A catalyst and method for the aerobic coupling of methane to ethylene

Abstract

The application relates to a catalyst and a method for preparing ethylene through methane oxygen-free coupling, and belongs to the fields of methane resource utilization and plasma chemistry technology. One-step methane oxygen-free coupling for preparing ethylene is realized through dielectric barrier discharge plasma and a metal oxide supported catalyst, CH4 is activated by plasma, a large amount of CH3 free radicals are generated through cracking, the CH3 free radicals are adsorbed on Cu + -O v ‑Ce 3+ sites and are dehydrogenated to generate CH2, and the CH2 is further coupled to generate C2H4. The catalyst is more beneficial to the dehydrogenation of CH3 to generate CH2 and further coupling to generate C2H4, instead of the coupling of CH3 to generate C2H6, so that the methane oxygen-free coupling can be realized to generate ethylene in one step. The reaction device is simple, convenient to operate, high in reaction stability, low in raw material cost and pollution-free.

Description

Technical Field

[0001] This invention belongs to the field of methane resource utilization and plasma chemical synthesis technology, and relates to a catalyst and method for the one-step plasma-catalyzed oxygen-free coupling of methane to ethylene. It is a supported metal oxide catalyst and method suitable for plasma-catalyzed one-step oxygen-free coupling of methane to ethylene. Background Technology

[0002] Methane, the main component of natural gas, is an important energy resource and also a greenhouse gas. Ethylene, a basic raw material in the chemical industry, is commonly used to produce polyethylene, vinyl chloride and polyvinyl chloride, ethylbenzene, styrene and polystyrene, ethylene propylene rubber, and ethylene terephthalate rubber, among others. The development of the ethylene industry determines the development speed of the chemical industry and plays a vital role in the overall development of the chemical sector. Therefore, the conversion of methane into ethylene is of great significance.

[0003] The conversion of methane to ethylene is mainly achieved through two pathways: oxidative coupling of methane to ethylene and anaerobic coupling of methane to ethylene. Anaerobic coupling of methane, in particular, does not produce excessive oxidation products (such as carbon dioxide and carbon monoxide) and has the advantage of high carbon atom utilization efficiency. However, under anaerobic conditions, methane activation and conversion are thermodynamically limited and must be carried out at extremely high reaction temperatures. Therefore, developing a catalyst and method for achieving anaerobic coupling of methane to ethylene at lower temperature conditions has significant scientific and practical value.

[0004] Currently, the following patents and documents have reported on the thermocatalytic system for the oxygen-free coupling of methane to ethylene.

[0005] 1. Thermocatalytic reaction system

[0006] (1) Patent CN104909975A (application date: 2015-09-16) discloses a method for preparing a microporous molecular sieve-supported metal compound solid catalyst, and a method for catalytically preparing ethylene from methane under anaerobic continuous flow conditions. In a fixed-bed reaction mode, the preferred reaction temperature is 600-850℃; the reaction pressure is atmospheric pressure; and the mass hourly space velocity (MSV) of the reactant gas is 1500-8000 ml / g / h. The methane conversion rate is 5-20%, and the ethylene selectivity is 10-40%.

[0007] (2) Patent CN106914243A (application date: 2017-07-04) discloses a method for preparing a Si-based catalyst doped with metal element lattice and a method for oxygen-free methane-to-ethylene production. In a fixed-bed reaction mode, the preferred reaction temperature is 750-1100℃, the reaction pressure is 0.1-0.3 MPa, and the mass hourly space velocity (MSV) of the reactant gas is 1000-30000 ml / g / h. The methane conversion rate is 10-60%, and the olefin selectivity is 60-95%.

[0008] (3) Patent CN105481626B (application date: 2017-05-17) discloses a method for the direct production of ethylene, aromatics, and hydrogen from methane using photovoltaic polycrystalline silicon cutting waste as a catalyst under anaerobic continuous flow conditions. This process realizes the economical utilization of inexpensive photovoltaic polycrystalline silicon cutting waste, and the obtained products are all basic chemical raw materials required by industry. In the fixed-bed reaction mode, the preferred reaction temperature is 750-1200℃; the reaction pressure is atmospheric pressure; and the mass hourly space velocity of the reactant gas is 1000-30000 mL / g / h. The conversion rate of methane is 3-30%; the olefin selectivity is 10-30%; and the aromatics selectivity is 10-50%.

[0009] (4) The published paper "Applied Catalysis A, 2020, 595, 117430" reports a novel stable supported GaN / SBA15 catalyst for the direct non-oxidative coupling of methane to ethylene. The preferred optimal nitriding temperature is 750 °C. The reaction was carried out in a fixed-bed quartz tube reactor, with a methane conversion of 0.32% and an ethylene selectivity of 71%.

[0010] (5) The published paper "Science, 2014, 344, 616-619" reports a novel single-atom catalyst, Fe@SiO2, for the anaerobic conversion of methane to ethylene, aromatics, and hydrogen. The preferred reaction temperature is 1363 K. The methane conversion rate is 48.1%, the ethylene selectivity is 48.4%, and the total hydrocarbon selectivity exceeds 99%.

[0011] (6) The published paper *Chemical Engineering Journal*, 2020, 396, 125182, reports a single-atom catalyst, Pt / CeO2, for the oxygen-free coupling of methane to C2 hydrocarbons. The preferred temperatures are 780-910℃, flow rates are 0.9-2.6 ml / min, and pressures are 1.5 bar. The methane conversion rate is 4.3%, and the C2 hydrocarbon selectivity is 60%, with ethylene accounting for 80% of the total C2 hydrocarbon selectivity.

[0012] (7) The published paper "ChemPhysChem, 2018, 19, 504-511" reports a novel catalyst, Mo2C / [B]ZSM-5, for the oxygen-free coupling of methane to ethylene. The preferred temperature is 923 K, achieving an ethylene selectivity of 90%.

[0013] From the aforementioned patents and published documents, it can be seen that in traditional thermocatalytic reactions, there are problems such as excessively high reaction temperatures or very low methane conversion rates.

[0014] 2. Plasma-based catalyst reaction system

[0015] Plasma, as the fourth state of matter, contains abundant high-energy electrons. These high-energy electrons can activate inert raw material molecules (methane and argon) into reactive species such as free radicals, excited-state atoms, and ions through inelastic collisions. As a form of non-volume work, plasma can promote thermodynamically unfavorable reactions under low-temperature conditions, providing a new opportunity for the anaerobic coupling of methane. Currently, plasma technology has been widely applied to the conversion of methane, but to date, only a very few published documents and patents have reported on the plasma-catalyzed conversion of methane to ethylene via anaerobic coupling.

[0016] (1) The published paper "Plasma Science and Technology, 2011, 13, 1" reported a novel two-stage spark discharge reactor with a catalyst (Pd-Ag / SiO2) and an ethylene yield of 52.1%.

[0017] (2) The published paper "Chemical Engineering Journal, 2020, 380, 122477" reported a nanosecond pulsed discharge plate reactor for plasma-based Pd-based catalyst catalytic oxygen-free coupling of methane to ethylene. The preferred conditions were: continuous preheating of the catalyst bed at 150°C, total gas velocity of 200 ml / min, gas molar ratio of CH4:H2 = 1:1, discharge gap of 2.5 mm, and pulse frequency of 3 kHz. The ethylene yield reached 20%.

[0018] The aforementioned published literature all employs thermal plasma to crack methane into acetylene, and then uses a palladium-based or other hydrogenation catalyst to convert the acetylene into ethylene, which is a two-step method for methane to ethylene conversion.

[0019] (3) The published paper "ACS Applied Materials & Interfaces, 2022, 14, 5363-5375" reports a method for plasma-catalyzed oxygen-free coupling conversion of methane using a novel catalyst, Pt / CeO2-SAC. The preferred conditions are CH4 / He = 10 / 10 ml / min, power of 54 W, and reaction temperature <153℃. The methane conversion rate is 39%, the ethane selectivity is 48%, and the ethylene selectivity is 6%.

[0020] (4) The published paper "Plasma Chem Plasma Process, 2014, 34, 175-186" reports a method for the oxygen-free coupling of methane to ethylene using a novel catalyst, Pt / Al2O3. The preferred conditions are CH4 / Ar = 1 / 9, total gas velocity of 336.0 ml / min, applied power of 14.2 W, Sn = 1:3, SiO2:Al2O3 = 280, and reaction temperature of 973 K-1123 K. The methane conversion rate is 18.2%, the ethane selectivity is 50%, and the ethylene selectivity is 10%.

[0021] The aforementioned published literature all employs cold plasma technology combined with platinum-based catalysts to convert methane, with ethane as the main product. The reason for this may be that, thermodynamically, the methyl groups produced by plasma cracking of methane are more likely to undergo coupling reactions to form ethane, rather than dehydrogenating to form methylene groups; therefore, the selectivity for ethylene is very low.

[0022] (5) The publicly available literature, *Journal of the American Chemical Society 2023, 145, 20792-20800*, reports a method for plasma-catalyzed oxygen-free coupling of methane to C2 hydrocarbons using a novel catalyst, MFM-300(Fe). The preferred conditions are CH4 / He = 1 / 100, total gas velocity of 60 ml / min, 60 mg catalyst, and a power of 2 W. The methane conversion rate is 10%, the ethane selectivity is 38%, and the ethylene selectivity is 58%. Without a catalyst, the ethylene selectivity reaches 47%, mainly because the low power (2 W) and low methane content (1%) lead to a chemical equilibrium in the reaction system that favors ethylene production. Therefore, the addition of this catalyst has a relatively small effect on improving the ethylene selectivity, and its catalytic effect is not significant.

[0023] In summary, a one-step anaerobic coupling technology for the production of C2H4 from CH4 has not yet been developed under a wide range of CH4 content and relatively low reaction temperatures. The main reason is that the methyl intermediate (CH3) generated by plasma-activated CH4 is thermodynamically more inclined to couple to C2H6 rather than dehydrogenate to CH2, and then couple to C2H4. In other words, the selective dehydrogenation of CH3 to CH2 is difficult to achieve, making the direct conversion of CH4 to C2H4 under mild conditions a challenge. Therefore, developing a new catalyst and method to promote the dehydrogenation of CH3 to CH2, and then the coupling to C2H4, is of great significance for developing a new anaerobic coupling technology for the production of ethylene from CH4. Summary of the Invention

[0024] The present invention aims to provide a novel catalyst and method for plasma-catalyzed oxygen-free coupling of methane to ethylene.

[0025] Technical principle: High-energy electrons generated by dielectric barrier discharge activate methane. Under the collision of high-energy electrons, reactant molecules are excited and dissociate to generate a large amount of CH3. CH3 undergoes dehydrogenation at the active sites of the catalyst proposed in this invention to generate CH2. CH2 is further coupled to directly generate C2H4, thereby realizing the direct coupling of methane to ethylene under low-temperature conditions.

[0026] The technical solution of this invention:

[0027] A catalyst for the oxygen-free coupling of methane to ethylene is a metal oxide supported catalyst, comprising an active component and a support. The active component is an oxide with variable valence characteristics, and the support is a metal oxide or non-metal oxide with Lewis acid-base pairs and capable of forming oxygen vacancies. The active component accounts for 1-20% of the mass percentage of the catalyst.

[0028] The active component is one or more of Fe, Co, Ni, Cu, and Zn; the support is one or more of CeO2, ZrO2, Al2O3, and SiO2.

[0029] A method for producing ethylene from methane via oxygen-free coupling, using the aforementioned catalyst, includes the following steps: introducing methane and argon gas into a dielectric barrier discharge reactor, activating and cracking the methane through dielectric barrier discharge, and directly converting the methane into ethylene under the action of the catalyst.

[0030] The volume ratio of methane to argon is 1:(0-10), the residence time of the mixed gas in the reaction zone is 0.01-100s, the dielectric barrier discharge uses a high-voltage AC plasma power supply with a specific input energy of 3-300kJ / L, a discharge frequency of 1kHz-20kHz, a pressure of -0.06MPa-0.5MPa, and a reaction temperature of 100-300℃.

[0031] The dielectric barrier discharge reactor is a wire-cylinder reactor, which is cylindrical in shape and has metal wire wound around its exterior as a grounding electrode. The upper end of the cylinder is equipped with an upper end cap with a central hole, through which a metal rod is installed along the reactor axis as a high-voltage electrode. The distance between the outer wall of the metal rod and the inner wall of the cylindrical reactor is 0.1-30 mm. The cylindrical reactor is made of dielectric insulating material. The upper end of the reactor is equipped with a gas inlet, the lower end of the reactor is the tail gas outlet, and the middle is the discharge zone. The catalyst is placed in the discharge zone inside the reactor, and the catalyst bed is supported by a quartz sand plate.

[0032] Preferably, the molar ratio of methane to argon is 1:1.

[0033] Preferably, the residence time of the methane and argon mixture in the discharge zone is 4.5 s; the specific input energy of the plasma power supply is 46.2 kJ / L, and the discharge frequency is 14.1 kHz.

[0034] Preferably, the active component accounts for 5-10% by weight in the metal-supported catalyst.

[0035] Preferably, the high-voltage electrode and the grounding electrode are made of copper, iron, tungsten, aluminum or stainless steel.

[0036] Preferably, the reactor material is quartz glass, hard glass, alumina ceramic, polytetrafluoroethylene, or a non-metallic composite material.

[0037] The beneficial effects of this invention: Experimental verification shows that the catalyst proposed in this invention exhibits a longer induction period (e.g., Figure 4 As shown, Cu2O and Cu in CuO / CeO2 0 (Content gradually increases). Using the method of this invention for ethylene preparation, the selectivity for ethane decreases, while the selectivity for ethylene increases (e.g., content gradually increases). Figure 3 (As shown). Under steady-state conditions, the methane conversion rate is greater than 6%, and the ethylene selectivity is greater than 35% (e.g.). Figure 2 (As shown); The main mechanism of the catalyst catalyzing the oxygen-free coupling of methane to ethylene is that the CH3 species generated by plasma undergoes chemisorption with the catalyst, leading to the gradual reduction of the catalyst to form active sites. These active sites can break the CH bonds of the CH3 species to generate adsorbed CH2 species (as shown). Figure 5 As shown in the diagram, the adsorbed CH2 species further generates ethylene via a coupling reaction. This method operates under mild conditions, uses inexpensive catalysts, and is a one-step direct synthesis process. It provides a class of catalysts and methods for the one-step oxygen-free coupling of methane to ethylene at low temperatures. The method features simple equipment, convenient operation, high reaction stability, inexpensive raw materials, and no pollution. Attached Figure Description

[0038] Figure 1 This is a diagram of a plasma-converted methane oxygen-free coupling reactor for the production of ethylene.

[0039] Figure 2 This is a comparative analysis chart of the products of plasma, plasma-filled CeO2, and plasma-filled CuO / CeO2 reactions;

[0040] Figure 3 This is a mass spectrometry analysis of the plasma-filled CuO / CeO2 product;

[0041] Figure 4 These are the XRD patterns of CuO / CeO2 at different reaction times;

[0042] Figure 5 This is the in-situ infrared spectrum of plasma-coordinated CuO / CeO2 conversion of methane to ethylene via oxygen-free coupling.

[0043] In the diagram: 1. Plasma power supply; 2. High-voltage probe; 3. Oscilloscope; 4. Raw material gas; 5. Current probe; 6. Capacitor; 7. Low-voltage probe; 8. Gas chromatograph; 9. Reactor. Detailed Implementation

[0044] The specific embodiments of the present invention are described in detail below with reference to the technical solutions and accompanying drawings.

[0045] Comparative Example 1

[0046] use Figure 1 The reaction apparatus, reactor 9, is a single-medium barrier wire-tube reactor. A stainless steel rod installed in a quartz tube serves as a high-voltage electrode connected to plasma power supply 1, and an iron wire wound around the outer wall of the quartz tube serves as a grounding electrode. A high-voltage probe 2, a current probe 5, and a low-voltage probe 7, connected to an oscilloscope 3, monitor the electrical signals in real time. In the circuit, the high-voltage probe 2 is connected to the high-voltage electrode and the ground electrode respectively, the current probe 5 is connected in series to the ground terminal, and the low-voltage probe 7 is connected in parallel with a capacitor 6 connected in series on both sides of the ground terminal. The diameter of the high-voltage electrode is 2 mm, the discharge gap is 2 mm, and the discharge zone length is 60 mm. The reaction pressure is 0.1 MPa. Argon and methane are introduced into the discharge reactor at a molar ratio of 1:1 (argon flow rate 10 ml / min, methane flow rate 10 ml / min). First, the reactant gas 4 is introduced to replace the air in the reaction system. After the reactant gas 4 is uniformly mixed, the plasma power supply is turned on to begin discharge.

[0047] The discharge parameters were: specific input energy of 46.2 kJ / L, frequency of 14.1 kHz, and discharge duration of 2 hours. The reaction products were analyzed online by gas chromatography-mass spectrometry (GC-MS). The results showed: methane conversion of 14.4%, ethane selectivity of 45.0%, ethylene selectivity of 4.3%, and other products including acetylene, propane, propylene, and butane. Figure 2 ).

[0048] Example 1

[0049] Comparative Example 1 was repeated, with 2.8 g of cerium dioxide-supported copper catalyst (denoted as CuO / CeO2) packed into the discharge zone of a dielectric barrier discharge plasma reactor. The molar ratio of argon to methane was 1:1 (argon flow rate 10 ml / min, methane flow rate 10 ml / min). The catalyst consisted of 20-40 mesh particles, with 10% of the active component being Cu-based. The catalyst was calcined at 540℃ for 3 h before the reaction. The discharge parameters were set as follows: specific input energy 46.2 kJ / L, frequency 14.1 kHz. After 2 h of discharge, product analysis showed a methane conversion rate of 6.2%, an ethane selectivity of 25.6%, and an ethylene selectivity of 36.1%. Figure 2 ).

[0050] Comparative Example 2

[0051] Repeat Example 1, loading 2.8 g of cerium dioxide-supported iron catalyst (Fe₂O₃ / CeO₂) into the discharge zone of a dielectric barrier discharge plasma reactor. The molar ratio of argon to methane was 1:1 (argon flow rate was 10 ml / min, and methane flow rate was 10 ml / min). The catalyst consisted of 20-40 mesh particles, with 10% of the active component being Cu-based. The catalyst was calcined at 540 °C for 3 h before the reaction. The discharge parameters were set as follows: specific input energy of 46.2 kJ / L and frequency of 14.1 kHz. After 2 h of discharge, product analysis showed a methane conversion rate of 4.7%, an ethane selectivity of 24.2%, and an ethylene selectivity of 12.2%.

[0052] Comparative Example 3

[0053] Repeat Example 1, loading 2.8 g of a cobalt catalyst supported on cerium dioxide (represented as Co2O3 / CeO2) into the discharge zone of a dielectric barrier discharge plasma reactor. The molar ratio of argon to methane was 1:1 (argon flow rate was 10 ml / min, and methane flow rate was 10 ml / min). The catalyst consisted of 20-40 mesh particles, with 10% of the active component being Cu-based. The catalyst was calcined at 540 °C for 3 h before the reaction. The discharge parameters were set as follows: specific input energy of 46.2 kJ / L and frequency of 14.1 kHz. After 2 h of discharge, product analysis showed a methane conversion rate of 5.6%, an ethane selectivity of 23.8%, and an ethylene selectivity of 11.8%.

[0054] Comparative Example 4

[0055] Repeating Example 1, 2.8 g of a cerium dioxide-supported nickel catalyst (denoted as NiO / CeO2) was packed into the discharge zone of a dielectric barrier discharge plasma reactor. The molar ratio of argon to methane was 1:1 (argon flow rate was 10 ml / min, and methane flow rate was 10 ml / min). The catalyst consisted of 20-40 mesh particles, with a Cu-based active component loading of 10%. The catalyst was calcined at 540 °C for 3 h before the reaction. The discharge parameters were set as follows: specific input energy of 46.2 kJ / L and frequency of 14.1 kHz. After 2 h of discharge, product analysis showed a methane conversion rate of 5.8%, an ethane selectivity of 24.1%, and an ethylene selectivity of 19.5%.

[0056] Comparative Example 5

[0057] Repeating Example 1, 2.8 g of cerium dioxide-supported zinc catalyst (denoted as ZnO / CeO2) was packed into the discharge zone of a dielectric barrier discharge plasma reactor. The molar ratio of argon to methane was 1:1 (argon flow rate was 10 ml / min, and methane flow rate was 10 ml / min). The catalyst consisted of 20-40 mesh particles, with 10% of the active component being Cu-based. The catalyst was calcined at 540 °C for 3 h before the reaction. The discharge parameters were set as follows: specific input energy of 46.2 kJ / L and frequency of 14.1 kHz. After 2 h of discharge, product analysis showed a methane conversion rate of 4.6%, an ethane selectivity of 16.7%, and an ethylene selectivity of 18.0%.

[0058] Table 1. Evaluation results of catalytic performance of cerium dioxide-supported metal catalysts.

[0059] Comparative Example 1 - 14.4 4.3 Comparative Example 2 <![CDATA[Fe2O3 / CeO2]]> 4.7 12.2 Comparative Example 3 <![CDATA[Co2O3 / CeO2]]> 5.6 11.8 Comparative Example 4 <![CDATA[NiO / CeO2]]> 5.8 19.5 Comparative Example 5 <![CDATA[ZnO / CeO2]]> 4.6 18.0 Example 1 <![CDATA[CuO / CeO2]]> 6.2 36.1

[0060] When CuO is the preferred active component, the selectivity for ethylene is the highest.

[0061] Comparative Example 6

[0062] Comparative Example 1 was repeated, with 2.8 g of a copper catalyst supported on silica (denoted as CuO / SiO2) packed into the discharge zone of a dielectric barrier discharge plasma reactor. The molar ratio of argon to methane was 1:1 (argon flow rate was 10 ml / min, and methane flow rate was 10 ml / min). The catalyst consisted of 20-40 mesh particles, with 10% of the active component being Cu-based. The catalyst was calcined at 540 °C for 3 h before the reaction. The discharge parameters were set as follows: specific input energy of 46.2 kJ / L and frequency of 14.1 kHz. After 2 h of discharge, product analysis showed a methane conversion rate of 16.9%, an ethane selectivity of 45.7%, and an ethylene selectivity of 4.7%.

[0063] Comparative Example 7

[0064] Comparative Example 1 was repeated, with 2.8 g of copper catalyst supported on alumina (denoted as CuO / Al2O3) packed into the discharge zone of a dielectric barrier discharge plasma reactor. The molar ratio of argon to methane was 1:1 (argon flow rate was 10 ml / min, and methane flow rate was 10 ml / min). The catalyst consisted of 20-40 mesh particles, with 10% of the active component being Cu-based. The catalyst was calcined at 540 °C for 3 h before the reaction. The discharge parameters were set as follows: specific input energy of 46.2 kJ / L and frequency of 14.1 kHz. After 2 h of discharge, product analysis showed a methane conversion rate of 15.8%, an ethane selectivity of 42.7%, and an ethylene selectivity of 5.7%.

[0065] Comparative Example 8

[0066] Comparative Example 1 was repeated, with 2.8 g of a copper catalyst supported on zirconium oxide (denoted as CuO / ZrO2) packed into the discharge zone of a dielectric barrier discharge plasma reactor. The molar ratio of argon to methane was 1:1 (argon flow rate was 10 ml / min, and methane flow rate was 10 ml / min). The catalyst consisted of 20-40 mesh particles, with 10% of the active component being Cu-based. The catalyst was calcined at 540 °C for 3 h before the reaction. The discharge parameters were set as follows: specific input energy of 46.2 kJ / L and frequency of 14.1 kHz. After 2 h of discharge, product analysis showed a methane conversion of 15.5%, an ethane selectivity of 41.4%, and an ethylene selectivity of 5.3%.

[0067] Table 2. Evaluation results of catalytic performance of copper-based catalysts supported on different carriers.

[0068] Comparative Example 6 <![CDATA[CuO / SiO2]]> 16.9 4.7 Comparative Example 7 <![CDATA[CuO / Al2O3]]> 15.8 5.7 Comparative Example 8 <![CDATA[CuO / ZrO2]]> 15.5 5.3 Example 1 <![CDATA[CuO / CeO2]]> 6.2 36.1

[0069] The highest selectivity for ethylene is achieved when CeO2 is the preferred support.

[0070] Example 2

[0071] Repeating Example 1, 2.8 g of a copper catalyst supported on cerium dioxide (represented as CuO / CeO2) was packed into the discharge zone of a dielectric barrier discharge plasma reactor. The molar ratio of argon to methane was 1:1 (argon flow rate was 10 ml / min, and methane flow rate was 10 ml / min). The catalyst consisted of 20-40 mesh particles, with a Cu-based active component loading of 1%. The catalyst was calcined at 540 °C for 3 h before the reaction. The discharge parameters were set as follows: specific input energy of 46.2 kJ / L and frequency of 14.1 kHz. After 2 h of discharge, product analysis showed a methane conversion rate of 3.9%, an ethane selectivity of 19.5%, and an ethylene selectivity of 10.6%.

[0072] Example 3

[0073] Repeating Example 1, 2.8 g of a copper catalyst supported on cerium dioxide (represented as CuO / CeO2) was packed into the discharge zone of a dielectric barrier discharge plasma reactor. The molar ratio of argon to methane was 1:1 (argon flow rate was 10 ml / min, and methane flow rate was 10 ml / min). The catalyst consisted of 20-40 mesh particles, with a Cu-based active component loading of 3%. The catalyst was calcined at 540 °C for 3 h before the reaction. The discharge parameters were set as follows: specific input energy of 46.2 kJ / L and frequency of 14.1 kHz. After 2 h of discharge, product analysis showed a methane conversion rate of 4.8%, an ethane selectivity of 31.3%, and an ethylene selectivity of 21.9%.

[0074] Example 4

[0075] Repeating Example 1, 2.8 g of a copper catalyst supported on cerium dioxide (represented as CuO / CeO2) was packed into the discharge zone of a dielectric barrier discharge plasma reactor. The molar ratio of argon to methane was 1:1 (argon flow rate was 10 ml / min, and methane flow rate was 10 ml / min). The catalyst consisted of 20-40 mesh particles, with a Cu-based active component loading of 5%. The catalyst was calcined at 540 °C for 3 h before the reaction. The discharge parameters were set as follows: specific input energy of 46.2 kJ / L and frequency of 14.1 kHz. After 2 h of discharge, product analysis showed a methane conversion rate of 5.2%, an ethane selectivity of 27.6%, and an ethylene selectivity of 31.2%.

[0076] Example 5

[0077] Repeating Example 1, 2.8 g of a copper catalyst supported on cerium dioxide (represented as CuO / CeO2) was packed into the discharge zone of a dielectric barrier discharge plasma reactor. The molar ratio of argon to methane was 1:1 (argon flow rate was 10 ml / min, and methane flow rate was 10 ml / min). The catalyst consisted of 20-40 mesh particles, with a Cu-based active component loading of 15%. The catalyst was calcined at 540 °C for 3 h before the reaction. The discharge parameters were set as follows: specific input energy of 46.2 kJ / L and frequency of 14.1 kHz. After 2 h of discharge, product analysis showed a methane conversion rate of 5.7%, an ethane selectivity of 20.9%, and an ethylene selectivity of 28.2%.

[0078] Example 6

[0079] Repeating Example 1, 2.8 g of a copper catalyst supported on cerium dioxide (represented as CuO / CeO2) was packed into the discharge zone of a dielectric barrier discharge plasma reactor. The molar ratio of argon to methane was 1:1 (argon flow rate was 10 ml / min, and methane flow rate was 10 ml / min). The catalyst consisted of 20-40 mesh particles, with 20% of the active component being Cu-based. The catalyst was calcined at 540 °C for 3 h before the reaction. The discharge parameters were set as follows: specific input energy of 46.2 kJ / L and frequency of 14.1 kHz. After 2 h of discharge, product analysis showed a methane conversion rate of 5.1%, an ethane selectivity of 19.4%, and an ethylene selectivity of 22.4%.

[0080] Table 3. Evaluation results of catalytic performance of CuO / CeO2 catalysts with different loadings

[0081]

[0082] The highest ethylene selectivity is achieved when the CuO loading is preferably 10%.

[0083] Example 7

[0084] Repeating Example 1, 2.8 g of a copper catalyst supported on cerium dioxide (represented as CuO / CeO2) was packed into the discharge zone of a dielectric barrier discharge plasma reactor. The molar ratio of argon to methane was 1:1 (argon flow rate was 10 ml / min, and methane flow rate was 10 ml / min). The catalyst consisted of 20-40 mesh particles, with 10% of the active component being Cu-based. The catalyst was calcined at 540 °C for 3 h before the reaction. The discharge parameters were set as follows: specific input energy of 37.5 kJ / L and frequency of 14.1 kHz. After 2 h of discharge, product analysis showed a methane conversion rate of 3.1%, an ethane selectivity of 17.3%, and an ethylene selectivity of 15.5%.

[0085] Example 8

[0086] Repeating Example 1, 2.8 g of a copper catalyst supported on cerium dioxide (represented as CuO / CeO2) was packed into the discharge zone of a dielectric barrier discharge plasma reactor. The molar ratio of argon to methane was 1:1 (argon flow rate was 10 ml / min, and methane flow rate was 10 ml / min). The catalyst consisted of 20-40 mesh particles, with 10% of the active component being Cu-based. The catalyst was calcined at 540 °C for 3 h before the reaction. The discharge parameters were set as follows: specific input energy of 40.5 kJ / L and frequency of 14.1 kHz. After 2 h of discharge, product analysis showed a methane conversion rate of 5.3%, an ethane selectivity of 19.1%, and an ethylene selectivity of 24.4%.

[0087] Example 9

[0088] Repeating Example 1, 2.8 g of a copper catalyst supported on cerium dioxide (represented as CuO / CeO2) was packed into the discharge zone of a dielectric barrier discharge plasma reactor. The molar ratio of argon to methane was 1:1 (argon flow rate was 10 ml / min, and methane flow rate was 10 ml / min). The catalyst consisted of 20-40 mesh particles, with 10% of the active component being Cu-based. The catalyst was calcined at 540 °C for 3 h before the reaction. The discharge parameters were set as follows: specific input energy of 52.8 kJ / L and frequency of 14.1 kHz. After 2 h of discharge, product analysis showed a methane conversion rate of 7.0%, an ethane selectivity of 26.2%, and an ethylene selectivity of 26.9%.

[0089] Example 10

[0090] Repeating Example 1, 2.8 g of a cerium dioxide-supported copper catalyst (denoted as CuO / CeO2) was packed into the discharge zone of a dielectric barrier discharge plasma reactor. The molar ratio of argon to methane was 1:1 (argon flow rate was 10 ml / min, and methane flow rate was 10 ml / min). The catalyst consisted of 20-40 mesh particles, with 10% of the active component being Cu-based. The catalyst was calcined at 540 °C for 3 h before the reaction. The discharge parameters were set as follows: specific input energy of 66.0 kJ / L and frequency of 14.1 kHz. After 2 h of discharge, product analysis showed a methane conversion rate of 8.9%, an ethane selectivity of 40.8%, and an ethylene selectivity of 13.4%.

[0091] Table 4. Evaluation results of the catalytic performance of CuO / CeO2 catalysts with different input energy ratios.

[0092]

[0093] The ethylene selectivity is highest when the preferred specific input energy is 46.2 kJ / L.

[0094] Example 11

[0095] Repeat Example 1, loading 2.8 g of cerium dioxide-supported copper catalyst (CuO / CeO2) into the discharge zone of a dielectric barrier discharge plasma reactor. The molar ratio of argon to methane was 1:1 (argon flow rate was 10 ml / min, and methane flow rate was 10 ml / min). The catalyst consisted of 20-40 mesh particles, with 10% of the active component being Cu-based. The catalyst was calcined at 540 °C for 3 h before the reaction. The discharge parameters were set as follows: specific input energy of 46.2 kJ / L and frequency of 13.1 kHz. After 2 h of discharge, product analysis showed a methane conversion rate of 4.2%, an ethane selectivity of 24.8%, and an ethylene selectivity of 25.2%.

[0096] Example 12

[0097] Repeat Example 1, loading 2.8 g of cerium dioxide-supported copper catalyst (represented as CuO / CeO2) into the discharge zone of a dielectric barrier discharge plasma reactor. The molar ratio of argon to methane was 1:1 (argon flow rate was 10 ml / min, and methane flow rate was 10 ml / min). The catalyst consisted of 20-40 mesh particles, with 10% of the active component being Cu-based. The catalyst was calcined at 540 °C for 3 h before the reaction. The discharge parameters were set as follows: specific input energy of 46.2 kJ / L and frequency of 13.7 kHz. After 2 h of discharge, product analysis showed a methane conversion rate of 5.1%, an ethane selectivity of 24.2%, and an ethylene selectivity of 26.2%.

[0098] Example 13

[0099] Repeating Example 1, 2.8 g of a copper catalyst supported on cerium dioxide (represented as CuO / CeO2) was packed into the discharge zone of a dielectric barrier discharge plasma reactor. The molar ratio of argon to methane was 1:1 (argon flow rate was 10 ml / min, and methane flow rate was 10 ml / min). The catalyst consisted of 20-40 mesh particles, with 10% of the active component being Cu-based. The catalyst was calcined at 540 °C for 3 h before the reaction. The discharge parameters were set as follows: specific input energy of 46.2 kJ / L and frequency of 14.5 kHz. After 2 h of discharge, product analysis showed a methane conversion rate of 3.3%, an ethane selectivity of 15.6%, and an ethylene selectivity of 17.4%.

[0100] Example 14

[0101] Repeat Example 1, loading 2.8 g of a copper catalyst supported on cerium dioxide (represented as CuO / CeO2) into the discharge zone of a dielectric barrier discharge plasma reactor. The molar ratio of argon to methane was 1:1 (argon flow rate was 10 ml / min, and methane flow rate was 10 ml / min). The catalyst consisted of 20-40 mesh particles, with 10% of the active component being Cu-based. The catalyst was calcined at 540 °C for 3 h before the reaction. The discharge parameters were set as follows: specific input energy of 46.2 kJ / L and frequency of 15.0 kHz. After 2 h of discharge, product analysis showed a methane conversion rate of 2.5%, an ethane selectivity of 10.9%, and an ethylene selectivity of 14.4%.

[0102] Table 5. Evaluation results of catalytic performance of CuO / CeO2 catalyst at different frequencies

[0103]

[0104] The selectivity of ethylene is highest at a preferred frequency of 14.1 kHz.

[0105] Example 15

[0106] Comparative Example 1 was repeated, with 2.8 g of cerium dioxide-supported copper catalyst (denoted as CuO / CeO2) packed into the discharge zone of a dielectric barrier discharge plasma reactor. The molar ratio of argon to methane was 1:1 (argon flow rate was 5 ml / min, and methane flow rate was 5 ml / min). The catalyst consisted of 20-40 mesh particles, with 10% of the active component being Cu-based. The catalyst was calcined at 540℃ for 3 h before the reaction. The discharge parameters were set as follows: specific input energy of 92.4 kJ / L and frequency of 14.1 kHz. After 2 h of discharge, product analysis showed a methane conversion rate of 7.4%, an ethane selectivity of 21.8%, and an ethylene selectivity of 25.5%.

[0107] Example 16

[0108] Comparative Example 1 was repeated, with 2.8 g of cerium dioxide-supported copper catalyst (denoted as CuO / CeO2) packed into the discharge zone of a dielectric barrier discharge plasma reactor. The molar ratio of argon to methane was 1:1 (argon flow rate was 7.5 ml / min, and methane flow rate was 7.5 ml / min). The catalyst consisted of 20-40 mesh particles, with 10% of the active component being Cu-based. The catalyst was calcined at 540 °C for 3 h before the reaction. The discharge parameters were set as follows: specific input energy of 61.6 kJ / L and frequency of 14.1 kHz. After 2 h of discharge, product analysis showed a methane conversion rate of 6.8%, an ethane selectivity of 23.3%, and an ethylene selectivity of 28.9%.

[0109] Example 17

[0110] Comparative Example 1 was repeated, with 2.8 g of cerium dioxide-supported copper catalyst (denoted as CuO / CeO2) packed into the discharge zone of a dielectric barrier discharge plasma reactor. The molar ratio of argon to methane was 1:1 (argon flow rate was 12.5 ml / min, and methane flow rate was 12.5 ml / min). The catalyst consisted of 20-40 mesh particles, with 10% of the active component being Cu-based. The catalyst was calcined at 540 °C for 3 h before the reaction. The discharge parameters were set as follows: specific input energy of 37.0 kJ / L and frequency of 14.1 kHz. After 2 h of discharge, product analysis showed a methane conversion rate of 5.9%, an ethane selectivity of 24.3%, and an ethylene selectivity of 30.3%.

[0111] Example 18

[0112] Comparative Example 1 was repeated, with 2.8 g of cerium dioxide-supported copper catalyst (denoted as CuO / CeO2) packed into the discharge zone of a dielectric barrier discharge plasma reactor. The molar ratio of argon to methane was 1:1 (argon flow rate was 15 ml / min, and methane flow rate was 15 ml / min). The catalyst consisted of 20-40 mesh particles, with 10% of the active component being Cu-based. The catalyst was calcined at 540 °C for 3 h before the reaction. The discharge parameters were set as follows: specific input energy of 30.8 kJ / L and frequency of 14.1 kHz. After 2 h of discharge, product analysis showed a methane conversion rate of 5.5%, an ethane selectivity of 17.7%, and an ethylene selectivity of 26.2%.

[0113] Example 19

[0114] Comparative Example 1 was repeated, with 2.8 g of cerium dioxide-supported copper catalyst (denoted as CuO / CeO2) packed into the discharge zone of a dielectric barrier discharge plasma reactor. The molar ratio of argon to methane was 1:1 (argon flow rate was 20 ml / min, and methane flow rate was 20 ml / min). The catalyst consisted of 20-40 mesh particles, with 10% of the active component being Cu-based. The catalyst was calcined at 540 °C for 3 h before the reaction. The discharge parameters were set as follows: specific input energy of 23.1 kJ / L and frequency of 14.1 kHz. After 2 h of discharge, product analysis showed a methane conversion rate of 5.1%, an ethane selectivity of 11.4%, and an ethylene selectivity of 15.7%.

[0115] Table 6. Evaluation results of the catalytic performance of CuO / CeO2 catalysts at different gas velocities.

[0116]

[0117] The selectivity of ethylene is highest when the total gas velocity of the feed gas is 20 ml / min.

[0118] Example 20

[0119] Repeating Example 1, 2.8 g of a copper catalyst supported on cerium dioxide (represented as CuO / CeO2) was packed into the discharge zone of a dielectric barrier discharge plasma reactor. The molar ratio of argon to methane was 9:1 (argon flow rate was 18 ml / min, and methane flow rate was 2 ml / min). The catalyst consisted of 20-40 mesh particles, with 10% of the active component being Cu-based. The catalyst was calcined at 540 °C for 3 h before the reaction. The discharge parameters were set as follows: specific input energy of 46.2 kJ / L and frequency of 14.1 kHz. After 2 h of discharge, product analysis showed a methane conversion rate of 28.4%, an ethane selectivity of 9.2%, and an ethylene selectivity of 8.1%.

[0120] Example 21

[0121] Repeating Example 1, 2.8 g of a copper catalyst supported on cerium dioxide (represented as CuO / CeO2) was packed into the discharge zone of a dielectric barrier discharge plasma reactor. The molar ratio of argon to methane was 3:1 (argon flow rate was 15 ml / min, and methane flow rate was 5 ml / min). The catalyst consisted of 20-40 mesh particles, with 10% of the active component being Cu-based. The catalyst was calcined at 540 °C for 3 h before the reaction. The discharge parameters were set as follows: specific input energy of 46.2 kJ / L and frequency of 14.1 kHz. After 2 h of discharge, product analysis showed a methane conversion rate of 11.8%, an ethane selectivity of 17.4%, and an ethylene selectivity of 18.3%.

[0122] Example 22

[0123] Repeating Example 1, 2.8 g of a copper catalyst supported on cerium dioxide (represented as CuO / CeO2) was packed into the discharge zone of a dielectric barrier discharge plasma reactor. The molar ratio of argon to methane was 1:3 (argon flow rate was 5 ml / min, and methane flow rate was 15 ml / min). The catalyst consisted of 20-40 mesh particles, with 10% of the active component being Cu-based. The catalyst was calcined at 540 °C for 3 h before the reaction. The discharge parameters were set as follows: specific input energy of 46.2 kJ / L and frequency of 14.1 kHz. After 2 h of discharge, product analysis showed a methane conversion rate of 3.3%, an ethane selectivity of 16.9%, and an ethylene selectivity of 26.1%.

[0124] Example 23

[0125] Repeat Example 1, loading 2.8 g of a copper catalyst supported on cerium dioxide (represented as CuO / CeO2) into the discharge zone of a dielectric barrier discharge plasma reactor. The molar ratio of argon to methane was 0:1 (argon flow rate was 0 ml / min, and methane flow rate was 20 ml / min). The catalyst consisted of 20-40 mesh particles, with 10% of the active component being Cu-based. The catalyst was calcined at 540 °C for 3 h before the reaction. The discharge parameters were set as follows: specific input energy of 46.2 kJ / L and frequency of 14.1 kHz. After 2 h of discharge, product analysis showed a methane conversion rate of 5.1%, an ethane selectivity of 12.4%, and an ethylene selectivity of 16.2%.

[0126] Table 7. Evaluation results of catalytic performance of CuO / CeO2 catalysts under different atmospheres.

[0127]

[0128]

[0129] The selectivity of ethylene is highest when the molar ratio of methane to argon is preferably 1:1.

Claims

1. A method for the oxygen-free coupling of methane to produce ethylene, characterized in that, The process includes the following steps: methane and argon are introduced into a dielectric barrier discharge reactor, where the methane is activated and cracked through dielectric barrier discharge, and then directly converted into ethylene under the action of a catalyst; The volume ratio of methane to argon is 1:(0-10), the residence time of the mixed gas in the reaction zone is 0.01-100s, the dielectric barrier discharge uses a high-voltage AC plasma power supply with a specific input energy of 3-300kJ / L, a discharge frequency of 1kHz-20kHz, a pressure of -0.06MPa-0.5MPa, and a reaction temperature of 100-300℃. The catalyst is a metal oxide supported catalyst, comprising an active component and a support. The active component is an oxide with variable valence characteristics, and the support is a metal oxide or non-metal oxide with Lewis acid-base pairs and capable of forming oxygen vacancies. The active component accounts for 1-20% of the mass percentage of the catalyst. The active component is Cu; the support is CeO2.

2. The method for producing ethylene from methane via oxygen-free coupling according to claim 1, characterized in that, The molar ratio of methane to argon is 1:

1.

3. A method for producing ethylene from methane via oxygen-free coupling according to claim 1 or 2, characterized in that, The residence time of the methane and argon mixture in the discharge zone is 4.5 s; the specific input energy of the plasma power supply is 46.2 kJ / L, and the discharge frequency is 14.1 kHz.

4. A method for producing ethylene from methane via oxygen-free coupling according to claim 1 or 2, characterized in that, The dielectric barrier discharge reactor is a wire-cylinder reactor, which is cylindrical in shape and has metal wire wound around its exterior as a grounding electrode. The upper end of the cylinder is equipped with an upper end cap with a central hole, through which a metal rod is installed along the reactor axis as a high-voltage electrode. The distance between the outer wall of the metal rod and the inner wall of the cylindrical reactor is 0.1-30 mm. The cylindrical reactor is made of dielectric insulating material. The upper end of the reactor is equipped with a gas inlet, the lower end of the reactor is the tail gas outlet, and the middle is the discharge zone. The catalyst is placed in the discharge zone inside the reactor, and the catalyst bed is supported by a quartz sand plate.

5. The method for producing ethylene from methane via oxygen-free coupling according to claim 4, characterized in that, The high-voltage electrode and the grounding electrode are made of copper, iron, tungsten, aluminum or stainless steel.

6. The method for producing ethylene from methane via oxygen-free coupling according to claim 4, characterized in that, The reactor is made of quartz glass, hard glass, alumina ceramic, polytetrafluoroethylene, or non-metallic composite materials.

7. A method for producing ethylene from methane via oxygen-free coupling according to claim 1 or 2, characterized in that, The active component accounts for 5-10% by weight in the catalyst.

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