Plasma enhanced reaction device and low-concentration light hydrocarbon oxidative conversion method

Abstract

The invention relates to the technical field of plasmas, and discloses a plasma enhanced reaction device and a low-concentration light hydrocarbon oxidative conversion method. The device comprises a high-voltage electrode, more than two ground electrodes, more than two third electrodes and a plasma reaction tube which are coaxially arranged, the high-voltage electrode is arranged along the axis of the plasma reaction tube, the ground electrodes and the third electrodes are arranged in parallel along the outer wall of the plasma reaction tube, and the ground electrodes and the third electrodes are arranged at intervals; a reaction cavity is formed between the high-voltage electrode and the inner wall of the plasma reaction tube, the high-voltage electrode and the ground electrode form more than two discharge areas in the reaction cavity, the high-voltage electrode and the third electrode form more than two induction electric field areas in the reaction cavity, and the induction electric field areas are filled with metal frame organic materials serving as catalysts. The plasma enhanced reaction device disclosed by the invention is used for carrying out oxidative conversion on low-concentration light hydrocarbon, and a relatively good conversion effect can be obtained.

Description

Technical Field

[0001] The invention relates to the field of plasma technology, and in particular to a plasma enhanced reaction device and a low-concentration light hydrocarbon oxidation conversion method. Background Art

[0002] Small molecule alkanes (C1-C5 alkanes) are a type of gaseous organic molecules that are difficult to activate. The chemical transformation of such molecules usually requires a thermal catalytic reaction under high temperature and pressure. Plasma method, as an electrically driven external field enhancement method, can enable the chemical transformation of small molecule alkanes to be carried out at room temperature and pressure. Its working principle is to apply a high-voltage electric field to the gas to cause the gas to ionize and produce highly chemically active particles (including electrons, positive and negative ions, and neutral particles, etc.), thereby promoting the reaction. At the same time, low-temperature plasma methods (such as dielectric barrier discharge and corona discharge) are easy to operate and can be started and stopped at any time, and have received widespread attention. For low concentrations (below 500ppm) of light hydrocarbon VOCs (mainly methane, ethane, propane, butane, and pentane), the recovery value is not high and harmless treatment is required. The highly active particles generated by plasma enhance the oxidative decomposition reaction of small molecule alkanes, and finally generate CO2 and H2O.

[0003] CN105396440B discloses a device and method for treating industrial waste gas VOCs by thermal corona discharge catalytic oxidation. A heating rod is placed in the center of a reaction tube, and a spiral discharge coil is installed in a purification channel, surrounding the outer circumference of the heating tube and extending spirally along the length of the heating tube. The corona discharge plasma is combined with high-temperature thermal oxidation degradation to treat industrial waste gas VOCs. However, the role of the catalytic part and the targeted degradation effect on C1-C5 light hydrocarbon VOCs have not yet been described.

[0004] CN108325349A discloses a method for treating VOCs and malodorous gases by low-temperature plasma coupled adsorption, comprising the following steps: (1) pretreatment; (2) low-temperature plasma degradation; (3) adsorption treatment, wherein the degradation process in step (2) uses an intermittent low-temperature plasma discharge device, which includes a low-temperature plasma power supply, a low-temperature plasma discharge unit and a low-temperature plasma reactor, and two or more low-temperature plasma discharge units are inserted into the low-temperature plasma reactor. The method of low-temperature plasma coupled adsorption can efficiently degrade the linear hydrocarbons, cycloalkanes, and thiols and sulfides with small molecular weights that are not conducive to adsorption by the adsorbent, thereby improving the adsorption effect of the adsorbent on organic waste gas. Therefore, the main method for solving the problem of C1-C5 light hydrocarbon VOCs is to use a plasma zone post-adsorbent, but the effect of complete degradation has not yet been achieved.

[0005] CN108465354A discloses a low-temperature plasma coordinated catalytic reaction unit and a VOCs treatment device based on a low-temperature plasma coordinated catalytic reactor. It includes a low-temperature plasma coordinated catalytic reaction unit and an ozone decomposition catalytic reaction unit. VOCs are converted into CO2 in the low-temperature plasma coordinated catalytic reaction unit, and the VOCs that are not completely decomposed are decomposed again by using the residual ozone generated by the decomposition discharge in the ozone decomposition catalytic reaction unit, and the purified gas is discharged from the device. Adding a catalyst in the low-temperature plasma coordinated catalytic reaction unit can increase the degradation rate of benzene from 15% to more than 90%. There is still no targeted degradation effect for C1-C5 light hydrocarbon VOCs.

[0006] CN110292854B discloses a device and method for catalytic degradation of VOCs by pulsed plasma coupled double fluidized beds. Dual-functional discharge electrodes, the upper section is a smooth discharge functional electrode, and the lower section is a thorn discharge functional electrode; a high-voltage pulse power supply is loaded on the above-mentioned discharge electrode so that the gas in the cylinder is ionized and excited to generate plasma; two layers of catalyst beds are arranged in the reaction cylinder, the lower bed is provided with a VOCs catalyst, and the upper bed is provided with a by-product catalyst, and the catalyst is in a fluidized state during operation. The VOCs catalyst is one of CuMn, CuMnCe, CoMn and CuMnZr. The raw materials of the by-product catalyst are: Ce and Mn doped with Ag and Pt as active components, and Al2O3 and molecular sieves are selected as carriers to prepare NTP synergistic decomposition of by-product catalysts. When the waste gas volume of VOCs (xylene, etc.) sprayed at room temperature is 4500m 3 / h, the initial concentration of VOCs is 350-450mg / m 3 When the working voltage is 76KV, the outlet VOCs concentration can meet the emission standards, and there is basically no secondary pollutant. The catalysts are all filled in the plasma area. There is still no targeted degradation effect on C1-C5 light hydrocarbon VOCs.

[0007] Low-concentration light hydrocarbon VOCs (C1-C5 alkanes) are treated by low-temperature plasma. The current literature reports that the dielectric barrier discharge area is assisted by heating, and a catalyst is added or not added to the plasma area. The literature PlasmaChem Plasma Process 2009, 29, 13-25 reported that a dielectric barrier reactor driven by a pulse power supply and assisted by heating degraded 1100ppm propane / air. The propane degradation rate was 21% under the conditions of 300K and 90J / L injection energy. When the temperature was raised to 800K, the propane degradation rate could reach more than 95%. Plasma Chem Plasma Process 2009, 29, 411-419 reported that the plasma zone in the dielectric barrier reactor was filled with Pt / γ-Al2O3 or MnO2 / γ-Al2O3 catalysts, and 100 ppm propane air was treated by heating. Under the conditions of 60 J / L injection energy at 473 K, the propane degradation rate of the plasma alone was about 55%. Under the same temperature, the propane degradation rate was 63% under the condition of Pt / γ-Al2O3 catalyst in the plasma zone. When the temperature was raised to 533 K, the propane degradation rate increased to 90%.

[0008] The degradation efficiency of this type of light hydrocarbon VOCs (C1-C5 alkanes) by low-temperature plasma alone is low, and the oxidation rate is low. Auxiliary heating and catalysts are usually required. For large-flux industrial applications, uniform heating consumes a lot of energy, and the catalyst is filled in the plasma discharge zone. The catalyst surface is easily passivated after the plasma action, resulting in reduced activity and inability to operate stably for a long period of time. In addition, the replacement of catalysts in the plasma zone is more cumbersome, which is not conducive to the promotion and application of the device. Summary of the invention

[0009] The purpose of the present invention is to provide a plasma enhanced reaction device and a method for oxidation conversion of low-concentration light hydrocarbons. The plasma enhanced reaction device described in the present invention can achieve complete oxidation degradation of difficult-to-degrade light hydrocarbons and ensure the long-term activity and stability of the catalyst material.

[0010] In order to achieve the above-mentioned object, the present invention provides a plasma enhanced reaction device on one hand, which comprises a coaxially arranged high-voltage electrode, two or more ground electrodes, two or more third electrodes and a plasma reaction tube, wherein the high-voltage electrode is arranged along the axis of the plasma reaction tube, the ground electrode and the third electrode are arranged in parallel along the outer wall of the plasma reaction tube, and the ground electrode and the third electrode are arranged at intervals from each other;

[0011] A reaction chamber is formed between the high-voltage electrode and the inner wall of the plasma reaction tube, the high-voltage electrode and the ground electrode form more than two discharge zones in the reaction chamber, and the high-voltage electrode and the third electrode form more than two induced electric field zones in the reaction chamber, wherein the induced electric field zones are filled with metal frame organic materials serving as catalysts.

[0012] Preferably, the number of the third electrodes is greater than the number of the ground electrodes by 1.

[0013] Preferably, the number of the ground electrodes is 2-6, and the number of the third electrodes is 3-7.

[0014] Preferably, an air inlet and an air outlet are respectively provided at both ends of the reaction chamber, the induced electric field zone close to the air inlet is the BI zone, the induced electric field zone close to the air outlet is the BIII zone, and the induced electric field zone between the BI zone and the BIII zone is the BII zone, wherein there is one BI zone, and there are one or more BII zones and BIII zones.

[0015] Preferably, the catalyst material filled in the BI zone is used to promote the oxidation of organic molecules.

[0016] Preferably, the catalyst material filled in the BI zone is selected from at least one of MOF-74 (Ni), MOF-74 (Co), MOF-74 (Mg), DUT-8 (Ni), MIL-125 (Ti), ZIF-67 (Co), UIO-66 (Zr), MIP-202 (Zr) and MOF-808 (Zr).

[0017] Preferably, the catalyst material filled in the BII region is used to enhance the oxidation of organic molecules and / or oxidize long carbon chain molecules into C1 small molecules.

[0018] Preferably, the catalyst material filled in the BII region is MIL-100 (Fe) and / or MIL-101 (Fe).

[0019] Preferably, the catalyst material filled in the BIII zone is used for continued oxidation to achieve complete oxidation of organic molecules into CO2.

[0020] Preferably, the catalyst material filled in the BIII zone is selected from one or more of Cu-BTC, MIL-101 (Cr), MOF-74 (Co), MOF-808 (Zn), MOF-808 (Cu), MOF-808 (Fe) and the above catalyst materials loaded with at least one of Pd, Ni and Pt.

[0021] Preferably, the ground electrode and the third electrode are both made of high temperature resistant conductive metal.

[0022] Preferably, the conductivity of the ground electrode and the third electrode is both 10 5 -10 8 S / m.

[0023] Preferably, the plasma reaction tube is an insulating medium tube made of any one of quartz, ceramic, corundum or polytetrafluoroethylene.

[0024] Preferably, the wall thickness of the plasma reaction tube is not greater than 5 mm.

[0025] Preferably, the high voltage electrode is a metal rod; or

[0026] The high voltage electrode comprises an insulating medium tube and conductive metal powder filled in the insulating medium tube; or

[0027] The high voltage electrode comprises an insulating medium tube and a conductive metal rod or a conductive metal tube embedded in the insulating medium tube;

[0028] Wherein, the insulating medium tube is made of quartz, ceramic, corundum or polytetrafluoroethylene.

[0029] Preferably, the length of each ground electrode is 1-5 times the discharge gap of the plasma reaction tube.

[0030] Preferably, the length of each third electrode is 1-3 times the discharge gap of the plasma reaction tube.

[0031] Preferably, the distance between the third electrode and the ground electrode adjacent to each other is 1-5 times the discharge gap of the plasma reaction tube.

[0032] Preferably, the discharge gap of the plasma reaction tube is related to the type of gas to be treated. When the main atmosphere of the gas to be treated is air and / or nitrogen, the discharge gap is less than 10 mm; when the main atmosphere of the gas to be treated is argon, the discharge gap is less than 20 mm; when the main atmosphere of the gas to be treated is helium, the discharge gap is less than 30 mm.

[0033] Another aspect of the present invention provides a method for oxidation conversion of low-concentration light hydrocarbons, which is implemented in the plasma enhanced reaction device described above, and comprises: injecting the gas to be treated from the gas inlet into the reaction chamber for treatment.

[0034] Preferably, when the complete oxidation of light hydrocarbons in the gas to be treated is more difficult and / or the concentration of light hydrocarbons is higher, the number of BII zones and / or BIII zones is increased; when the complete oxidation of light hydrocarbons in the gas to be treated is less difficult and / or the concentration of light hydrocarbons is lower, the number of BII zones and / or BIII zones is reduced.

[0035] According to the plasma enhanced reaction device described in the present invention, multiple discharge zones and induced electric field zones are formed by spacing each other, and metal frame organic materials with high activity are filled in the induced electric field zone as catalysts. Such catalysts are very easily destroyed by filamentary discharge caused by high voltage in the discharge zone, while in the induced electric field zone, such catalysts can not only maintain a good microstructure morphology, but also the molecular polarization under the action of a weak electric field can extend the life of active ions on the surface of the material, extend the contact and collision time between the molecules to be treated and the active particles, improve the catalytic effect of such materials, and thus enhance the degradation effect of difficult-to-degrade light hydrocarbons. In a more preferred embodiment, according to the position of the induced electric field and the reaction principle, filling different types of metal frame organic materials as catalysts can not only further enhance the degradation effect and achieve complete degradation of difficult-to-degrade light hydrocarbons, but also ensure the long-term activity and stability of the catalyst material.

[0036] In the low-concentration light hydrocarbon oxidation conversion method of the present invention, for mixed exhaust gases of different concentrations and different degradation difficulties, different induction electric field catalytic zones are combined to achieve complete degradation of light hydrocarbons while avoiding the generation of secondary pollutants (such as NO x ). BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 It is a structural schematic diagram of an embodiment of the plasma enhanced reaction device of the present invention;

[0038] Figure 2 is a schematic structural diagram of another embodiment of the plasma enhanced reaction device of the present invention;

[0039] Figure 3 It is a structural schematic diagram of another embodiment of the plasma enhanced reaction device described in the present invention.

[0040] Description of Reference Numerals

[0041] 1. High voltage electrode; 2. Ground electrode; 3. Third electrode; 4. Plasma reaction tube; 5. Reaction chamber; 6. Discharge area; 7. Induction electric field area; 8. Pre-activated catalyst; 9. Enhanced oxidation catalyst; 10. Complete oxidation catalyst; 11. Air inlet; 12. Air outlet. DETAILED DESCRIPTION

[0042] The specific implementation of the present invention is described in detail below in conjunction with the accompanying drawings. It should be understood that the specific implementation described here is only used to illustrate and explain the present invention, and is not used to limit the present invention.

[0043] like Figure 1-3As shown, the plasma enhanced reaction device described in the present invention includes a coaxially arranged high-voltage electrode 1, two or more ground electrodes 2, two or more third electrodes 3 and a plasma reaction tube 4, wherein the high-voltage electrode 1 is arranged along the axis of the plasma reaction tube 4, the ground electrode 2 and the third electrode 3 are arranged in parallel along the outer wall of the plasma reaction tube 4, and the ground electrode 2 and the third electrode 3 are arranged at intervals from each other.

[0044] In the plasma enhanced reaction device of the present invention, the high voltage electrode 1 is connected to a high voltage power supply, the ground electrode 2 is grounded, and the third electrode 3 is not grounded and is not connected to the high voltage power supply. In the present invention, the high voltage power supply used for discharge can be an AC power supply or a pulse power supply.

[0045] In the plasma enhanced reaction device described in the present invention, a reaction chamber 5 is formed between the high-voltage electrode 1 and the inner wall of the plasma reaction tube 4, the high-voltage electrode 1 and the ground electrode 2 form more than two discharge zones 6 in the reaction chamber 5, and the high-voltage electrode 1 and the third electrode 3 form more than two induced electric field zones 7 in the reaction chamber 5, wherein the induced electric field zones are filled with metal frame organic materials as catalysts.

[0046] In the plasma enhanced reaction device of the present invention, in a preferred case, the number of the third electrodes 3 is 1 greater than the number of the ground electrodes 2. Specifically, the number of the ground electrodes 2 can be 2-6, and the number of the third electrodes 3 can be 3-7. In the above embodiment, the electrodes close to both ends of the plasma reaction tube 4 are the third electrodes.

[0047] In the plasma enhanced reaction device described in the present invention, an air inlet 11 and an air outlet 12 are respectively provided at both ends of the reaction chamber 5, the induced electric field zone close to the air inlet 11 is the BI zone, the induced electric field zone close to the air outlet 12 is the BIII zone, and the induced electric field zone located between the BI zone and the BIII zone is the BII zone, wherein the BI zone is one, and the BII zone and the BIII zone are one or more.

[0048] In one embodiment, if Figure 1 As shown, in the reaction chamber 5, from the gas inlet end to the gas outlet end, the BI zone, the A zone, the BII zone, the A zone and the BIII zone (also recorded as BI→A→BII→A→BIII) are arranged in sequence, wherein the BI zone, the BII zone and the BIII zone are all induction electric field zones, and the A zone is all discharge zone.

[0049] In another embodiment, if Figure 2As shown, in the reaction chamber 5, from the gas inlet end to the gas outlet end, they are sequentially arranged as BI zone, A zone, BII zone, A zone, BII zone, A zone and BIII zone (also recorded as BI→A→BII→A→BII→A→BIII), BI zone, BII zone and BIII zone are all induction electric field zones, and A zone is all discharge zone.

[0050] In another embodiment, if Figure 3 As shown, in the reaction chamber 5, from the gas inlet end to the gas outlet end, the BI area, A area, BII area, A area, BIII area, A area and BIII area (also recorded as BI→A→BII→A→BIII→A→BIII) are arranged in sequence, and the BI area, BII area and BIII area are all induction electric field areas, and the A area is all discharge area.

[0051] According to a preferred embodiment of the present invention, in the plasma enhanced reaction device, the BI zone, the BII zone and the BIII zone are respectively filled with different catalyst materials, wherein the catalyst material filled in the BI zone is used to promote the oxidation of organic molecules, the catalyst material filled in the BII zone is used to enhance the oxidation of organic molecules and / or the oxidation of long carbon chain molecules into C1 small molecules, and the catalyst material filled in the BIII zone is used to continue oxidation to achieve complete oxidation of organic molecules into CO2. According to this preferred embodiment, the gas to be treated containing light hydrocarbons passes through the BI zone, the BII zone and the BIII zone in sequence. In the BI zone, the catalyst accepts the escaped electrons, hydrogen particles (including hydrogen ions and hydrogen atoms) and other active particles generated in the adjacent discharge zone, so that the organic molecules passing through the BI zone are charged, which plays a role of pre-activation; in the BII zone, the catalyst uses the oxygen-containing active particles generated in the discharge zone to produce more active metal-oxygen active sites, and then oxidizes the light hydrocarbon molecules to be treated, and the long carbon chain molecules are oxidized into C1 small molecules (including formic acid, methanol, formaldehyde, CO2, CO and carbene, etc.); in the BIII zone, the catalyst continues to oxidize the C1 small molecules or molecular fragments, and completely oxidizes them into CO2, thereby achieving the purpose of complete degradation and harmless treatment.

[0052] In a preferred case, the metal center of the catalyst material filled in the BI region has an unsaturated coordination site. Further preferably, the catalyst material filled in the BI region is selected from at least one of MOF-74 (Ni), MOF-74 (Co), MOF-74 (Mg), DUT-8 (Ni), MIL-125 (Ti), ZIF-67 (Co), UIO-66 (Zr), MIP-202 (Zr) and MOF-808 (Zr).

[0053] In a preferred case, the metal center of the catalyst material filled in the BII region has Fe. Further preferably, the catalyst material filled in the BII region is MIL-100 (Fe) and / or MIL-101 (Fe).

[0054] In a preferred case, the catalyst material filled in the BIII zone is selected from one or more of Cu-BTC, MIL-101 (Cr), MOF-74 (Co), MOF-808 (Zn), MOF-808 (Cu), MOF-808 (Fe) and the above catalyst materials loaded with at least one of Pd, Ni and Pt.

[0055] In the present invention, in the BI zone, the BII zone and the BIII zone, the catalyst may be filled in the form of particles, blocks or powder, etc. The powder may be dispersed on quartz wool and placed at corresponding positions.

[0056] In the plasma enhanced reaction device of the present invention, preferably, the ground electrode 2 and the third electrode 3 are both made of high temperature resistant conductive metal. Further preferably, the conductivity of the ground electrode 2 and the third electrode 3 is 10 5 -10 8 S / m, more preferably 10 7 -10 8 Specifically, the material of the ground electrode 2 and the third electrode 3 is selected from one or more of platinum, rhodium, palladium, gold, copper, tungsten, iron and stainless steel containing nickel and titanium, and more preferably iron, copper or tungsten.

[0057] In the plasma enhanced reaction device of the present invention, the ground electrode 2 may be a metal mesh or a metal sheet, etc. When a metal mesh is used as the ground electrode, the mesh number of the metal mesh may be 5-500 meshes, preferably 10-100 meshes.

[0058] In the plasma enhanced reaction device of the present invention, the third electrode 3 may be a metal mesh, a metal sheet, a spiral metal wire, etc. When a metal mesh is used as the third electrode, the mesh number of the metal mesh may be 5-500 meshes, preferably 10-100 meshes.

[0059] In the plasma enhanced reaction device described in the present invention, there is no particular limitation on the plasma reaction tube 4, and it can be any conventional reaction tube with insulating properties in the art. In the present invention, preferably, the plasma reaction tube 4 is an insulating medium tube; more preferably, the insulating medium is quartz, ceramic, corundum or polytetrafluoroethylene. In one specific embodiment of the present invention, the plasma reaction tube 4 is a quartz tube; in another specific embodiment of the present invention, the plasma reaction tube 4 is a corundum tube.

[0060] In the plasma enhanced reaction device of the present invention, the wall thickness of the plasma reaction tube 4 is not greater than 5 mm, preferably 0.1-5 mm, more preferably 0.5-5 mm, and further preferably 1-5 mm.

[0061] In the plasma enhanced reaction device of the present invention, there is no particular limitation on the shape of the high voltage electrode 1, and it can be any shape of electrodes conventionally used in the art. In the present invention, preferably, the high voltage electrode 1 is tubular or rod-shaped.

[0062] In one embodiment, the high voltage electrode 1 is a metal rod. The material of the metal rod can be a material with a conductivity of 10 5 -10 8 S / m (25°C). In one embodiment, the high voltage electrode 1 is a metal with a conductivity of 9.9×10 6 Iron metal rod of S / m.

[0063] In another embodiment, the high voltage electrode 1 comprises an insulating medium tube and a conductive metal powder filled in the insulating medium tube. The insulating medium tube can be a quartz, ceramic, corundum or polytetrafluoroethylene tube. In one embodiment of the present invention, the insulating medium tube is a quartz tube; in another embodiment of the present invention, the insulating medium tube is a corundum tube.

[0064] There is no particular limitation on the above-mentioned conductive metal powder. In the present invention, preferably, the conductive metal powder is one or more of iron, copper or magnesium. In a specific embodiment, iron powder is selected as the conductive metal powder and filled in an insulating medium tube (specifically a quartz tube) as a central high-voltage electrode. Those skilled in the art may also select other metal powders with conductive properties to be filled in an insulating medium tube as a central high-voltage electrode as needed.

[0065] In another embodiment, the high voltage electrode 1 includes an insulating medium tube and a conductive metal rod or a conductive metal tube embedded in the insulating medium tube. The insulating medium tube can be a quartz, ceramic, corundum or polytetrafluoroethylene tube. There is no particular limitation on the material of the conductive metal rod or conductive metal tube embedded in the insulating medium tube. For example, it can be a conductive metal rod with a conductivity of 10 5 -10 8 S / m (25°C) metal. In a specific embodiment of the present invention, an iron rod is selected and embedded in a quartz tube as a central high voltage electrode.

[0066] In the plasma enhanced reaction device of the present invention, preferably, the length of each ground electrode is 1-5 times, more preferably 2-4 times, the discharge gap of the plasma reaction tube. In the present invention, the discharge gap of the plasma reaction tube refers to the distance between the outer edge of the high voltage electrode 1 and the inner wall of the plasma reaction tube 4.

[0067] In the plasma enhanced reaction device of the present invention, preferably, the length of each third electrode is 1-3 times, more preferably 1.5-2.5 times, and most preferably 2 times, of the discharge gap of the plasma reaction tube.

[0068] In the plasma enhanced reaction device of the present invention, preferably, the distance between the third electrode and the ground electrode adjacent to each other is 1-5 times, more preferably 2-4 times, the discharge gap of the plasma reaction tube.

[0069] In the plasma enhanced reaction device described in the present invention, the discharge gap of the plasma reaction tube 4 is related to the type of gas to be treated. When the main atmosphere of the gas to be treated is air and / or nitrogen, the discharge gap is less than 10 mm (such as 1-10 mm); when the main atmosphere of the gas to be treated is argon, the discharge gap is less than 20 mm (such as 1-20 mm); when the main atmosphere of the gas to be treated is helium, the discharge gap is less than 30 mm (such as 1-30 mm).

[0070] The present invention also provides a method for oxidation conversion of low-concentration light hydrocarbons, which is implemented in the plasma enhanced reaction device described above, and comprises: injecting the gas to be treated into the reaction chamber from the gas inlet for treatment.

[0071] In a more preferred embodiment, the gas to be treated containing light hydrocarbons is injected through the air inlet, and then reacts in sequence through the BI zone, the BII zone and the BIII zone. The gas undergoes pre-activation → enhanced oxidation → complete oxidation, and then flows out from the air outlet 12, thereby achieving complete degradation of low-concentration light hydrocarbons (C1-C5 alkanes).

[0072] In a more preferred embodiment, the number of discharge zones can be adjusted according to the difficulty and concentration of the complete oxidation of the gas to be treated, and the number of BI zones, BII zones and BIII zones equipped with different catalyst materials can also be adjusted. Specifically, when the complete oxidation of light hydrocarbons in the gas to be treated is more difficult and / or the concentration of light hydrocarbons is higher, the number of BII zones and / or BIII zones is increased; when the complete oxidation of light hydrocarbons in the gas to be treated is less difficult and / or the concentration of light hydrocarbons is lower, the number of BII zones and / or BIII zones is reduced.

[0073] In a specific embodiment, for light hydrocarbons with a relatively low concentration (such as below 100 ppm), the gas to be treated flows in from the gas inlet 11 and passes through the corresponding induction electric field area and discharge area in the order of BI→A→BII→A→BIII.

[0074] In another specific embodiment, for light hydrocarbons with higher concentrations (such as above 300 ppm), the number of BII zones can be increased so that the gas to be treated flows in from the gas inlet 11 and passes through the corresponding induced electric field zones and discharge zones in the order of BI→A→BII→A→BII→A→BIII.

[0075] In another specific embodiment, for light hydrocarbons (such as butane and pentane) with high concentrations (such as above 300 ppm) and greater difficulty in complete oxidation, the number of BIII zones can be increased so that the gas to be treated flows in from the gas inlet 11 and passes through the corresponding induced electric field zones and discharge zones in the order of BI→A→BII→A→BIII→A→BIII.

[0076] In another specific embodiment, for a mixed gas (such as a mixture of ethane and pentane) with a high concentration (such as above 300 ppm), the number of BII zones and BIII zones can be increased at the same time, so that the gas to be treated flows in from the gas inlet 11 and passes through the corresponding induced electric field zone and discharge zone in the order of BI→A→BII→A→BII→A→BIII→A→BIII.

[0077] The following examples further illustrate the plasma enhanced reaction device and the low-concentration light hydrocarbon treatment method of the present invention. The examples are implemented based on the technical solution of the present invention, and provide detailed implementation methods and specific operation processes, but the protection scope of the present invention is not limited to the following examples.

[0078] The experimental methods in the following examples, unless otherwise specified, are all conventional methods in the art. The experimental materials used in the following examples, unless otherwise specified, are all commercially available.

[0079] In the following examples and comparative examples, the test method for the light hydrocarbon treatment effect is as follows:

[0080] The concentration of light hydrocarbons was detected using an Agilent 7890B gas chromatograph equipped with a six-way valve injector, a hydrogen flame ionization detector, and an HP-AL / S capillary column (50m×0.53mm, 15μm); the injection port temperature was 150℃, the detector temperature was 250℃; the carrier gas was high-purity nitrogen, the flow rate was 6.0ml / min; the injection volume was 1.0ml; the split ratio was 2:1. The column heating program was: initial temperature 50℃, maintained for 5min; heated to 170℃ at a rate of 7℃ / min.

[0081] The concentrations of COx and NOx were detected using a ThermoFisher Antaris IGS infrared gas analyzer with a gas pressure of 1 atm and a temperature of 40 °C.

[0082] Example 1

[0083] like Figure 2 As shown, the plasma enhanced reaction device includes a coaxially arranged high-voltage electrode 1, three ground electrodes 2, four third electrodes 3 and a plasma reaction tube 4, wherein the high-voltage electrode 1 is arranged along the axis of the plasma reaction tube 4, the ground electrode 2 and the third electrode 3 are arranged in parallel along the outer wall of the plasma reaction tube 4, and the ground electrode 2 and the third electrode 3 are arranged at intervals from each other. A reaction chamber 5 is formed between the high-voltage electrode 1 and the inner wall of the plasma reaction tube 4, the high-voltage electrode 1 and the ground electrode 2 form three discharge zones (A) in the reaction chamber 5, and the high-voltage electrode 1 and the third electrode 3 form four induced electric field zones (respectively BI zone, BII zone, BII zone and BIII zone) in the reaction chamber 5. An air inlet 11 and an air outlet 12 are respectively arranged at both ends of the reaction chamber 5, the BI zone is close to the air inlet 11, and the BIII zone is close to the air outlet 12.

[0084] Among them, the high-voltage electrode 1 includes a quartz tube (outer diameter 5mm, inner diameter 3mm) and iron powder filled in the quartz tube. The plasma reaction tube 4 is a quartz tube with an outer diameter of 12mm and an inner diameter of 8mm, and the discharge gap is 1.5mm. The ground electrode 2 is a metal sheet made of iron, and the length of each ground electrode is 3mm. The third electrode 3 is a metal sheet made of iron, and the length of each third electrode is 3mm. The spacing between the adjacent ground electrodes and the third electrodes is 6mm.

[0085] Along the direction from the air inlet to the air outlet, the four induced electric field zones are set as BI zone, BII zone, BII zone and BIII zone in sequence, among which BI zone is filled with MOF-74 (Ni), BII zone is filled with MIL-101 (Fe), and BIII zone is filled with Cu-BTC, which are filled in the induced electric field zone in the form of small balls with a diameter of 0.5-1 mm.

[0086] The high voltage power supply is a high frequency sinusoidal AC power supply with a frequency of 9kHz and a voltage amplitude of 21.5kV.

[0087] The air to be treated containing 300 ppm ethane is injected into the reaction chamber 5 from the air inlet 11 at a flow rate of 200 ml / min, and is oxidatively converted through BI→A→BII→A→BII→A→BIII in sequence.

[0088] Through testing and calculation, it is known that the light hydrocarbon treatment effect is: ethane conversion rate 98%, CO2 yield 99%, and by-product NOx: not detected.

[0089] Comparative Example 1

[0090] The air to be treated containing 300 ppm ethane was subjected to oxidation conversion treatment according to the method of Example 1, except that no catalyst material was filled in the induction electric field areas (BI area, BII area, BII area and BIII area).

[0091] Through testing and calculation, it is known that the light hydrocarbon treatment effect is: ethane conversion rate 58%, CO2 yield 39%, by-product NOx: 658ppm.

[0092] Comparative Example 2

[0093] The air to be treated containing 300 ppm ethane was subjected to oxidation conversion treatment according to the method of Example 1, except that no catalyst material was filled in the BIII zone.

[0094] Through testing and calculation, it is known that the light hydrocarbon treatment effect is: ethane conversion rate 85%, CO2 yield 58%, by-product NOx: 456ppm.

[0095] Comparative Example 3

[0096] The air to be treated containing 300 ppm ethane is subjected to oxidation conversion treatment according to the method of Example 1, except that no catalyst material is filled in the BI zone.

[0097] Through testing and calculation, it is known that the light hydrocarbon treatment effect is: ethane conversion rate 82%, CO2 yield 73%, by-product NOx: not detected.

[0098] Comparative Example 4

[0099] The air to be treated containing 300 ppm ethane is subjected to oxidation conversion treatment according to the method of Example 1, except that the catalyst materials in the BII zone and the BIII zone are sequentially filled in the discharge zone of the A zone.

[0100] Through testing and calculation, the light hydrocarbon treatment effect is: ethane conversion rate 87%, CO2 yield 60%, by-product NOx: not detected. After 10 minutes of discharge, the catalyst fails, the ethane conversion rate drops to 60%, the CO2 yield drops to 40%, and the by-product NOx: 300ppm.

[0101] Comparative Example 5

[0102] The air to be treated containing 300 ppm ethane was subjected to oxidation conversion treatment according to the method of Example 1, except that Pt / γ-Al2O3 was filled in the BI, BII and BIII zones.

[0103] Through testing and calculation, it is known that the light hydrocarbon treatment effect is: ethane conversion rate 60%, CO2 yield 40%, and by-product NOx: not detected.

[0104] Example 2

[0105] According to the method of Example 1, the air to be treated containing 300 ppm propane was subjected to oxidation conversion treatment.

[0106] Through testing and calculation, it is known that the light hydrocarbon treatment effect is: propane conversion rate 98%, CO2 yield 99%, and by-product NOx: not detected.

[0107] Example 3

[0108] The air to be treated gas containing 300 ppm ethane was subjected to oxidation conversion treatment according to the method of Example 1, except that the distance between the ground electrode and the third electrode adjacent to each other on the reactor used was 8 mm.

[0109] Through testing and calculation, it is known that the light hydrocarbon treatment effect is: ethane conversion rate 91%, CO2 yield 92%, and by-product NOx: not detected.

[0110] Example 4

[0111] The air to be treated gas containing 300 ppm ethane was subjected to oxidation conversion treatment according to the method of Example 1, except that the length of each ground electrode and the third electrode on the reactor used was 2 mm.

[0112] Through testing and calculation, it is known that the light hydrocarbon treatment effect is: ethane conversion rate 90%, CO2 yield 91%, and by-product NOx: not detected.

[0113] Example 5

[0114] The plasma enhanced reaction device is configured according to Example 1, except that Figure 1 As shown, two ground electrodes are configured, three third electrodes are configured, and the high-voltage electrode and the third electrode form three induced electric field regions (respectively, BI region, BII region and BIII region) in the reaction chamber.

[0115] The air to be treated containing 80 ppm ethane is injected into the reaction chamber 5 from the air inlet 11 at a flow rate of 200 ml / min, and is oxidized and converted in sequence through BI→A→BII→A→BIII. The operation is carried out according to the power supply conditions of Example 1.

[0116] Through testing and calculation, it is known that the light hydrocarbon treatment effect is: ethane conversion rate 96%, CO2 yield 97%, and by-product NOx: not detected.

[0117] Example 6

[0118] The plasma enhanced reaction device is configured according to Example 1, except that four ground electrodes are configured, five third electrodes are configured, and the high-voltage electrode and the third electrode form five induced electric field zones in the reaction chamber (respectively BI zone, BII zone, BII zone, BIII zone and BIII zone).

[0119] The air to be treated gas mixed with 100 ppm ethane and 400 ppm n-pentane is injected into the reaction chamber 5 from the air inlet 11 at a flow rate of 200 ml / min, and is oxidized and converted in sequence through BI→A→BII→A→BII→A→BIII→A→BIII. The operation is carried out according to the power supply conditions of Example 1.

[0120] Through testing and calculation, it is known that the light hydrocarbon treatment effect is: ethane conversion rate 98%, n-pentane conversion rate 99%, CO2 yield 99%, and by-product NOx: not detected.

[0121] Example 7

[0122] The plasma enhanced reaction device is configured according to Example 1, except that Figure 3 As shown, three ground electrodes are configured, four third electrodes are configured, and the high-voltage electrode and the third electrode form four induced electric field regions (respectively BI region, BII region, BIII region and BIII region) in the reaction chamber.

[0123] The air to be treated containing 80 ppm of n-pentane is injected into the reaction chamber 5 from the air inlet 11 at a flow rate of 200 ml / min, and is oxidized and converted in sequence through BI→A→BII→A→BIII→A→BIII. The operation is carried out according to the power supply conditions of Example 1.

[0124] Through testing and calculation, it was found that the light hydrocarbon treatment effect was: n-pentane conversion rate 96%, CO2 yield 96%, and by-product NOx: not detected.

[0125] Example 8

[0126] The plasma enhanced reaction device was configured according to Example 1 and the air to be treated containing 300 ppm ethane was subjected to oxidation conversion treatment. The difference was that the BI area was filled with DUT-8 (Ni), the BII area was filled with MIL-100 (Fe), and the BIII area was filled with MOF-808 (Zn), which were filled in the induced electric field area in the form of small balls with a diameter of 0.5-1 mm.

[0127] Through testing and calculation, it is known that the light hydrocarbon treatment effect is: ethane conversion rate 96%, CO2 yield 97%, and by-product NOx: not detected.

[0128] Example 9

[0129] The plasma enhanced reaction device was configured according to Example 1 and the air to be treated containing 300 ppm ethane was subjected to oxidation conversion treatment. The difference was that the BI zone was filled with MIL-125 (Ti), the BII zone was filled with MIL-101 (Fe), and the BIII zone was filled with MIL-101 (Cr), which were filled in the induced electric field zone in the form of small balls with a diameter of 0.5-1 mm.

[0130] Through testing and calculation, it is known that the light hydrocarbon treatment effect is: ethane conversion rate 98%, CO2 yield 99%, and by-product NOx: not detected.

[0131] Example 10

[0132] The plasma enhanced reaction device was configured according to Example 1 and 300 ppm ethane in the air to be treated was subjected to oxidation conversion treatment, except that the BI zone was filled with UIO-66 (Zr), the BII zone was filled with MIL-100 (Fe), and the BIII zone was filled with MOF-74 (Co), which were filled in the induced electric field zone in the form of small balls with a diameter of 0.5-1 mm.

[0133] Through testing and calculation, it is known that the light hydrocarbon treatment effect is: ethane conversion rate 97%, CO2 yield 96%, and by-product NOx: not detected.

[0134] Embodiment 11

[0135] The plasma enhanced reaction device was configured according to Example 1 and the air to be treated containing 300 ppm ethane was subjected to oxidation conversion treatment, except that the BI zone was filled with MIP-202 (Zr), the BII zone was filled with MIL-101 (Fe), and the BIII zone was filled with MOF-808 (Fe), which were filled in the induced electric field zone in the form of small balls with a diameter of 0.5-1 mm.

[0136] Through testing and calculation, it is known that the light hydrocarbon treatment effect is: ethane conversion rate 96%, CO2 yield 98%, and by-product NOx: not detected.

[0137] It can be seen from the results of the above embodiments and comparative examples that the use of the plasma enhanced reaction device described in the present invention to degrade low-concentration light hydrocarbons can achieve better degradation effects. Specifically, the light hydrocarbon conversion rate is high and no byproduct NOx is generated.

[0138] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the protection scope of the present invention.

Claims

1. A plasma enhanced reaction device, characterized in that: The device comprises a coaxially arranged high-voltage electrode (1), two or more ground electrodes (2), two or more third electrodes (3) and a plasma reaction tube (4), wherein the high-voltage electrode (1) is arranged along the axis of the plasma reaction tube (4), the ground electrode (2) and the third electrode (3) are arranged in parallel along the outer wall of the plasma reaction tube (4), and the ground electrode (2) and the third electrode (3) are arranged at intervals from each other; A reaction chamber (5) is formed between the high-voltage electrode (1) and the inner wall of the plasma reaction tube (4); the high-voltage electrode (1) and the ground electrode (2) form more than two discharge zones in the reaction chamber (5); the high-voltage electrode (1) and the third electrode (3) form more than two induced electric field zones in the reaction chamber (5); wherein the induced electric field zones are filled with a metal frame organic material serving as a catalyst.

2. The plasma enhanced reaction device according to claim 1, characterized in that: The number of the third electrodes (3) is greater than the number of the ground electrodes (2) by 1.

3. The plasma enhanced reaction device according to claim 2, characterized in that: The number of the ground electrodes (2) is 2-6, and the number of the third electrodes (3) is 3-7.

4. The plasma enhanced reaction device according to claim 3, characterized in that: An air inlet (11) and an air outlet (12) are respectively provided at both ends of the reaction chamber (5); the induced electric field region close to the air inlet (11) is the BI region, the induced electric field region close to the air outlet (12) is the BIII region, and the induced electric field region between the BI region and the BIII region is the BII region, wherein there is one BI region, and there are one or more BII regions and BIII regions.

5. The plasma enhanced reaction device according to claim 4, characterized in that: The catalyst material filled in the BI zone is used to promote the oxidation of organic molecules; Preferably, the catalyst material filled in the BI zone is selected from at least one of MOF-74 (Ni), MOF-74 (Co), MOF-74 (Mg), DUT-8 (Ni), MIL-125 (Ti), ZIF-67 (Co), UIO-66 (Zr), MIP-202 (Zr) and MOF-808 (Zr).

6. The plasma enhanced reaction device according to claim 4, characterized in that: The catalyst material filled in the BII region is used to enhance the oxidation of organic molecules and / or oxidize long carbon chain molecules into C1 small molecules; Preferably, the catalyst material filled in the BII region is MIL-100 (Fe) and / or MIL-101 (Fe).

7. The plasma enhanced reaction device according to claim 4, characterized in that: The catalyst material filled in the BIII zone is used for continued oxidation to achieve complete oxidation of organic molecules into CO2; Preferably, the catalyst material filled in the BIII zone is selected from one or more of Cu-BTC, MIL-101 (Cr), MOF-74 (Co), MOF-808 (Zn), MOF-808 (Cu), MOF-808 (Fe) and the above catalyst materials loaded with at least one of Pd, Ni and Pt.

8. The plasma enhanced reaction device according to any one of claims 1 to 7, characterized in that: The ground electrode (2) and the third electrode (3) are both made of high temperature resistant conductive metal.

9. The plasma enhanced reaction device according to any one of claims 1 to 7, characterized in that: The conductivity of the ground electrode (2) and the third electrode (3) is 10 at 25°C. 5 -10 8 S / m.

10. The plasma enhanced reaction device according to any one of claims 1 to 7, characterized in that: The plasma reaction tube (4) is an insulating medium tube made of any one of quartz, ceramic, corundum or polytetrafluoroethylene; Preferably, the wall thickness of the plasma reaction tube (4) is not greater than 5 mm.

11. The plasma enhanced reaction device according to any one of claims 1 to 7, characterized in that: The high voltage electrode (1) is a metal rod; or The high voltage electrode (1) comprises an insulating medium tube and conductive metal powder filled in the insulating medium tube; or The high-voltage electrode (1) comprises an insulating medium tube and a conductive metal rod or a conductive metal tube embedded in the insulating medium tube; Wherein, the insulating medium tube is made of quartz, ceramic, corundum or polytetrafluoroethylene.

12. The plasma enhanced reaction device according to any one of claims 1 to 11, characterized in that: The length of each ground electrode is 1-5 times of the discharge gap of the plasma reaction tube.

13. The plasma enhanced reaction device according to any one of claims 1 to 11, characterized in that: The length of each third electrode is 1 to 3 times the discharge gap of the plasma reaction tube.

14. The plasma enhanced reaction device according to any one of claims 1 to 11, characterized in that: The distance between the third electrode and the ground electrode adjacent to each other is 1-5 times of the discharge gap of the plasma reaction tube.

15. The plasma enhanced reaction device according to any one of claims 1 to 14, characterized in that: The discharge gap of the plasma reaction tube is related to the type of gas to be processed. When the main atmosphere of the gas to be treated is air and / or nitrogen, the discharge gap is less than 10 mm; When the main atmosphere of the gas to be treated is argon, the discharge gap is less than 20 mm; When the main atmosphere of the gas to be treated is helium, the discharge gap is less than 30 mm.

16. A method for oxidation conversion of low-concentration light hydrocarbons, characterized in that: The method is implemented in the plasma enhanced reaction device described in any one of claims 1 to 15, and comprises: injecting the gas to be treated into the reaction chamber from the gas inlet for treatment.

17. The method according to claim 16, characterized in that When the complete oxidation of light hydrocarbons in the gas to be treated is difficult and / or the concentration of light hydrocarbons is high, the number of BII zones and / or BIII zones is increased; When the complete oxidation of light hydrocarbons in the gas to be treated is less difficult and / or the concentration of light hydrocarbons is lower, the number of BII zones and / or BIII zones is reduced.

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