A system and method for pressurized low-temperature plasma coupled catalytic CO2 gas

Abstract

The present invention relates to electrohydrodynamics and plasma chemical synthesis technology, and aims to provide a system and method for pressurized low-temperature plasma coupled catalytic CO2 gas. The system includes a pressurized gas supply system, a DBD reactor and an AC power supply; the main body of the reactor is a composite tubular structure, with an external stainless steel round tube as the outer electrode and an axially arranged metal cylinder as the inner electrode; an annular tubular barrier dielectric layer is provided on the inner side of the outer electrode, and its material is a quartz fiber reinforced silica ceramic-based polymer; a spacing is reserved between the outer side of the inner electrode and the barrier dielectric layer to form an annular tubular cavity as a discharge zone; a powdered Cu / Zn / Al catalyst with a particle size of 40 to 60 mesh is uniformly filled in the discharge zone. The system of the present invention can be used to carry out plasma catalytic conversion reactions under medium and high pressure environments; by designing the reactor structure, selecting the material of the barrier dielectric layer and adjusting the parameters of the input power supply, a stable and high-intensity dielectric barrier discharge can be achieved to convert CO 2 Provide conditions for gas catalytic reaction.

Description

Technical Field

[0001] The invention belongs to the technical field of electrohydrodynamics and plasma chemical synthesis, and relates to a method and a device for low-temperature plasma coupled catalytic conversion of CO2 under high pressure conditions. Background Art

[0002] In the field of thermodynamics, there are many gases that are difficult to react, such as carbon dioxide and methane, which usually have the following characteristics: (1) Inertness: These gases are usually chemically stable and do not react easily with other substances; (2) Low reactivity: The reaction rate of difficult-to-react gases is slow under normal conditions; (3) High activation energy: The reaction of these gases requires overcoming a high energy barrier to react effectively. Take CO2 as an example. CO2 is a very stable linear molecule, which makes it very difficult to make it reactive. Due to its high stability, a large amount of energy input, optimized reaction conditions, and catalysts with high stability and activity are required to convert CO2 into value-added chemicals. In traditional industry, the conversion of CO2 into value-added chemicals requires high temperature conditions to convert it into synthesis gas, and then high-pressure Fischer-Tropsch synthesis to achieve the final synthesis. This process is harsh, costly, and inefficient. Low-temperature plasma (NTP) technology provides an alternative to traditional thermal catalysis, which can solve the challenge of CO2 activation under low temperature and normal pressure conditions. The large amount of high-energy electrons generated by NTP can replace the "catalyst" to activate the reactants and transform them into a series of chemically reactive substances (free radicals and excited atoms, ions and molecules), thereby initiating and propagating chemical reactions.

[0003] In the field of synthetic chemistry, NTP technology is generally used under normal pressure conditions. This is because in medium and high pressure environments, the discharge has a fluctuating characteristic and is difficult to maintain stably, thus affecting the synthesis effect. Secondly, the increase in pressure also places higher demands on the material of the reactor. For example, in terms of CO2 catalytic conversion, NTP technology under low pressure environments performs poorly, and the product selectivity is poor, and it will be converted to high-carbon hydrocarbon products. This is also one of the drawbacks of the current normal pressure NTP technology, which cannot accurately control the selectivity of the product. Therefore, the research on low-temperature plasma technology and equipment under medium and high pressure environments has become a key difficulty in this field.

[0004] At present, there is little research on the performance of NTP technology in different pressure environments. According to existing public reports, the current research on plasma in medium and high pressure environments mainly remains at the basic research level of analyzing discharge characteristics, and has not yet solved problems such as discharge instability caused by pressurized environments. In particular, there is no report on the research on the conversion of CO2 in medium and high pressure environments. Summary of the invention

[0005] The technical problem to be solved by the present invention is to overcome the deficiencies in the prior art and provide a system and method for pressurized low-temperature plasma coupled catalytic CO2 gas.

[0006] To solve the technical problem, the solution of the present invention is:

[0007] A system for pressurized low-temperature plasma coupled catalytic CO2 gas is provided, comprising a pressurized gas supply system, a DBD reactor and an AC power supply; wherein:

[0008] The main body of the DBD reactor is a composite tubular structure, with an external stainless steel round tube as the outer electrode and an axially arranged metal cylinder as the inner electrode; both the outer electrode and the inner electrode are provided with insulating protective sleeves for safety protection, the former is grounded and the latter is connected to an AC power supply through a cable; a ring-shaped blocking medium layer is provided on the inner side of the outer electrode, and its material is quartz fiber reinforced silica ceramic-based polymer; a gap is reserved between the outer side of the inner electrode and the blocking medium layer to form a ring-shaped cavity as a discharge zone; a powdered Cu / Zn / Al catalyst with a particle size of 40 to 60 mesh is uniformly filled in the discharge zone, and the two axial ends of the discharge zone are sealed with quartz wool; the two ends of the reactor are respectively installed in end face seats of insulating material, and an inlet manifold and an outlet manifold connected to the discharge zone are respectively provided on the two end face seats; a thermocouple for monitoring the reaction temperature is provided in the discharge zone; the outlet manifold is connected to a cold trap for collecting reaction products through a discharge pipeline;

[0009] The pressurized gas supply system includes a CO2 gas cylinder and a hydrogen gas cylinder for providing reaction gas, and an inert gas cylinder for increasing the gas supply pressure; an intake pressure regulator and a mass flow meter are provided on the outlet pipeline of each cylinder, which are connected to the intake pipeline and then connected to the intake manifold.

[0010] As a preferred solution of the present invention, the stainless steel round tube is a tubular structure with hollow parts made of stainless steel mesh.

[0011] As a preferred solution of the present invention, the AC power supply is connected to an oscilloscope via a wire.

[0012] As a preferred embodiment of the present invention, the inert gas cylinder includes an argon gas cylinder; the mass flow meter is connected to a flow meter controller via a wire; and a pressure gauge or a pressure sensor is provided on the air intake pipeline.

[0013] As a preferred embodiment of the present invention, the gas outlet manifold is connected to a flow meter, a gas outlet pressure regulator and a GC gas chromatograph in sequence through a gas outlet pipeline, and the discharge pipeline of the GC gas chromatograph is connected to a cold trap; the gas outlet pipeline is provided with a heating belt; the inert gas cylinder includes a helium cylinder for providing chromatograph carrier gas.

[0014] As a preferred solution of the present invention, the distance between the inner electrode and the blocking dielectric layer is 1 mm, the thickness of the blocking dielectric layer is 2 mm, and the length of the discharge region is 50 mm.

[0015] As a preferred embodiment of the present invention, the quartz fiber reinforced silica ceramic-based polymer is prepared by the following method:

[0016] (1) Pre-treating a 2.5D quartz fiber fabric by soaking it in an organic solvent for 24 hours; drying it at 150° C., laying it out and molding it into a cylindrical preform;

[0017] (2) impregnating the preform with a silica sol having a solid content of 20 to 25 wt%, evacuating the preform and maintaining the pressure for 48 h; after the impregnation, drying the preform with air at 50 to 80° C. for 4 h; repeating this step 4 times to obtain a composite material blank;

[0018] (3) The composite material blank is calcined at 600° C. for 1 hour in an air atmosphere; after cooling, a quartz fiber reinforced silica ceramic-based polymer ring tube serving as a barrier medium layer is obtained.

[0019] As a preferred embodiment of the present invention, the Cu / Zn / Al catalyst is prepared by the following method:

[0020] (1) taking Al2O3 solid used as a carrier, calcining it to remove impurities, and then grinding it into powder; dissolving copper salt and zinc salt in deionized water to prepare a metal precursor solution;

[0021] (2) adding Al2O3 powder to the precursor solution, stirring and mixing thoroughly, and leaving the mixture at room temperature overnight to obtain a mixed solution containing a precipitate;

[0022] (3) Drying the mixed solution to obtain an unreduced solid catalyst; after grinding and pulverizing, transferring it to a tubular furnace and reducing it under the condition of continuous introduction of hydrogen to obtain a Cu / Zn / Al catalyst; the molar ratio of Cu:Zn:Al contained in the catalyst is in the range of 4.5:4.5:1.

[0023] The present invention further provides a method for realizing plasma-coupled catalytic CO2 gas under pressurized low temperature conditions using the aforementioned system, comprising the following steps:

[0024] (1) Open the valves of each cylinder, control the gas flow rate of each channel through the flow meter controller, and adjust the mixed gas flow rate and pressure entering the reactor; wherein CO2 is used as the reaction gas, helium is used as the carrier gas of the GC gas chromatograph, and argon is used as the protective gas to increase the gas supply pressure;

[0025] (2) Turn on the AC power supply, power the DBD reactor, and carry out a plasma-coupled catalytic hydrogenation reaction of CO2 gas in the discharge zone to generate CH3OH; during the reaction, control the temperature of the discharge zone in the reactor to be 180-220°C and the pressure to be 0.1-5 MPa;

[0026] (3) Using the oscilloscope to observe the data, the actual input power of the reaction is calculated as a reference for adjusting the power supply voltage; using the GC gas chromatograph to analyze the composition of the reaction products, and using the cold trap to condense and collect the liquid products.

[0027] As a preferred embodiment of the present invention, the total air flow rate range that the pressurized air supply system can provide is: 0.1~200mL / min, the adjustment range of air intake pressure is: 0.1~10MPa; the voltage adjustment range of AC power supply is: 25V~75V.

[0028] Description of the invention principle:

[0029] In order to solve the problems such as poor discharge performance of plasma technology in medium and high voltage environments, the present invention improves the discharge stability and discharge intensity and accurately controls the selectivity of the corresponding products of CO2 conversion by organically combining the use of a pressurized gas supply system, changing the reactor medium material, and designing a new dielectric barrier discharge (DBD)-single medium structure.

[0030] The present invention constructs a high-pressure environment in the reactor by increasing the pressure of the pressurized system. The increase in gas pressure increases the concentration of reaction gas molecules, reduces the mean free path of electrons, and increases the probability of gas molecules and high-energy electrons colliding and recombining with each other. Under the action of the high-frequency alternating electric field between the electrodes, the gas molecules in the discharge area are excited and dissociated after colliding with the high-energy electrons, generating various active groups and quickly forming filamentary discharges.

[0031] At the same time, the average energy of electrons is proportional to the reduced field strength (defined as the ratio of electric field strength to gas particle number density); the increase in gas pressure inside the reactor leads to an increase in its molecular number density, which reduces the reduced field strength and leads to a decrease in the average energy of electrons. The present invention can improve the reduced field strength for energy compensation by adjusting the parameters of the internal discharge zone spacing and input power supply inside the reactor. In addition, during the discharge, the specially designed barrier dielectric layer can keep the relative dielectric constant unchanged within a certain pressure range, thereby maintaining a stable high-intensity dielectric barrier discharge.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] 1. The pressurized low-temperature plasma coupled catalytic conversion system provided by the present invention can be used to carry out plasma catalytic conversion reactions under normal pressure, especially under medium and high pressure environments. Through the design of the reactor structure, the selection of the material of the barrier medium layer and the adjustment of the parameters of the input power supply, a stable high-intensity dielectric barrier discharge is achieved, providing conditions for the catalytic reaction of CO2 gas.

[0034] 2. The present invention simulates the influence of different pressures and voltages on the discharge performance of the system through numerical calculation, and verifies that the system has a significant promoting effect on the plasma catalytic conversion reaction.

[0035] 3. The present invention provides a new technical idea for the application of NTP technology in the conversion of difficult-to-react gases in medium and high pressure environments in actual production. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 It is a schematic diagram of the overall device used for low-temperature plasma coupled catalytic conversion.

[0037] Figure 2 It is a schematic diagram of the structure of a coaxial cylindrical single dielectric barrier discharge reactor used for low-temperature plasma coupled catalytic conversion.

[0038] Figure 3 It is a schematic diagram of the radial cross section of the DBD reactor.

[0039] Figure 4 It is a schematic diagram of the overall mesh corresponding to the one-dimensional symmetric model of the DBD reactor.

[0040] Figure 5-7 This is the COMSOL simulation cloud diagram of the electric potential under the pressure range of 0.1-5MPa.

[0041] Figure 8-10 This is the COMSOL simulation cloud diagram of electron density under the pressure range of 0.1-5MPa.

[0042] Figure 11-13 This is the COMSOL simulation cloud diagram of the electric potential under the voltage range of 25-75V.

[0043] Figure 14-16 This is the COMSOL simulation cloud diagram of electron density under the voltage range of 25-75V.

[0044] The reference numerals in the figure are: 1 gas cylinder; 2 inlet pressure regulator; 3 mass flow meter; 4 flow meter controller; 5 pressure gauge; 6 reactor; 7 AC power supply; 8 oscilloscope; 9 outlet pipeline (with heating belt); 10 flow meter; 11 outlet pressure regulator; 12 GC gas chromatograph; 13 cold trap; 21 inlet manifold; 22 outlet manifold; end face seat 23; end face seat 24; inner electrode insulating protection sleeve 25; outer electrode insulating protection sleeve 26; outer electrode 61; blocking dielectric layer 62; discharge area 63; inner electrode 64. DETAILED DESCRIPTION

[0045] The present invention is further described below in conjunction with specific embodiments and drawings. The present invention includes but is not limited to the following embodiments.

[0046] In the present invention, DBD refers to dielectric barrier discharge; therefore, the present invention abbreviates the dielectric barrier discharge low-temperature plasma reactor as a DBD reactor. In addition, low-temperature plasma is a specific term well known in the industry and is an inseparable concept. The low temperature here does not refer to the low temperature of the reaction environment, but to the low temperature state of the entire system. Explanation of ambient temperature: the actual environment does not require external heating, and the temperature generated by the discharge itself is measured to be 180-220°C, so the temperature of the discharge area inside the reactor is 180-220°C.

[0047] like Figure 1-3 As shown, the system of pressurized low-temperature plasma coupled catalytic CO2 gas of the present invention comprises a pressurized gas supply system, a DBD reactor and an AC power supply.

[0048] The main body of the DBD reactor is a composite tubular structure, with an external stainless steel tube as the outer electrode and an axially arranged metal cylinder as the inner electrode. Both the outer electrode and the inner electrode are provided with insulating protective sleeves (such as quartz glass) for safety protection, the former is grounded, and the latter is connected to the AC power supply through a cable, and the AC power supply is connected to the oscilloscope through a wire.

[0049] An annular tube-shaped barrier dielectric layer is provided on the inner side of the outer electrode, and its material is quartz fiber reinforced silica ceramic-based polymer; a gap is reserved between the outer side of the inner electrode and the barrier dielectric layer to form an annular tube-shaped cavity as a discharge zone; the discharge zone is uniformly filled with powdered Cu / Zn / Al catalyst with a particle size of 40 to 60 meshes, and the two axial ends of the discharge zone are blocked with quartz wool; when the particle size of the catalyst meets the condition of 40 to 60 meshes, it can ensure that the pressurized gas supply can flow smoothly in the catalyst filling gap of the reactor. The two ends of the reactor are respectively installed in the end face seats of insulating material, and the two end face seats are respectively provided with an inlet manifold and an outlet manifold connected to the discharge zone. The outlet manifold is connected to the flow meter, the outlet pressure regulator and the GC gas chromatograph in sequence through the outlet pipeline, and the discharge pipeline of the GC gas chromatograph is connected to the cold trap; the outlet pipeline is accompanied by a heating belt.

[0050] The pressurized gas supply system includes a CO2 gas cylinder and a hydrogen gas cylinder for providing reaction gas, an argon gas cylinder for increasing the gas supply pressure, and a helium gas cylinder for providing chromatograph carrier gas. The outlet pipeline of each cylinder is provided with an intake pressure regulator and a mass flow meter, which are connected to the intake manifold after being connected to the intake pipeline; the mass flow meter is connected to the flow meter controller through a wire; and a pressure gauge or pressure sensor is provided on the intake pipeline.

[0051] As a preferred example, the outer electrode is made of stainless steel mesh to form a tubular structure with a hollow part. The advantages of this structural design are good uniform conductivity, dense texture, and tight connection between wires. Compared with the simple use of an integrated metal cylinder as the outer electrode, a large number of contact points are formed between the wires in the stainless steel mesh, which ensures that the current is evenly transmitted throughout the stainless steel mesh to maintain high-intensity dielectric barrier discharge. Compared with other structures, this structure is conducive to the diffusion of discharge filaments under medium and high voltage environments, can effectively increase the effective discharge area, and produce more filamentary discharge channels. The stainless steel material can be 304 stainless steel. The material of the inner electrode can be tungsten steel, and the material of the end seat can be polytetrafluoroethylene. The distance between the inner electrode and the barrier dielectric layer is 1mm, the thickness of the barrier dielectric layer is 2mm, and the length of the discharge zone is 50mm. The total air intake flow range that the pressurized gas supply system can provide is: 0.1~200mL / min, the adjustable range of the air intake pressure is: 0.1~10MPa; the voltage adjustable range of the AC power supply is: 25V~75V.

[0052] The quartz fiber reinforced silica ceramic-based polymer is prepared by the following method:

[0053] (1) Pre-treating a 2.5D quartz fiber fabric by soaking it in an organic solvent for 24 hours; drying it at 150° C., laying it out and molding it into a cylindrical preform;

[0054] (2) impregnating the preform with a silica sol having a solid content of 20 to 25 wt%, evacuating the preform and maintaining the pressure for 48 h; after the impregnation, drying the preform with air at 50 to 80° C. for 4 h; repeating this step 4 times to obtain a composite material blank;

[0055] (3) The composite material blank is calcined at 600° C. for 1 hour in an air atmosphere; after cooling, a quartz fiber reinforced silica ceramic-based polymer ring tube serving as a barrier medium layer is obtained.

[0056] The Cu / Zn / Al catalyst is prepared by the following method:

[0057] (1) taking Al2O3 solid used as a carrier, calcining it to remove impurities (such as adsorbed water), and then grinding it into powder; dissolving copper salt and zinc salt in deionized water to prepare a metal precursor solution;

[0058] (2) adding Al2O3 powder to the precursor solution, stirring and mixing thoroughly, and leaving the mixture at room temperature overnight to obtain a mixed solution containing a precipitate;

[0059] (3) Drying the mixed solution to obtain an unreduced solid catalyst; after grinding and pulverizing, transferring to a tube furnace, and reducing the mixture under the condition of continuous introduction of hydrogen to obtain a Cu / Zn / Al catalyst; the molar ratio of Cu:Zn:Al in the catalyst is in the range of 4.5:4.5:1. The final form of the catalyst is a powder with a particle size of 40 to 60 mesh.

[0060] The method of using this system to realize plasma-coupled catalytic CO2 gas under pressurized low-temperature conditions is to send the raw gas into the discharge area of ​​the reactor through the pressurized gas supply system, ionize it in the dielectric barrier discharge mode, react with the catalyst in the plasma reaction area, and synthesize the product gas CH3OH in one step. The specific operation process includes the following steps:

[0061] (1) Open the valves of each cylinder and control the gas flow rate of each channel through the flow meter controller to adjust the mixed gas flow rate and pressure entering the reactor; wherein CO2 is used as the reaction gas, helium is used as the carrier gas of the GC gas chromatograph, and argon is used as the protective gas to increase the gas supply pressure;

[0062] (2) Turn on the AC power supply, power the DBD reactor, and carry out a plasma-coupled catalytic hydrogenation reaction of CO2 gas in the discharge zone to generate CH3OH; during the reaction, control the temperature of the discharge zone in the reactor to be 180-220°C and the pressure to be 0.1-5 MPa;

[0063] (3) Using the oscilloscope to observe the data, the actual input power of the reaction is calculated as a reference for adjusting the power supply voltage; using the GC gas chromatograph to analyze the composition of the reaction products, and using the cold trap to condense and collect the liquid products.

[0064] The following describes some more detailed technical solutions of the present invention:

[0065] 1. In the pressurized gas supply system, the outlet pipeline of each cylinder is equipped with a corresponding flow meter and an inlet pressure regulator to monitor and control the gas supply in real time. The inlet pressure regulator can be installed after the flow meter to adjust the valve opening of each cylinder accordingly by monitoring the pressure in the reactor to maintain the required pressure level. Before the gas is introduced from the DBD reactor into the GC gas chromatograph, an outlet pressure regulator (pressure reducing regulator) is required to reduce the pressure of the gas to a pressure level that the instrument can withstand. The inlet pressure regulator and the outlet pressure regulator can control the flow and pressure of the gas, and the valve opening can be adjusted according to the experimental needs.

[0066] 2. There are many types of gas cylinders. Except for helium used as GC carrier gas and argon used as protective gas to increase pressure, other gases are used as reaction gases according to demand. The pressure regulator controls the pressure conditions required by the system, the flow meter controls the flow of different gases into the reactor, and the pressure gauge monitors the pressure condition of the reactor.

[0067] 3. The AC power supply includes a transformer, which can adjust the voltage and frequency in conjunction with an oscilloscope to provide a continuous and stable AC electric field to ensure the uniformity of discharge during the reaction. The actual input power of the reaction can be calculated by recording the Lissajous figure generated by the oscilloscope. During the reaction, the voltage is adjusted to correspond to different stable discharge frequencies. After adjusting the voltage, the frequency is adjusted to achieve stable discharge in the discharge zone of the DBD reactor. Powdered Cu / Zn / Al catalyst bodies are loaded in the discharge zone to generate a non-equilibrium plasma with uniform discharge, which is used to provide a controllable reaction zone for the reaction gas. The flowmeter, GC gas chromatograph and cold trap at the outlet are used to detect the composition and flow of gas products and collect liquid products;

[0068] 4. The barrier dielectric layer material in the DBD reactor of the present invention is a quartz fiber reinforced silica ceramic-based polymer. Compared with the traditional dielectric quartz glass, it has good high specific strength and high specific stiffness, can still maintain an extremely low relative dielectric constant under medium and high pressure environments, and exhibits excellent electrical insulation. The mechanical parameters of the material are shown in the following table.

[0069] Table 1 Mechanical parameters of barrier materials

[0070]

[0071] As a preferred example, the quartz fiber reinforced silica ceramic-based polymer of the present invention is prepared by a sol-gel method, and the specific process is as follows:

[0072] First, the 2.5D quartz fiber fabric is pretreated and soaked in an organic solvent for 24 hours; it is dried in a drying oven at 150°C. Then, the dried fiber fabric is laid out and molded into a cylindrical preform, and the preform is impregnated with a silica sol with a solid content of 20-25wt%, and the vacuum is evacuated to a vacuum degree of -0.06 to -0.1MPa, and the pressure is maintained for 48 hours, and then the normal pressure is restored to complete the impregnation. It is laid flat on the metal mesh of the oven and dried with air at 50 to 80°C for 4 hours. The above impregnation-drying operation is repeated 4 times to obtain a composite material blank. Finally, the blank is subjected to a high-temperature treatment at 600°C in an air atmosphere for 1 hour to obtain a quartz fiber reinforced silica ceramic-based polymer ring tube used as a barrier medium layer.

[0073] When in use, the annular tube-shaped barrier medium layer is nested inside the stainless steel round tube serving as the outer electrode.

[0074] 5. The system provided by the present invention can be used for the conversion reaction of CO2 gas by coupling catalysis with pressurized low-temperature plasma, that is, to produce CH3OH by hydrogenation of CO2. In this reaction process, the application of Cu / Zn / Al catalyst is involved.

[0075] As a preferred example, the preparation steps of the catalyst are as follows:

[0076] First, the Al2O3 solid used as a carrier is calcined for a certain period of time to remove impurities (such as adsorbed water). Copper salt and zinc salt are dissolved in deionized water to prepare a metal precursor solution. The calcined Al2O3 is then fully ground into a powder solid, added to the precursor solution, and magnetically stirred for 30 minutes until fully mixed. The resulting mixture is stored at room temperature overnight to obtain a mixed solution containing a precipitate. It is then placed in a muffle furnace for drying to obtain an unreduced solid catalyst. After further grinding and crushing, it is placed in a tubular furnace and reduced with hydrogen to obtain a powdered Cu / Zn / Al catalyst. In the catalyst, the molar ratio of Cu:Zn:Al is in the range of 4.5:4.5:1, and the mesh size is 40-60.

[0077] When in use, disassemble the reactor and place it vertically (the air inlet side is down), first fill part of the quartz wool on the axial air inlet side of the discharge area, then pour the powdered Cu / Zn / Al catalyst evenly into the discharge area without compaction, then fill the remaining quartz wool on the air outlet side of the discharge area to complete the catalyst plugging, and finally complete the reactor assembly. This operation can prevent the catalyst from leaking to other areas due to gas flow during the reaction.

[0078] The mesh number of the catalyst powder is set to 40-60, which can ensure that the gas can flow normally in the reactor within the specified flow rate and pressure range.

[0079] The following is an explanation of the method of using the system of the present invention:

[0080] 1. Before use, build the system and load the catalyst according to the connection relationship described above. Ensure that all equipment and components can operate normally and the system air tightness meets the requirements.

[0081] As an example, the distance between the inner electrode and the barrier dielectric layer in the reactor is 1 mm, the thickness of the barrier dielectric layer is 2 mm, and the length of the discharge zone is 50 mm.

[0082] 2. Open each gas cylinder, open the inlet pressure regulator 2, mass flow meter 3 and flow meter controller 4, and adjust the pressure and flow rate according to the test plan. Use the pressure gauge on the pipeline before the inlet manifold to monitor the pressure inside the reactor, and use the thermocouple inside the reactor to monitor the temperature of the discharge zone. Turn on the accompanying heating belt of the pipeline after the outlet manifold to ensure that the outflow product can be completely vaporized. Turn on the condensed gas circulation in the cold trap to collect some liquid products.

[0083] As an example, the total air flow rate range that the pressurized air supply system can provide is: 0.1~200mL / min, the adjustment range of the air intake pressure is: 0.1~10MPa; the voltage adjustment range of the AC power supply is: 25V~75V.

[0084] 3. After the overall pressure and temperature of the device are stable, turn on the AC power supply and oscilloscope to power the reactor. According to the monitoring situation of the oscilloscope, adjust the voltage and frequency of the AC power supply to make the reactor discharge evenly. After the voltage and frequency are stable, turn on the GC gas chromatograph for real-time analysis.

[0085] During the reaction, the temperature of the discharge zone in the reactor is controlled to be 180-220°C and the pressure is controlled to be 0.1-5 MPa.

[0086] 4. Examples and comparative examples of the use of the above-mentioned system:

[0087] Embodiment 1:

[0088] Cu / Zn / Al catalyst The catalyst is in powder form (40-60 mesh). The discharge voltage is adjusted to 45V, the CO2 / H2 gas ratio is 1:3, the total gas flow rate is 40mL / min, and the pressure is 1MPa.

[0089] Embodiment 2:

[0090] The Cu / Zn / Al catalyst is in powder form (40-60 mesh). The discharge voltage is adjusted to 45V, the CO2 / H2 gas ratio is 1:3, the total gas flow rate is 40mL / min, and the pressure is 5Mpa.

[0091] Comparative Example 1:

[0092] The Cu / Zn / Al catalyst is in powder form (40-60 mesh). The discharge voltage is adjusted to 45V, the CO2 / H2 gas ratio is 1:3, the total gas flow rate is 40mL / min, and the pressure is 0.1MPa (normal pressure).

[0093] Table 2 CO2 conversion and CH3OH selectivity at different pressures

[0094]

[0095] It can be seen from the data in the above table that compared with the low-temperature plasma conversion of CO2 hydrogenation to methanol under ordinary normal pressure environment, the conversion effect of the present invention under high pressure environment is better, with the CO2 conversion rate up to 20.42% and the CH3OH selectivity up to 40.56%.

[0096] The discharge characteristic test process of the system of the present invention is described below:

[0097] 1. Referring to the cross section of the discharge zone in the reactor, the applicant established a one-dimensional symmetrical DBD reactor model using COMSOL simulation software, as shown in the attached figure. Figure 3 By changing the internal pressure and input voltage of the reactor, the change of discharge intensity (electron density, potential) in the reaction area is tested.

[0098] The reason for using COMSOL simulation software to build a model to test the discharge characteristics is that low-temperature plasma discharge is relatively complex, and whether the discharge is stable can only be determined by observation. The power supply and oscilloscope can only reflect the change of the input current but cannot obtain the actual change of the discharge process. There is currently no other suitable means to test the discharge characteristics, so simulation is used to verify the discharge effect of the present invention after pressurization.

[0099] 2. The discharge area of ​​the reactor model uses a free triangle mesh with 200 distributed units, a unit size ratio of 5, and an exponential growth rate. The other domains use the default free triangle mesh settings. The overall mesh is shown in the attached Figure 4 .

[0100] In order to focus on describing the physical effects during the discharge process, argon was selected instead of CO2 as the ionization gas during the simulation; on the one hand, the amount of substances and reactions was reduced as much as possible, and on the other hand, the ionization characteristics were as similar as possible to the actual reaction process.

[0101] The reactions involved in the ionization process are shown in Table 3.

[0102] Table 3. Simulated collision and reaction table

[0103]

[0104]

[0105] 3. Example of the test based on the above simulation model:

[0106] Embodiment 3:

[0107] The pressure was set to 0.1 MPa, the reactor temperature was 473 K, the applied peak voltage was 75 V, and the frequency was 27500 Hz. A one-dimensional transient calculation was performed. The results are shown in Figure 5 , Figure 8 .

[0108] Embodiment 4:

[0109] The pressure was set to 1 MPa, the reactor temperature was 473 K, the applied peak voltage was 75 V, and the frequency was 27500 Hz. A one-dimensional transient calculation was performed. The results are shown in Figure 6 , Fig. 9 .

[0110] Embodiment 5:

[0111] The pressure was set to 5 MPa, the reactor temperature was 473 K, the applied peak voltage was 75 V, and the frequency was 27500 Hz. A one-dimensional transient calculation was performed. The results are shown in Figure 7 , Fig.10 .

[0112] Table 4 Electron density corresponding to different pressure conditions

[0113]

[0114] It can be seen from the data in the above table and the attached figure that the minimum electron density is located on the surface of the medium, and the maximum electron density is located on the surface of the inner electrode. The accumulation of electrons on both sides causes a stable plasma discharge to occur in the gap. As the internal pressure gradually increases, the electron difference on both sides gradually increases, but the medium is still not broken down. There is no electron accumulation inside the medium and the potential is 0, indicating that the dielectric barrier discharge is still maintained.

[0115] Embodiment 6:

[0116] The applied peak voltage was set to 25V, the frequency to 27500Hz, the reactor temperature to 473K, and the pressure to 5MPa. A one-dimensional transient calculation was performed. The results are shown in Fig.11 , Fig.14 .

[0117] Embodiment 7:

[0118] The applied peak voltage was set to 45V, the frequency was 27500Hz, the reactor temperature was 473K, and the pressure was 5MPa. A one-dimensional transient calculation was performed. The results are shown in Fig.12 , Fig.15 .

[0119] Embodiment 8:

[0120] The applied peak voltage was set to 75V, the frequency was 27500Hz, the reactor temperature was 473K, and the pressure was 5MPa. A one-dimensional transient calculation was performed. The results are shown in Fig.13 , Fig.16 .

[0121] Table 5 Electron density corresponding to different voltage conditions

[0122]

[0123] It can be seen from the data in the above table and the attached figure that as the input voltage gradually increases, the electron difference on both sides gradually decreases, causing the discharge intensity to gradually increase.

Claims

1. A method for plasma-coupled catalysis of CO2 gas under pressurized low temperature conditions, characterized in that: The method is implemented based on a system of pressurized low-temperature plasma coupled with catalytic CO2 gas; the system includes a pressurized gas supply system, a DBD reactor and an AC power supply; wherein, The main body of the DBD reactor is a composite tubular structure, with an external stainless steel round tube as the outer electrode and an axially arranged metal cylinder as the inner electrode; both the outer electrode and the inner electrode are provided with insulating protective sleeves for safety protection, the former is grounded and the latter is connected to an AC power supply through a cable; a ring-shaped blocking medium layer is provided on the inner side of the outer electrode, and its material is quartz fiber reinforced silica ceramic-based polymer; a gap is reserved between the outer side of the inner electrode and the blocking medium layer to form a ring-shaped cavity as a discharge zone; a powdered Cu / Zn / Al catalyst with a particle size of 40 to 60 mesh is uniformly filled in the discharge zone, and the two axial ends of the discharge zone are sealed with quartz wool; the two ends of the reactor are respectively installed in end face seats of insulating material, and an inlet manifold and an outlet manifold connected to the discharge zone are respectively provided on the two end face seats; a thermocouple for monitoring the reaction temperature is provided in the discharge zone; the outlet manifold is connected to a cold trap for collecting reaction products through a discharge pipeline; The pressurized gas supply system includes a CO2 gas cylinder and a hydrogen gas cylinder for providing reaction gas, and an inert gas cylinder for increasing the gas supply pressure; an intake pressure regulator and a mass flow meter are provided on the outlet pipeline of each cylinder, and are connected to the intake pipeline and then connected to the intake manifold; The quartz fiber reinforced silica ceramic-based polymer is prepared by the following method: (1) Pre-treating a 2.5D quartz fiber fabric by soaking it in an organic solvent for 24 hours; drying it at 150° C., laying it out and molding it into a cylindrical preform; (2) impregnating the preform with a silica sol having a solid content of 20 to 25 wt%, evacuating the preform and maintaining the pressure for 48 h; after the impregnation, drying the preform with air at 50 to 80° C. for 4 h; repeating this step 4 times to obtain a composite material blank; (3) calcining the composite material blank at 600° C. for 1 hour in an air atmosphere; after cooling, a quartz fiber reinforced silica ceramic-based polymer ring tube serving as a barrier medium layer is obtained; The Cu / Zn / Al catalyst is prepared by the following method: (1) taking Al2O3 solid used as a carrier, calcining it to remove impurities, and then grinding it into powder; dissolving copper salt and zinc salt in deionized water to prepare a metal precursor solution; (2) adding Al2O3 powder to the precursor solution, stirring and mixing thoroughly, and leaving the mixture at room temperature overnight to obtain a mixed solution containing a precipitate; (3) drying the mixed solution to obtain an unreduced solid catalyst; after grinding and pulverizing, transferring the mixture to a tube furnace and performing reduction treatment under the condition of continuous introduction of hydrogen to obtain a Cu / Zn / Al catalyst; the molar ratio of Cu:Zn:Al contained in the catalyst is in the range of 4.5:4.5:1; The method for plasma-coupled catalytic CO2 gas under pressurized low-temperature conditions specifically comprises the following steps: (1) Open the valves of each cylinder, control the gas flow rate of each channel through the flow meter controller, and adjust the mixed gas flow rate and pressure entering the reactor; wherein CO2 is used as the reaction gas, helium is used as the carrier gas of the GC gas chromatograph, and argon is used as the protective gas to increase the gas supply pressure; (2) Turn on the AC power supply, power the DBD reactor, and carry out a plasma-coupled catalytic hydrogenation reaction of CO2 gas in the discharge zone to generate CH3OH; during the reaction, control the temperature of the discharge zone in the reactor to be 180-220°C and the pressure to be 0.1-5 MPa; (3) Using the oscilloscope to observe the data, the actual input power of the reaction is calculated as a reference for adjusting the power supply voltage; using the GC gas chromatograph to analyze the composition of the reaction products, and using the cold trap to condense and collect the liquid products.

2. The method according to claim 1, characterized in that The stainless steel round tube is a tubular structure with hollow parts made of stainless steel mesh.

3. The method according to claim 1, characterized in that The AC power source is connected to an oscilloscope via a wire.

4. The method according to claim 1, characterized in that The inert gas cylinder includes an argon gas cylinder; the mass flow meter is connected to a flow meter controller via a wire; and a pressure gauge or a pressure sensor is provided on the air intake pipeline.

5. The method according to claim 1, characterized in that The outlet manifold is connected to a flow meter, an outlet pressure regulator and a GC gas chromatograph in sequence through an outlet pipeline, and the discharge pipeline of the GC gas chromatograph is connected to a cold trap; the outlet pipeline is provided with a heating belt; the inert gas cylinder includes a helium cylinder for providing chromatograph carrier gas.

6. The method according to claim 1, characterized in that The distance between the inner electrode and the blocking dielectric layer is 1 mm, the thickness of the blocking dielectric layer is 2 mm, and the length of the discharge region is 50 mm.

7. The method according to claim 1, characterized in that The total air flow rate range that the pressurized air supply system can provide is: 0.1~200mL / min, the adjustment range of the air intake pressure is: 0.1~10MPa; the voltage adjustment range of the AC power supply is: 25V~75V.

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