apply microwave power to form a non-thermal plasma that converts a feed gas into its products.

[0067] Schematic diagrams of embodiments of a microwave subsystem are shown in FIGS. 5 and 6, which are described in more detail below. FIG. 5 provides an overview of the subsystem components. As shown in FIG. 5, an embodiment of microwave subsystem 500 includes a power source 502, a magnetron 504, a waveguide assembly 508, and an applicator 510, where microwave energy generated by magnetron 504 encounters an inlet gas within a plasma reaction chamber 512 within an elongated reactor tube 514 (seen here in cross section) to generate plasma. Reactor tube 514 may be made of quartz, as described in more detail below. In one embodiment, to energize the magnetron, power source 502 requires 480 V, 150 A AC power to generate 20 kV, 5.8 A low-ripple DC power at 96% efficiency. In one embodiment, magnetron 504 is also rated at 100 kW and produces microwave power at 83-89% efficiency. In an embodiment, the generated microwaves are in the L-band having a frequency of 915 MHz.

[0068] As shown in this figure, microwaves enter a waveguide assembly 508 that directs the microwaves to an applicator 510, which then directs the microwaves to a plasma reaction chamber 512 within a reactor tube 514. In the embodiment shown, waveguide assembly 508 includes two circulators 518 and 520 that direct the microwaves to applicator 510 and prevent reflected microwave power from coupling back into magnetron 504 and damaging it. Each circulator 518 and 520 includes a ferrite array 516 and 526, respectively, that deflects the reflected microwaves to direct them to applicator 510 and plasma reaction chamber 512, as described in more detail below. Each circulator 518 and 520 has a respective water load 522 and 524 at its end to collect the reflected microwaves. As shown, second circulator 520 includes a power tuner 528 that reduces power using a three-stub tuner 530 in the arm distal to the three-stub tuner-to-applicator junction. In the arm of second circulator 520 that interfaces with applicator 510, a three-stub tuner 532 is positioned distal to a bidirectional coupler 534; this placement is intended to minimize microwave reflections and optimize microwave energy directed toward applicator 510. A quartz window 538 is inserted between second circulator 520 and applicator 510 to prevent arcing. A standing wave is configured in the applicator 510 between the three-stub tuner 532 and a sliding shorting plate 540 at the end of the applicator 510 so that when the plasma is turned off and the microwave is turned on, the electric field is sufficient to initiate decomposition of the feed gas within the reactor tube 514 containing the plasma reaction chamber 512. The reactor tube 514 travels through the broad wall of the applicator 510 but does not come into direct contact with the microwave waveguide 508.Once the initialization of the plasma state is achieved, the three-stub tuner 532 can then be adjusted to match the impedance of the microwave signal entering the plasma load applicator 510. The microwave energy entering the applicator 510 is adjusted to peak at the center of the plasma reaction chamber 512, using the shorting plate 540 if necessary to change the dimensions of the cavity in which the plasma is formed.

[0069] To optimize the power for generating the plasma, it is desirable to match the impedance of the waveguide 508 to the impedance of the applicator 510 in the presence and absence of plasma. However, plasma impedance is dynamic and can change based on the operating pressure, gas flow, and gas composition within the plasma reaction chamber 512. In embodiments, the microwave subsystem can include a standard three-stub autotuner 532 having three metal stubs inserted into the waveguide. The depth to which each of these stubs is inserted into the waveguide changes the phase of the microwaves entering the reactor 510, allowing the power to be matched to the plasma. By measuring the microwave power and phase in the autotuner 532, the autotuner 532 algorithmically varies the depth of the stubs so that reflected power (i.e., power not absorbed by the plasma) is minimized. In embodiments, a bidirectional coupler 534 equipped with a power diode (not labeled) can be included to measure the forward and reflected power in the subsystem. Coupler 534 may be fitted with two small holes that couple microwaves with known attenuation to a diode that converts the microwaves to a voltage. In embodiments, the reflected power is less than 1% of the total microwave power transmitted to the system. In embodiments, microwave applicator 510 is a single-mode resonant cavity that couples microwaves to a flowing gas feed within plasma reaction chamber 512. A sliding electrical short 540 may be incorporated into applicator 510 to vary the total cavity length. In embodiments, for a 100 kW demo unit, the plasma may generate more than 10 kW of heat, which can be removed via a water and gas cooling subsystem.

[0070] Plasma is generated within plasma reaction chamber 512 within elongated reactor tube 514. In embodiments, reactor tube 514 may comprise a long aspect ratio fused silica tube, with an outer diameter of about 30 to about 120 mm, a length of about 6 ft, and a thickness varying from about 2.5 to about 6.0 mm. In one embodiment, reactor tube may have a 50 mm outer diameter or a 38 mm outer diameter. In embodiments, tube sizes may have an outer diameter (OD) and corresponding inner diameter (ID) of 120 / 114 mm OD / ID, 120 / 108 mm OD / ID, 80 / 75 mm OD / ID, 50 / 46 mm OD / ID, or 38 / 35 mm OD / ID. In embodiments, reactor tube 514 has a constant diameter throughout its length. In other embodiments, reactor tube 514 may have a varying diameter, with certain portions of tube 514 having a smaller diameter and other regions having a larger diameter. In embodiments, the tube may have an outer diameter of about 50 mm at the top and about 65 mm at the bottom. In embodiments, the tube may have a narrower diameter at a preselected portion of the tube, for example, approximately in the middle of the tube. Quartz is an advantageous material for the reactor tube 514 because of its high temperature handling, thermal shock resistance, and low microwave absorption.

[0071] Figure 6 shows in more detail a microwave subsystem 600, such as that shown in Figure 5, and the paths of microwave energy 605, 607, and 615 flowing within the microwave subsystem; in Figure 6, certain features of microwave subsystem 600 are shown schematically, but for clarity, have not been labeled as they are in Figure 5. As shown in the embodiment shown in Figure 6, microwave energy generated by magnetron 604 is directed in a forward direction along forward energy path 605 from magnetron 604 to the distal end of waveguide assembly 608, from which the microwave energy is reflected along forward reflected path 607. The direction of forward reflected path 607 is shaped by the encounter of the forward reflected path with ferrite array 626 within second circulator 620, which deflects the reflected microwaves 607 toward applicator 610 and plasma reaction chamber 612. Microwaves may also be reflected retrogradely from the applicator 610 along a retrograde (reverse) reflection path 615, traveling back through a second circulator 620 to a first circulator 618, where the microwaves in this path 615 are collected by a water load 622 in the first circulator 618. The retrograde (reverse) reflection path 615 is deflected by a ferrite array 626 in the second circulator 620 and then by a ferrite array 616 in the first circulator 618 to establish its final direction. In one embodiment, the forward power in the system is about 25 kW, and the reflected power is 1% or less of this, with 0% reflected microwave energy being the goal. In embodiments, the forward power in the system is about 30 kW; in other embodiments, the forward power in the system is about 100 kW. In still other embodiments, forward power levels of about 8 kW, about 10 kW, or about 19-20 kW may be used. In embodiments, the system may advantageously include a forward power level of less than about 100 kW.

[0072] In one embodiment, the microwave subsystem includes a single-arm path toward the plasma reaction chamber as shown in FIGS. 5 and 6. In other embodiments, a two-arm applicator path can be used, as shown below in FIG. 7. As shown schematically in FIG. 7, two-arm microwave subsystem 700 includes a magnetron 704 that generates microwave energy that enters a circulator assembly 703 that includes two circulators, labeled "1" and "2." The microwave energy passes through the circulators substantially as shown in FIG. 6 and enters a power splitter 706 that directs the microwaves into two waveguide arms 709a and 709b, where they are directed to the arms' respective applicators 710a and 710b. In embodiments, the two-arm waveguides 709a and 709b and applicators 710a and 710b can split the incident power in a 50:50 ratio, although in other embodiments, a power split of a selected ratio can be implemented.

[0073] Certain maintenance measures in the microwave subsystem can extend component life and optimize product output. In embodiments, for example, the reactor can be cleaned periodically. It is understood that when converting methane to acetylene using non-thermal plasma technology, carbon soot buildup can occur within the reactor tube, and the presence of soot can lead to overheating of localized areas on the quartz surface, subsequently damaging the reactor tube. Also, soot that accumulates distal to the microwave coupling can become conductive, leading to the formation of undesirable arcs. Therefore, in embodiments, regular cleaning of the reactor is performed to minimize these problems. Cleaning can be done on a periodic basis, or based on discontinuous demand for commercial operation, or in response to observable characteristics of the plasma or effluent. For cleaning purposes, several steps are typically used: 1) de-energizing the plasma process in the plasma reaction chamber by either switching off the microwave power generating the plasma or by switching the gas inflow from the process gas to an inert cleaning gas or gas mixture (e.g., a combination of pure N2 or nitrogen with air or other cleaning gases), or both; 2) interrupting the feed gas inflow and introducing an inert gas mixture (e.g., nitrogen) to purge the inlet line of flammable feed gas; 3) filling the reactor with cleaning gas (e.g., nitrogen mixed with air); 4) re-energizing the plasma reaction chamber with microwave energy to generate a plasma state from the cleaning gas, including monitoring and adjusting the microwave energy and pressure to allow effective cleaning; 5) once the reactor tube is cleared, the process is reversed by evacuating or replacing the cleaning gas with the feed gas, resulting in filling the reactor tube with the feed gas and then energizing the feed gas to form the plasma.

[0074] In embodiments, soot buildup (and the resulting need for cleaning) can be minimized by increasing the hydrogen component of the inlet gas; however, this approach has the drawback of reducing the efficiency of hydrocarbon (e.g., methane) conversion. In other embodiments, soot buildup can be directly managed by periodic manual cleaning; this approach has the drawback of requiring physical intervention to access the interior surfaces of the reactor tubes where soot accumulates. In yet other embodiments, soot buildup can be managed by periodically changing the gas input to the plasma reaction chamber from the hydrocarbon:hydrogen feedstock used to produce acetylene to a hydrogen:nitrogen mixture that forms a low-power plasma that removes soot buildup from the interior surfaces of the reactor tubes. In one embodiment, a pure CO2 plasma can be used as the cleaning plasma. In one embodiment, a hydrogen:nitrogen gas mixture can be used, with a H:N ratio of 5-15:1 at approximately 8 kW of power. In one embodiment, this gas system cleaning protocol can be performed on a periodic basis (e.g., 1-2 minute cleaning attempts every hour or two), targeting a 1-2% downtime for cleaning out of a continuous attempt scheme. In another embodiment, a 50:4 ratio nitrogen:air mixture can be used, resulting in approximately 3 minutes of cleaning time every 2-3 hours.

[0075] An embodiment of this system includes a multiplexed parallel microwave reactor setup with a first reactor and a second reactor connected after reactor tubes and heat exchangers and isolation valves for each reactor but sharing a vacuum pump. While the second reactor is operating to energize the feed gas in its plasma reaction chamber, the magnetron of the first reactor can be shut off, the reactor can be isolated by the isolation valve, and then opened to an alternate vacuum system. A cleaning plasma can then be used on the first reactor. Once cleaned, the cleaning gas mixture is evacuated from the first reactor system, purged with nitrogen, then purged again with a mixture of each of the new feed gases used in the process and recycled gas, and then reopened to the main vacuum system and reignited. The second reactor can then be cleaned using the same sequence. In some embodiments, the total number of parallel reactors can be increased to include three or more reactors, and their cleaning cycles can be arranged so that the total throughput of the combined system remains constant while any one reactor undergoes cleaning. Therefore, this cleaning process can be cycled indefinitely in multiple reactor systems, either individually or in small groups, with cycle times set so that there is no loss of product throughput over successive runs.

[0076] c. Vacuum sub-system In embodiments, a vacuum system is disposed around all components between the gas injector providing the gas inlet to the reactor and the product outlet distal to the reactor. Maintaining low pressure within the system contributes to the efficiency of the system (where efficiency is measured in eV of energy per mole of methane converted to acetylene). In embodiments, a vacuum is maintained within the reactor or a low-pressure environment is created, typically at about 30 to about 120 Torr, about 60 to about 100 Torr, or about 70 to about 80 Torr. In one embodiment, an operating pressure of about 70 Torr is maintained for all hydrocarbon feed gases except ethane, which is processed at an operating pressure of about 120 Torr.

[0077] A simplified schematic diagram of a plasma-based hydrocarbon treatment system 800 highlighting vacuum subsystems 802a and 802b is shown in Figure 8, with arrows indicating the direction of gas flow within system 800. Vacuum subsystems 802a and 802b enclose certain components of treatment system 800 and maintain pressures within such components in the range of about 30 to about 120 Torr. As shown in Figure 8, the vacuum subsystem, indicated by dotted line 802a, creates a first reduced pressure environment around reactor 810 and its effluent stream 816, as well as around various components downstream from reactor 810, all as described in more detail below; the vacuum subsystem, indicated by dotted line 802b, creates a second reduced pressure environment around gas delivery subsystem 804. For purposes of clarity, a portion of the vacuum subsystem is identified by dotted line 802a and a portion of the vacuum subsystem is identified by dotted line 802b; these two dotted lines may represent separate subsystems, or these dotted lines may merge together to represent a single vacuum subsystem. The subsystems and components shown in this figure for clarity are: (i) a gas delivery subsystem 804 that passes input gases, including a hydrocarbon feed gas 806 and a hydrogen-bearing recycle gas 812, through their respective feed gas inlets (not shown) to the reactor 810; (ii) a gas delivery subsystem 804 that acts on the input gases (i.e., the hydrocarbon feed gas 806 and the hydrogen-bearing recycle gas 812) within the reactor 810 to generate a plasma for the two input gases 806 and 812 in the plasma reaction chamber 811 region of the reactor 810. (iii) an effluent separation and disposal system including an acetylene separator 814 and a hydrogen separator 818 that separate the effluent stream 816 into its gaseous components, the remainder of the effluent stream 816 distal to the acetylene separator 814 and the hydrogen separator 818 becoming a recycled gas stream 812. As previously described and shown in this figure, certain components located downstream from the reactor 810, such as a filter 820 for the effluent stream 816, a heat exchanger / separator 822, and a series of pumps 824 and 828, are also included within the vacuum sub-system, indicated by dotted line 802a.In this figure, a cold trap 830 for removing higher hydrocarbons, as well as an acetylene separator 814 and a hydrogen separator 818, are located outside the vacuum subsystem as indicated by dotted line 802a.

[0078] Filter 820, shown in this figure, is intended to remove carbon solids from effluent stream 816. In embodiments, the plasma process produces small amounts of carbon solids as a by-product; for example, carbon solids may be produced in the range of 0.1-0.5%. Therefore, it is desirable to filter effluent stream 816 to remove these carbon solids to prevent these particles from fouling downstream components of the system. Because filter 820 is the first surface that effluent stream 816 encounters after leaving reactor 810, the gases in this stream are very hot (approximately 400-1000°C). Therefore, materials for filter 820 are selected to withstand such temperatures, with or without additional cooling. In embodiments, filter 820 may be made of a ceramic material or stainless steel, with added cooling if necessary.

[0079] d. Cooling subsystem In embodiments, a cooling subsystem may be implemented to control the operating temperatures of the various components of the gas processing system described herein. In embodiments, the plasma formed within the reactor reaches temperatures of 2000-3000 K (1700-2700°C) and exits the reactor at temperatures of about 400 to about 1100°C. Cooling is provided to protect downstream components of the system from thermal damage. It may also be desirable to cool the reactor itself, for example, to maintain the temperature outside the reactor tube below 500°C. Furthermore, because the reactor tube is more likely to retain heat during gas system cleanup (described above) than during acetylene production, more cooling power may be required intermittently to protect the reactor tube from thermal stress. In embodiments, cooling for the system includes two types of cooling: water cooling and gas cooling. Water cooling may be used for many components of the system, such as magnetrons, power sources, vacuum pumps, applicators, etc. Gas cooling may be used for other components, such as the reactor tube, the reactor itself, and various O-ring seals within the system, where appropriate. In embodiments, nitrogen is used for gas cooling. Nitrogen has the added benefit of displacing atmospheric gases in the enclosed portion of the system, thereby increasing safety. In one embodiment, the reactor tube and applicator can be enclosed in a sealed, nitrogen-purged (oxygen-free) environment, where the presence of nitrogen provides cooling and also acts as a safety feature by displacing oxygen in the environment surrounding the reactor system, and the nitrogen gas coolant reduces the possibility of explosion in the event of a leak.

[0080] e. Waste Separation and Disposable Subsystem In embodiments, the effluent stream originates from the low-pressure environment created by the vacuum sub-system and then undergoes further management to separate the desired gaseous products from each other and from waste products. Methane and other hydrocarbon-containing gases, such as ethane, propane, butane, along with particulate carbon and higher hydrocarbons, produce acetylene and hydrogen when energized in a non-thermal plasma as described herein. To optimize process economics and provide customized gas flows for recycling, a set of components is located distal to the vacuum sub-system to separate specific gaseous components from each other in the effluent stream.

[0081] In embodiments, the plasma-based hydrocarbon processing system and method of use described herein are envisioned to convert methane at a net hydrogen-positive stoichiometry, with 1.5 moles of hydrogen produced for every mole of methane consumed. Thus, the effluent stream contains a mixture of hydrocarbons, including the desired product acetylene, with a predominance of hydrogen. In embodiments, this hydrogen can be separated from the effluent stream, for example, by using a membrane separator to separate the hydrogen from the remainder of the effluent. After separation, the hydrogen can be purified and commercialized as another gas product; alternatively, or additionally, the hydrogen can be recycled into the system as illustrated in the previous figures. In other embodiments, instead of or in addition to hydrogen separation, acetylene can be separated from the effluent stream. For example, acetylene can be absorbed in an absorption column, then desorbed and collected. In one embodiment, the effluent stream from the reactor can be first treated to remove particulate carbon and condensates, and then the acetylene can be removed. After the acetylene is removed, the hydrogen can optionally be removed, captured or recycled.

[0082] When the effluent stream exits the plasma reaction chamber, it contains a combination of gas, volatilized higher hydrocarbons, and particulate carbon. As previously described, the particulate carbon can be filtered immediately downstream from the reactor chamber. In embodiments, the effluent stream can subsequently pass through a cold trap to remove certain higher hydrocarbons as condensates from the effluent stream. After passing through the cold trap, the effluent stream can be further separated. For example, other higher hydrocarbons can be removed from the effluent stream as described below. These compounds are typically considered waste products and can be discarded or disposed of after their removal. After or simultaneously with the removal of the higher hydrocarbons, acetylene and hydrogen are separated from the effluent stream via an effluent separation and disposal subsystem. The separation process proceeds using one or more separation techniques, such as adsorption techniques, absorption techniques, chemical reaction techniques, such as oxidation or catalytic conversion.

[0083] i. Adsorption In some embodiments, for example, the effluent stream may be passed through an adsorption column, where the column contains a high surface area adsorbent material capable of selectively removing acetylene or higher hydrocarbons from the effluent stream flowing through the column. In embodiments, the adsorbent material may include appropriately sized materials such as activated carbon, zeolites, silica aerosols, molecular sieves, metal-organic frameworks (MOFs), coordination polymers, clay, diatomaceous earth, or pumice. The adsorbent material may be a powder or film, or may be formed into spherical pellets, rods, or other shapes that may be useful. These adsorbent materials may be modified by calcination at high temperatures, ion exchange, or doping with molecules that enhance adsorption affinity or capacity. Furthermore, a combination of two or more adsorbent materials may be used to take advantage of multiple physical properties. The adsorbent material may be contained within a single adsorption column or may be divided into multiple adsorption columns for trapping different impurities from the effluent stream at different locations. Advantageously, the adsorbent material can be selected to minimize product loss when the effluent stream passes through the adsorbent column: in some instances, higher hydrocarbon impurities have a higher affinity for the adsorbent material than the desired product; in other instances, impurities can displace product molecules from the surface of the adsorbent. In either case, product loss is minimal.

[0084] Under certain circumstances, the adsorbent may be disposed of after a single use if the adsorbent's capacity and impurity concentration allow for sufficient impurity removal before disposal. Under other circumstances, for example, when disposal is not feasible for economic or logistical reasons, the adsorbent may be regenerated and cyclically reused. Methods for regenerating the adsorbent include pressure reduction, solvent washing, heating, and replacement with another gas. During regeneration, the impurities may be desorbed from the surface of the adsorbent or converted in situ to another chemical that is easier to desorb. If the impurity is converted to an acceptable derivative molecule, this molecule may be desorbed in-line and released into the process stream. If the impurity remains unchanged on the surface of the adsorbent, it may not be released into the downstream flow but may be diverted to a side stream where it is discharged for waste disposal, incinerated, or collected. In embodiments, automated systems may schedule changes between or within multiple adsorber vessels, enabling regeneration cycles in continuous operation; such systems are referred to in the art as swing adsorbers.

[0085] An adsorber can be used for further separation of the effluent stream after removal of higher hydrocarbons. Depending on the preferred mode of adsorption and desorption, a pressure swing adsorber (PSA), a vacuum swing adsorber (VSA), or a temperature swing adsorber (TSA) can be used. For example, in some embodiments, the effluent stream can be fed to a PSA system to separate hydrogen gas from the effluent stream. In a PSA system, the effluent stream is pressurized and fed to an adsorption column where all non-hydrogen components are adsorbed onto an adsorption material. All non-hydrogen materials are removed from the stream, and purified hydrogen exits the column. In some embodiments, the feed for the PSA system can be the effluent stream from the plasma reactor, or the collected gas from the first absorption column described above, or some combination thereof.

[0086] Alternatively, for example, the effluent stream can be fed to a TSA system adapted to separate higher acetylenes from the effluent stream. As used herein, the term "higher acetylenes" refers to at least alkynes containing 3 and 4 carbon atoms, but the higher acetylenes can also apply to all gaseous alkynes and gaseous aromatics. Through the use of a TSA system, higher acetylenes can be significantly and completely separated from the acetylene stream without acetylene loss. In embodiments, higher acetylene molecules can displace acetylene on the surface of the adsorber, allowing for maximum selectivity in the separation of higher acetylenes from the acetylene stream. To achieve this, the adsorption process is advantageously terminated before the higher acetylenes themselves are displaced by heavier molecules such as benzene. Therefore, the adsorption cycle within the TSA should be adjusted to adsorb and retain higher acetylenes on the adsorber surface, but prevent the higher acetylenes from being displaced. Therefore, before displacing the higher acetylenes from the adsorber surface, the reactor is sealed off to the process stream. The adsorber can then be disposed of and replaced, or alternatively, regenerated. In regeneration, the effluent stream is diverted from the adsorber and hot air (>300°C) is passed over the adsorber bed. Impurities are released from the adsorber and either vented or combusted. In several iterations, multiple vessels can be used for continuous operation, with some vessels adsorbing and others being regenerated.

[0087] ii. Absorption In some embodiments, the effluent stream can be passed through an absorption column, where a solvent at an optimal flow rate, flowing countercurrent to the effluent stream, preferentially absorbs higher hydrocarbons from the flowing effluent stream instead of absorbing the desired gaseous product, such as acetylene. The higher hydrocarbons can then be separated from the solvent in a second column, and the solvent returned to the absorption column. Examples of solvents that have a stronger affinity for higher hydrocarbons over the desired gaseous product include methanol, ammonia, toluene, benzene, kerosene, butyrolactone, acetonitrile, propionitrile, methoxypropionitrile, acetone, furfural, N,N-dimethylformamide, N,N-diethylformamide, N,N-dimethylacetamide, N,N-diethylacetamide, N-formylmorpholine, and N-alkylpyrrolidones, such as N-methylpyrrolidone (NMP).

[0088] In other embodiments, the effluent stream can be passed through an absorption column, where a solvent having a strong affinity for acetylene, preferably flowing countercurrent to the effluent stream, absorbs acetylene from the flowing effluent stream. The absorbed acetylene can be removed from the solvent by heating the solvent in a second column to restore the solvent, which can then be returned to the absorption column. Examples of solvents having a stronger affinity for acetylene over other effluent gases include methanol, ammonia, toluene, benzene, kerosene, butyrolactone, acetonitrile, propionitrile, methoxypropionitrile, acetone, furfural, N,N-dimethylformamide, N,N-diethylformamide, N,N-dimethylacetamide, N,N-diethylacetamide, N-formylmorpholine, and N-alkylpyrrolidones, such as N-methylpyrrolidone (NMP).

[0089] iii. Chemical Reactions In some embodiments, higher hydrocarbons in the effluent stream can be oxidized, thereby removing them from the effluent stream. For example, certain higher hydrocarbons, particularly diacetylenes and substituted acetylenes such as methylacetylene and vinylacetylene, can be difficult to separate from acetylene and can be removed by converting the higher hydrocarbons to non-acetylene compounds. To achieve this, the effluent stream can be passed through a column or vessel containing an oxidizing agent, such as a concentrated liquid acid, e.g., nitric acid, sulfuric acid, or phosphoric acid, that can act as an oxidizing agent. Higher hydrocarbons, such as diacetylenes and substituted acetylenes, can react with the oxidizing agent or concentrated acid to produce other hydrocarbon compounds that can be more easily separated from the effluent stream. In some embodiments, the effluent stream can be contacted with phosphoric acid on a solid support to convert higher hydrocarbons, such as diacetylenes and substituted acetylenes, to other hydrocarbon products that can be more easily separated from the effluent stream.

[0090] In certain embodiments, the effluent stream may be passed through a catalyst bed using a catalyst comprising a transition metal, transition metal oxide, transition metal salt, or zeolite to convert various higher hydrocarbons into other carbon species that are more easily separable from the gaseous product stream. When exposed to the appropriate catalyst, these higher hydrocarbons may be converted to more easily removable compounds by catalytically induced mechanisms such as polymerization, oxidation, hydrogenation, and disproportionation. Depending on the mechanistic mode of catalytic conversion and the resulting products, these derivatives of higher hydrocarbons may be removed through further downstream processes, such as those described herein.

[0091] iv. Other separation techniques In certain embodiments, higher hydrocarbons can be removed from the effluent stream using a condenser, which collects these compounds on a high surface area material, such as silica gel, activated carbon, activated alumina, or zeolite. For example, certain higher hydrocarbons, such as methyl acetylene and vinyl acetylene, can be difficult to separate from acetylene in gaseous form, but their condensation points (5.01°C and 10.3°C, respectively) contrast with the condensation point of acetylene (-84°C), making them suitable for removal via condensation from the effluent stream. In this embodiment, a cooling bed containing a high surface area material at a temperature between -84°C and 10°C can effectively condense the higher hydrocarbons from the effluent stream.

[0092] In some embodiments, the effluent stream can be passed through a gas separation membrane system, where gas molecules are separated by size exclusion. For example, smaller molecules, such as hydrogen, flow preferentially through the membrane element to form a permeate stream, while larger molecules, such as methane, acetylene, higher hydrocarbons, nitrogen, carbon dioxide, and any other larger molecules, do not flow through the membrane (depending on the membrane's porosity) and form a retentate stream. In some embodiments, the permeate stream is a hydrogen-enriched stream, and the retentate stream is a hydrogen-depleted stream. The gas separation membrane element can be formed from a variety of materials, such as hollow fiber polymer membranes, where the polymer can be polycarbonate, polyamide, or cellulose acetate; inorganic membranes, where the inorganic material can be mesoporous silica, zeolite, metal-organic framework, or mixed metal oxide; metal membranes, where the metal can be palladium or a palladium-silver alloy; and the like. In some embodiments, the feed for the membrane separation system can be the effluent stream from the plasma reactor, or the collected gas from the first absorption column described above, or some combination thereof.

[0093] Depending on these particular effluent separation criteria, in embodiments, the effluent stream containing acetylene, hydrogen, and higher hydrocarbons may be further separated into its components so that desired gaseous products may be recovered. In other embodiments, the effluent stream is not subjected to further separation, for example, if it is used for further chemical processing or if it is provided as a mixed stream to a consumer or end user.

[0094] f. Data Management and Safety Subsystem Advantageously, the entire gas production system includes interconnected data management and safety subsystems, and the safety measures incorporated into these systems and processes are informed by data collected about the system's performance. In embodiments, data management can include devices, procedures, and algorithms for data collection and performance diagnostics, as well as storage facilities for recording and storing data. In embodiments, performance diagnostics include monitoring the system's status within normal parameters to facilitate overall integration and control and to identify signals of impending or active failure conditions. Optical diagnostics, such as visible light cameras, mid-IR pyrometers, broadband spectrometers, etc., can be assigned to monitor the plasma region. Equipment diagnostics can include pressure transducers, thermocouples, flow meters, microwave power sensors, etc. Other diagnostic devices, such as full-scale spectrometers and oscilloscopes, can be used where appropriate. In embodiments, various diagnostic modalities can be automatically and / or manually integrated and monitored during a trial.

[0095] In embodiments, manual and automated diagnostic procedures may be integrated with safety procedures that may include fault-interlocks. In one embodiment, diagnostic inputs may be actively monitored by hardware and software. If an anomaly is detected, an error signal may be triggered that activates a predetermined response pattern. For these most serious errors, such as a suddenly confirmed pressure spike, an immediate automated "hard" shutdown may be triggered. For errors of moderate severity, where the consequences are less severe, a slower automated shutdown may be triggered, intended to halt operation over the course of several seconds. For these errors, where parameters are outside of expected ranges but no serious consequences are expected, an operator may be redirected so that appropriate action can be taken to correct the situation and clarify the error without requiring a system shutdown.

[0096] 3. Exemplary Systems and Subsystems a. 100kW powered plasma hydrocarbon treatment system A plasma-based hydrocarbon processing system that uses plasma technology to convert hydrocarbon-containing inlet gases to acetylene and hydrogen can provide a high degree of feedstock hydrocarbon conversion combined with a high degree of selectivity for the production of acetylene and / or hydrogen. The system described below uses a 100 kW power source to generate microwaves that form the plasma and carry out the chemical conversion.

[0097] The central reaction of this process occurs when methane (e.g., derived from natural gas or biogas) or another C2-C4 source hydrocarbon is fed into a microwave energy deposition region where it is decomposed into a plasma. Without being bound by theory, the plasma decomposes the hydrocarbon into excited CH4 which, after the plasma energy state, recombines to form a spectrum of hydrocarbon products and hydrogen. x It is hypothesized that the decomposition of hydrocarbons into radicals drives the reaction from the source hydrocarbons to acetylene and hydrogen. Using C2-C4 hydrocarbons as the feedstock can improve overall process efficiency compared to methane, while maintaining a high degree of selectivity for acetylene. However, using methane contained in natural gas or biogas has advantages in operational efficiency and cost effectiveness.

[0098] The methane conversion process in a 100 kW power system (i.e., using methane or pure methane feed, such as might be found in natural gas or biogas feed) uses approximately 9.5 kWhr per kg of acetylene product formed, with an acetylene yield of 90%: for the feed gas used, approximately 90% is converted to acetylene. The resulting product mixture is influenced by the non-thermal nature of the plasma temperature. Gas temperatures are 3000-4000 K, while vibrational and electrical temperatures are two to three times higher, pushing the reaction equilibrium to form acetylene with high selectivity and enrichment in hydrogen as a by-product. Hydrogen produced by the plasma reaction can be recycled back into the system as a secondary feed gas for subsequent reactions and / or the hydrogen can be separated as a separate gaseous product. The presence of both hydrogen and hydrocarbons as components of the reaction reduces the solids production of the reaction. To achieve the desired ratio of hydrogen and methane for the reaction, the system recycles the produced hydrogen to participate in the methane-based reaction, as described in more detail below.

[0099] i. Overall system The 100 kW powered plasma-based hydrocarbon treatment system includes four subsystems: gas delivery, microwave, vacuum, and cooling. The gas delivery subsystem includes two inlet lines. The first inlet line is a feed line carrying a gas mixture, such as natural gas continuously supplied from a local utility company or improved biogas, containing a mixture of primarily methane with small amounts of ethane, propane, carbon dioxide, and nitrogen (depending on the source of the raw gas mixture). This inlet can be cleaned using conventional techniques before entering the plasma reaction chamber, resulting in a nearly pure methane stream, with other remaining gas mixture components present at roughly about 100 ppm. The total flow from this inlet line is scalable to the total microwave power of the system, with a flow of approximately 3 SLM methane / kW of microwave power. The second inlet line carries recycle gas produced by the reactor, containing about 85 to 90% hydrogen, along with small amounts of methane, other reactants, and about 5 to 6% unreactive nitrogen. The total flow from this inlet line is also scaled up by the total microwave power of the system, with a flow of approximately 5 SLM recycle gas / kW microwave power.

[0100] Each inlet stream is delivered to the plasma reaction chamber through its own inlet, which injects the flow into the entry region of the quartz tube and through the tube to the region where the plasma is generated. The inlet of each inlet stream can be angled by a gas injector device to create a vortex flow that mixes the streams within the quartz tube as they flow toward the reaction region, i.e., the plasma reaction chamber. The flow of gas entering through each inlet is controlled by a mass flow controller adjusted to produce a hydrogen-to-methane molar ratio of 1.5H2:1CH4. As methane is converted to plasma, a spectrum of reaction products is formed within the plasma reaction chamber within the quartz tube.

[0101] When methane is used as the feed gas, approximately 95% of the methane undergoes chemical transformation within the plasma. Acetylene accounts for 95% of the hydrocarbons produced from the plasma energy deposition reactions, resulting in an overall acetylene yield of approximately 90%. Hydrogen is the other major reaction product from these reactions, accounting for approximately 80% by volume of the total effluent stream.

[0102] An exemplary 100 kW powered plasma-based hydrocarbon processing system 900 is generally represented by the block diagram shown in Figure 9. As shown in this figure, a central reactor 902, including an injection region 904, a reaction region 908, and an outlet region 910, receives two separate gas streams: (1) a feed gas 912 containing source hydrocarbons (e.g., methane or a single C1-C4 hydrocarbon or a customized mixture of C1-C4 hydrocarbons in a mixed gas such as natural gas or biogas) and (2) a recycle gas flow 914 containing hydrogen and mixed hydrocarbon-containing gases and, optionally, non-reactive nitrogen.

[0103] As represented schematically in the figure, inlet gas streams 912 and 914 are processed in reactor 902 to form effluent stream 918 comprising acetylene, hydrogen, and small proportions of mixed hydrocarbons. Effluent stream 918 is then separated into its gaseous components by gas separation system 928 (e.g., adsorption, absorption, or a combination thereof) to produce acetylene stream 920 and hydrogen-dominated gas stream 922 comprising hydrogen 936 and a mixture of hydrocarbons 924. Having been so directed from main effluent stream 918 by gas separation system 928, acetylene stream 920 can be purified by further segregation of impurities in purification system 926 to produce purified acetylene gas product 932. Once acetylene component 920 is removed from effluent stream 918, the remaining gas stream 922 is primarily hydrogen, i.e., hydrogen-dominated, along with a mixture of hydrocarbon reaction products. This hydrogen-dominated gas stream 922 can be subjected to further separation, if desired, so that the hydrogen gas is sequestered as a separate gas stream 930. The hydrogen gas product stream 930 can be further purified, if necessary, and sold as a product, or recycled back to the reactor 902 for further reaction with the feed gas 912. In this system 900, instead of recycling the hydrogen gas product stream 930, the combined hydrogen-dominated gas stream 922 is recycled to form a recycle gas flow 914 and reintroduced into the reactor 902 for further reaction with the feed gas 912. Mass flow controllers 940 and 942 adjust the flow of the feed gas 912 and the recycle gas 914 into the reactor 902 to produce the desired ratio of hydrogen to methane (or hydrogen to other source hydrocarbon) within the reactor 902.

[0104] ii. Reactor The reactor identified in Figure 9 is shown in more detail in Figure 10. Figure 10 schematically illustrates a reactor 1002, its components, and its integration with a microwave subsystem 1004. As shown and outlined by the gray shaded box, the microwave subsystem includes a power source and magnetron complex 1016 for generating microwaves, and a waveguide assembly 1020 for directing the microwaves toward a reaction region 1012 within the quartz tube where a microwave plasma 1018 is formed. As shown in Figure 10, a quartz tube 1008 includes the components of the reactor 1002: an injection region 1010, a reaction region or reaction chamber 1012, and an exit region 1014. Within the quartz tube 1008, a microwave plasma 1018 is generated by microwaves (not shown) directed at a gas flow 1006 within the tube 1008, thereby effecting the conversion of a source hydrocarbon to hydrogen and various hydrocarbon-derived products. This quartz tube 1008 is inserted into the broad wall of a microwave waveguide assembly 1020. The size of the quartz tube 1008 depends on the amount of microwave power used in the system. For the system shown, which uses 100 kW of power to generate microwaves, the quartz tube 1008 has an outer diameter of 80 mm, an inner diameter of 75 mm, and a length of 1700 mm, and is maintained at a pressure of approximately 70 Torr by a downstream vacuum pump (not shown). The relationship of the quartz tube 1008 to the microwave subsystem 1004 is described in more detail below.

[0105] As shown in Figure 10, recycled gas stream 1022 mixes with feed gas stream 1024 in injection region 1010 of reactor 1002, with each stream entering injection region 1010 of reactor 1002 through an inlet (not shown) in the reactor itself. The passage of each gas stream into reactor 1002 through gas injector device 1032 (also shown schematically in Figure 11) affects its direction, flow rate, and velocity. As shown in Figure 10, any gas stream or streams 1028 can be directed into injection region 1010 and mix with recycled gas stream 1022 and feed gas stream 1024 to create vortex gas flow 1006. After mixing, the gases in gas flow 1006 flow distally through quartz tube 1008, encounter microwave energy generated by power source and magnetron composite 1016, and are delivered through waveguide assembly 1020 to reaction region 1012 of reactor 1002. Interaction of the microwave energy with the gases in reaction region 1012 of reactor 1002 creates plasma 1018. An outlet gas stream 1034 containing reaction products emerges from plasma 1018, enters outlet region 1038 of quartz tube 1008, and proceeds out of reactor 1002 for further separation 1040. As shown in this figure, microwave subsystem 1004 includes power source and magnetron composite 1016 and waveguide assembly 1020; additional elements of the microwave subsystem, which are shown and described in the following figures, are not shown in this figure.

[0106] Figure 11A is a cross-sectional schematic diagram (not drawn to scale) of an embodiment of a gas injector suitable for use with a 100 kW powered plasma-based hydrocarbon processing system, such as the gas injector 1032 shown in Figure 10. For illustrative purposes, the cross-sectional view of Figure 11A corresponds to the cross-section taken at line A-A' in Figure 10. Figure 11A shows a gas injector 1106 positioned within the reaction chamber 1102 of the plasma reactor 1100 and providing multiple gas flows within the reaction chamber 1102 for the multiple gases to encounter microwave energy as described above. As shown in this figure, the gas injector 1106 provides flow paths into the reactor 1102 for two different gas streams, each directed into the reactor 1102 through its own nozzle and flow paths within the gas injector device 1106. 11A, there are four injector ports: two for recycled gas flows 1104a and 1104b and two for feed gas flows 1108a and 1108b. In the figure, two recycled gas nozzles 1104a and 1104b are in fluid communication with a first central flow channel 1110 through which the recycled gas flows enter the gas injector 1106 and are directed to the recycled gas nozzles 1104a and 1104b. Similarly, there is a second centrally disposed channel 1112 within the gas injector 1106 for the feed gas, which is different from the first central flow channel 1110 for the recycled gas flows. There are two nozzles for feed gases 1108a and 1108b in fluid communication with a second centrally located channel 1112, these nozzles 1108a and 1108b entering the reactor 1102 at a different level than the nozzles 1104a and 1104b for the recycle gas. The nozzles for both types of gas flow are oriented in directions conducive to the formation of a vortex gas flow within the reactor 1102. The channel 1110 for the recycle gas and the channel 1112 for the feed gas do not intersect with each other, but rather provide separate gas flows within their respective nozzles 1104a / 1104b and 1108a / 1108b; neither nozzle intersects with each other, but rather provides their gas flows separately within the reactor 1102.The gas flow through each nozzle can be coordinated with other gas flows in other nozzles in terms of flow rate, path length and pressure drop.

[0107] It will be understood by those skilled in the art that the relative positions of the feed gas channels 1112 and recycle gas channels 1110 can be rearranged, for example, as parallel channels, as a spiral, at different levels within the gas injector 1106, or in other arrangements aside from that shown in Figure 11A, provided that the channels for each gas are maintained separate from each other within the gas injector 1106, and further that each different gas stream enters the reactor 1102 through its own different nozzle(s). Furthermore, the number, arrangement, and direction of the nozzles can vary, provided that the gas stream for each component gas (i.e., the feed gas and recycle gas and any additional gases) enters the reactor through its own nozzle without mixing with the other gas streams.

[0108] FIG. 11B is a cross-sectional schematic view (not drawn to scale) of another embodiment of a gas injector suitable for use with a 100 kW powered plasma-based hydrocarbon processing system, such as the gas injector 1032 shown in FIG. 10. For illustrative purposes, the cross-sectional view of FIG. 11B corresponds to the cross-section taken at line A-A' in FIG. 10. FIG. 11B shows a gas injector 1156 positioned within the reaction chamber 1152 of the plasma reactor 1150 and providing multiple gas flows to the reaction chamber 1152 for encountering microwave energy as described above. As shown in this figure, the gas injector 1156 provides flow paths for two different gas flows into the reactor 1152, with each gas flow being directed into the reactor 1152 through a set of nozzles within the gas injector device 1156. 11B, there are eight injector ports or nozzles: four (1154a, 1154b, 1154c, and 1154d) for the first gas flow, e.g., the recycle gas flow, and four (1158a, 1158b, 1158c, and 1158d) for the second gas flow, e.g., the feed gas flow. In that figure, the four nozzles (1154a, 1154b, 1154c, and 1154d) for the first gas flow are in fluid communication with a central flow channel 1162, through which the first gas flow enters the gas injector 1156 and is directed to the appropriate nozzles 1154a, 1154b, 1154c, and 1154d. Nozzles 1158a, 1158b, 1158c, and 1158d for the second gas flow are each fed by a separate flow channel 1160a, 1160b, 1160c, and 1160d, respectively. Other arrangements of flow channels for feeding nozzles 1158a, 1158b, 1158c, and 1158d for the second gas flows can be envisioned, provided that the flow channels for the second gas flows do not mix the second gas flow with the first gas flow. Instead, each gas flow is carried by its own different set of nozzles and its own flow channel(s).Nozzles 1154a, 1154b, 1154c, and 1154d for the first gas flow and nozzles 1158a, 1158b, 1158c, and 1158d for the second gas flow are oriented in a direction conducive to the formation of a vortex gas flow within reactor 1152. The gas flow through each of the nozzles can be coordinated with the other gas flows in the other nozzles in terms of flow rate, path length, and pressure drop.

[0109] iii. Microwave sub-system The microwave subsystem shown in Figure 10 is shown in more detail schematically in Figure 12. With reference to Figure 10, the reaction region 1012 of the reactor 1002 can be seen to intersect with a waveguide assembly 1020, where microwaves are directed at the gas flow 1006 to enter the reaction region 1012 and form a plasma 1018. The microwave subsystem 1004 is responsible for generating and directing microwaves into the reactor 1002.

[0110] The microwave subsystem is shown in more detail in FIG. 12. As shown in this figure, microwave subsystem 1200 includes a power source 1208, a magnetron 1210, a waveguide assembly 1202 (including a waveguide 1212 and certain other standard microwave components described below), and an applicator 1204. Power source 1208 converts 480 V, 150 A AC power into 20 kV / 21 kV, 5.8 A low-ripple DC power, with 96% conversion energizing magnetron 1210. Magnetron 1210 is rated at 100 kW and produces continuous microwave power with an efficiency of 83-89%. The microwaves produced are in the L-band frequency range, approximately 915 MHz. Microwaves are launched into a waveguide assembly 1202, in which a waveguide 1212 directs the microwaves through other components of the system to an applicator 1204, where they interact with the gas / plasma within a plasma reaction chamber 1214. The waveguide 1212 features a 90° bend 1216. One of the waveguide components is an isolator 1218, to which a water load 1220 is attached, located distal to the magnetron 1210 and protecting the magnetron 1210 from reflected (unabsorbed) microwaves by directing them toward the water load 1220 via a ferrite core 1222. Other components of the waveguide assembly 1202 are tuned to guide the microwaves into the plasma reaction chamber 1214 and optimize the generation of plasma therein. The applicator 1204 provides the interface between the microwaves and a quartz tube 1224 in which the plasma is generated. A plasma is formed within the plasma reaction chamber 1214, which is the region of the quartz tube 1224, within which the chemical transformation occurs. As shown in cross section in Figure 12, the quartz tube 1224 is positioned within the applicator 1204, but is separated from the applicator by an air gap (not labeled).

[0111] When the plasma is off and the microwave is on, a standing wave forms in the applicator 1204 between the three-stub tuner 1230 and the sliding shorting plate 1232 on the end of the applicator 1204, and the electric field is sufficient to initiate the breakdown of gas molecules within the quartz tube. The microwave energy entering the applicator 1204 is adjusted to peak at the center of the plasma reaction chamber 1214, using the shorting plate 1232 if necessary to change the length of the plasma reaction chamber 1214, and the three-stub tuner 1230 to change the phase of the input microwaves. Once the plasma is initiated, the position of the stubs within the tuner 1230 can be changed to preferentially match the microwave power to the plasma and minimize unabsorbed power. The three-stub tuner 1230 includes power and phase sensors (not shown) and can algorithmically adjust the motor-driven stubs to minimize unabsorbed power. A directional coupler 1234 containing two small pinholes for coupling microwaves with known attenuation is included in the waveguide 1212 proximal to the three-stub tuner 1230. A power meter (not shown) is coupled to these pinhole ports, converts microwave power to a voltage, and outputs a measurement of the forward reflected power. A thin quartz window 1238 is added to the waveguide system to prevent environmental debris and dust from entering the waveguide components.

[0112] b. Torch system for acetylene production In embodiments, plasma-based hydrocarbon processing systems for producing acetylene and hydrogen can be of any scale and can deliver a range of purity and acetylene concentrations depending on the desired end use. Plasma-based hydrocarbon processing systems, such as those previously described, can be designed for small-scale applications and tailored to the needs of the end user. To facilitate this customization, plasma-based hydrocarbon processing systems can be configured to separate the effluent (exhaust) stream from the reactor into gas streams with different compositions, such as a stream with a higher concentration of acetylene and a stream with a higher concentration of hydrogen. Small-scale plasma-based hydrocarbon processing systems can be designed to deliver a pure gas stream or can deliver an acetylene-hydrogen mixture with or without other gases included in the output gas flow. The small-scale systems or "mini-units" described above can be designed to produce only an acetylene-hydrogen mixture in the reactor, with the gaseous output varying from 0.5% to 75% acetylene, thereby minimizing the amount of separation required and reducing the complexity of the system. In embodiments, the end user can manipulate the parameters of the separation subsystem to produce a desired composition of acetylene mixed with hydrogen; in embodiments, the parameters of the microwave plasma reactor module of the mini-unit can also be adjusted, although for more extensive parameter customization, a larger unit is desirable.

[0113] In one embodiment, the overall size of the plasma-based hydrocarbon treatment system can be adjusted from smaller units, such as table-sized mini-units (e.g., 4 feet wide x 8 feet long x 4 feet high), to larger units measuring 20 x 20 x 20 feet or more. In one embodiment, the plasma-based hydrocarbon treatment system can be sized to be portable. Desired sizing for portable units ranges from table-sized dimensions (e.g., 4 x 8 x 4) to the size of a standard shipping container. While shipping container sizes vary, a standard 20-foot ISO shipping container size allows for the transportation of portable-sized units; such containers are typically approximately 8 feet wide, 20 feet long, and 8.5 to 9.5 feet high. Other smaller shipping containers can be used for smaller portable devices, such as those having a 10-foot or 8-foot length combined with the height and width dimensions mentioned above.

[0114] Such small-scale systems can be attached to small end-user equipment (e.g., welding torches such as acetylene or oxyacetylene torches) or to small storage facilities or tanks. In one embodiment, a 5 kW plasma-based hydrocarbon treatment system mini-unit with dimensions of 4 feet wide by 8 feet long by 4 feet high can produce an acetylene-hydrogen mixture with more than 50% acetylene in a quantity sufficient to supply at least five oxygen-fuel cutting torches in simultaneous, continuous use. In embodiments, the power range for the plasma-based hydrocarbon treatment system mini-unit can range from about 1 kW to about 500 kW, and a power range can be selected for the desired commercial application. Such plasma-based hydrocarbon treatment systems can be designed to be mobile. As mentioned above, larger units, for example, up to the size of a standard ISO 20-foot shipping container, can also be designed to be mobile. In embodiments, mobile plasma-based hydrocarbon treatment systems can be deployed to remote locations such as construction sites, demolition sites, shipyards, or pipelines or offshore oil rigs, depending on the availability of a mixed gas stream, such as natural gas or biogas, electricity, and water.

[0115] FIG. 13 provides a block diagram of a plasma-based hydrocarbon processing system 1300 suitable for industrial applications, and capable of small- and large-scale scalability. As shown in FIG. 13 , a plasma reactor 1302, substantially as described above, has an input feed gas 1304 containing hydrocarbons, such as methane, ethane, propane, butane, etc., derived from a tank or pipeline, such as a natural gas line or a biogas tank or line. This input feed gas 1304 has a preselected inflow calibrated to produce an exit (exhaust) gas flow 1306 from the system 1300 that is ultimately suitable for a particular industrial purpose, such as metal cutting. In embodiments, an input feed gas 1304 such as methane or a methane-dense mixture, e.g., natural gas or biogas, may be used. In embodiments, a liquid source of input feed gas 1304, such as propane or butane, is advantageous because such a feed gas source may be readily available in certain regions or facilities where locally produced gas sources, such as natural gas or biogas, are not available.

[0116] In this figure, the direction of gas flow is indicated by arrow 1308 and other directional arrows. As an example of gas flows useful for system 1300, a gas inlet in the range of about 0 to about 50 SLM can be selected; in one embodiment, a gas inlet of 5 SLM can result in a gas outlet of about 10 SLM. In an embodiment, input feed gas 1304 enters plasma reactor 1302 as the sole gas inlet. In another embodiment, a separate gas input from recycled gas stream 1310 enters plasma reactor 1302 through a separate inlet nozzle (not shown) and is combined with input feed gas 1304 within plasma reactor 1302, for example, using a gas injector (not shown) as described in previous figures.

[0117] In one embodiment, the effluent 1306 from the plasma reactor 1302 contains approximately 14% acetylene, 84% hydrogen, and 2% methane, which may be further processed by other components of the system. Various carbon species by-products, including higher carbon products and carbon particles, are entrained in the gaseous effluent 1306, which may be removed in certain embodiments before delivering the gaseous product to an end user. These by-products may be removed in a solids and liquids trap 1312, through which the effluent gas 1306 passes after processing in the plasma reactor 1302. After removing the by-products, the gaseous stream 1306 is processed by a hydrogen separation membrane system 1314 or a pressure swing adsorber, which removes hydrogen. Such processing may separate an acetylene-rich stream 1318 from a hydrogen-rich stream 1320, making the acetylene-rich stream 1318 available to an end user for industrial purposes, such as metal cutting. In other embodiments, for example, if the gaseous effluent is used for welding or other industrial applications that do not require a purified acetylene stream, there is no advantage to removing the higher carbon products. However, it is understood that higher carbon products can foul hydrogen separation membranes, so these species should be removed if a hydrogen separation membrane system is used; alternatively, a mixed effluent stream containing higher carbon products may use a hydrotreating system such as a pressure swing adsorber in place of a hydrogen separation membrane system, where commercially convenient.

[0118] As shown in the figure, the acetylene-rich stream 1318, which has been treated to remove higher carbon products and hydrogen, can be directed to various end uses or storage 1322. For example, the acetylene-rich stream 1318 can be directed to a pressurized tank, from which an end user can withdraw the gas mixture for use in a metal-cutting torch; advantageously, if the acetylene-rich stream 1318 is stored, the plasma-based hydrocarbon treatment system can be run intermittently on an as-needed basis to fill the tank(s) for subsequent use. In one embodiment, the acetylene-rich stream 1318 can contain approximately 50% acetylene, along with other components such as hydrogen, methane, and, if applicable, other gaseous additives. The acetylene-rich stream 1318 can be produced at a flow of approximately 2.1 SLM. In one embodiment, the hydrogen-rich stream 1320 can contain approximately 4% acetylene and 96% hydrogen for a total flow of approximately 7.9 SLM. In embodiments, two or more separation membrane systems may be used to increase the concentration of acetylene in the acetylene-rich product stream 1318, although small-scale systems may be designed with a single separation membrane system to limit the overall size of the apparatus.

[0119] 13, the hydrogen-rich stream 1320 may be directed through a splitter 1322 that may separate the hydrogen-rich stream 1320 into two sub-streams 1320a and 1320b, one (1320a) for end use, disposal, and / or storage, and one (1320b) for recycle as recycle gas stream 1310 to the plasma reactor 1302, where the recycle gas stream may be processed along with the input feed gas 1304. The splitter 1322 may be formed of components well known to those skilled in the art, such as, for example, Y-valves, mass flow controllers, etc. The non-recycled hydrogen-rich sub-stream 1320a may be vented, disposed of, collected, combusted, or otherwise used as required by the particular industrial setting.

[0120] The hydrogen-rich substream 1320b used for recycle can have the same composition as the substream 1320a directed to end use, disposal, and / or storage. In one embodiment, a recycle flow 1310 of approximately 5 SLM, having a composition of approximately 97.5% hydrogen and 2.5% acetylene, can be redirected to the plasma reactor 1302, resulting in a recycle flow of approximately 5 SLM hydrogen. The recycle stream 1310 combined with the input feed gas 1304 is used for chemical conversion in the plasma reactor 1302 to produce the effluent gas 1306, as described above. In embodiments, the percentage for recycle can be adjusted based on user requirements. For recycle, a mass flow controller metering the amount of hydrogen-rich gas 1320b for recycle provides a specific consistency, with the remainder directed to end use, disposal, or storage.

[0121] FIG. 14 shows in more detail a modular plasma-based hydrocarbon treatment system 1400 suitable for small- or large-scale use, with arrows indicating the direction of gas flow. As shown in FIG. 14, a gas pipeline 1404, e.g., a natural gas pipeline, can provide the inlet gas for the microwave plasma reactor 1402, although any source of inlet gas can be used (e.g., a supply tank containing gas such as that available for C1-C4 alkanes, or a line or tank delivering biogas). The inlet gas can be supplemented with a recycle stream 1408 containing hydrogen-rich gas. After processing in the microwave plasma reactor 1402, the effluent gas passes through a heavy liquid trap 1412, which removes higher hydrocarbons using a combination of cold traps and / or carbon adsorbers. As a next step, the effluent gas passes through a filter 1414, which removes particulate matter, e.g., carbon soot. A vacuum pump 1418 then adjusts the air pressure, and the gas is then compressed by a compressor 1422 and passed through a hydrogen separator 1424. The plasma reactor 1402, heavy liquid trap 1412, solids filter 1414, and vacuum pump 1418 are grouped together as reactor subsystem 1420, which may be located near hydrogen recycle subsystem 1410 and emissions control subsystem 1434, or these subsystems may be in fluid communication with each other but located remotely from each other, as is convenient for a particular industrial application.

[0122] As previously described, hydrogen separator 1424 can include one or more hydrogen separation units; in an exemplary embodiment, each hydrogen separation unit can include one or more hydrogen separation membranes, although other configurations and separator technologies (e.g., pressure swing adsorber technology for separating hydrogen) can be used. The configuration of the hydrogen separator units can be adapted to allow for less or more acetylene enrichment in the effluent acetylene-rich stream 1428. Depending on the desired industrial application, this effluent stream 1428 can be used directly as a cutting stream or stored as a product stream. In one embodiment, the gas remaining after removing the acetylene-rich stream 1424 contains a high percentage of hydrogen. As previously described, this hydrogen-rich stream can be split into two substreams in splitter 1432, with one stream 1408 designated for recycle and one stream 1430 designated for disposal, discharge, combustion, commercialization, or other use if desired.

[0123] An effluent management subsystem, substantially as previously described, may be integrated with a reactor subsystem (including a gas delivery subsystem, microwave subsystem, and vacuum subsystem, previously described but not shown in FIG. 14) within a single mini-unit for specific applications. The size, number, and complexity of the components required for the effluent separation process may affect the overall system size. In one embodiment, a single plasma reactor may use a single hydrogen separation subsystem to provide a small footprint, which may include one or two hydrogen separation membranes or other separation subsystem technologies such as pressure swing adsorption. In one embodiment, a separation subsystem, for example, for hydrogen separation, may be integrated with a plasma-based hydrocarbon processing system.

[0124] In an embodiment of a modular plasma-based hydrocarbon processing system using a single hydrogen separation unit with a single separation membrane, the effluent gas from the reactor may contain the following gas components at a flow rate of 10 SLM: 14% acetylene, 81% hydrogen, 2% methane, and 3% nitrogen. After processing through the hydrogen separation unit with a single separation membrane, a hydrogen-rich stream is formed at a flow rate of 7 SLM containing the following gas components: 4% acetylene, 96% hydrogen. Simultaneously, an acetylene-rich stream is formed at a flow rate of 3 SLM containing the following gas components: 50% acetylene, 27% hydrogen, 9% methane, and 14% nitrogen. Using this process, 93.75% acetylene retention is achieved in the acetylene-rich stream, and 86.5% hydrogen is recycled. The flow rates and molar ratios of the various gas stream components for the single-membrane hydrogen separation system are shown in Table 3 below. [Table 3]

[0125] The two-membrane hydrogen separation unit allows more hydrogen to be extracted from the reactor effluent gas, producing a hydrogen-rich stream containing 1.2% acetylene and 98.8% hydrogen at a flow rate of 7 SLM. This system is used to produce an acetylene-rich stream containing the following gas components: 45% acetylene, 38% hydrogen, 7% methane, and 10% nitrogen at a flow rate of 3 SLM. The flow rates and molar ratios of the various gas stream components for the two-membrane hydrogen separation system are shown in Table 4 below. [Table 4]

[0126] A wide variety of industrial applications can be envisioned for the small-scale or modular plasma-based hydrocarbon processing system described herein. As mentioned above, a major industrial application for acetylene is in the metalworking industry, e.g., metal cutting. For these purposes, an appropriately sized plasma-based hydrocarbon processing system according to the present disclosure can be used directly or via a storage tank to provide fuel for metal cutting. The plasma-based hydrocarbon processing system can also be coupled with other systems to provide product versatility and increase efficiency in the metalworking industry. As an example, in an oxyacetylene steel cutting facility, the plasma-based hydrocarbon processing system can be used in combination with an air separation unit (ASU). The ASU can separate air into a nitrogen-rich stream and an oxygen-rich stream, which can then be combined with the gas stream(s) used by or produced by a microwave plasma reactor unit. Using this combination of equipment, operators can generate all the gas feedstocks needed for steel fabrication on-site. [Example]

[0127] Example Example 1 A precursor gas flow consisting of 60 standard liters per minute of 99.9% pure methane, 90 standard liters per minute of 99.9% pure hydrogen, and 6 standard liters per minute of nitrogen was delivered through a gas injector apparatus similar to that described in Figures 4A and 4B to a 50 mm outer diameter, 45 mm inner diameter quartz tube maintained at 70 Torr pressure. The precursor gas was subjected to 19 kW of incident 915 MHz microwave power in a plasma reactor apparatus similar to that described in Figure 3. 95.7% of the methane contained in the precursor gas was converted to hydrogen and hydrocarbon products. The hydrocarbon composition of the effluent gas leaving the reactor, as analyzed by gas chromatography, is listed in Table 5 below. [Table 5]

[0128] The effluent gases from the reactor were passed through an air-cooled heat sink and then through a corrugated filter paper before being exhausted from the vacuum pump. The effluent gases were then passed through a cold trap operating at 10°C and a further filter.

[0129] A portion of the effluent gas was then passed through an adsorption column containing high surface area activated carbon. The composition of the effluent gas at the outlet of the adsorption column is shown in Table 6 below. [Table 6]

[0130] After passing through the adsorption column, a portion of the effluent gas was then passed through an absorption column. To preferentially absorb acetylene, a solvent, N-methylpyrrolidone, was flowed countercurrently to the effluent gas. Upon exiting the absorption column, the solvent with the absorbed acetylene was pumped to a second column for solvent recovery and heated to 120-140°C. In the second column, acetylene and related gases were removed from the solvent as a purified product gas stream, which was recycled back into the system. Table 7 below shows the composition of the purified product gas stream exiting the second column. [Table 7]

[0131] Example 2 A precursor gas flow consisting of 20 standard liters per minute of 99.9% pure methane, 20 standard liters per minute of ethane, 95 standard liters per minute of 99.9% pure hydrogen, and 6 standard liters per minute of nitrogen was fed through the plasma reactor apparatus described in Example 1 and reacted with 18 kW of incident 915 MHz microwave power using the plasma reactor apparatus used in Example 1. 97.9% of the methane and ethane contained in the feed gas was converted to hydrogen and hydrocarbon products. The hydrocarbon composition of the reactor effluent gas, as analyzed by gas chromatography, is set forth below in Table 8. [Table 8]

[0132] Example 3 A precursor gas flow consisting of 110 standard liters per minute of 99.9% pure methane and 11 standard liters per minute of nitrogen was delivered to an 80 mm outer diameter, 75 mm inner diameter quartz tube through a gas injector apparatus similar to that described in Figures 4A and 4B. The precursor gas was subjected to 11 kW of incident 915 MHz microwave power in the plasma reactor apparatus described in Figure 3. 50.7% of the methane contained in the precursor gas was converted to hydrogen and hydrocarbon products. 7% of the converted methane yielded carbon solids and polycyclic aromatic hydrocarbons. 76% of the converted methane yielded acetylene.

[0133] Example 4 A precursor gas flow consisting of 100 standard liters per minute of 99.9% pure methane, 160 standard liters per minute of 99.9% pure hydrogen, and 10 standard liters per minute of nitrogen was delivered through a gas injector similar to that described in Figures 4A and 4B to a 50 mm outer diameter, 45 mm inner diameter quartz tube maintained at 70 Torr. The precursor gas was subjected to 29 kW of incident 915 MHz microwave power in a plasma reactor apparatus similar to that described in Figure 3. 90.3% of the methane contained in the precursor gas was converted to hydrogen products and hydrocarbons. The hydrocarbon composition of the effluent gas leaving the reactor is listed in Table 9 below. [Table 9]

[0134] Example 5 A precursor gas flow consisting of 130 standard liters per minute of 99.9% pure methane and 13 standard liters per minute of nitrogen was delivered to an 80 mm outer diameter, 75 mm inner diameter quartz tube maintained at 48 Torr through a gas injector apparatus similar to that described in Figures 4a and 4b. The precursor gas was subjected to 24.3 kW of incident 915 MHz microwave power in a plasma reactor apparatus similar to that described in Figure 3. 85.2% of the methane contained in the precursor gas was converted to hydrogen and hydrocarbon products.

[0135] Example 6 A precursor gas flow consisting of 74 standard liters per minute of 99.9% pure methane, 40 standard liters per minute of 99.9% pure hydrogen, and 88 standard liters per minute of nitrogen was delivered to an 80 mm outer diameter, 75 mm inner diameter quartz tube maintained at 70 Torr through a gas injector apparatus similar to that described in Figures 4A and 4B. The precursor gas was subjected to 23.9 kW of incident 915 MHz microwave power in a plasma reactor apparatus similar to that described in Figure 3. 95.1% of the methane contained in the precursor gas was converted to hydrogen and hydrocarbon products.

[0136] Example 7 A precursor gas flow consisting of 47 standard liters per minute of 99.9% pure methane, 110 standard liters per minute of 99.9% pure hydrogen, and 5 standard liters per minute of nitrogen was delivered to an 80 mm outer diameter, 75 mm inner diameter quartz tube maintained at 65 Torr through a gas injector apparatus similar to that described in Figures 4a and 4b. The precursor gas was subjected to 15.6 kW of incident 915 MHz microwave power in a plasma reactor apparatus similar to that described in Figure 3. 89.7% of the methane contained in the precursor gas was converted to hydrogen and hydrocarbon products.

[0137] Example 8 A precursor gas flow consisting of 90 standard liters per minute of 99.9% pure methane, 135 standard liters per minute of 99.9% pure hydrogen, and 9 standard liters per minute of nitrogen was delivered to a 38 mm outer diameter, 35 mm inner diameter quartz tube maintained at 105 Torr through a gas injector apparatus similar to that described in Figures 4A and 4B. The precursor gas was subjected to 25 kW of incident 915 MHz microwave power in a plasma reactor apparatus similar to that described in Figure 3. 92.0% of the methane contained in the precursor gas was converted to hydrogen and hydrocarbon products.

[0138] Example 9 A precursor gas flow consisting of 15 standard liters per minute of 99.9% pure butane, 90 standard liters per minute of 99.9% pure hydrogen, and 6 standard liters per minute of nitrogen was delivered to a 50 mm outer diameter, 45 mm inner diameter quartz tube maintained at 50 Torr through a gas injector apparatus similar to that described in Figures 4a and 4b. The precursor gas was subjected to 17.7 kW of incident 915 MHz microwave power in a plasma reactor apparatus similar to that described in Figure 3. 100% of the butane contained in the precursor gas was converted to hydrogen and hydrocarbon products with a methane yield of 0.6%.

[0139] Example 10 A precursor gas flow consisting of 30 standard liters per minute of 99.9% pure ethane, 90 standard liters per minute of 99.9% pure hydrogen, and 6 standard liters per minute of nitrogen was delivered to a 50 mm outer diameter, 45 mm inner diameter quartz tube maintained at 126 Torr through a gas injector apparatus similar to that described in Figures 4a and 4b. The precursor gas was subjected to 16 kW of incident 915 MHz microwave power in a plasma reactor apparatus similar to that described in Figure 3. 100% of the ethane contained in the precursor gas was converted to hydrogen and hydrocarbon products with a methane yield of 3.3%. The hydrocarbon composition of the effluent gas leaving the reactor is listed in Table 10 below. [Table 10]

[0140] Example 11 A precursor gas flow consisting of 8.6 standard liters per minute of 99.9% pure propane, 8.6 standard liters per minute of 99.9% pure butane, 88 standard liters per minute of 99.9% pure hydrogen, and 6 standard liters per minute of nitrogen was delivered to a 50 mm outer diameter, 45 mm inner diameter quartz tube maintained at 70 Torr through a gas injector apparatus similar to that described in Figures 4A and 4B. The precursor gas was subjected to 16 kW of incident 915 MHz microwave power in a plasma reactor apparatus similar to that described in Figure 3. 100% of the ethane contained in the precursor gas was converted to hydrogen and hydrocarbon products with a methane yield of 3.2%. The hydrocarbon composition of the effluent gas leaving the reactor is listed in Table 11 below. [Table 11]

[0141] Example 12 The plasma reactor system described in Example 1 was used, producing an effluent gas at 250 liters per minute. After the system's internal vacuum pump, solid carbon by-products were removed with a simple in-line filter. Liquid hydrocarbon condensates containing more than 14 carbon atoms were separated from the stream in a cold trap operated at -20°C. Without further hydrocarbon removal, the effluent was passed directly into an 8-inch internal diameter stainless steel vessel containing 0.4 kg of blank 100-200 mesh alpha alumina mixed with 1.8 kg of 100-200 mesh alpha alumina doped with 3 wt% metallic palladium and 4 wt% metallic silver. The catalyst bed, with an internal, open-loop water cooling system, was maintained at 350°C. A gas mixture containing 50% hydrogen, 11% ethylene, 0.5% ethane, and 38.5% methane was obtained; the acetylene content in the gas mixture was intentionally kept below 100 ppm.

[0142] Example 13 The plasma reactor system described in Example 1 was used. The 1 liter per minute effluent gas stream was further divided and processed as described in this example. After the vacuum pump, solid carbon by-products were removed with a ceramic regenerated filter. Liquid hydrocarbon condensates containing more than 10 carbon atoms were separated from the stream in a cold trap operated at -30°C. The effluent gas then passed through a stainless steel vessel containing 20 grams of high-surface-area activated carbon doped with 0.01% metallic palladium. At this point, the effluent gas contained 85% hydrogen, 8% acetylene, 4% ethylene, 0.6% vinyl acetylene, and the balance methane. Vinyl acetylene was removed by bubbling it through a 500 mL vessel containing 300 mL of concentrated sulfuric acid at room temperature, followed by bubbling it through a vessel containing 100 mL of room-temperature water to trap the evaporated sulfuric acid. Finally, the gas stream was dried by passing it through 10 grams of calcium sulfate desiccant.

[0143] While the present invention has been particularly shown and described with reference to preferred embodiments thereof, it will be apparent to those skilled in the art that various changes in form and detail can be made therein without departing from the scope of the invention as encompassed by the appended claims. Unless otherwise indicated, all numbers expressing reaction conditions, quantities, amounts, ranges, and the like used in the specification and claims are understood to be modified in all instances by the term "about." Accordingly, unless indicated to the contrary, the numerical parameters set forth herein are approximations that may vary depending upon the desired properties sought to be achieved by the present invention.

Claims

1. 1. A method for processing a hydrocarbon-containing inlet gas into an outlet gas product, comprising: The method includes delivering a hydrocarbon-containing inlet gas and a further gas to a system; The system is: Includes a gas delivery subsystem, a plasma reaction chamber, a microwave subsystem, and an effluent separation and disposal subsystem; a hydrocarbon-containing inlet gas and a further gas are delivered to a plasma reaction chamber; the hydrocarbon-containing inlet gas comprises methane and the further gas comprises hydrogen; The ratio of methane to hydrogen is 1:1 to 1:3; a gas delivery subsystem in fluid communication with the plasma reaction chamber; the gas delivery subsystem includes a delivery conduit and a gas injector, the delivery conduit including a supply gas delivery circuit that delivers the hydrocarbon-containing input gas to the gas injector, and the delivery conduit including a further gas delivery circuit that delivers a further gas to the gas injector; a delivery conduit in fluid communication with the gas injector, the delivery conduit delivering the hydrocarbon-containing input gas and hydrogen to the gas injector, each being delivered to the plasma reaction chamber through separate paths; the plasma reaction chamber is disposed within an elongated reactor tube having a proximal end and a distal end, the elongated reactor tube being dimensionally suitable for interaction with a microwave subsystem; a microwave subsystem directing microwave energy to the plasma reaction chamber to impart energy to the hydrocarbon-containing inlet gas, thereby forming a non-thermal plasma in the plasma reaction chamber, the plasma effecting conversion of methane in the hydrocarbon-containing inlet gas to effluent gas products, the effluent gas products comprising acetylene and hydrogen; an effluent gaseous product emerges from the distal end of the elongated reactor tube to form an effluent stream that enters an effluent separation and disposal subsystem; the microwave subsystem includes an applicator for directing microwave energy to the plasma reaction chamber, the plasma reaction chamber being disposed in a region of the elongated reactor tube that passes through and perpendicularly intersects the applicator; the microwave subsystem further includes a power source, a magnetron, and a waveguide, the power source energizing the magnetron to produce microwave energy, the microwave energy being conveyed by the waveguide to the applicator, and the applicator directing the microwave energy to the reaction chamber within the elongated reactor tube, thereby forming a plasma in the plasma reaction chamber; the effluent separation and disposal subsystem includes an absorption column, the absorption column absorbing acetylene; the gas injector includes an injector body portion including two or more coaxially aligned separate gas feed bodies, a first gas feed body delivering a hydrocarbon-containing inlet gas to the plasma reaction chamber through a first set of one or more nozzles, and a second gas feed body delivering an additional gas to the plasma reaction chamber through a second set of one or more nozzles; The method, wherein at least one of the one or more nozzles is oriented at an angle relative to a longitudinal axis of the plasma reaction chamber or at an angle relative to a transverse axis of the plasma reaction chamber.

2. A method for processing a hydrocarbon-containing inlet gas into an outlet gas product, comprising: The method includes delivering a hydrocarbon-containing inlet gas and a further gas to a system; The system is: Includes a gas delivery subsystem, a plasma reaction chamber, a microwave subsystem, and an effluent separation and disposal subsystem; a hydrocarbon-containing inlet gas and a further gas are delivered to a plasma reaction chamber; the hydrocarbon-containing inlet gas comprises methane and the further gas comprises hydrogen; The ratio of methane to hydrogen is 1:1 to 1:3; a gas delivery subsystem in fluid communication with the plasma reaction chamber; the gas delivery subsystem includes a delivery conduit and a gas injector, the delivery conduit including a supply gas delivery circuit that delivers the hydrocarbon-containing input gas to the gas injector, and the delivery conduit including a further gas delivery circuit that delivers a further gas to the gas injector; a delivery conduit in fluid communication with the gas injector, the delivery conduit delivering the hydrocarbon-containing input gas and hydrogen to the gas injector, each being delivered to the plasma reaction chamber through separate paths; the plasma reaction chamber is disposed within an elongated reactor tube having a proximal end and a distal end, the elongated reactor tube being dimensionally suitable for interaction with a microwave subsystem; a microwave subsystem directing microwave energy to the plasma reaction chamber to impart energy to the hydrocarbon-containing inlet gas, thereby forming a non-thermal plasma in the plasma reaction chamber, the plasma effecting conversion of methane in the hydrocarbon-containing inlet gas to effluent gas products, the effluent gas products comprising acetylene and hydrogen; an effluent gaseous product emerges from the distal end of the elongated reactor tube to form an effluent stream that enters an effluent separation and disposal subsystem; the microwave subsystem includes an applicator for directing microwave energy to the plasma reaction chamber, the plasma reaction chamber being disposed in a region of the elongated reactor tube that passes through and perpendicularly intersects the applicator; the microwave subsystem further includes a power source, a magnetron, and a waveguide, the power source energizing the magnetron to produce microwave energy, the microwave energy being conveyed by the waveguide to the applicator, and the applicator directing the microwave energy to the reaction chamber within the elongated reactor tube, thereby forming a plasma in the plasma reaction chamber; the effluent separation and disposal subsystem includes an absorption column, the absorption column absorbing acetylene; the gas injector includes an injector body portion including two or more coaxially aligned separate gas feed bodies, a first gas feed body delivering a hydrocarbon-containing inlet gas to the plasma reaction chamber through a first set of one or more nozzles, and a second gas feed body delivering an additional gas to the plasma reaction chamber through a second set of one or more nozzles; The method, wherein at least one of the one or more nozzles is oriented at an angle relative to a longitudinal or lateral axis of the injector body.

3. A method for processing a hydrocarbon-containing inlet gas into an outlet gas product, comprising: The method includes delivering a hydrocarbon-containing inlet gas and a further gas to a system; The system is: Includes a gas delivery subsystem, a plasma reaction chamber, a microwave subsystem, and an effluent separation and disposal subsystem; a hydrocarbon-containing inlet gas and a further gas are delivered to a plasma reaction chamber; the hydrocarbon-containing inlet gas comprises methane and the further gas comprises hydrogen; The ratio of methane to hydrogen is 1:1 to 1:3; a gas delivery subsystem in fluid communication with the plasma reaction chamber; the gas delivery subsystem includes a delivery conduit and a gas injector, the delivery conduit including a supply gas delivery circuit that delivers the hydrocarbon-containing input gas to the gas injector, and the delivery conduit including a further gas delivery circuit that delivers a further gas to the gas injector; a delivery conduit in fluid communication with the gas injector, the delivery conduit delivering the hydrocarbon-containing input gas and hydrogen to the gas injector, each being delivered to the plasma reaction chamber through separate paths; the plasma reaction chamber is disposed within an elongated reactor tube having a proximal end and a distal end, the elongated reactor tube being dimensionally suitable for interaction with a microwave subsystem; a microwave subsystem directing microwave energy to the plasma reaction chamber to impart energy to the hydrocarbon-containing inlet gas, thereby forming a non-thermal plasma in the plasma reaction chamber, the plasma effecting conversion of methane in the hydrocarbon-containing inlet gas to effluent gas products, the effluent gas products comprising acetylene and hydrogen; an effluent gaseous product emerges from the distal end of the elongated reactor tube to form an effluent stream that enters an effluent separation and disposal subsystem; the microwave subsystem includes an applicator for directing microwave energy to the plasma reaction chamber, the plasma reaction chamber being disposed in a region of the elongated reactor tube that passes through and perpendicularly intersects the applicator; the microwave subsystem further includes a power source, a magnetron, and a waveguide, the power source energizing the magnetron to produce microwave energy, the microwave energy being conveyed by the waveguide to the applicator, and the applicator directing the microwave energy to the reaction chamber within the elongated reactor tube, thereby forming a plasma in the plasma reaction chamber; the effluent separation and disposal subsystem includes an absorption column, the absorption column absorbing acetylene; a gas injector conveying the hydrocarbon-containing inlet gas and the additional gas to a proximal portion of the elongated reactor tube, the hydrocarbon-containing inlet gas and the additional gas flowing distally from the proximal portion toward the plasma reaction chamber; The method wherein the gas injector is centrally located within the proximal portion and the first set of one or more nozzles and the second set of one or more nozzles are oriented peripherally.

4. A method for processing a hydrocarbon-containing inlet gas into an outlet gas product, comprising: The method includes delivering a hydrocarbon-containing inlet gas and a further gas to a system; The system is: Includes a gas delivery subsystem, a plasma reaction chamber, a microwave subsystem, and an effluent separation and disposal subsystem; a hydrocarbon-containing inlet gas and a further gas are delivered to a plasma reaction chamber; the hydrocarbon-containing inlet gas comprises methane and the further gas comprises hydrogen; The ratio of methane to hydrogen is 1:1 to 1:3; a gas delivery subsystem in fluid communication with the plasma reaction chamber; the gas delivery subsystem includes a delivery conduit and a gas injector, the delivery conduit including a supply gas delivery circuit that delivers the hydrocarbon-containing input gas to the gas injector, and the delivery conduit including a further gas delivery circuit that delivers a further gas to the gas injector; a delivery conduit in fluid communication with the gas injector, the delivery conduit delivering the hydrocarbon-containing input gas and hydrogen to the gas injector, each being delivered to the plasma reaction chamber through separate paths; the plasma reaction chamber is disposed within an elongated reactor tube having a proximal end and a distal end, the elongated reactor tube being dimensionally suitable for interaction with a microwave subsystem; a microwave subsystem directing microwave energy to the plasma reaction chamber to impart energy to the hydrocarbon-containing inlet gas, thereby forming a non-thermal plasma in the plasma reaction chamber, the plasma effecting conversion of methane in the hydrocarbon-containing inlet gas to effluent gas products, the effluent gas products comprising acetylene and hydrogen; an effluent gaseous product emerges from the distal end of the elongated reactor tube to form an effluent stream that enters an effluent separation and disposal subsystem; the microwave subsystem includes an applicator for directing microwave energy to the plasma reaction chamber, the plasma reaction chamber being disposed in a region of the elongated reactor tube that passes through and perpendicularly intersects the applicator; the microwave subsystem further includes a power source, a magnetron, and a waveguide, the power source energizing the magnetron to produce microwave energy, the microwave energy being conveyed by the waveguide to the applicator, and the applicator directing the microwave energy to the reaction chamber within the elongated reactor tube, thereby forming a plasma in the plasma reaction chamber; the effluent separation and disposal subsystem includes an absorption column, the absorption column absorbing acetylene; a gas injector conveying the hydrocarbon-containing inlet gas and the additional gas to a proximal portion of the elongated reactor tube, the hydrocarbon-containing inlet gas and the additional gas flowing distally from the proximal portion toward the plasma reaction chamber; The method wherein the gas injector is peripherally positioned within the proximal portion and the first set of one or more nozzles and the second set of one or more nozzles are centrally oriented.

5. A method according to any one of claims 1 to 4, wherein the hydrocarbon-containing inlet gas is derived from a mixed gas source.

6. 6. The method of claim 5, wherein the mixed gas source is natural gas or biogas.

7. A process according to any one of claims 1 to 4, wherein the hydrocarbon-containing inlet gas comprises methane.

8. 5. The method according to any one of claims 1 to 4, wherein the further gas transport circuit is a recycled gas transport circuit that delivers recycled gas to the gas injector, and the further gas is recycled gas.

9. 9. The method of claim 8, wherein the recycle gas is a hydrogen-rich reactant gas.

10. 3. The method of claim 1 or 2, wherein the combined gas flow from the first set of nozzles and the second set of nozzles creates a vortex flow within the plasma reaction chamber.

11. The method of any one of claims 1 to 4, wherein the elongated reactor tube is a quartz tube.

12. 5. The method of claim 1, wherein the plasma reaction chamber is located approximately midway along the elongated reactor tube.

13. 3. The method of claim 1 or 2, wherein the gas injector conveys the hydrocarbon-containing inlet gas and the additional gas to a proximal portion of the elongated reactor tube, and the hydrocarbon-containing inlet gas and the additional gas flow distally from the proximal portion toward the plasma reaction chamber.

14. 14. The method of claim 13, wherein the gas injector is centrally located within the proximal portion and the first set of one or more nozzles and the second set of one or more nozzles are oriented peripherally.

15. 14. The method of claim 13, wherein the gas injector is peripherally disposed within the proximal portion, and the first set of one or more nozzles and the second set of one or more nozzles are centrally oriented.

16. 5. The method of any one of claims 1 to 4, wherein the magnetron produces L-band microwave energy.

17. 5. The method of any one of claims 1 to 4, wherein the method further comprises removing higher hydrocarbons and / or carbon solids, wherein higher hydrocarbons are hydrocarbons having 3 or more carbon atoms.

18. The method of any one of claims 1 to 4, wherein the effluent separation and disposal subsystem further comprises a hydrogen separation subsystem.

19. 20. The method of claim 18, wherein the hydrogen separation subsystem is in fluid communication with a recycle gas delivery circuit, and wherein hydrogen collected by the hydrogen separation subsystem is recycled to the recycle gas delivery circuit.

20. 5. The method of claim 1, wherein the system comprises the gas delivery subsystem, the plasma reaction chamber, the microwave subsystem, and the effluent separation and disposable subsystem, and further comprises a vacuum subsystem that creates a first reduced pressure environment for effluent products passing through one or more components of the effluent separation and disposable subsystem.

21. 21. The method of claim 20, wherein the vacuum sub-system creates a second reduced pressure environment within the elongated reactor tube.

22. 22. The method of claim 21, wherein the vacuum subsystem creates a third reduced pressure environment for the gas delivery subsystem.

23. 23. The method of claim 22, wherein the vacuum subsystem produces first, second, and third reduced pressure environments.

24. 24. The method of claim 23, wherein the first, second and third reduced pressure environments are similar.

25. 5. The method according to claim 1, wherein the acetylene is absorbed using a solvent having an affinity for acetylene selected from the group consisting of methanol, ammonia, toluene, benzene, kerosene, butyrolactone, acetonitrile, propionitrile, methoxypropionitrile, acetone, furfural, N,N-dimethylformamide, N,N-diethylformamide, N,N-dimethylacetamide, N,N-diethylacetamide, N-formylmorpholine, and N-alkylpyrrolidone.

26. 26. The method of claim 25, wherein the acetylene is absorbed using N-methylpyrrolidone.

27. 5. The process according to claim 1, wherein the acetylene is desorbed and then recovered.

28. 26. The method of claim 25, wherein the absorbed acetylene is separated from the solvent.

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