RU2841079C2 - Plasma reactor with sliding arc and method of methane conversion using plasma - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: invention relates to a sliding arc plasma reactor comprising a reactor chamber and a sliding arc plasma generator placed in the reactor chamber. Sliding arc plasma generator comprises at least two electrodes (3) with an arcuate surface arranged in a symmetrical manner, wherein all discharge surfaces of each electrode with an arc-shaped surface are arc-shaped surface structures, wherein electrode (3) with an arc-shaped surface is a completely closed arc-shaped surface structure and is a rod-like electrode or a hollow tubular electrode, or electrode (3) with an arcuate surface is a semi-closed arcuate surface structure. Central angle corresponding to each electrode with arc-shaped surface is equal to α, where 360° > α ≥ 60° , and location of electrodes with arc-shaped surface provide formation of discharge zone between said electrodes (3). At that, sliding arc plasma generator further comprises gas nozzle (2) and base (6), wherein electrode (3) with arc-shaped surface is located on base (6), and gas nozzle (2) is located on base (6) and/or electrode (3) with arc-shaped surface, so that reaction gas can enter plasma reactor with sliding arc from inlet hole (1) of reactor through gas nozzle (2), wherein electrode (3) with arc-shaped surface is connected to base (6) by means of active connection mechanism so that position of electrode (3) with arc-shaped surface can be adjusted both in vertical and horizontal directions. Invention also relates to a method of converting methane using plasma.

EFFECT: use of the present invention enables efficient conversion of methane directly to an olefin.

20 cl, 2 dwg, 8 ex

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority from Chinese Patent Applications Nos. 202111567211.X, 202111565360.2, 202111567220.9, 202111567216.2, 202111567218.1, 202111565366.X, 202111565369.3, 202111567199.2, 202111567219.6, filed on December 20, 2021, the contents of which are incorporated herein by reference.

AREA OF TECHNOLOGY

This invention relates to the field of chemical energy production, in particular to a sliding arc plasma reactor and a method for converting methane using plasma.

BACKGROUND OF THE INVENTION

Plasma methane conversion technology has been researched in China for the past 80 years and has been continuously patented since 2000.

Document CN 100999432 A describes a method for processing _C2 hydrocarbons by ionic liquid catalytic plasma methane reforming, but the patent rights were terminated in 2015.

Document CN 101734620 A describes a method for producing hydrogen using methane-rich gas plasma, but the patent rights were terminated in 2014.

Southwest Chemical Research and Design Institute has published a series of patents on plasma methane cracking technology (CN 210367505 U, CN 109294284 A, CN 106478332 A and CN 101921163 A), and this technology is mainly developed for the purpose of producing carbon black or acetylene and hydrogen by converting methane with plasma, with special attention paid to the design and optimization of the technology.

The technology of producing acetylene by plasma cracking of coal (CN 203582763 U, CN 102068953 A, CN 101734620 A, CN 101550057 A, CN 101734995 A and CN 1613839 A) is jointly developed by Tsinghua University, Taiyuan University of Technology and Xinjiang Tianye Co., Ltd., using coal as the raw material mainly, natural gas and additionally hydrogen as the acetylene, and hydrogen as the working gas.

Zhejiang University mainly develops a continuous plasma coke removal method (CN 104056828 A and CN 104056829 A), where _CO2 or _H2 can be introduced to remove carbon from the electrode surface. Rotating plasma arc (C 103333044 A, CN 101844744 A) is also used to split methane to produce acetylene, where the working gas rotates while entering the discharge gap, and at the same time, millisecond cracking occurs due to the action of an external magnetic field.

At present, foreign research in this field shows that the hydrocarbon products formed during methane conversion using plasma mainly belong to two types, where one type generally contains alkanes such as ethane, etc., and the other type mainly contains acetylene.

The researchers found that the distribution of products could be controlled by changing the flow rate of the supplied gas or adding inert gases. The technology was implemented abroad on an industrial scale and includes four processes: the HUELS method, the AVCO method, the Du Pont method and the Romanian method.

As follows from the comparison of literature data, the use of an electric arc with the formation of high-temperature cracked natural gas to produce acetylene has a low energy efficiency, while the production of 1 ton of acetylene consumes 13900 kW/h, and the costs account for more than 50% of the total cost, so the problem of saving energy and reducing costs is solved by changing the reactor design, and according to foreign patent literature, this method is one of the key innovative solutions.

In the process of further actions based on this technology, "warm" and "cold" plasma technologies are successively developed, energy consumption is reduced by changing the method of energy production, and a catalyst is added to form bonds, so that methane is purposefully converted into the desired product. At present, this process is still in the research stage.

Thanyachotpaiboon et al. (article "Conversion of methane to high hydrocarbons in AC noneqmlibrrum plasmas" published in AIChE Journal, 1998, 44(10): 2252-7) analyzed the conversion of methane using DBD (dielectric barrier discharge) discharge at room temperature and studied the effect of adding He and C ₂ H ₆ on the conversion in methane discharge. When only CH ₄ is used as a reactant, with the increase of discharge voltage (from 6 to 11 kV), the conversion rate of CH ₄ increases and the product selectivity remains almost unchanged: the main products are C ₂ H ₆ and C ₃ H ₈ ; The conversion of _CH4 obtained at a _CH4 flow rate of 20 ml/min and a discharge voltage of 11 _{kV was about 23%, and the selectivity of the products C2H6 , C3H8} , _{C4H10 ,} and _C2H4 was ₄₀ %, ₁₅ %, 5%, and 2%, respectively.

RUEANGJITT N et al. (article “Non-oxidative reforming of methane in a mini-gliding arc discharge reactor: Effects of feed methane concentration, feed flow rate, electrode gap distance, residence time, and catalyst distance” published in Plasma Chemistry and Plasma Processing, 2011, 31(4): 517-534) use a gliding arc discharge to convert methane to acetylene as the main product, and at a power of 110-190 W, the methane conversion is ₄₀ %-50%, and the selectivity for _C2H2 is 20%.

However, there are currently no technical reports on the direct conversion of methane to olefins using plasma.

DESCRIPTION OF THE INVENTION

The aim of this invention is to eliminate the disadvantage of the prior art, which is the low efficiency of converting methane directly into olefin.

In order to achieve the above-mentioned object, according to the first aspect of the present application, a sliding arc plasma reactor is proposed, comprising a reactor chamber and a sliding arc plasma generator located in said chamber,

wherein the sliding arc plasma generator comprises at least two electrodes 3 with an arc-shaped surface, which are arranged in a symmetrical manner, wherein all discharge surfaces of each electrode with an arc-shaped surface are arc-shaped surface structures, and the central angle corresponding to each electrode with an arc-shaped surface is equal to α, where 360°≥α>5°; wherein the locations of the electrodes with an arc-shaped surface ensure the formation of a discharge zone between said electrodes 3.

According to a second aspect of the present invention, a method is proposed for converting methane using plasma, which is carried out in a sliding arc plasma reactor constructed according to the first aspect, and comprises:

introducing a reaction gas containing methane into a sliding arc plasma reactor under plasma discharge conditions to carry out a methane conversion reaction.

Compared with the known state of the art, the solution proposed in this invention has at least the following advantages:

1) in the sliding arc plasma reactor proposed in this invention, electrodes are used to form the discharge zone, and the point of formation of the discharge arc is located on the arc-shaped surface, so that more discharge channels are formed, and the sliding arc plasma reactor has a higher conversion efficiency of reactants,

2) the sliding arc plasma reactor proposed in the present invention can provide a more intensive passage of the source gas through the discharge zone formed by the electrodes, so that the gas flow passing through the discharge zone is effectively increased, the conversion efficiency of the reactants is increased, and the energy consumption is reduced,

3) The sliding arc plasma reactor proposed in the present invention can achieve one-stage methane conversion with efficient production of olefin at a higher conversion efficiency of reactants, can maintain a continuous and stable reaction, and compared with the traditional method of producing olefin from methane, there is no formation of _CO2 ; the possibility of ignition and explosion is eliminated, and the reactor is safer and more environmentally friendly.

Additional features and advantages of the present invention are set forth in the detailed description provided below.

BRIEF DESCRIPTION OF DRAWINGS

Fig. 1 shows a block diagram of a preferred embodiment of a sliding arc plasma reactor according to the present invention.

Fig. 2 shows a block diagram of another preferred embodiment of a sliding arc plasma reactor according to the present invention.

LIST OF ELEMENTS

1. Reactor inlet

2. Gas injector

3. Electrode

4. Lower reaction zone

5. Product release hole

6. Foundation

7. Mechanism of active connection.

DETAILED DESCRIPTION OF PREFERRED EXECUTION OPTIONS

The end values of the ranges and any values given herein are not limited to the specifically stated range or value, and it should be understood that such ranges or values cover values close to them. With respect to numerical ranges, each range between its end values and individual point values, as well as each individual point value, can be combined with each other to obtain one or more new numerical ranges, and such numerical ranges should be considered as specifically stated herein.

A detailed description of an embodiment of the present invention is given below with reference to Fig. 1 and Fig. 2.

As described above, according to the first aspect of the present application, a sliding arc plasma reactor is provided, comprising a reactor chamber and a sliding arc plasma generator located in the reactor chamber,

wherein the sliding arc plasma generator comprises at least two electrodes 3 with an arc-shaped surface, which are arranged in a symmetrical manner, wherein all discharge surfaces of each electrode with an arc-shaped surface are arc-shaped surface structures, and the central angle corresponding to each electrode with an arc-shaped surface is equal to α, wherein 360°≥α>5°; preferably 360°≥α>10°; wherein the locations of the electrodes with an arc-shaped surface ensure the formation of a discharge zone between said electrodes 3.

According to a particularly preferred embodiment, the reactor comprises an inlet opening 1, a sliding arc plasma generator and an opening 5 for discharging the product,

wherein the sliding arc plasma generator contains at least two electrodes 3 with an arc-shaped surface, which are arranged in a symmetrical manner, and the locations of the electrodes with an arc-shaped surface ensure the formation of a discharge zone between the said electrodes 3.

the sliding arc plasma generator additionally contains a gas nozzle 2 and a base 6,

an electrode 3 with an arc-shaped surface is located on a base 6, a gas nozzle 2 is located on the base 6 and/or the electrode 3 with an arc-shaped surface, so that the reaction gas can enter the plasma reactor with a sliding arc from the inlet opening 1 of the reactor through the gas nozzle 2,

wherein the central angle corresponding to the arc-shaped surface structure of the electrode is equal to α, where 360°≥α>5°.

According to the present invention, the point of formation of the discharge arc in the electrode is located on a curved surface, so that more discharge zones can be formed in the arc-shaped channel, and the ability of the reactants to conversion is increased.

Preferably, the arc-shaped surface structure of the electrode 3 is a semi-closed arc-shaped surface, wherein the central angle corresponding to the arc-shaped surface is equal to α, where 270°≥α>30°; more preferably, the central angle α corresponding to the semi-closed arc-shaped surface is at least one of the angles selected from 180°, 120°, 90°, 72°, 60°.

According to a preferred embodiment, the arc-shaped surface structure of the electrode 3 is a completely closed arc-shaped surface. The inventor has found that when using a completely closed arc-shaped surface structure as the arc-shaped surface structure of the electrode 3, the efficiency of the conversion of the reactant is increased and the heat removal is simplified.

Preferably, the electrode 3 with an arc-shaped surface is a rod-shaped electrode or a hollow tubular electrode.

Preferably, the ratio of the length d2 of the discharge zone to the height d3 of the reactor chamber satisfies the condition 1:1.2-1.8.

According to a preferred embodiment, the sliding arc generator of the electrode is a sliding arc plasma generator, and the center of the base of the sliding arc plasma generator is provided with a gas nozzle that communicates with a pipeline for supplying gas to the inlet of the reactor.

Preferably, the central angle corresponding to the arc-shaped surface structure of the electrode 3 is equal to α, where 360°≥α>10°.

Preferably, the sliding arc plasma generator comprises two or six electrodes 3 with an arc-shaped surface, which are arranged in a symmetrical manner.

Preferably, for each electrode 3, the ratio of the distance between two adjacent gas injectors 2 to the internal diameter r2 of the gas injector satisfies the condition 1:0.5-1.5.

Preferably, the ratio of the internal diameter r2 of the gas injector 2 to the minimum width r3 of the discharge zone satisfies the condition 1:2-8.

According to a particularly preferred embodiment, the reactor according to the present invention comprises an inlet, a sliding arc electrode generator, a lower reaction zone and a product outlet,

wherein the sliding arc generator of the electrode comprises a gas nozzle, an electrode and a base,

at least a set of electrodes arranged in a symmetrical manner are distributed over the base of the sliding arc generator of the electrode, so that a discharge zone can be formed between the electrodes; a gas nozzle is located on the electrode and/or the base, so that the reaction gas can enter the plasma reactor with a sliding arc from the inlet of the reactor through the gas nozzle,

the designs of each two symmetrically located electrodes correspond to each other to ensure the possibility of discharge, and

The sliding arc electrode generator is a sliding arc electrode generator comprising an electrode with an arc-shaped surface and/or a sliding arc tubular electrode generator comprising a tubular electrode.

Preferably, in the present invention, the symmetrical arrangement refers to a symmetrical arrangement relative to the central vertical axis of the base, and the installation position of the electrode does not affect the discharge.

In the present invention, the shape and material of the base are not particularly limited, and the base may have a round shape or various other shapes that can achieve the above-mentioned object of the present invention, and the material of the base may be an insulating material or various other materials that can achieve the above-mentioned object of the present invention.

Preferably, the gas nozzle 2 is located in the center of the base 6 of the sliding arc plasma generator and communicates with a pipeline for supplying gas to the inlet opening 1 of the reactor.

Preferably, the gas nozzle 2 is located in the corresponding direction of each two electrodes 3 with an arcuate surface, which are in a symmetrical position, and communicates with a pipeline for supplying gas to the inlet opening 1 of the reactor.

More preferably, at least a portion of the outer surface of the fully closed arcuate surface structure has a coating.

Preferably, the coating comprises at least two galvanic layers of single-layer thin films obtained from a metal oxide by atomic layer deposition, wherein the galvanic layers are made of semiconductor materials, the number of galvanic layers is at least two, and the coating materials used to form any two adjacent galvanic layers are different.

Preferably, the number of galvanic coating layers is at least three.

According to a preferred embodiment, the number of layers in the galvanic coating is three, and the coating materials forming the three galvanic layers are different; the dielectric constant of the coating material forming the outermost galvanic layer is 10-22 C ² /(N⋅M ² ) higher than that of the coating materials used for the other galvanic layers.

Preferably, the coating material is an organic substance containing a metallic element.

Preferably, the semiconductor material is a metal oxide; more preferably, the semiconductor material is selected from Al ₂ O ₃ , ZrO ₂ , SnO ₂ , ZnO, HfO ₂ , TiO ₂ , La ₂ O ₃ , Ta ₂ O ₅ , Y ₂ O ₃ .

Preferably, the outer surface of the fully closed arcuate surface structure is coated using atomic layer deposition, wherein the coating step preferably comprises the following steps, performed in an atomic layer deposition device:

(1) opening an ALD valve (atomic layer deposition valve) of a metal source tank in the presence of a carrier gas for coating, wherein the coating material in said tank enters a reaction chamber containing oxygen, so that the coating material and oxygen react on the surface of a paddle electrode in the reaction chamber and form a galvanic compound that is a single-layer thin film of metal oxide obtained by atomic layer deposition,

(2) repeating step (1) to obtain a galvanic layer, each time repeatedly forming a thin film of metal oxide obtained by atomic layer deposition, and adjusting the thickness of the galvanic layer by adjusting the number of repetitions,

(3) repeating the above steps (1)-(2) using another coating material to form another galvanic layer.

Preferably, in step (1), the temperature of the metal source tank is 140-160°C, the temperature of the reaction chamber is 50-400°C, and the temperatures of the transport pipeline and the ALD valve are 180-200°C.

Preferably, at step (1), the reaction chamber and the transport line are evacuated to a pressure of 10-200 Pa.

Preferably, in step (1), the flow rate of the carrier gas for coating is 10-200 ^cm3 /min.

Preferably, at step (1), the opening time of the ALD valve is 50-2000 ms.

Preferably, at step (1), an inert gas pulse is supplied to clean the reaction chamber, preferably the cleaning time is 1-200 s.

According to a preferred embodiment, a coating is applied to the outer surface of the fully closed arcuate surface structure using atomic layer deposition, wherein the coating application step preferably includes the following steps, carried out in an atomic layer deposition device:

(1) placing the coating material in a tank with a metal source and placing the paddle electrode to be coated in a reaction chamber,

(2) heating the metal source tank, the reaction chamber, the transport pipeline and the ALD valve, wherein the temperature of the metal source tank is 140-160°C, the temperature of the reaction chamber is 50-400°C, and the temperatures of the transport pipeline and the ALD valve are 180-200°C, and evacuating the reaction chamber and the transport pipeline to a pressure of 10-200 Pa,

(3) turning on the supply of carrier gas used for coating application to the tank with the metal source, while the flow rate of carrier gas for coating application is 10-200 ^cm3 /min,

(4) opening the ALD valve of the metal source tank at an ALD valve opening time of 50-2000 ms, so that the coating material enters the reaction chamber, and introducing oxygen into the reaction chamber, so that the coating material and oxygen react on the surface of the paddle electrode in the reaction chamber to form a galvanic compound, wherein the galvanic compound is a single-layer thin film of a metal oxide obtained by atomic layer deposition,

(5) cleaning the reaction chamber by pulsed supply of inert gas, with the cleaning time being 1-200 s,

(6) repeating steps (1) to (5) to obtain a galvanic layer, each time repeatedly forming a thin film of metal oxide obtained by atomic layer deposition, and adjusting the thickness of the galvanic layer by adjusting the number of repetitions,

(7) repeating the above steps (1)-(6) using a different coating material to form another galvanic layer.

Preferably, the fully closed arcuate surface is at least one of a tubular surface and a rod surface.

According to another preferred embodiment, the sliding arc generator of the electrode is a sliding arc generator of the tubular electrode, wherein the gas nozzles are located in the corresponding directions of each two tubular electrodes located in symmetrical positions and communicate with the feed pipe of the inlet opening of the reactor.

Preferably, the material from which the gas nozzle is made is selected from at least one of a conductive material and an insulating material.

According to a preferred embodiment, the material from which the gas nozzle is made is an insulating material.

The inventors have found that in this preferred case the process according to this application can be carried out in a more stable manner.

According to another preferred embodiment, the material forming the gas nozzle 2 is a conductive material, and the position of the gas nozzle 2 upon release does not overlap in the vertical direction with the electrode 3 having an arcuate surface.

Preferably, the electrical conductivity of the conductive material forming the gas nozzle 2 is >1 MS/m, preferably >10 MS/m; the thermal conductivity is >10 W/(m⋅°C), preferably >50 W/(m⋅°C).

Preferably, the material forming the electrodes is a conductive material.

More preferably, the conductive material forming the electrode is selected from at least one of the following: stainless steel grade 316L, tungsten-cerium alloy, nickel-chromium alloy, zinc-copper alloy, copper-chromium alloy, nickel-copper alloy, cobalt-nickel alloy, cobalt-cadmium alloy and graphite. The material from which the electrode is formed may also be other heat-resistant conductive materials resistant to arc corrosion.

Preferably, the electrode is connected to the base by means of an active connection mechanism so that the position of the electrode in the lower zone of the base can be freely adjusted.

More preferably, the electrode is connected to the base by means of an active connection mechanism such that the position of the electrode can be adjusted in both vertical and horizontal directions.

Preferably, the active connection mechanism is connected to the base in a vertical manner.

More preferably, the active connection mechanism may also be connected to the base in a non-perpendicular manner.

Preferably, the electrode is connected to an active connection mechanism with the possibility of rotating the electrode so that it can be freely rotated to adjust the angle.

More preferably, the electrode is connected to an active connection mechanism with the possibility of rotating the electrode so that it can rotate to adjust the internal angle relative to the vertical direction.

Preferably, the internal angle θ formed by the lines of continuation of the axes of symmetry of each two electrodes 3 located in a symmetrical position is 5° - 160°

Preferably, a sliding arc plasma reactor is used to carry out the methane conversion reaction, and the internal angle θ between the extension lines of the symmetry axes of each two electrodes 3 located in a symmetrical position is 10° - 90°, more preferably 30° - 60°.

The sliding arc plasma reactor proposed in this invention can provide a more intensive passage of the source gas through the discharge zone formed by the electrodes, thereby effectively increasing the flow of gas passing through the discharge zone and increasing the efficiency of conversion of the reactants.

Preferably, the material forming the outer cylinder of the sliding arc plasma reactor is selected from at least one of the following: an insulating material, a conductive material, and a conductive material with an insulating coating.

More preferably, the material forming the outer cylinder of the sliding arc plasma reactor is an insulating material or a conductive material with an insulating coating.

Furthermore, preferably the insulating material forming the outer cylinder is selected from at least one of the following: ordinary glass, quartz glass and corundum.

In the present invention, provided that contact between the electrode and the outer cylinder of the sliding arc plasma reactor is excluded, the material forming the outer cylinder may also be a conductive material.

In the present invention, the shape of the outer cylinder of the sliding arc plasma reactor is not particularly limited and may be any shape that can form a closed space for the reactor, such as cylindrical, rectangular or any other shape that can achieve the above-mentioned objective of the present invention.

Preferably, the lower reaction zone, which can be filled with a catalyst, is located downstream of the sliding arc plasma generator.

Preferably, the material forming the lower reaction zone is a metallic material.

More preferably, the lower reaction zone is made narrowed, which is more favorable for the distribution of the reaction gas.

Preferably, the ratio between the length d2 of the discharge zone, the length d4 of the separation zone and the height d5 of the lower reaction zone satisfies the condition 1:0.1-0.8:0.5-1.5; wherein the length d4 of the separation zone represents the distance between the bottom of the discharge zone and the top of the lower reaction zone.

The sliding arc plasma reactor of the present invention may be filled with a catalyst capable of accelerating the hydrogenation conversion of an alkyne to an olefin, with the catalyst preferably filling the lower reaction zone in the reactor.

The sliding arc plasma reactor proposed in the present invention can carry out a continuous and stable reaction with a higher conversion efficiency of reactants, and compared with the traditional method of producing olefin from methane, there is no formation of _CO2 , the possibility of ignition and explosion is eliminated, and the reactor is safer and more environmentally friendly.

As stated above, according to a second aspect of the present invention, a method is provided for the conversion of methane using plasma, which is carried out in a sliding arc plasma reactor described in relation to the first aspect, and comprises:

introducing a reaction gas containing methane into a sliding arc plasma reactor under plasma discharge conditions to carry out a methane conversion reaction.

According to a particularly preferred embodiment, under plasma discharge conditions, a reaction gas containing methane is introduced into a plasma reactor with a sliding arc through an inlet opening 1 of the reactor, so that the reaction gas passes through a discharge zone formed by electrodes 3 with an arc-shaped surface, with the implementation of a methane conversion reaction, and the products obtained upon completion of the reaction are removed from said reactor through an opening 5 for discharging the product.

The reaction conditions associated with the conversion of methane to olefins in the sliding arc plasma reactor proposed in the present invention are not particularly limited, and the reaction can be carried out under various conditions provided in plasma conversion methods conventionally used in the art, while the conditions associated with the conversion of methane to olefins are given in the description section of the examples of the present invention, and should not be considered by those skilled in the art as limiting the present invention.

The sliding arc plasma reactor proposed in the present invention has no particular limitation on the methane concentration in the reaction gas at the reactor inlet, and, for example, the methane concentration in the gas can be 0.01-100 vol.%, such as 5 vol.%, 10 vol.%, 15 vol.%, 20 vol.%, 25 vol.%, 30 vol.%, 35 vol.%, 40 vol.%, 45 vol.%, 50 vol.%, 55 vol.%, 60 vol.%, 65 vol.%, 70 vol.%, 75 vol.%, 80 vol.%, 85 vol.%, 90 vol.%, 95 vol.%.

According to another preferred embodiment, the method further includes passing the reaction gas through a discharge zone formed by an electrode 3 with an arc-shaped surface, and then through a lower reaction zone 4 to carry out a methane conversion reaction.

Preferably, the lower reaction zone 4 is a reaction zone which may contain a catalyst layer, wherein the flow rate of the reaction gas containing methane is such that its volumetric velocity when passing through the lower reaction zone in the sliding arc plasma reactor is 1000-10000 units/hour, more preferably 5000-8000 units/hour.

Preferably, the conditions of the methane conversion reaction include the following conditions: the discharge voltage U1 is 1.0-5.0 kV, and the discharge current is 100-3000 mA; the ratio between the flow rate VI of the reaction gas passing through the minimum distance D2 between each two electrodes 3 with an arcuate surface located in a symmetrical position, and the discharge voltage U1 is determined by the expression V1:U1=50-100:1.

Preferably, the methane conversion reaction conditions include the following conditions: the discharge voltage U1 is 2.0-5.0 kV, and the discharge current is 1000-3000 mA.

Preferably, the ratio between the flow rate V1 of the reaction gas passing through the minimum distance D2 between each two electrodes 3 located in a symmetrical position and the discharge voltage U1 is determined by the expression V1:U1=50-80:1, more preferably V1:U1=60-80:1.

Preferably, the catalyst located in the catalyst layer contains a carrier doped with titanium oxide and an active component embedded in the carrier, wherein the active component contains a first active component and a second active component, wherein the first active component is selected from at least one of the non-noble metals of group VIII and metals of group IB, and the second active component is selected from at least one of the noble metals of group VIII, wherein the weight ratio of the first active component to the second active component, calculated by metallic elements, is 0.1-200:1.

More preferably, the molar ratio of L-acid to B-acid in the titanium oxide-doped carrier is 0.1-50:1.

Preferably, the titanium oxide-doped support is selected from at least one of the following: titanium oxide-doped Al ₂ O ₃ , titanium oxide-doped SiO ₂ , titanium oxide-doped MgO, and titanium oxide-doped molecular sieve.

Preferably, in the titanium oxide doped carrier, the amount of titanium oxide doping is 0.1-10 wt.% of the total weight of the carrier.

Preferably, the first active component is selected from at least one of Cu, Ag, Au, Ni and Fe.

Preferably, the second active component is selected from at least one of Pt, Rh, Pd and Ir.

Preferably, the weight ratio of the first active component to the second active component, calculated on a metallic element basis, is 0.1-10:1.

Preferably, the weight ratio of the first active component to the total weight of the catalyst is 0.1-2:100, wherein the weight of the first active component is calculated based on metallic elements.

According to a preferred embodiment, the reaction gas is a gas obtained by mixing methane with a carrier gas.

Preferably, the carrier gas is hydrogen.

Preferably, the methane feed rate is 0.5-5.0 L/min, and the hydrogen feed rate is 1.0-5.0 L/min; more preferably, the methane feed rate is 0.5-2.5 L/min, and the hydrogen feed rate is 1.0-2.5 L/min.

According to a preferred embodiment, the method further comprises subjecting the product withdrawn from the product outlet opening 5 to a first separation to obtain an olefin product and a first gaseous feedstock containing hydrogen and a carrier gas.

Preferably, the first gaseous material is recycled, with or without separation, back into the sliding arc plasma reactor to perform a continuous methane reforming reaction.

Preferably, the first separation conditions include separating the carrier gas and hydrogen from the olefin product using at least one process selected from the group consisting of membrane separation, cryogenic separation, and pressure swing adsorption processes.

Preferably, the method further comprises performing a second separation of the system product to obtain, respectively, a carbon diolefin and carbon tetraolefins.

Preferably, the second separation operation comprises separating the olefin products to obtain ethylene, ethane, carbon tetraolefins and carbon tetraalkane.

More preferably, the second separation conditions include separation by a rectification process.

Below is shown another preferred embodiment according to this application for converting methane to olefins using the above described sliding arc plasma reactor:

Gaseous nitrogen is supplied to the sliding arc plasma reactor from the reactor inlet, ensuring that the discharge zone is cleared of air and that the gas is discharged from the product outlet. Then, a reaction gas containing methane is introduced into the sliding arc plasma reactor, supplying it from the reactor inlet, after the reaction gas flow is stabilized, the high-voltage power source is turned on and a plasma discharge field is formed between the electrodes by regulating the voltage and frequency. The reaction gas passes successively through the discharge zone and the lower reaction zone formed by the electrodes to carry out ionization and hydrogenation reactions, respectively, and the product obtained after the reaction is discharged from the reactor through the product outlet.

In this invention, after the reaction gas passes through the discharge zone formed by the electrodes, the reaction gas transfers the heat generated by the discharge and the reacting components to the input of the lower reaction zone, wherein said heat can provide the necessary heat for the catalyst layer in the lower reaction zone, wherein said layer does not require additional heating, and energy consumption can be reduced provided that this does not affect the conversion efficiency.

The present invention is described in more detail below using examples.

In the following examples, all starting materials are commercially available unless otherwise stated. Other process and equipment parameters are set the same in each example unless otherwise stated.

In the following examples, methane conversion, ethylene selectivity, ethane selectivity, acetylene selectivity, selectivity for hydrocarbons above _C3 and carbon deposition are calculated according to the following formulas:

methane conversion rate, % = (amount of methane before reaction - amount of methane after reaction)/amount of methane before reaction × 100%,

selectivity for hydrocarbon product (C _n H _m ), % = (amount of C _n H _m after reaction) × n/(amount of methane before reaction - amount of methane after reaction) × 100%, where n is an integer from 2 to 5,

carbon deposition, % = 1 - selectivity for hydrocarbon product (C _n H _m ), %, where n is an integer from 2 to 5.

Example 1 of preparatory work

Palladium nitrate is dissolved in deionized water to form a palladium nitrate solution (the palladium content is 18 wt.%), copper nitrate is dissolved in deionized water to form a copper nitrate solution (the copper content is 30 wt.%), wherein the palladium nitrate solution and the copper nitrate solution are mixed according to the ratio of the components in the mixture, in which the amount of palladium loaded is 0.5 wt.% of the catalyst weight, and the amount of copper loaded is 1 wt.% of the catalyst weight, a TiO ₂ -Al ₂ O ₃ carrier is taken, the excess impregnation method is used, the two solutions are mixed, impregnated for 12 hours, dried for 4 hours at a temperature of 80 ° C by rotary evaporation, then additionally dried for 8 hours at a temperature of 120 ° C in an oven, then placed in a muffle furnace and fired for 5 hours at a temperature 450°C to obtain catalyst 1, which has the following chemical composition:

the content of Pd element is 0.5 wt%, the content of Cu element is 1 wt%, the rest is TiO ₂ -Al ₂ O ₃ ; the particle size of the active component is 5.4 nm, and the ratio of L-acid to B-acid is 15.6.

All Examples 1-4 were performed using the method scheme shown in Fig. 1.

In Examples 1-4, the methane conversion reaction is carried out using a sliding arc plasma reactor, wherein a sliding arc plasma generator is used as the sliding arc electrode generator, and an electrode with an arc-shaped surface is used as the electrode.

Example 1

The specific design and construction parameters of the reactor are as follows:

the reactor has an inlet, contains a sliding arc electrode generator, a lower reaction zone and a product outlet, wherein the sliding arc electrode generator contains a gas nozzle, an electrode, a base and an active connection mechanism,

the base of the sliding arc generator of the electrode is made with two electrodes which are arranged in a symmetrical manner so that a discharge zone can be formed between the electrodes, while in the center of the base there is a gas nozzle which communicates with a pipeline for feeding gas to the inlet of the reactor so that the reaction gas can enter the plasma reactor with a sliding arc from the inlet of the reactor through the gas nozzle,

the electrode is connected to the base by means of an active connection mechanism so that the position of the electrode can be adjusted in the vertical and horizontal directions, the active connection mechanism is connected to the base in a vertical manner, the electrode is connected to the active connection mechanism with the possibility of rotation of the electrode so that it can be rotated to adjust the internal angle relative to the vertical direction,

the electrode is an electrode with a semi-closed arcuate surface, wherein the central angle α corresponding to the arcuate surface is 90°, and the material for making the electrode is a zinc-copper alloy (the main components of the zinc-copper alloy are 60 wt.% copper, 37 wt.% zinc, 1 wt.% titanium, 1 wt.% graphene and 1 wt.% other materials),

the internal angle θ formed by the lines of continuation of the axes of symmetry of two electrodes located in a symmetrical position is 77°,

the outer cylinder of the sliding arc plasma reactor is made of quartz glass,

the thickness of the catalyst layer ensures a volumetric flow rate of the catalyst through the supplied gas of 2000 units/hour,

The volume of the sliding arc plasma reactor in this example is 3 l.

The operating conditions of the sliding arc plasma reactor in this example are as follows:

the discharge power is adjusted to 300 W, the voltage is 3.0 kV, the discharge frequency is 22.3 kHz, the gas flow rate at the inlet is 1 l/min for methane and 3 l/min for hydrogen, the height of the catalyst layer placed in the reactor in the lower reaction zone is 15 mm, and the catalyst portion is 60 g, the catalyst is catalyst 1 prepared in accordance with Example 1 of the preparatory work,

nitrogen is introduced into the reactor through the inlet for 30 minutes at a gas inflow rate of 3 l/min, the oxygen in the reactor is replaced, mixed gas is introduced (the gas inflow rate is 2 l/min for nitrogen and 1 l/min for hydrogen), the power source is turned on, the voltage and frequency are adjusted, the voltage is adjusted to 2.0 kV and the frequency to 20 kHz, the discharge is initiated, the catalyst reduction reaction is carried out in the lower reaction zone for about 3 hours and is completed, the color of the catalyst as a whole becomes black, the power source is turned off, mixed gas is introduced (the gas inflow rate is 1 l/min for methane and 3 l/min for hydrogen), the power source is turned on, the voltage and frequency are adjusted, the voltage is adjusted to 2.0 kV and the frequency is adjusted to 22.3 kHz, the discharge is initiated, the voltage is adjusted to 3.0 kV, the power at this point being 300 W, and the reaction is carried out for 8 hours,

They perform an analysis of the tail gas and obtain the following result: the degree of methane conversion is 47.9%, the selectivity for ethylene is 88.7%, the selectivity for ethane is 5.9%, the selectivity for hydrocarbons above _C3 is 5.4%, and there is no visible carbon deposition.

Example 2

In this example, a sliding arc plasma reactor similar to the reactor in Example 1 is used to carry out the methane conversion reaction, except that in this example:

the electrode is an electrode with a semi-closed arcuate surface, where the central angle α, corresponding to the arcuate surface, is 120°, and the material for the manufacture of the electrode is stainless steel grade 316G,

the internal angle θ formed by the lines of continuation of the axes of symmetry of two electrodes located in a symmetrical position is 46°,

The outer cylinder of the sliding arc plasma reactor is made of 304 stainless steel with a quartz lining,

the thickness of the catalyst layer ensures a volumetric flow rate of the catalyst through the supplied gas of 6000 units/hour,

The volume of the sliding arc plasma reactor in this example is 4 l.

In this example, the discharge power is adjusted to 250 W, the voltage is 1.8 kV, the discharge frequency is 25.5 kHz, the gas flow rate at the inlet is 0.5 l/min for methane and 2 l/min for hydrogen,

nitrogen is introduced into the reactor through the inlet for 30 minutes at a gas inflow rate of 3 l/min, the oxygen in the reactor is replaced, mixed gas is supplied (the gas inflow rate is 2.5 l/min for nitrogen and 1.5 l/min for hydrogen), the power source is turned on, the voltage and frequency are adjusted, with the voltage being adjusted to 3.0 kV and the frequency to 16.3 kHz, the discharge is initiated, the catalyst reduction reaction is carried out in the lower reaction zone for approximately 2.5 hours and completed, with the color of the catalyst as a whole becoming black, the power source is turned off, mixed gas is introduced (the gas inflow rate is 0.5 l/min for methane and 2 l/min for hydrogen), the power source is turned on, the voltage and frequency are adjusted, with the voltage being adjusted to 1.5 kV and the frequency to 25.5 kHz, the discharge is initiated, the voltage is adjusted to a predetermined value of 1.8 kV, with the power at this point being 250 W, and the reaction is carried out for 8 hours.

The rest of the process is the same as in Example 1.

The tail gas is analyzed and the following result is obtained: the degree of methane conversion is 48.7%, the selectivity for ethylene is 89.2%, the selectivity for ethane is 4.7%, the selectivity for hydrocarbons above _C3 is 6.1%, and there is no visible carbon deposition.

Example 3

In this example, a sliding arc plasma reactor similar to the reactor in Example 1 is used to carry out the methane conversion reaction, except that in this example:

the electrode is an electrode with a completely closed arc-shaped surface, and the material forming the electrode is graphite,

the internal angle θ formed by the lines of continuation of the axes of symmetry of two electrodes located in a symmetrical position is 15°,

the outer cylinder of the sliding arc plasma reactor is made of tempered glass,

the thickness of the catalyst layer ensures a volumetric flow rate of the catalyst through the supplied gas of 8000 units/hour,

The volume of the sliding arc plasma reactor in this example is 3.3 l.

In this example, the discharge power is adjusted to 280 W, the voltage is 3.5 kV, the discharge frequency is 17.5 kHz, the gas flow rate at the inlet is 1.75 l/min for methane and 2.3 l/min for hydrogen,

nitrogen is introduced into the reactor through the inlet for 30 minutes at a gas inflow rate of 3 l/min, the oxygen in the reactor is replaced, mixed gas is introduced (the gas inflow rate is 3 l/min for nitrogen and 2.5 l/min for hydrogen), the power source is turned on, the voltage and frequency are adjusted, with the voltage being adjusted to 3.0 kV and the frequency to 21.2 kHz, the discharge is initiated, the catalyst reduction reaction is carried out in the lower reaction zone for approximately 3.5 hours and is completed, with the color of the catalyst as a whole becoming black, the power source is turned off, mixed gas is introduced (the gas inflow rate is 2.5 l/min for methane and 2.5 l/min for hydrogen), the power source is turned on, the voltage and frequency are adjusted, with the voltage being adjusted to 2.5 kV and the frequency to 17.5 kHz, the discharge is initiated, the voltage is adjusted to a predetermined value of 3.5 kV, with the power at this point being 280 W, and the reaction is carried out for 8 hours.

The rest of the process is the same as in Example 1.

The tail gas is analyzed and the following result is obtained: the degree of methane conversion is 47.5%, the selectivity for ethylene is 91.3%, the selectivity for ethane is 5.6%, the selectivity for hydrocarbons above _C3 is 3.1%, and there is no visible carbon deposition.

Example 4

In this example, a sliding arc plasma reactor similar to the reactor in Example 1 is used to carry out the methane conversion reaction, except that in this example:

the electrode is an electrode with a semi-closed arc-shaped surface, the central angle α corresponding to the arc-shaped surface is 72°, and the material for making the electrode is nickel-chromium alloy (the main components of the nickel-chromium alloy are 10 wt.% iron, 17 wt.% chromium, 1 wt.% aluminum, 2 wt.% titanium, 1 wt.% niobium, 0.5 wt.% molybdenum, 0.1 wt.% tungsten, 0.2 wt.% silicon, 0.05 wt.% carbon, 0.05 wt.% zirconium, and the rest is nickel),

the internal angle θ formed by the lines of continuation of the axes of symmetry of two electrodes located in a symmetrical position is 40°,

the outer cylinder of the sliding arc plasma reactor is made of ceramics,

the thickness of the catalyst layer ensures a volumetric flow rate of the catalyst through the supplied gas of 3500 units/hour,

The volume of the sliding arc plasma reactor in this example is 5 l.

In this example, the discharge power is adjusted to 350 W, the voltage is 4.2 kV, the discharge frequency is 25.5 kHz, the gas flow rate at the inlet is 2.9 l/min for methane and 3.8 l/min for hydrogen,

nitrogen is introduced into the reactor through the inlet for 30 minutes, the gas inflow is 2.5 l/min, the oxygen in the reactor is replaced, mixed gas is supplied (the gas inflow is 2.5 l/min for nitrogen and 1.5 l/min for hydrogen), the power source is turned on, the voltage and frequency are adjusted, the voltage being adjusted to 1.6 kV and the frequency to 20.4 kHz, the discharge is initiated, the catalyst reduction reaction is carried out in the lower reaction zone for approximately 4 hours and is completed, the color of the catalyst as a whole becoming black, and the power source is turned off, mixed gas is introduced (the gas inflow is 2.9 l/min for methane and 3.8 l/min for hydrogen), the power source is turned on, the voltage and frequency are adjusted, the voltage being adjusted to 2.5 kV and the frequency to 25.5 kHz, the discharge is initiated, the voltage is adjusted to a given value of 4.2 kV, and the power at this the moment is 350 W, and the reaction is carried out for 8 hours.

The rest of the process is the same as in Example 1.

The tail gas is analyzed and the following result is obtained: the degree of methane conversion is 48.7%, the selectivity for ethylene is 90.5%, the selectivity for ethane is 6.7%, the selectivity for hydrocarbons above _C3 is 2.8%, and there is no visible carbon deposition.

All Examples 5-8 were performed using the method scheme shown in Fig. 2.

In Examples 5-8, the methane conversion reaction is carried out using a sliding arc plasma reactor, wherein a sliding arc generator with a tubular electrode is used as the sliding arc generator of the electrode, and the average thickness of the electrode material (excluding any possible coating layer) is 2 mm.

Example 5

The specific design and construction parameters of the reactor are as follows:

the reactor has an inlet, contains a sliding arc electrode generator, a lower reaction zone and a product outlet, wherein the sliding arc electrode generator contains a gas nozzle, an electrode, a base and an active connection mechanism,

the base of the sliding arc generator of the electrode is made with two electrodes which are arranged in a symmetrical manner so that a discharge zone can be formed between the electrodes, wherein the gas nozzle is arranged in a direction corresponding to the electrode and communicates with a pipeline for supplying gas to the inlet of the reactor so that the reaction gas can enter the plasma reactor with a sliding arc from the inlet of the reactor through the gas nozzle,

the electrode is connected to the base by means of an active connection mechanism so that the position of the electrode can be adjusted in the vertical and horizontal directions, the active connection mechanism is connected to the base in a vertical manner, the electrode is connected to the active connection mechanism with the possibility of rotation of the electrode so that it can be rotated to adjust the internal angle relative to the vertical direction,

gas injectors are staggered in the corresponding direction of the electrodes,

the material for forming the electrode is a nickel-copper alloy (the main composition of the nickel-copper alloy is as follows: 0.15 wt.% silicon, 7.0 wt.% manganese, 0.15 wt.% phosphorus, 22.0 wt.% nickel, 3.0 wt.% cobalt, 3.0 wt.% zinc, 0.20 wt.% lead, 3.0 wt.% iron, 0.15 wt.% rare earth elements, 0.006 wt.% arsenic, and the rest is copper),

the internal angle θ formed by the lines of continuation of the axes of symmetry of two electrodes located in a symmetrical position is 35°,

the outer cylinder of the sliding arc plasma reactor is made of quartz glass,

the thickness of the catalyst layer ensures a volumetric flow rate of the catalyst through the supplied gas of 2000 units/hour,

The volume of the sliding arc plasma reactor in this example is 3 l.

The operating conditions of the sliding arc plasma reactor in this example are as follows:

the discharge power is adjusted to 230 W, the voltage is 2.7 kV, the discharge frequency is 25.7 kHz, the gas flow rate at the inlet is 1.3 l/min for methane and 2.1 l/min for hydrogen, the height of the catalyst layer placed in the reactor in the lower reaction zone is 15 mm, and the catalyst portion is 60 g, the catalyst is catalyst 1 prepared in accordance with Example 1 of the preparatory work,

nitrogen is introduced into the reactor through the inlet for 30 min, with the gas inflow being 3 l/min, the oxygen in the reactor is replaced, mixed gas is supplied (the gas inflow is 1.8 l/min for nitrogen and 1.5 l/min for hydrogen), the power source is turned on, the voltage and frequency are adjusted, with the voltage being adjusted to 2.0 kV and the frequency to 25.7 kHz, the discharge is initiated, the catalyst reduction reaction is carried out in the lower reaction zone for approximately 3.5 h and is completed, with the color of the catalyst as a whole becoming black, the power source is turned off, mixed gas is introduced (the gas inflow is 1.3 l/min for methane and 2.1 l/min for hydrogen), the power source is turned on, the voltage and frequency are adjusted, with the voltage being adjusted to 2.0 kV and the frequency to 25.7 kHz, the discharge is initiated, the voltage is adjusted to a given value of 2.7 kV, with the power at this point is 230 W, and the reaction is carried out for 8 hours.

The tail gas is analyzed and the following results are obtained: the degree of methane conversion is 50.4%, the selectivity for ethylene is 89.3%, the selectivity for ethane is 6.5%, the selectivity for hydrocarbons above _C3 is 4.2%, while there is no visible carbon deposition.

Example 6

This example uses a sliding arc plasma reactor similar to the reactor in Example 5, except that in this example:

the gas injectors are mutually aligned in the corresponding directions of the electrodes,

the material from which the electrode is made is 316L stainless steel,

the internal angle θ formed by the lines of continuation of the axes of symmetry of two electrodes located in a symmetrical position is 63°,

The outer cylinder of the sliding arc plasma reactor is made of 304 stainless steel with a quartz lining,

the thickness of the catalyst layer ensures a volumetric flow rate of the catalyst through the supplied gas of 6000 units/hour,

The volume of the sliding arc plasma reactor in this example is 4 l.

In this example, the discharge power is adjusted to 257 W, the voltage is 1.9 kV, the discharge frequency is 14.9 kHz, the gas flow rate at the inlet is 2.1 l/min for methane and 2.8 l/min for hydrogen,

nitrogen is introduced into the reactor through the inlet for 30 minutes at a gas inflow rate of 3 l/min, the oxygen in the reactor is replaced, mixed gas is introduced (the gas inflow rate is 2.2 l/min for nitrogen and 2.8 l/min for hydrogen), the power source is turned on, the voltage and frequency are adjusted, with the voltage being adjusted to 2.0 kV and the frequency to 14.9 kHz, the discharge is initiated, the catalyst reduction reaction is carried out in the lower reaction zone for approximately 4 hours and is completed, with the color of the catalyst as a whole becoming black, the power source is turned off, mixed gas is introduced (the gas inflow rate is 2.1 l/min for methane and 2.8 l/min for hydrogen), the power source is turned on, the voltage and frequency are adjusted, with the voltage being adjusted to 1.5 kV and the frequency to 14.9 kHz, the discharge is initiated, the voltage is adjusted to a predetermined value of 1.9 kV, with the power at this point being 257 W, and the reaction is carried out for 8 hours.

The rest of the process is the same as in Example 5.

The tail gas is analyzed and the following result is obtained: the degree of methane conversion is 51.2%, the selectivity for ethylene is 90.1%, the selectivity for ethane is 5.4%, the selectivity for hydrocarbons above _C3 is 3.3%, and there is no visible carbon deposition.

Example 7

This example uses a plasma reactor similar to the reactor in Example 5, except that in this example:

the gas injectors are mutually aligned in the corresponding directions of the electrodes,

the material from which the electrode is made is a tungsten-cerium alloy (Ce _x Y _y Cs _z W _m O ₃ , where x:y:z:m=0.1:0.1:0.5:1),

the internal angle θ formed by the lines of continuation of the axes of symmetry of two electrodes located in a symmetrical position is 85°,

the outer cylinder of the sliding arc plasma reactor is made of tempered glass,

the thickness of the catalyst layer ensures a volumetric flow rate of the catalyst through the supplied gas of 8000 units/hour,

The volume of the sliding arc plasma reactor in this example is 3.3 l.

In this example, the discharge power is adjusted to 149 W, the voltage is 2.5 kV, the discharge frequency is 26.5 kHz, the gas flow rate at the inlet is 1.1 l/min for methane and 1.6 l/min for hydrogen,

nitrogen is introduced into the reactor through the inlet for 30 min at a gas inflow rate of 3 l/min, the oxygen in the reactor is replaced, mixed gas is supplied (the gas inflow rate is 2.5 l/min for nitrogen and 1.6 l/min for hydrogen), the power source is turned on, the voltage and frequency are adjusted, the voltage is adjusted to 2 kV and the frequency to 26.5 kHz, the discharge is initiated, the catalyst reduction reaction is carried out in the lower reaction zone for about 4.5 h and is completed, the color of the catalyst as a whole becomes black, and the power source is turned off, mixed gas is introduced (the gas inflow rate is 1.1 l/min for methane and 1.6 l/min for hydrogen), the power source is turned on, the voltage and frequency are adjusted, the voltage is adjusted to 2 kV and the frequency is adjusted to 26.5 kHz, the discharge is initiated, the voltage is adjusted to a predetermined value of 2.5 kV, and the power at this point is 149 W, and the reaction is carried out for 8 hours.

The rest of the process is the same as in Example 5.

The tail gas is analyzed and the following result is obtained: the degree of methane conversion is 52.1%, the selectivity for ethylene is 88.4%, the selectivity for ethane is 6.7%, the selectivity for hydrocarbons above _C3 is 4.9%, and there is no visible carbon deposition.

Example 8

This example uses a sliding arc plasma reactor similar to the reactor in Example 5, except that in this example:

The reverse side of the outer surfaces of the two electrodes (half the circumference of the electrode) has a coating, while the opposite surfaces (the other half the circumference of the electrode) have no coating.

The coating is applied as described above for the preferred embodiment, sequentially applying Al ₂ O ₃ -ZnO-HfO ₂ films from below, with one coating containing 100 single thin films of metal oxide obtained by atomic layer deposition.

The rest of the process is the same as in Example 5.

The tail gas is analyzed and the following result is obtained: the degree of methane conversion is 52.3%, the selectivity for ethylene is 93.3%, the selectivity for ethane is 2.3%, the selectivity for hydrocarbons above _C3 is 4.4%, and there is no visible carbon deposition.

From the above results it follows that if the plasma reactor with sliding arc proposed in this invention is used for methane conversion to obtain olefin, the methane conversion rate can be significantly increased, the ethylene selectivity in the product can be improved, and carbon deposition can be significantly reduced compared to the known state of the art. The reactor proposed in this invention can provide a continuous and stable reaction with a higher conversion efficiency of the reactants, and compared to the traditional method for obtaining olefin from methane, there is no formation of CO ₂ , the probability of ignition and explosion is excluded, and the reactor is safer and more environmentally friendly.

The above is a detailed description of preferred embodiments of the present invention, however, the present invention is not limited to the indicated embodiments. It is possible to make many simple modifications of the technical solution according to the invention within the scope of the technical idea, including combining various technical features in any other suitable way, and such simple modifications and combinations should also be considered as related to the essence of the invention, and all of them are within the scope of the invention.

Claims (36)

1. A sliding arc plasma reactor comprising a reactor chamber and a sliding arc plasma generator located in the reactor chamber, wherein the sliding arc plasma generator comprises at least two electrodes (3) with an arc-shaped surface, arranged in a symmetrical manner, wherein all discharge surfaces of each electrode with an arc-shaped surface are arc-shaped surface structures, wherein the electrode (3) with an arc-shaped surface is a completely closed arc-shaped surface structure and is a rod-shaped electrode or a hollow tubular electrode, or the electrode (3) with an arc-shaped surface is a semi-closed arc-shaped surface structure, wherein the central angle corresponding to each electrode with an arc-shaped surface is equal to α, where 360° > α ≥ 60°, and the locations of the electrodes with an arc-shaped surface ensure the formation of a discharge zone between said electrodes (3), wherein the sliding arc plasma generator additionally comprises a gas nozzle (2) and a base (6), wherein the electrode (3) with an arc-shaped surface is located on the base (6), and the gas nozzle (2) is located on the base (6) and/or the electrode (3) with an arc-shaped surface, so that the reaction gas can enter the sliding arc plasma reactor from the inlet (1) of the reactor through the gas nozzle (2), wherein the electrode (3) with an arc-shaped surface is connected to the base (6) by means of an active connection mechanism so that the position of the electrode (3) with an arc-shaped surface can be adjusted both in the vertical and horizontal directions. 2. The plasma reactor according to claim 1, wherein the electrode (3) with an arcuate surface is a semi-closed arcuate surface structure, wherein 270° > α > 30°, and preferably the value of α is selected from at least one of 180°, 120°, 90°, 72°, 60°. 3. A plasma reactor according to claim 1 or 2, in which the ratio between the length d2 of the discharge zone and the height d3 of the reactor chamber satisfies the condition 1: 1.2-1.8. 4. A plasma reactor according to claim 1 or 2, in which the sliding arc plasma generator comprises two or six electrodes (3) with an arc-shaped surface, arranged in a symmetrical manner, and/or In the center of the upper part of the sliding arc plasma generator there is a gas nozzle (2), which communicates with the pipeline for supplying gas to the inlet (1) of the reactor chamber. 5. A plasma reactor according to claim 1 or 2, in which at least several gas nozzles (2) are located in the corresponding direction of each two arc-shaped electrodes (3) located in symmetrical positions, and each gas nozzle (2) communicates with a pipeline for supplying gas to the inlet opening (1) of the reactor chamber, preferably, for each electrode (3) with an arcuate surface, the ratio of the distance between two adjacent gas nozzles (2) and the internal diameter r2 of the gas nozzle satisfies the condition 1: 0.5-1.5. 6. A plasma reactor according to item 4 or 5, in which the ratio between the internal diameter r2 of the gas nozzle (2) and the minimum width r3 of the discharge zone satisfies the condition 1:2-8, preferably the material forming the gas nozzle (2) is a conductive material, preferably the electrical conductivity of the conductive material forming the gas nozzle (2) is > 1 MS/m, preferably > 10 MS/m, and the thermal conductivity is > 10 W/(m⋅°C), preferably > 50 W/(m⋅°C). 7. A plasma reactor according to claim 1 or 2, in which each electrode (3) with an arcuate surface is located in an inclined manner, wherein the internal angle θ formed by the lines of continuation of the axes of symmetry of each two electrodes (3) with an arcuate surface located in a symmetrical position is 5° - 160°, preferably 10° - 90°, more preferably 30° - 60°. 8. A plasma reactor according to claim 1 or 2, in which downstream from the sliding arc plasma generator in the reactor chamber there is a lower reaction zone, designed with the possibility of filling it with a catalyst, preferably the lower reaction zone is tapered, preferably, the ratio between the length d2 of the discharge zone, the length d4 of the separation zone and the height d5 of the lower reaction zone satisfies the condition 1: 0.1-0.8: 0.5-1.5, wherein the length d4 of the separation zone represents the distance between the bottom of the discharge zone and the top of the lower reaction zone. 9. A method for converting methane using plasma, which is a process for directly converting methane into olefins using plasma, wherein said method is carried out in a sliding arc plasma reactor according to any one of claims 1 to 8, and said method comprises: introducing a reaction gas containing methane into a sliding arc plasma reactor under plasma discharge conditions to carry out a methane conversion reaction, wherein said reaction gas containing methane is a mixture containing methane and a carrier gas, and the carrier gas is hydrogen. 10. The method according to claim 9, wherein the flow rate of the reaction gas containing methane is such that its volumetric velocity when passing through the lower reaction zone in the sliding arc plasma reactor, located in the reactor chamber downstream from the sliding arc plasma generator, is 1000-10000 units/hour, preferably 5000-8000 units/hour. 11. The method according to claim 9 or 10, wherein the methane conversion reaction conditions include the following conditions: the discharge voltage U1 is 1.0-5.0 kV, and the discharge current is 100-3000 mA, and/or the ratio between the flow rate V1 of the reaction gas containing methane and passing through the upper part of the discharge zone and the discharge voltage U1 is determined by the expression V1 : U1 = 50-100 : 1, where V1 is measured in l/min and U1 is measured in kV. 12. The method according to claim 11, wherein the conditions of the methane conversion reaction include the following conditions: the discharge voltage U1 is 2.0-5.0 kV, and the discharge current is 1000-3000 mA, and/or V1: U1 = 50-80: 1, preferably V1: U1 = 60-80: 1. 13. The method according to any one of claims 9 to 12, wherein the catalyst placed in the lower reaction zone in the sliding arc plasma reactor located in the reactor chamber downstream of the sliding arc plasma generator comprises a carrier doped with titanium oxide and an active component carried by the carrier, wherein the active component comprises a first active component and a second active component, wherein the first active component is selected from at least one of the non-noble metals of group VIII and the metals of group IB, and the second active component is selected from at least one of the noble metals of group VIII. 14. The method according to claim 13, wherein the weight ratio of the content of the element of the first active component to the element of the second active component, calculated based on metallic elements, is 0.1-200:1, preferably 0.1-10:1. 15. The method according to claim 13, wherein the molar ratio of L-acid and B-acid in the titanium oxide-doped carrier is 0.1-50:1. 16. The method of claim 13, wherein the titanium oxide-doped support is selected from at least one of titanium oxide-doped Al ₂ O ₃ , titanium oxide-doped SiO ₂ , titanium oxide-doped MgO, and titanium oxide-doped molecular sieve, and/or in a carrier doped with titanium oxide, the doping amount of titanium oxide is 0.1-10 wt.% of the total weight of the carrier. 17. The method according to any one of claims 13 to 16, wherein the element of the first active component is selected from at least one of Cu, Ag, Au, Ni and Fe, and/or the element of the second active component is selected from at least one of Pt, Rh, Pd and Ir. 18. The method according to any one of claims 13 to 17, wherein the content of the element of the first active component in the catalyst is 0.1 to 2 wt.%, calculated as a metallic element. 19. The method according to claim 9, wherein methane and the carrier gas are fed separately through a pipeline, wherein the methane feed rate is 0.5-5.0 l/min, and the hydrogen feed rate is 1.0-5.0 l/min, Preferably, the methane feed rate is 0.5-2.5 L/min, and the hydrogen feed rate is 1.0-2.5 L/min. 20. The method according to any one of claims 9 to 19, further comprising separating the product exiting the outlet (5) of the sliding arc plasma reactor to obtain carbon diolefin, carbon tetraolefins and gaseous feedstock that can be returned by recycling to the inlet (1) of the sliding arc reactor.