Plasma synergistic discharge reactor for co-production of hydrogen and carbon nanotubes through methane cracking

Abstract

The invention discloses a plasma synergistic discharge reactor for co-producing hydrogen and a carbon nano tube through methane cracking, a discharge cavity is formed in a reaction tube body, and a shared high-voltage electrode is arranged at the upper part in the discharge cavity; the low-voltage electrode system is arranged in the discharge cavity, the low-voltage electrode system comprises a multi-needle low-voltage electrode and a metal net ground electrode, the multi-needle low-voltage electrode is located under the common high-voltage electrode, and the metal net ground electrode is wound on the quartz dielectric tube; an annular dielectric barrier discharge area is formed between the shared high-voltage electrode and the metal net ground electrode, an axial spark discharge area is formed between the shared high-voltage electrode and the multi-needle low-voltage electrode, and the annular dielectric barrier discharge area and the axial spark discharge area are nested in the discharge cavity in space and are continuously communicated. And the metal net ground electrode wraps the common high-voltage electrode and the multi-needle low-voltage electrode. According to the invention, methane gas is ensured to be uniformly distributed before entering a plasma field, and the problems of serious carbon deposition and blockage of the electrode caused by overhigh local concentration are effectively avoided.

Description

Technical Field

[0001] This invention relates to a plasma synergistic discharge reactor for the co-production of hydrogen and carbon nanotubes from methane cracking, belonging to the fields of plasma chemistry and energy and environmental protection technology. Background Technology

[0002] Methane cracking (MDH) is a promising hydrogen production technology that generates clean hydrogen without carbon dioxide while also producing high-value-added solid carbon products such as carbon nanotubes and carbon nanofibers. Compared to traditional thermocatalytic methane cracking, plasma technology offers advantages such as rapid start-up, mild reaction conditions, no need for expensive catalysts, and the ability to handle high concentrations of methane, making it a research hotspot in recent years. Current plasma methane cracking technologies mainly include dielectric barrier discharge (DBD) and spark discharge. However, a single discharge mode has the following limitations in practical applications: 1. Dielectric barrier discharge (DBD): Although the discharge is uniform and highly stable, its electron energy is low, which often makes it difficult to effectively break the CH bonds of methane molecules, resulting in low methane conversion rate and low energy efficiency; 2. Spark discharge: It has extremely high local energy density and can rapidly activate methane molecules, but because it is a filamentary discharge, the discharge area is extremely limited, and the high temperature can easily lead to local overheating in the reactor, causing serious carbon buildup and blockage, resulting in poor stability during continuous operation.

[0003] To combine the advantages of both, existing technologies have proposed a technical route of spark discharge coupled with dielectric barrier discharge. The ideal logic is to use spark discharge to provide high-energy electrons to "ignite" the reaction, and then use dielectric barrier discharge to expand the active reaction region and maintain discharge stability. However, in existing synergistic discharge reactors, the arrangement of the electrode structure is often not scientifically sound, leading to spatial interference or insufficient coupling between the two discharge modes. For example, if the electrode spacing or position is improperly set, the violent shock wave generated by spark discharge may disrupt the uniformity of dielectric barrier discharge, or uneven electric field distribution may cause carbon products to rapidly adhere and deposit on the electrode surface, not only reducing the quality of carbon nanotubes but also causing electrode short circuits or reactor blockage. Summary of the Invention

[0004] The technical problem this invention aims to solve is to overcome the shortcomings of existing technologies and provide a plasma-coordinated discharge reactor for the co-production of hydrogen and carbon nanotubes from methane cracking. This invention employs a reactor coupled with dielectric barrier and spark discharge, utilizing a porous metal plate as a shared high-voltage electrode, which serves as both the high-voltage electrode for dielectric barrier and spark discharge. The dielectric barrier discharge uses a quartz tube with a wall thickness of 4 mm as the dielectric, with an outer metal wire mesh as the dielectric ground electrode. The spark discharge plasma ground electrode adopts a multi-needle-plate structure, with a 32 mm diameter, multi-sixteen-hole disk as its base. Five bullet-shaped multi-needle electrodes, each 2 mm in diameter, are evenly arranged on the disk. The coupling of dielectric barrier and spark discharge enhances the methane cracking capability. This invention develops a reactor with a novel electrode arrangement structure that achieves efficient spatial coupling of spark discharge and dielectric barrier discharge, effectively prevents carbon buildup and blockage, and improves co-production efficiency. This addresses a key problem urgently needing to be solved in the current field of plasma methane cracking.

[0005] Preferably, the present invention provides a plasma co-discharge reactor for methane cracking to co-produce hydrogen and carbon nanotubes, comprising a reaction tube body, a common high-voltage electrode and a low-voltage electrode system. A sealed discharge cavity is formed inside the reaction tube body. The common high-voltage electrode is disposed in the upper part of the discharge cavity and has a porous metal plate structure. The low-voltage electrode system is disposed in the discharge cavity and includes a multi-needle low-voltage electrode and a metal mesh ground electrode. The multi-needle low-voltage electrode is located directly below the common high-voltage electrode, and the metal mesh ground electrode is wound around the quartz dielectric tube.

[0006] A ring-shaped dielectric barrier discharge region is formed between the shared high-voltage electrode and the metal mesh ground electrode, and an axial spark discharge region is formed between the shared high-voltage electrode and the multi-needle low-voltage electrode. The ring-shaped dielectric barrier discharge region and the axial spark discharge region are nested and continuously connected within the discharge cavity. The metal mesh ground electrode encloses the shared high-voltage electrode and the multi-needle low-voltage electrode.

[0007] Preferably, the multi-needle low-voltage electrode includes a porous disk substrate and a number of needle electrodes arranged vertically on the porous disk substrate, with the ends of the needle electrodes being semi-elliptical in shape.

[0008] Preferably, there are 5 needle electrodes, which are evenly distributed on a porous disk substrate with a diameter of 32 mm.

[0009] Preferably, the metal mesh ground electrode is a metal wire mesh wound around the outer wall of the quartz dielectric tube, and the metal mesh ground electrode covers the quartz dielectric tube area corresponding to the annular dielectric barrier discharge region.

[0010] Preferably, the preset distance between the tips of the shared high-voltage electrode and the multi-needle low-voltage electrode is 5-20mm.

[0011] Preferred, the porous metal plate structure is a cylinder with a height of 2mm and a diameter of 32mm, and several large holes with a diameter of 2mm and several small holes with a diameter of less than 2mm are opened on the common high voltage electrode.

[0012] Preferably, the reaction tube body is a quartz dielectric tube with an outer diameter of 40 mm, a wall thickness of 4 mm, and an inner diameter of 32 mm.

[0013] Preferably, a method for using a reactor according to any one of the above claims to perform methane cracking and co-production of hydrogen and carbon nanotubes includes:

[0014] Methane and inert carrier gas are mixed at a preset volume ratio to obtain a methane mixed gas, which is then introduced into the reaction tube body through the gas inlet.

[0015] The plasma power supply is turned on, and dielectric barrier discharge is generated by sharing a high-voltage electrode and a metal mesh ground electrode to preactivate the methane mixture.

[0016] By using a shared high-voltage electrode and a multi-needle low-voltage electrode to generate spark discharge, and in conjunction with dielectric barrier discharge, the pre-activated methane mixture is deeply cracked to produce hydrogen, gaseous hydrocarbons, and carbon nanotubes.

[0017] Hydrogen and gaseous hydrocarbons are collected at the outlet of the quartz dielectric tube, while solid carbon nanotubes are collected at the bottom of the multi-needle low-pressure electrode or the reaction tube body.

[0018] Preferredly, methane and inert carrier gas are mixed at a preset volume ratio of 2:1 to obtain a methane mixed gas.

[0019] Preferably, the plasma power supply has a discharge frequency of 50Hz-1000kHz and an output voltage of 20kV-240kV.

[0020] The beneficial effects achieved by this invention are as follows:

[0021] The common high-voltage electrode of this invention utilizes its porous structure to act as a gas distributor while serving as a discharge electrode, ensuring that the methane gas is evenly distributed before entering the plasma field, effectively avoiding the problem of severe carbon buildup and blockage of the electrode caused by excessively high local concentration.

[0022] The bullet-shaped multi-needle low-voltage electrodes of this invention are evenly distributed, and the multi-point discharge mode expands the coverage area of ​​the spark discharge, solving the problem of limited area of ​​traditional single-point spark discharge, and significantly improving the primary conversion rate of methane molecules.

[0023] This invention relates to a quartz dielectric tube and an externally wound metal mesh ground electrode. The invention uses a quartz tube of a specific thickness as the dielectric, combining its low dielectric constant (range 3.7 to 3.9) and high temperature resistance (long-term operating temperature approximately 600°C). This not only achieves efficient electric field coupling but also solves the technical problem of reactor damage under high-energy spark discharge. A stable dielectric barrier discharge region is formed on the outer periphery of the reactor. The long-lived active particles generated in the annular dielectric barrier discharge region pre-activate methane, reducing the ignition energy consumption of the core region's spark discharge and achieving efficient synergistic energy utilization.

[0024] This invention relates to a spatial coupling layout of needle-plate and dielectric barrier. A high-energy-density spark region is nested within a uniform annular dielectric barrier discharge region. Through the synergistic regulation of the temperature and electric fields, carbon atoms are induced to grow into high-purity carbon nanotubes, while simultaneously suppressing the formation of amorphous carbon and increasing the added value of byproducts.

[0025] This invention enables the annular dielectric barrier discharge region and the spark discharge region to share the same high-voltage electric field source by using a shared high-voltage electrode, thus avoiding electric field interference between the two discharge regions. At the same time, the annular dielectric barrier discharge region surrounds the spark discharge region, forming a spatial layout of "peripheral pre-activation + central deep pyrolysis". After the methane gas is uniformly distributed through the porous metal plate, it is first pre-activated through the annular dielectric barrier discharge region (generating CH3 and H free radicals) and then directly enters the core region of the spark discharge region. This eliminates the need for long-distance transmission and solves the pain points of "insufficient coupling between the two discharge regions and easy recombination of free radicals" in the prior art. Attached Figure Description

[0026] To more clearly illustrate the technical solution of this application, the drawings used in the embodiments will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0027] Figure 1 These are cross-sectional views of some embodiments of this application;

[0028] The meanings of the labels in the attached diagram are as follows: 1-Air inlet; 2-Common high-voltage electrode; 3-Multi-needle low-voltage electrode; 4-Metal mesh ground electrode; 5-Quartz dielectric tube. Detailed Implementation

[0029] In this invention, the terms "first" and "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined with "first" and "second" may explicitly or implicitly include at least one of those features. Furthermore, the technical solutions of the various embodiments can be combined with each other, but only on the basis of being achievable by those skilled in the art. When the combination of technical solutions is contradictory or impossible to implement, such a combination of technical solutions should be considered non-existent and not within the scope of protection claimed by this invention.

[0030] See Figure 1 This application provides a plasma co-discharge reactor for the co-production of hydrogen and carbon nanotubes from methane cracking, comprising: a reaction tube body, the reaction tube body being a quartz dielectric tube 5, the reaction tube body having an outer diameter of 40 mm, a wall thickness of 4 mm, an inner diameter of 32 mm, and forming a closed discharge cavity inside;

[0031] A common high-voltage electrode 2 is set in the upper part of the discharge cavity. The common high-voltage electrode 2 is a porous metal plate structure with a height of 2 mm and a diameter of 32 mm. It is a cylinder with 5 large holes with a diameter of 2 mm and many small holes with a diameter of less than 2 mm.

[0032] The low-voltage electrode system includes: a multi-needle low-voltage electrode 3 disposed in the discharge cavity and located directly below the common high-voltage electrode 2, and a metal mesh ground electrode 4 wound around the quartz dielectric tube 5;

[0033] In this configuration, an annular dielectric barrier discharge region is formed between the shared high-voltage electrode 2 and the metal mesh ground electrode 4, and an axial spark discharge region is formed between the shared high-voltage electrode 2 and the multi-needle low-voltage electrode 3. The two discharge regions are nested and continuously connected within the discharge cavity. The 42mm long metal mesh ground electrode 4 encloses the shared high-voltage electrode 2 and the multi-needle low-voltage electrode.

[0034] The shared high-voltage electrode 2 serves as both the high-voltage end for dielectric barrier discharge and the high-voltage end for spark discharge.

[0035] The multi-needle low-voltage electrode 3 includes a porous disk substrate and a plurality of needle electrodes arranged vertically on the porous disk substrate; the ends of the needle electrodes are semi-elliptical in shape.

[0036] The number of needle electrodes is 5, and the needle electrodes are evenly distributed on a porous disc substrate with 16 small holes and a diameter of 32 mm. The porous disc substrate has 16 small holes.

[0037] The metal mesh ground electrode 4 is a metal wire mesh wound around the outer wall of the quartz dielectric tube 5, and the metal mesh ground electrode 4 covers the tube wall area of ​​the quartz dielectric tube 5 corresponding to the annular dielectric barrier discharge region.

[0038] There is a preset distance between the tips of the common high-voltage electrode 2 and the multi-needle low-voltage electrode 3. The preset distance between the tips can be 5-20mm. The energy density of the spark discharge can be controlled by adjusting the preset distance.

[0039] A method for methane cracking and co-production of hydrogen and carbon nanotubes using the aforementioned reactor includes the following steps:

[0040] Gas proportioning and introduction: Methane and inert carrier gas are mixed in a volume ratio of 2:1 to obtain a methane mixed gas, which is then introduced into the reaction tube body through inlet 1.

[0041] Discharge start-up and activation: Turn on the plasma power supply and generate dielectric barrier discharge through the shared high voltage electrode 2 and the metal mesh ground electrode 4 to pre-activate the methane mixture gas;

[0042] Energy-coordinated pyrolysis: Spark discharge is generated by a shared high-voltage electrode 2 and a multi-needle low-voltage electrode 3. Under the coordination of dielectric barrier discharge, the pre-activated methane mixture is deeply pyrolyzed to generate hydrogen, gaseous hydrocarbons, and carbon nanotubes.

[0043] Product collection: Hydrogen and gaseous hydrocarbons are collected at the outlet of the quartz dielectric tube 5, and solid carbon nanotubes are collected at the multi-needle low-pressure electrode 3 or the bottom of the reaction tube body.

[0044] By adjusting the frequency and voltage of the plasma power supply, a pale purple glow discharge state is achieved within the discharge cavity. The plasma power supply has a discharge frequency of 50Hz-1000kHz and an output voltage of 20kV-240kV.

[0045] The common high-voltage electrode 2 (3mm aperture, 4mm thickness) is fixed to the upper part of the quartz dielectric tube 5 (32mm inner diameter) using a quartz bracket, 50mm from the upper end of the quartz dielectric tube 5. The multi-needle low-voltage electrode (5 needle electrodes, 2mm diameter each) is fixed via a bottom flange, with the needle tip distance from the lower surface of the common high-voltage electrode 2 adjusted to 10mm. The metal mesh ground electrode 4 is wound along the outer wall of the dielectric quartz tube 5 (6 turns / cm), covering the corresponding outer wall area of ​​the common high-voltage electrode 2 (50mm in length). The metal mesh ground electrode 4 is connected to the low-voltage end of the power supply, and the common high-voltage electrode 2 is connected to the high-voltage end of the power supply. The common high-voltage electrode 2 is a porous metal plate, and the metal mesh ground electrode 4 is a 304 stainless steel mesh.

[0046] The various embodiments in this specification are described in a progressive manner. The same or similar parts between the various embodiments can be referred to each other. Each embodiment focuses on describing the differences from other embodiments.

[0047] Other embodiments of the invention will readily occur to those skilled in the art upon consideration of the specification and practice of the invention described herein. This application is intended to cover any variations, uses, or adaptations of the invention that follow the general principles of the invention and include common knowledge or customary techniques in the art not invented herein. The specification and embodiments are to be considered exemplary only.

[0048] Finally, the following points should be noted: First, in the description of this application, it should be noted that, unless otherwise specified and limited, the terms "installation", "connection", "joining", and "fitting" should be interpreted broadly, and can refer to mechanical or electrical connections, or internal connections between two components, or direct connections. "Up", "down", "left", "right", etc. are only used to indicate relative positional relationships. When the absolute position of the described object changes, the relative positional relationship may change.

[0049] Secondly: The accompanying drawings of the embodiments disclosed in this invention only involve the structures involved in the embodiments disclosed in this invention. Other structures can refer to the general design. The above specific embodiments have further described the purpose, technical solution and beneficial effects of this application in detail. It should be understood that the above are only specific embodiments of this application and are not intended to limit the scope of protection of this application. Any modifications, equivalent substitutions, improvements, etc. made on the basis of the technical solution of this application should be included within the scope of protection of this application.

Claims

1. A plasma-co-discharge reactor for methane cracking and co-production of hydrogen and carbon nanotubes, characterized in that, The reaction tube body includes a common high-voltage electrode (2) and a low-voltage electrode system. A sealed discharge cavity is opened inside the reaction tube body. The common high-voltage electrode (2) is located in the upper part of the discharge cavity and has a porous metal plate structure. The low-voltage electrode system is located in the discharge cavity and includes a multi-needle low-voltage electrode (3) and a metal mesh ground electrode (4). The multi-needle low-voltage electrode (3) is located directly below the common high-voltage electrode (2), and the metal mesh ground electrode (4) is wound around the quartz dielectric tube (5). A ring-shaped dielectric barrier discharge region is formed between the shared high-voltage electrode (2) and the metal mesh ground electrode (4), and an axial spark discharge region is formed between the shared high-voltage electrode (2) and the multi-needle low-voltage electrode (3). The ring-shaped dielectric barrier discharge region and the axial spark discharge region are nested in space within the discharge cavity and are continuously connected. The metal mesh ground electrode (4) wraps the shared high-voltage electrode (2) and the multi-needle low-voltage electrode (3).

2. The plasma-coordinated discharge reactor for methane cracking and co-production of hydrogen and carbon nanotubes according to claim 1, characterized in that, The multi-needle low-voltage electrode (3) includes a porous disk substrate and several needle electrodes arranged vertically on the porous disk substrate, with the ends of the needle electrodes being semi-elliptical.

3. The plasma-co-discharge reactor for methane cracking and co-production of hydrogen and carbon nanotubes according to claim 2, characterized in that, There are 5 needle electrodes, which are evenly distributed on a porous disc substrate with a diameter of 32 mm.

4. The plasma-coordinated discharge reactor for methane cracking and co-production of hydrogen and carbon nanotubes according to claim 1, characterized in that, The metal mesh ground electrode (4) is a metal wire mesh wrapped around the outer wall of the quartz dielectric tube (5). The metal mesh ground electrode (4) covers the area of ​​the quartz dielectric tube (5) corresponding to the annular dielectric barrier discharge area.

5. The plasma-coordinated discharge reactor for methane cracking and co-production of hydrogen and carbon nanotubes according to claim 1, characterized in that, The preset distance between the tips of the shared high-voltage electrode (2) and the multi-needle low-voltage electrode (3) is 5-20mm.

6. The plasma-co-discharge reactor for methane cracking and co-production of hydrogen and carbon nanotubes according to claim 1, characterized in that, The porous metal plate structure is a cylinder with a height of 2mm and a diameter of 32mm. Several large holes with a diameter of 2mm and several small holes with a diameter of less than 2mm are opened on the common high voltage electrode (2).

7. The plasma-coordinated discharge reactor for methane cracking and co-production of hydrogen and carbon nanotubes according to claim 1, characterized in that, The reaction tube body is a quartz medium tube (5), with an outer diameter of 40 mm, a wall thickness of 4 mm, and an inner diameter of 32 mm.

8. A method for methane cracking and co-production of hydrogen and carbon nanotubes using the reactor according to any one of claims 1-7, characterized in that, include: Methane and inert carrier gas are mixed at a preset volume ratio to obtain a methane mixture gas. The methane mixture gas is then introduced into the reaction tube body through the inlet (1). Turn on the plasma power supply and generate dielectric barrier discharge through the shared high voltage electrode (2) and the metal mesh ground electrode (4) to pre-activate the methane mixture gas; Using a shared high-voltage electrode (2) and a multi-needle low-voltage electrode (3) to generate spark discharge, and with the synergy of dielectric barrier discharge, the pre-activated methane mixture is deeply cracked to generate hydrogen, gaseous hydrocarbons, and carbon nanotubes. Hydrogen and gaseous hydrocarbons are collected at the outlet of the quartz dielectric tube (5), and solid carbon nanotubes are collected at the multi-needle low-pressure electrode (3) or the bottom of the reaction tube body.

9. The method for co-producing hydrogen and carbon nanotubes by methane cracking using a reactor according to claim 8, characterized in that, Methane and inert carrier gas are mixed at a preset volume ratio of 2:1 to obtain a methane mixed gas.

10. The method for co-producing hydrogen and carbon nanotubes by methane cracking using a reactor according to claim 8, characterized in that, The plasma power supply has a discharge frequency of 50Hz-1000kHz and an output voltage of 20kV-240kV.

Images