Method for preparing ethylene by catalyzing anaerobic conversion of methane under plasma condition

Abstract

The invention relates to the technical field of low-temperature plasma catalysis, in particular to a method for preparing ethylene by catalyzing anaerobic conversion of methane under a plasma condition, which comprises the following steps: 1) preparing a high-entropy alloy catalyst expressed as FeuNivVwZrxAgyCuz; (2) under the plasma condition, mixed gas formed by methane and argon generates plasma under the action of a high-entropy alloy catalyst, and a catalytic reaction is carried out; a product containing ethylene is obtained. The invention develops a method for directly preparing ethylene by efficiently catalyzing anaerobic conversion of methane under a mild condition in combination with a high-entropy alloy catalyst under a plasma condition, and efficient conversion of methane can be realized.

Description

Technical Field

[0001] The invention relates to the technical field of low-temperature plasma catalysis, and in particular to a method for catalyzing the oxygen-free conversion of methane to produce ethylene under plasma conditions. Background Art

[0002] Ethylene is an important chemical raw material, and its output is a symbol of a country's petrochemical development level. Considering my country's resource endowment and sustainable development requirements, it is of great strategic significance to seek the development of non-petroleum routes to produce ethylene to meet the needs of the ethylene industry. The anaerobic conversion of methane to ethylene is a chemical technology direction that has received much attention in recent years. The development of anaerobic conversion of methane to ethylene technology can reduce dependence on petroleum resources while improving the sustainable production capacity of ethylene. The anaerobic conversion of methane to ethylene, that is, the direct cracking of methane to produce ethylene, is a highly endothermic reaction due to the extremely high chemical stability of methane, which is extremely difficult to occur thermodynamically. Traditional thermal catalytic methods require extremely high temperatures, usually above 1500K, to produce ethylene. However, under such high temperature conditions, ethylene itself is not stable, so methane is more inclined to generate carbon and hydrogen.

[0003] The existing method for synthesizing ethylene by reacting methane and argon uses a thermal catalytic methane non-oxidative coupling technology, which has the disadvantages of usually requiring a high temperature of more than 500°C, low methane conversion rate, high energy consumption, and rapid catalyst deactivation. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a method for catalyzing the anaerobic conversion of methane to produce ethylene under plasma conditions based on plasma technology.

[0005] In order to solve the above problems, the present invention provides a method for catalyzing methane anaerobic conversion to ethylene under plasma conditions, comprising the following steps:

[0006] 1) Preparation of high entropy alloy catalysts;

[0007] 2) Under plasma conditions, a mixed gas formed by methane and argon generates plasma and catalytic reaction under the action of a high entropy alloy catalyst to obtain a product containing ethylene.

[0008] As an improvement of the method for catalyzing methane oxygen-free conversion to ethylene under plasma conditions of the present invention, the specific steps are as follows:

[0009] 1) Preparation of high entropy alloy catalyst, comprising the following steps:

[0010] S1. Powdered iron, nickel, vanadium, zirconium, silver and copper powders are mixed in a molar ratio of (0.5-2):(0.5-2):(0.5-2):(0.5-2):(0.5-2) to prepare alloy raw material powders;

[0011] The alloy raw material powder is melted into an alloy ingot under an inert gas atmosphere;

[0012] Melting can be carried out in a vacuum arc melting furnace;

[0013] S2, annealing the alloy ingot, and then cooling it naturally to obtain an annealed alloy ingot;

[0014] The annealing temperature is 1000-1500K, and the annealing time is 1-4h (preferably 2h);

[0015] Note: K = °C + 273.15;

[0016] S3, grinding the annealed alloy ingot in an inert gas (such as argon) atmosphere (using a high-energy ball mill) to obtain alloy particles;

[0017] S4, using a nitric acid solution with a concentration of 0.2 to 1 mol / L as an etching solution to dealloy the alloy particles for 12 to 48 hours; then washing and drying to obtain a high entropy alloy catalyst;

[0018] 2) The reaction device used comprises a cylindrical quartz dielectric shell with a cavity therein, the cavity of the quartz dielectric shell serves as a discharge gap; a high-voltage electrode is arranged close to the upper surface of the quartz dielectric shell, the high-voltage wire is electrically connected to the high-voltage electrode, a grounding electrode is arranged close to the lower surface of the quartz dielectric shell, the grounding wire is electrically connected to the grounding electrode, and a raw material inlet and a product outlet are arranged on two corresponding side surfaces of the quartz dielectric shell, both of which are connected to the cavity of the quartz dielectric shell;

[0019] Fill the discharge gap (i.e., fill the discharge area) with a high entropy alloy catalyst, exhaust the air in the reaction device first; then introduce a mixed gas formed by methane and argon into the discharge gap from the raw material inlet, generate plasma and catalyze the reaction under the action of the high entropy alloy catalyst and plasma high voltage electricity; obtain a product containing ethylene;

[0020] The volume content of methane in the mixed gas is 10-50%.

[0021] Note: In addition to ethylene, the product also includes hydrogen.

[0022] As a further improvement of the method for catalyzing methane oxygen-free conversion to ethylene under plasma conditions of the present invention:

[0023] In step S1, the purity of iron, nickel, vanadium, zirconium, silver and copper are all ≥99.95%.

[0024] As a further improvement of the method for catalyzing methane oxygen-free conversion to ethylene under plasma conditions of the present invention:

[0025] In the step S1: the alloy ingot is repeatedly smelted for multiple times to ensure uniform composition; the number of smelting times is 2 to 10 times;

[0026] In the step S3, grinding is performed until the particle size of the obtained alloy particles is 20 to 100 μm.

[0027] As a further improvement of the method for catalyzing methane oxygen-free conversion to ethylene under plasma conditions of the present invention:

[0028] The voltage peak value of the plasma high voltage is 12-18 kV, and the residence time of the mixed gas of methane and argon in the discharge gap is 0.04-0.08 min.

[0029] The input frequency of the high voltage power supply is 9kHz, and the total flow rate is 100-180mL / min.

[0030] The present invention realizes the efficient catalytic anaerobic conversion of methane to ethylene under mild conditions. In order to avoid the problems existing under high temperature conditions, it is a feasible way to introduce high-quality energy into the reaction system by using low-temperature plasma catalysis, so that methane can be converted to ethylene under mild conditions without anaerobic conditions.

[0031] Beneficial effects of the present invention:

[0032] 1. A method for direct anaerobic conversion of methane to ethylene has been developed, achieving efficient utilization of methane.

[0033] Note: Argon, as an inert gas, does not participate in the reaction, but only plays a role in diluting methane, improving the reaction conversion rate, increasing the electron density, and enhancing the reaction performance.

[0034] 2. The proposed high entropy alloy catalyst has high activity and high selectivity for the target product.

[0035] 3. Plasma inputs high-quality energy into the reaction, allowing methane to be directly converted under mild conditions, avoiding high temperature conditions.

[0036] In summary, the present invention has developed a method for efficiently catalyzing the anaerobic conversion of methane to directly produce ethylene under mild conditions by combining a high entropy alloy catalyst under plasma conditions, thereby achieving efficient methane conversion. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] The specific implementation modes of the present invention are further described in detail below with reference to the accompanying drawings.

[0038] Figure 1 The schematic diagram of the plasma reactor device used in the present invention is shown in FIG. 1 is a quartz medium, 2 is a high voltage electrode, 3 is a ground electrode, 4 is a discharge gap, 5 is a high voltage wire, 6 is a ground wire, 7 is a raw material inlet, and 8 is a product outlet. DETAILED DESCRIPTION

[0039] The present invention is further described below in conjunction with specific embodiments, but the protection scope of the present invention is not limited thereto:

[0040] Device Example 1: A plasma reactor device:

[0041] A parallel plate dielectric barrier discharge plasma reactor is used as a reaction device for catalyzing the oxygen-free conversion of methane to ethylene under plasma conditions; the specific structure is as follows:

[0042] The invention comprises a cylindrical quartz dielectric shell 1 with a cavity therein, the upper surface and the lower surface of the quartz dielectric shell 1 are both circular, and the upper surface and the lower surface are parallel to each other with a certain gap, which serves as a barrier medium. The cavity formed by the gap between the upper surface and the lower surface serves as a discharge gap 4, and the discharge gap 4 is also a catalyst filling area and a gas passage.

[0043] A quartz branch pipe connected to the discharge gap 4 is respectively arranged on the two corresponding side surfaces of the quartz dielectric shell 1, serving as a raw material inlet 7 (gas raw material inlet) and a product outlet 8, that is, the axis of the raw material inlet 7, the product outlet 8 and the quartz dielectric shell 1 coincides.

[0044] A copper electrode is provided as a high-voltage electrode 2 in close contact with the upper surface of the quartz dielectric housing 1 , and a high-voltage wire 5 is electrically connected to the high-voltage electrode 2 ; the distance between the high-voltage electrode 2 and the upper surface of the quartz dielectric housing 1 is ≤0.05 mm, thereby ensuring a close contact effect.

[0045] A copper electrode is provided close to the lower surface of the quartz dielectric housing 1 as the grounding electrode 3, and the grounding wire 6 is electrically connected to the grounding electrode 3; the distance between the grounding electrode 3 and the lower surface of the quartz dielectric housing 1 is ≤0.05 mm, thereby ensuring a close contact effect.

[0046] Catalyst fillers are arranged in the discharge gap 4 to cooperate with the plasma catalytic reaction during discharge.

[0047] The plasma high voltage power supply provides high voltage alternating current with adjustable frequency and voltage peak.

[0048] In actual use:

[0049] After the high voltage is passed through the high voltage conductor 5, the high voltage electrode 2 discharges to the ground electrode 3, with the quartz medium 1 as the dielectric material. The plasma high voltage power supply provides high voltage alternating current with adjustable frequency and voltage peak.

[0050] Specific:

[0051] The wall thickness of the upper surface and the lower surface of the quartz dielectric housing 1 is 1 mm to 3 mm, and the diameter is 30 to 100 mm.

[0052] The high voltage electrode 2 and the ground electrode 3 are cylindrical and made of copper; they are 10 mm to 30 mm thick and 20 mm to 80 mm in diameter, that is, the diameters of the high voltage electrode 2 and the ground electrode 3 are slightly smaller than the upper surface and the lower surface of the quartz dielectric shell 1 .

[0053] The high-voltage electrode 2 is connected to a high-voltage power source via a high-voltage wire 5 , and the grounding electrode 3 is grounded via a grounding wire 6 .

[0054] The plasma high voltage power supply can generate a stable alternating current with a voltage peak of 0-30 kV and a frequency of 1 kHz-50 kHz. The width of the discharge gap 4 (i.e., the distance between the upper surface and the lower surface of the quartz dielectric shell 1) is 1.5 mm-11 mm, and the discharge area = the common coverage area of ​​the high voltage electrode 2 and the ground electrode 3, which is 300 mm 2 -4800mm 2 , the catalyst filled area is the discharge gap 4.

[0055] The raw material gas is a mixed gas of methane and argon, wherein the methane accounts for 10% to 50%; the raw material gas flow rate is 100 to 180 mL / min.

[0056] Catalyst Preparation Example 1: Preparation of high entropy alloy catalyst:

[0057] This scheme prepares high entropy alloys containing elements such as iron, nickel, vanadium, zirconium, silver, and copper, which are used to catalyze the oxygen-free conversion of methane to ethylene under plasma conditions.

[0058] The main steps are as follows:

[0059] S1. Weigh and fully mix powdered high-purity (purity ≥ 99.95%) iron, nickel, vanadium, zirconium, silver, and copper powders in a molar ratio of (0.5-2):(0.5-2):(0.5-2):(0.5-2):(0.5-2) to prepare alloy raw material powders;

[0060] The alloy raw material powder is placed in a vacuum arc melting furnace and melted into an alloy ingot under an inert gas (such as argon) atmosphere; the alloy ingot is repeatedly melted for multiple times (the number of melting times is 2 to 10 times) to ensure that the alloy composition is uniform.

[0061] S2, annealing the alloy ingot, and then cooling it naturally to obtain an annealed alloy ingot;

[0062] The annealing temperature is 1000-1500K, and the annealing time is 1-4h.

[0063] S3, in an inert gas (such as argon) atmosphere, grinding the annealed alloy ingot using a high-energy ball mill to obtain alloy particles with a particle size of 20 to 100 μm;

[0064] S4, using a nitric acid solution with a concentration of 0.1 to 2 mol / L as an etching solution to dealloy the alloy particles for 12 to 48 hours; then washing and drying to obtain a high entropy alloy catalyst;

[0065] High entropy alloy catalyst is represented by Fe u Ni v V w Zr x Ag y Cu z , u, v, w, x, y, z are the molar ratios of Fe, Ni, V, Zr, Ag and Cu elements respectively; u:v:w:x:y:z=(0.5~2):(0.5~2):(0.5~2):(0.5~2):(0.5~2):(0.5~2).

[0066] Example 1: A method for catalyzing methane anaerobic conversion to ethylene under plasma conditions

[0067] 1. A plasma reactor device according to device example 1

[0068] The upper and lower surfaces of the quartz dielectric shell 1 are both 2 mm thick and 80 mm in diameter; the high-voltage electrode 2 and the grounding electrode 3 are 20 mm thick and 60 mm in diameter, and overlap each other in the upper and lower directions (the coverage area of ​​the high-voltage electrode 2 and the grounding electrode 3 overlaps with respect to the quartz dielectric shell 1), so the coverage area is about 2800 mm 2 The distance between the upper surface and the lower surface of the quartz dielectric housing 1 is 3 mm, that is, the width of the discharge gap 4 is 3 mm.

[0069] 2. FeNiVZrAgCu (the molar amount of each metal is the same, i.e. u, v, w, x, y, z = 1) high entropy alloy catalyst prepared by catalyst preparation example 1. 30g mixed metal powders of high purity iron, nickel, vanadium, zirconium, silver and copper powders (purity is greater than 99.95%) are weighed according to the atomic ratio, mixed and put into a vacuum arc melting furnace, and melted (temperature is about 2000°C) into alloy ingots under argon atmosphere; cooled naturally, and the alloy ingots are repeatedly melted 5 times; then annealed at 1373K for 2h, cooled naturally; after grinding and high-energy ball milling, particles with a particle size between 30 and 60μm are screened; de-alloyed with 1mol / L nitric acid for 24h, fully washed and dried (washed with water until the eluent meets Ph neutrality, and dried at 120°C to constant weight), which is the required high entropy alloy catalyst (hereinafter referred to as catalyst).

[0070] 3. During the reaction, the reactor was assembled, the catalyst was filled into the discharge gap 4 (i.e., the discharge area was filled), nitrogen was introduced continuously for 30 min through the raw material inlet 7 (gas raw material inlet), and the air in the discharge gap 4 was discharged from the product outlet 8; thereby the air in the reactor was discharged; the volume flow rate of methane and argon was 1:9, and the total flow rate was 100 mL / min (the residence time of the mixed gas of methane and argon in the discharge gap 4 was 0.08 min); the high-voltage power supply input frequency was 9 kHz, and the voltage peak was 12 kV AC, plasma was generated and catalytic reaction was carried out;

[0071] The catalytic reaction formula is:

[0072] 2CH4→C2H4+2H2

[0073] The product is detected by gas chromatography-mass spectrometry. The separation method of ethylene and hydrogen is conventional technology in the industry, for example, ethylene and hydrogen can be separated by conventional pressure swing adsorption.

[0074] Example 2 series:

[0075] Compared with Example 1, the molar ratio of iron in the alloy is changed, that is, u is changed, and other operations are the same as Example 1 to obtain the series of Example 2. The comparison of process parameters and reaction results with Example 1 is shown in Table 1.

[0076] Table 1

[0077]

[0078]

[0079] Embodiment 3 series:

[0080] Compared with Example 1, the molar ratio of nickel in the alloy is changed, that is, v is changed, and other operations are the same as Example 1 to obtain the series of Example 3. The comparison of process parameters and reaction results with Example 1 is shown in Table 2.

[0081] Table 2

[0082] Example v Methane conversion rate (%) Ethylene selectivity (%) 1 1 85 90 3-1 0.5 81 85 3-2 1.6 90 94 3-3 2 93 96

[0083] Embodiment 4 series:

[0084] Compared with Example 1, the molar ratio of vanadium in the alloy is changed, that is, w is changed, and other operations are the same as Example 1 to obtain the series of Example 4. The comparison of process parameters and reaction results with Example 1 is shown in Table 3.

[0085] Table 3

[0086] Example w Methane conversion rate (%) Ethylene selectivity (%) 1 1 85 90 4-1 0.5 80 84 4-2 1.6 88 92 4-3 2 91 95

[0087] Embodiment 5 series:

[0088] Compared with Example 1, the molar ratio of zirconium in the alloy is changed, that is, x is changed, and other operations are the same as Example 1 to obtain the series of Example 5. The comparison of process parameters and reaction results with Example 1 is shown in Table 4.

[0089] Table 4

[0090] Example x Methane conversion rate (%) Ethylene selectivity (%) 1 1 85 90 5-1 0.5 82 83 5-2 1.6 89 94 5-3 2 93 95

[0091] Embodiment 6 series:

[0092] Compared with Example 1, the molar ratio of silver in the alloy is changed, that is, y is changed, and other operations are the same as Example 1 to obtain the series of Example 6. The comparison of process parameters and reaction results with Example 1 is shown in Table 5.

[0093] Table 5

[0094] Example y Methane conversion rate (%) Ethylene selectivity (%) 1 1 85 90 6-1 0.5 79 87 6-2 1.6 90 94 6-3 2 92 96

[0095] Embodiment 7 series:

[0096] Compared with Example 1, the molar ratio of copper in the alloy is changed, that is, z is changed, and other operations are the same as Example 1 to obtain Example 7 series. See Table 6 for a comparison of process parameters and reaction results with Example 1.

[0097] Table 6

[0098] Example z Methane conversion rate (%) Ethylene selectivity (%) 1 1 85 90 7-1 0.5 78 85 7-2 1.6 89 94 7-3 2 93 96

[0099] Embodiment 8 series:

[0100] Compared with Example 1, the annealing temperature was changed, and other operations were the same as Example 1, to obtain the series of Example 8. The comparison of process parameters and reaction results with Example 1 is shown in Table 7.

[0101] Table 7

[0102] Example Annealing temperature(K) Methane conversion rate (%) Ethylene selectivity (%) 1 1373 85 90 8-1 1073 80 84 8-2 1173 82 87 8-3 1273 83 88 8-4 1473 89 92

[0103] Embodiment 9 series:

[0104] Compared with Example 1, the melting times were changed, and other operations were the same as Example 1 to obtain the Example 9 series. The comparison of process parameters and reaction results with Example 1 is shown in Table 8.

[0105] Table 8

[0106] Example Melting times Methane conversion rate (%) Ethylene selectivity (%) 1 5 85 90 9-1 3 82 89 9-2 7 88 92 9-3 9 90 93

[0107] Embodiment 10 series:

[0108] Compared with Example 1, the concentration of nitric acid was changed, and other operations were the same as Example 1 to obtain Example 10 series. The comparison of process parameters and reaction results with Example 1 is shown in Table 9.

[0109] Table 9

[0110] Example Nitric acid concentration (mol / L) Methane conversion rate (%) Ethylene selectivity (%) 1 1 85 90 10-1 0.2 76 81 10-2 0.4 79 84 10-3 0.6 81 85 10-4 0.8 84 88

[0111] Embodiment 11 series:

[0112] Compared with Example 1, the proportion of methane in the raw gas was changed, and the flow rate of the mixed gas remained unchanged; other operations were the same as Example 1, and the series of Example 11 was obtained. The comparison of process parameters and reaction results with Example 1 is shown in Table 10.

[0113] Table 10

[0114] Example Methane ratio (%) Methane conversion rate (%) Ethylene selectivity (%) 1 10 85 90 11-1 20 83 92 11-2 30 80 93 11-3 40 76 95 11-4 50 74 96

[0115] Embodiment 12 series:

[0116] Compared with Example 1, the voltage peak-to-peak value was changed (twice the voltage peak value), and other operations were the same as Example 1, to obtain the series of Example 12. The comparison of process parameters and reaction results with Example 1 is shown in Table 11.

[0117] Table 11

[0118] Example Voltage peak to peak value (kV) Methane conversion rate (%) Ethylene selectivity (%) 1 24 85 90 12-1 20 83 88 12-2 28 89 93 12-3 32 90 94 12-4 36 92 96

[0119] Embodiment 13 series:

[0120] Compared with Example 1, the flow rate of the methane-argon mixed gas is changed, and the residence time of the mixed gas in the discharge gap 4 is changed accordingly. The other operations are the same as those of Example 1, and the series of Example 13 is obtained. The comparison of the process parameters and reaction results with those of Example 1 is shown in Table 12.

[0121] Table 12

[0122] Example Flow rate (mL / min) Dwell time Methane conversion rate (%) Ethylene selectivity (%) 1 100 0.08 85 90 13-1 120 ≈0.07 82 91 13-2 140 ≈0.06 79 92 13-3 160 ≈0.05 76 95 13-4 180 ≈0.04 75 96

[0123] Comparative Example 1-1: The amount of Fe in Example 1 was changed to 0, that is, u in Example 1 was changed to 0, and the rest was the same as Example 1. The results are shown in Table 13 below.

[0124] Comparative Example 1-2: The amount of Ni in Example 1 was changed to 0, that is, v in Example 1 was changed to 0, and the rest was the same as Example 1. The results are shown in Table 13 below.

[0125] Comparative Example 1-3: The amount of V in Example 1 was changed to 0, that is, w in Example 1 was changed to 0, and the rest was the same as Example 1. The results are shown in Table 13 below.

[0126] Comparative Examples 1-4: The amount of Zr in Example 1 was changed to 0, that is, x in Example 1 was changed to 0, and the rest was the same as Example 1. The results are shown in Table 13 below.

[0127] Comparative Example 1-5: The amount of Ag in Example 1 was changed to 0, that is, y in Example 1 was changed to 0, and the rest was the same as Example 1. The results are shown in Table 13 below.

[0128] Comparative Example 1-6: The amount of Cu in Example 1 was changed to 0, that is, z in Example 1 was changed to 0, and the rest was the same as Example 1. The results are shown in Table 13 below.

[0129] Comparative Example 2-1: The number of smelting times in Example 1 was changed to 1, and the rest was the same as Example 1. The obtained results are shown in Table 13 below.

[0130] Comparative Example 2-2: The annealing treatment in Example 1 was eliminated, and the rest was the same as Example 1. The obtained results are shown in Table 13 below.

[0131] Comparative Example 3-1: The catalyst in Example 1 was replaced with quartz sand, and the rest was the same as Example 1. The results are shown in Table 13 below.

[0132] Comparative Example 3-2: The catalyst in Example 1 was changed to none, and the rest was the same as Example 1. The results are shown in Table 13 below.

[0133] Table 13

[0134] Comparative Example Methane conversion rate (%) Ethylene selectivity (%) Comparative Example 1-1 72 78 Comparative Example 1-2 73 77 Comparative Examples 1-3 71 79 Comparative Examples 1-4 74 76 Comparative Examples 1-5 73 77 Comparative Examples 1-6 71 75 Comparative Example 2-1 65 72 Comparative Example 2-2 70 75 Comparative Example 3-1 51 42 Comparative Example 3-2 32 19

[0135] Finally, it should be noted that the above examples are only some specific embodiments of the present invention. Obviously, the present invention is not limited to the above embodiments, and there are many variations. All variations that can be directly derived or associated with the content disclosed by a person skilled in the art should be considered as the protection scope of the present invention.

Claims

1. A method for preparing ethylene by catalytic conversion of methane without oxygen under plasma conditions, characterized in that The following steps are involved: 1) Preparation of high entropy alloy catalysts; 2) Under plasma conditions, a mixed gas formed by methane and argon generates plasma and catalytic reaction under the action of a high entropy alloy catalyst to obtain a product containing ethylene.

2. The method for preparing ethylene by catalytic conversion of methane to ethylene under plasma conditions according to claim 1, characterized in that: 1) Preparation of high entropy alloy catalyst, comprising the following steps: S1. Powdered iron, nickel, vanadium, zirconium, silver and copper powders are mixed in a molar ratio of (0.5-2):(0.5-2):(0.5-2):(0.5-2):(0.5-2) to prepare alloy raw material powders; The alloy raw material powder is melted into an alloy ingot under an inert gas atmosphere; S2, annealing the alloy ingot, and then cooling it naturally to obtain an annealed alloy ingot; The annealing temperature is 1000-1500K, and the annealing time is 1-4h; S3, grinding the annealed alloy ingot in an inert gas atmosphere to obtain alloy particles; S4, using a nitric acid solution with a concentration of 0.2 to 1 mol / L as an etching solution to dealloy the alloy particles for 12 to 48 hours; then washing and drying to obtain a high entropy alloy catalyst; 2) The reaction device comprises a cylindrical quartz dielectric shell (1) with a cavity therein, the cavity of the quartz dielectric shell (1) serving as a discharge gap (4); a high-voltage electrode (2) is arranged close to the upper surface of the quartz dielectric shell (1), a high-voltage wire (5) is electrically connected to the high-voltage electrode (2), a grounding electrode (3) is arranged close to the lower surface of the quartz dielectric shell (1), a grounding wire (6) is electrically connected to the grounding electrode (3), and a raw material inlet (7) and a product outlet (8) are arranged on two corresponding side surfaces of the quartz dielectric shell (1), both of which are connected to the cavity of the quartz dielectric shell (1); The discharge gap (4) is filled with a high entropy alloy catalyst, and the air in the reaction device is first exhausted; then a mixed gas formed by methane and argon is introduced into the discharge gap (4) from a raw material inlet (7), and plasma is generated and catalytic reaction is performed under the action of the high entropy alloy catalyst and plasma high voltage electricity; a product containing ethylene is obtained; The volume content of methane in the mixed gas is 10-50%.

3. The method for preparing ethylene by catalytic conversion of methane to ethylene under plasma conditions according to claim 2, characterized in that: In step S1, the purity of iron, nickel, vanadium, zirconium, silver and copper are all ≥99.95%.

4. The method for preparing ethylene by catalytic conversion of methane to ethylene under plasma conditions according to claim 3, characterized in that: In the step S1, the alloy ingot is repeatedly smelted for multiple times to ensure uniform composition; the smelting times are 2 to 10 times.

5. The method for preparing ethylene by catalytic conversion of methane to ethylene under plasma conditions according to claim 4, characterized in that: In the step S3, grinding is performed until the particle size of the obtained alloy particles is 20 to 100 μm.

6. The method for preparing ethylene by catalytic anaerobic conversion of methane under plasma conditions according to any one of claims 1 to 5, characterized in that: The peak voltage of the plasma high voltage is 12-18 kV, and the residence time of the mixed gas of methane and argon in the discharge gap (4) is 0.04-0.08 min.

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