A plasma enhanced reaction device and a method for oxidative conversion of low-concentration light hydrocarbons

Abstract

The present invention relates to the field of plasma technology and discloses a plasma-enhanced reaction device and a method for the oxidation conversion of low-concentration light hydrocarbons. The device comprises a coaxially arranged high-voltage electrode, two or more ground electrodes, two or more third electrodes, and a plasma reaction tube. The high-voltage electrode is arranged along the axis of the plasma reaction tube, while the ground electrode and the third electrode are arranged parallel to and spaced from each other along the outer wall of the plasma reaction tube. 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 two or more discharge zones within the reaction chamber, and the high-voltage electrode and the third electrode form two or more induced electric field zones within the reaction chamber. The induced electric field zones are filled with a metal-framed organic material serving as a catalyst. The plasma-enhanced reaction device of the present invention can achieve good oxidation conversion results for low-concentration light hydrocarbons.

Description

Technical Field

[0001] The present invention relates to the field of plasma technology, and in particular to a plasma enhanced reaction device and a method for oxidative conversion of low-concentration light hydrocarbons. 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 high pressure. Plasma method, as an electrically driven external field enhancement method, can enable the chemical transformation of small molecule alkanes to proceed at room temperature and pressure. Its working principle is to apply a high-voltage electric field to the gas to cause gas ionization to 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 500 ppm) 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, ultimately producing CO2 and H2O.

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

[0004] CN108325349A discloses a method for treating VOCs and malodorous gases by a low-temperature plasma coupled adsorption method, comprising the following steps: (1) pretreatment; (2) low-temperature plasma degradation; (3) adsorption treatment, wherein the degradation process in step (2) uses an interval-type 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 low-temperature plasma coupled adsorption method can efficiently degrade the linear hydrocarbons, cycloalkanes, and mercaptans 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, for C1-C5 light hydrocarbon VOCs, the method of post-adsorbent in the plasma zone is mainly used to solve the problem, but the effect of complete degradation has not yet been achieved.

[0005] CN108465354A discloses a low-temperature plasma synergistic catalytic reaction unit and a VOCs treatment device based on a low-temperature plasma synergistic catalytic reactor. These include a low-temperature plasma synergistic catalytic reaction unit and an ozone decomposition catalytic reaction unit. VOCs are converted into CO2 within the low-temperature plasma synergistic catalytic reaction unit. In the ozone decomposition catalytic reaction unit, residual ozone generated by decomposition discharge is used to further decompose incompletely decomposed VOCs, and the purified gas is discharged from the device. Adding a catalyst to the low-temperature plasma synergistic catalytic reaction unit can increase the benzene degradation rate from 15% to over 90%. However, there is still no specific treatment for the degradation of C1-C5 light hydrocarbon VOCs.

[0006] CN110292854B discloses a device and method for catalytic degradation of VOCs by pulsed plasma coupled double fluidized beds. The dual-function discharge electrode has a smooth discharge function electrode on the upper section and a thorn discharge function electrode on the lower section; a high-voltage pulse power supply is loaded on the 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 sieve are selected as carriers to prepare NTP synergistic decomposition 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 350-450 mg / m 3 At an operating voltage of 76 kV, outlet VOC concentrations meet emission standards, with virtually no secondary pollutants. The catalysts are placed in the plasma zone. However, specific degradation of C1-C5 light hydrocarbon VOCs remains undetermined.

[0007] Low-concentration light hydrocarbon VOCs (C1-C5 alkanes) are treated using low-temperature plasma. Current literature reports use a dielectric barrier discharge (DBD) reactor with heating, with or without catalysts added to the plasma. PlasmaChem Plasma Process 2009, 29, 13-25 reports the degradation of 1100 ppm propane / air using a pulsed power supply-driven DBD reactor with heating. At 300 K and 90 J / L of injected energy, the propane degradation rate was 21%, reaching over 95% at 800 K. Plasma Chem Plasma Process 2009, 29, 411-419 reported that the plasma region in a dielectric barrier reactor was filled with Pt / γ-Al2O3 or MnO2 / γ-Al2O3 catalysts and treated with heating as an auxiliary method to treat 100 ppm propane in air. Under the conditions of 60 J / L injection energy at 473 K, the propane degradation rate of the plasma alone was about 55%. At the same temperature, under the condition of the plasma region containing Pt / γ-Al2O3 catalyst, the propane degradation rate was 63%. 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) using low-temperature plasma alone is low, and the oxidation rate is low. Auxiliary heating and catalysts are usually required. For high-throughput 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 the 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] To achieve the above objectives, the present invention provides, in one aspect, a plasma enhanced reaction device, comprising 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 parallel to the outer wall of the plasma reaction tube, and the ground electrode and the third electrode are arranged spaced apart 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 two or more discharge zones in the reaction chamber. The high-voltage electrode and the third electrode form two or more induced electric field zones in the reaction chamber. The induced electric field zones are filled with a metal frame organic material serving as a catalyst.

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

[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 region close to the air inlet is the BI region, the induced electric field region close to the air outlet is the BIII region, and the induced electric field region located 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.

[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 10 at 25°C. 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 no more 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 includes 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 adjacent third electrodes and the ground electrode 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. The method includes: injecting the gas to be treated into the reaction chamber from the gas inlet 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 them apart, and a highly active metal-framed organic material is filled in the induced electric field zone as a catalyst. This type of catalyst is easily destroyed by the filamentary discharge caused by high voltage in the discharge zone. In the induced electric field zone, this type of catalyst can not only maintain a good microstructural morphology, but also, under the action of a weak electric field, the molecular polarization effect can extend the life of the active ions on the surface of the material, prolong the contact and collision time between the molecules to be treated and the active particles, enhance the catalytic effect of this type of material, and thus improve the degradation effect of difficult-to-degrade light hydrocarbons. In a more preferred embodiment, filling different types of metal-framed organic materials as catalysts according to the position of the induced electric field and the reaction principle 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 This is a schematic structural diagram of an embodiment of the plasma enhanced reaction device of the present invention;

[0038] Figure 2 This 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 region; 7. Induction electric field region; 8. Pre-activated catalyst; 9. Enhanced oxidation catalyst; 10. Complete oxidation catalyst; 11. Air inlet; 12. Air outlet. DETAILED DESCRIPTION

[0042] The following describes the specific embodiments of the present invention in detail with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present invention and are not intended to limit the present invention.

[0043] like Figure 1-3As shown, the plasma enhanced reaction device of 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 parallel to 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 two or more discharge zones 6 in the reaction chamber 5. The high-voltage electrode 1 and the third electrode 3 form two or more induced electric field zones 7 in the reaction chamber 5. The induced electric field zones are filled with a metal-framed organic material serving as a catalyst.

[0046] In the plasma-enhanced reaction apparatus of the present invention, preferably, the number of the third electrodes 3 is greater than the number of the ground electrodes 2 by one. 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 near both ends of the plasma reaction tube 4 are 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 region near the air inlet 11 is the BI region, the induced electric field region near the air outlet 12 is the BIII region, and the induced electric field region located between the BI region and the BIII region is the BII region. Among them, there is one BI region, and there are one or more BII regions and BIII regions.

[0048] In one embodiment, Figure 1 As shown, in the reaction chamber 5, from the air inlet end to the air outlet end, the BI area, the A area, the BII area, the A area and the BIII area (also recorded as BI→A→BII→A→BIII) are sequentially arranged, among which the BI area, the BII area and the BIII area are all induced electric field areas, and the A area is all discharge area.

[0049] In another embodiment, Figure 2As shown, in the reaction chamber 5, from the air inlet end to the air outlet end, the areas 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 induced electric field zones, and area A is all discharge zone.

[0050] In another embodiment, Figure 3 As shown, in the reaction chamber 5, from the air inlet end to the air 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 sequentially arranged, and the BI area, BII area and BIII area are all induced 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 oxidize 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, thereby charging the organic molecules passing through the BI zone and playing a pre-activation role; 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] Preferably, 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 embodiment, 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] 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.

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

[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 at 25°C. 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, more preferably iron, copper or tungsten.

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

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

[0059] In the plasma-enhanced reaction apparatus described herein, the plasma reaction tube 4 is not particularly limited and may be any conventionally insulating reaction tube in the art. In the present invention, the plasma reaction tube 4 is preferably an insulating medium tube; more preferably, the insulating medium is quartz, ceramic, corundum, or polytetrafluoroethylene. In one embodiment of the present invention, the plasma reaction tube 4 is a quartz tube; in another embodiment, 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 no more 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, which can be any shape commonly 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 includes an insulating dielectric tube and a conductive metal powder filled within the insulating dielectric tube. The insulating dielectric tube may be made of quartz, ceramic, corundum, or polytetrafluoroethylene. In one embodiment of the present invention, the insulating dielectric tube is a quartz tube; in another embodiment of the present invention, the insulating dielectric tube is a corundum tube.

[0064] There are no particular limitations on the conductive metal powder. In the present invention, the conductive metal powder is preferably one or more of iron, copper, or magnesium. In one embodiment, iron powder is used as the conductive metal powder and filled into an insulating dielectric tube (specifically, a quartz tube) to serve as the central high-voltage electrode. Those skilled in the art may also select other conductive metal powders to be filled into the insulating dielectric tube as needed for use as the central high-voltage electrode.

[0065] In another embodiment, the high voltage electrode 1 includes an insulating medium tube and a conductive metal rod or conductive metal tube embedded in the insulating medium tube. The insulating medium tube can be 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 In one embodiment of the present invention, an iron rod is embedded in a quartz tube and used 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, and 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, the discharge gap of the plasma reaction tube.

[0068] In the plasma enhanced reaction device of the present invention, preferably, the distance between the adjacent third electrode and the ground electrode 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 processed. When the main atmosphere of the gas to be processed is air and / or nitrogen, the discharge gap is less than 10 mm (e.g., 1-10 mm); when the main atmosphere of the gas to be processed is argon, the discharge gap is less than 20 mm (e.g., 1-20 mm); when the main atmosphere of the gas to be processed is helium, the discharge gap is less than 30 mm (e.g., 1-30 mm).

[0070] The present invention also provides a method for oxidative conversion of low-concentration light hydrocarbons, which is implemented in the plasma-enhanced reaction device described above. The method includes: 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 based on the difficulty and concentration of the gas to be treated, as can the number of BI, BII, and BIII zones equipped with different catalyst materials. 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 high, the number of BII 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 low, the number of BII and / or BIII zones is reduced.

[0073] In a specific embodiment, for light hydrocarbons with a low concentration (such as below 100 ppm), the gas to be treated flows into the gas inlet 11 and passes through the corresponding induced 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 air 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 mixed gases (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 zones and discharge zones 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 low-concentration light hydrocarbon treatment method of the present invention. These examples are based on the technical solutions of the present invention and provide detailed implementation methods and specific operating procedures. However, the scope of protection 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] Light hydrocarbon concentrations were determined using an Agilent 7890B gas chromatograph equipped with a six-port valve injector, a flame ionization detector, and an HP-AL / S capillary column (50 m × 0.53 mm, 15 μm). The inlet temperature was 150°C, and the detector temperature was 250°C. The carrier gas was high-purity nitrogen at a flow rate of 6.0 ml / min. The injection volume was 1.0 ml, and the split ratio was 2:1. The column temperature program was as follows: initial temperature 50°C, hold for 5 min, and then increase to 170°C at a rate of 7°C / 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. The high-voltage electrode 1 is arranged along the axis of the plasma reaction tube 4, and the ground electrodes 2 and third electrodes 3 are arranged parallel to the outer wall of the plasma reaction tube 4, with the ground electrodes 2 and third electrodes 3 spaced apart 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) within the reaction chamber 5. The high-voltage electrode 1 and the third electrodes 3 form four induced electric field zones (B1, BII, BII, and BIII) within the reaction chamber 5. An air inlet 11 and an air outlet 12 are provided at each end of the reaction chamber 5, with B1 located near the air inlet 11 and BIII located near the air outlet 12.

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

[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 them, 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 9 kHz and a voltage amplitude of 21.5 kV.

[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 undergoes oxidation conversion in sequence through BI→A→BII→A→BII→A→BIII.

[0088] Through testing and calculation, it was found that the light hydrocarbon treatment effect was: 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 induced electric field areas (BI area, BII area, BII area and BIII area).

[0091] Through testing and calculation, it was found that the light hydrocarbon treatment effect was: ethane conversion rate 58%, CO2 yield 39%, and 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 was found that the light hydrocarbon treatment effect was: ethane conversion rate 85%, CO2 yield 58%, and by-product NOx: 456ppm.

[0095] Comparative Example 3

[0096] 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 BI zone.

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

[0098] Comparative Example 4

[0099] The air to be treated containing 300 ppm ethane was 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 were sequentially filled into the discharge zone of the A zone.

[0100] Testing and calculations revealed that the light hydrocarbon treatment achieved an ethane conversion of 87%, a CO2 yield of 60%, and undetectable NOx byproducts. After 10 minutes of discharge, the catalyst failed, with ethane conversion dropping to 60%, CO2 yield dropping to 40%, and NOx byproducts reaching 300 ppm.

[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 regions.

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

[0104] Example 2

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

[0106] Through testing and calculation, it was found that the light hydrocarbon treatment effect was: 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 adjacent ground electrode and the third electrode on the reactor was 8 mm.

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

[0110] Example 4

[0111] The air to be treated 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 was found that the light hydrocarbon treatment effect was: 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 was injected into the reaction chamber 5 from the air inlet 11 at a flow rate of 200 ml / min, and oxidized and converted in the following order: BI → A → BII → A → BIII. The operation was carried out according to the power supply conditions of Example 1.

[0116] Through testing and calculation, it was found that the light hydrocarbon treatment effect was: 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 regions in the reaction chamber (respectively, BI region, BII region, BII region, BIII region and BIII region).

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

[0120] Through testing and calculation, it was found that the light hydrocarbon treatment effect was: 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 was injected into the reaction chamber 5 from the air inlet 11 at a flow rate of 200 ml / min, and oxidized and converted in the following order: BI→A→BII→A→BIII→A→BIII. The operation was 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 was found that the light hydrocarbon treatment effect was: ethane conversion rate 96%, CO2 yield 97%, and by-product NOx: not detected.

[0128] Example 9

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

[0130] Through testing and calculation, it was found that the light hydrocarbon treatment effect was: 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 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 UIO-66 (Zr), the BII area was filled with MIL-100 (Fe), and the BIII area was filled with MOF-74 (Co), which were filled in the induced electric field area in the form of small balls with a diameter of 0.5-1 mm.

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

[0134] Example 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. The difference was that the BI area was filled with MIP-202 (Zr), the BII area was filled with MIL-101 (Fe), and the BIII area was filled with MOF-808 (Fe), which were filled in the induced electric field area in the form of small balls with a diameter of 0.5-1 mm.

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

[0137] It can be seen from the results of the above examples 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 good degradation effects. Specifically, the light hydrocarbon conversion rate is high and no byproduct NOx is generated.

[0138] The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, various simple variations of the technical solution of the present invention may be made, including combining the various technical features in any other appropriate manner. These simple variations and combinations should also be regarded as disclosed in the present invention and fall within the scope of protection 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 two or more discharge zones in the reaction chamber (5); the high-voltage electrode (1) and the third electrode (3) form two or more 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 near the air inlet (11) is the BI region, the induced electric field region near 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 region is used to promote the oxidation of organic molecules.

6. The plasma enhanced reaction device according to claim 5, characterized in that: 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).

7. 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.

8. The plasma enhanced reaction device according to claim 7, characterized in that: The catalyst material filled in the BII region is MIL-100 (Fe) and / or MIL-101 (Fe).

9. The plasma enhanced reaction device according to claim 4, characterized in that: The catalyst material filled in the BIII zone is used for continuing oxidation to achieve complete oxidation of organic molecules into CO2.

10. The plasma enhanced reaction device according to claim 9, characterized in that: 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.

11. The plasma enhanced reaction device according to any one of claims 1 to 10, characterized in that: The ground electrode (2) and the third electrode (3) are both made of high-temperature resistant conductive metal.

12. The plasma enhanced reaction device according to any one of claims 1 to 10, 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.

13. The plasma enhanced reaction device according to any one of claims 1 to 10, characterized in that: The plasma reaction tube (4) is an insulating medium tube made of any one of quartz, ceramic, corundum or polytetrafluoroethylene.

14. The plasma enhanced reaction device according to claim 13, characterized in that: The wall thickness of the plasma reaction tube (4) is no more than 5 mm.

15. The plasma enhanced reaction device according to any one of claims 1 to 10, 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.

16. The plasma enhanced reaction device according to any one of claims 1 to 10, characterized in that: The length of each ground electrode is 1-5 times the discharge gap of the plasma reaction tube.

17. The plasma enhanced reaction device according to any one of claims 1 to 10, characterized in that: The length of each third electrode is 1-3 times the discharge gap of the plasma reaction tube.

18. The plasma enhanced reaction device according to any one of claims 1 to 10, characterized in that: 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.

19. The plasma enhanced reaction device according to any one of claims 1 to 10, 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.

20. A method for oxidation conversion of low-concentration light hydrocarbons, characterized in that: The method is implemented in the plasma enhanced reaction device according to any one of claims 1 to 19, and comprises: injecting the gas to be treated into the reaction chamber from the gas inlet for treatment.

21. The method according to claim 20, characterized in that 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.

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