Plasma reactor and method for converting lower alkanes

Abstract

The present application relates to the technical field of low carbon alkane conversion, and particularly relates to a kind of plasma reactor and the method for low carbon alkane conversion, the plasma reactor includes reactor body and at least one electrode arranged in the reactor body, it further includes the flow guide tube arranged in the reactor body, the distance from the upper end of the flow guide tube to the lower part of the reactor body is greater than the distance from the lower end of at least one electrode to the lower part of the reactor body, and the lower end of the flow guide tube extends to the downstream of reactant stream direction.The flow guide tube is additionally arranged in the reactor body, so that the raw material gas more concentratedly passes through the plasma area, and the flow guide tube reduces the flow area, improves the inlet gas flow rate, which is conducive to improving the non-equilibrium type of sliding arc;it can improve the conversion rate of low carbon alkane in low carbon alkane conversion, and is especially suitable for methane conversion.

Description

Technical Field

[0001] This invention relates to the field of low-carbon alkane conversion technology, specifically to a plasma reactor and a method for low-carbon alkane conversion. Background Technology

[0002] Research on plasma methane conversion technology began in China in the 1980s, and patents gradually emerged starting in 2000. For example, CN1180058C, published by Tianjin University, discloses a method for producing gasoline from methane and carbon dioxide using plasma conversion. This method adds CO2 as another reactant, and gasoline is the main product. In this study, methane will be used as the raw material, or an inert gas may be added, without introducing a second reactant. The target product is mainly low-carbon hydrocarbons. CN1235846C discloses a method for producing acetylene from methane-containing gas via thermal plasma cracking, which mainly uses methane as the raw material and acetylene as the main byproduct.

[0003] The Southwest Chemical Research and Design Institute has published a series of patents related to plasma methane cracking (CN210367505U, CN109294284B, CN106478332B, CN101921163B), primarily focusing on the development of plasma conversion processes for methane to produce carbon black or acetylene and hydrogen, with an emphasis on process design and optimization. Tsinghua University, Taiyuan University of Technology, and Xinjiang Tianye Group have jointly developed a plasma coal cracking process for acetylene production (CN203582763U, CN102068953B, CN101734620B, CN101550057A, CN101734995B, CN1240647C), mainly using coal as raw material and natural gas as an auxiliary agent for acetylene and hydrogen production, with hydrogen as the working gas. Zhejiang University has mainly developed a method for online plasma decoking (CN104056828A, CN104056829B), which can introduce CO2 or H2 to remove carbon deposits on the electrode surface. They have also developed a rotating arc plasma cracking method for producing acetylene from methane (CN103333044B, CN101844744B), in which the working gas rotates into the discharge gap, and is driven by an external magnetic field to cause millisecond-level cracking.

[0004] CN106925086A discloses a plasma degradation treatment device for organic waste gas. This plasma treatment device is a plasma reactor, including a reactor cylinder, a gas inlet at the top of the reactor cylinder, a gas outlet at the bottom of the reactor, a plasma discharge electrode located inside the reactor cylinder, and a power interface for supplying power to the plasma discharge device. The reactor cylinder is equipped with an energy utilization device that expands the area and length of the sliding arc. The energy utilization device is an arc-expanding rod, an arc-expanding plate, or a combination of both. However, when this reactor is used for the directional conversion of methane, the methane conversion rate is low, and the olefin selectivity is low.

[0005] In summary, existing plasma reactors used for methane conversion all suffer from low methane conversion rates and low target selectivity. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of existing plasma reactors used in methane conversion, which have low methane conversion rates and low target selectivity. This invention provides a plasma reactor and a method for converting low-carbon alkanes, in which the plasma reactor achieves high methane conversion rates and high target selectivity.

[0007] To achieve the above objectives, a first aspect of the present invention provides a plasma reactor, comprising a reactor body and at least one electrode disposed within the reactor body, and further comprising a flow guide tube disposed within the reactor body, wherein the distance from the upper end of the flow guide tube to the lower part of the reactor body is greater than the distance from the lower end of the at least one electrode to the lower part of the reactor body, and the lower end of the flow guide tube extends downstream in the direction of the reactant flow.

[0008] A second aspect of the present invention provides a method for converting low-carbon alkane, the method comprising: introducing low-carbon alkane into a reactor for a discharge reaction; wherein the reactor is the plasma reactor described in the first aspect above.

[0009] The inventors of this invention, considering the need for later process scale-up, focused on the development of a sliding arc plasma reactor. By adding a guide tube to the reactor body, the feed gas can pass through the plasma region more concentratedly. The guide tube also reduces the flow area and increases the inlet gas velocity, which is beneficial for improving the non-equilibrium type of the sliding arc. It can improve the conversion rate of low-carbon alkane in the conversion of low-carbon alkane, and is especially suitable for methane conversion. Attached Figure Description

[0010] Figure 1 This is a schematic diagram of the structure of the plasma reactor of the present invention in the first specific embodiment;

[0011] Figure 2 This is a schematic diagram of the structure of the plasma reactor of the present invention in a second specific embodiment;

[0012] Figure 3 This is a schematic diagram of the third specific embodiment of the plasma reactor of the present invention;

[0013] Figure 4 This is a schematic diagram of the structure in which the electrodes and insulating base cooperate with each other in the plasma reactor of the present invention.

[0014] Explanation of reference numerals in the attached figures

[0015] 1-Reactor shell 2-Flow guide tube 3-Electrode

[0016] 4-Jacket 5-Heat exchange chamber 6-Gas nozzle

[0017] 7-Reactant outlet; 8-Catalyst bed; 9-Heat exchange medium inlet

[0018] 10-Heat exchange medium outlet

[0019] 101-Reactor body; 102-Insulation seat; 103-Reaction chamber

[0020] 104-Reaction cavity 301-Blade edge 302-Blade body

[0021] 303 - Electrode post; 304 - Positioning screw Detailed Implementation

[0022] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0023] In this invention, unless otherwise stated, directional terms such as "upper" and "lower" generally refer to the direction of reaction material flow (e.g., Figure 1-3 Upstream or downstream (as shown in the top-down direction). "Inner" and "outer" refer to the inner and outer contours of the corresponding components.

[0024] The first aspect of the present invention provides a plasma reactor, such as Figure 1-3 As shown, the reactor includes a reactor body 101 and at least one electrode 3 disposed within the reactor body 101. It also includes a flow guide 2 disposed within the reactor body 101. The distance from the upper end of the flow guide 2 to the lower part of the reactor body 101 is greater than the distance from the lower end of the at least one electrode 3 to the lower part of the reactor body 101 (meaning the height of the upper end of the flow guide 2 is higher than the height of the lower end of the at least one electrode 3). The lower end of the flow guide 2 extends downstream in the direction of the reactant flow. In this invention, the portion located inside the flow guide 2 is the inner reaction chamber 103, and the portion located outside the flow guide 2 and inside the reactor body 101 is the outer reaction chamber 104. The flow guide 2 of this invention guides the raw material gas to concentrate it within the inner reaction chamber 103, thereby better promoting the reaction, and the reaction mainly occurs within the inner reaction chamber 103.

[0025] According to the present invention, preferably, at least one electrode 3 is arranged intersecting the guide tube 2 or the curved surface on which the guide tube 2 is located. In the present invention, the curved surface on which the guide tube 2 is located is a curved surface formed by extending both ends of the guide tube 2 in their respective directions.

[0026] Of course, the electrode 3 and the guide tube 2 or the curved surface where the guide tube 2 is located can also be arranged in parallel (i.e., without intersecting), for example, the electrode 3 is located on the inner side of the curved surface where the guide tube 2 is located; in this invention, it is preferred to arrange them in an intersecting manner.

[0027] The phrase "at least one electrode 3 is intersected with the guide tube 2 or the curved surface where the guide tube 2 is located" refers to the following two situations: 1. such as Figure 1-2 As shown, at least one electrode 3 is arranged intersecting with the guide tube 2. 2. As Figure 3 As shown, at least one electrode 3 is arranged to intersect with the curved surface where the guide tube 2 is located.

[0028] According to a preferred embodiment of the present invention, such as Figure 1 As shown, the upper end of the guide tube 2 is located above the upper end of the electrode 3; more preferably, the upper end of the guide tube 2 extends to the upper end of the plasma reactor. This preferred design facilitates the concentrated flow of more feed gas into the plasma region, thereby further improving the methane conversion rate.

[0029] According to another preferred embodiment of the present invention, such as Figure 2 and Figure 3 As shown, the upper end of the guide tube 2 is located between the upper and lower ends of the electrode 3, and the distances from the upper end of the guide tube 2 to the upper and lower ends of the electrode 3 are L1 and L2, respectively (e.g., ...). Figure 2 The label shown is Figure 3 (Not marked in the text), the ratio of L1 to L2 is 0.1-10:1, more preferably 0.5-1:1.

[0030] Preferably, the guide tube 2 is provided with slots for the electrode 3 to move in the vertical and / or horizontal directions, ensuring that the electrode 3 can move fully within the guide tube 2. It is understood that the vertical and horizontal directions refer to the directions shown in the figures, where the horizontal direction is perpendicular to the guide tube 2. In this invention, each slot corresponds to one electrode 3.

[0031] According to the present invention, the plasma reactor further includes a gas nozzle 6 and a reactant outlet 7. Preferably, the gas nozzle 6 and the reactant outlet 7 are located at opposite ends of the reactor body 101.

[0032] More preferably, the gas nozzle 6 and the reactant outlet 7 are located at the upper and lower ends of the reactor body 101, respectively, so that the gas inlet direction of the reactor body 101 is top-inlet and bottom-outlet. Of course, the gas inlet direction can also be adjusted to bottom-inlet and top-outlet according to actual needs. It is understood that the gas nozzle 6 is used to transport raw material gas (e.g., at least one of hydrogen, nitrogen, and methane).

[0033] According to the present invention, preferably, the distance from the upper end of the guide tube 2 to the lower part of the reactor body 101 is not greater than the distance from the lower end of the gas nozzle 6 to the lower part of the reactor body 101. That is, the height of the upper end of the guide tube 2 is higher than the height of the lower end of the gas nozzle 6. Under this preferred embodiment, the reactant gas (i.e., the raw material gas) diffuses to the outer reaction chamber 104 as little as possible, and instead concentrates more into the inner reaction chamber 103, thereby further improving the methane conversion rate.

[0034] According to the present invention, preferably, the plasma reactor further includes an insulating base 102 connected to the upper part of the reactor body 101, and the electrode 3 and the gas nozzle 6 are respectively disposed on the insulating base 102.

[0035] According to the present invention, preferably, the electrode 3 is movably connected to the insulating base 102 for adjusting the position of the electrode 3 in the horizontal or vertical direction, thereby facilitating the adjustment of the spacing parameters between the gas nozzle 6 and the electrode 3 (e.g., minimum spacing h, shortest distance H between the electrode 3 and the gas nozzle 6).

[0036] The present invention offers a wide range of possible connection methods between the electrode 3 and the insulating base 102, as long as the electrode 3 can be adjusted in either the horizontal or vertical direction; preferably, such as Figure 4 As shown, the electrode 3 is connected to the insulating base 102 by a positioning screw 304. The positioning screw 304 is provided with multiple positioning holes. The horizontal position of the electrode 3 can be adjusted by changing the relative position between the positioning holes and the electrode 3. The electrode 3 is connected to the insulating base 102 by an electrode post 303 (e.g., threaded connection). The position of the electrode 3 in the vertical direction can be adjusted by adjusting the position of the electrode post 303 up and down.

[0037] In this invention, preferably, the electrode 3 is a blade electrode (it is understood that, as Figure 1As shown, electrode 3 includes a blade and electrode post 303. The blade includes a cutting edge 301 and a blade body 302. The cutting edge 301 of the blade electrode is positioned with one side facing the central axis of the reactor body 101. The cutting edge 301 can be arc-shaped or straight, preferably the former. This invention does not impose any limitations on the material of the electrode 3; for example, the blade can be made of 316L stainless steel or tungsten-cerium alloy. The preferred size of the electrode 3 is 50-100 mm in length (length refers to...). Figure 1 The blade of the electrode shown is 2-4 mm thick and has a vertical length.

[0038] In this invention, those skilled in the art can select the position and size of the gas nozzle 6 according to actual needs. The gas nozzle 6 is preferably located at the center of the insulating base 102. The diameter of the gas nozzle 6 is preferably 1-2 mm.

[0039] In this invention, it is understood that the reactor body 101, the insulating base 102, the inner reaction cavity 103, and the outer reaction cavity 104 together constitute the reactor shell 1. Of course, the reactor body 101 can be an integrally formed cylinder with an opening only at the top (or a cylindrical structure with an irregular shape at the bottom, such as...). Figure 1 The inverted conical shape shown can also be composed of a cylindrical shape (i.e., a cylinder open at both ends) and a bottom part. Generally, it is required that the gaps (which can be understood as the distances from the ends of the electrode blades) of each end of the cylinder (i.e., the upper and lower ends) from the electrodes must be greater than twice the minimum discharge gap (which can be understood as the minimum distance between the two blades) to avoid affecting the normal generation of plasma. This is existing technology and will not be elaborated further here. The length of the reactor body 101 (which can be understood as the length refers to...) Figure 1 The length (in the vertical direction shown) is preferably 150-300 mm. In this invention, this length refers to... Figure 1 The length of the cylindrical portion shown in the vertical direction does not include the length of the inverted conical portion at the bottom of the reactor body 101. It is understood that when the reactor body 101 is a conventional cylindrical structure, the length refers to the overall length of the cylindrical structure. This invention does not limit the length of the inverted conical portion; those skilled in the art can freely choose it as needed.

[0040] In this invention, the material of the reactor body 101 can be selected according to actual needs, such as quartz glass or corundum, to facilitate providing a sealed space for the reaction. Those skilled in the art can select the shape and size of the insulating base 102 according to actual needs; for example, it can be circular, with a preferred diameter of 70-100 mm. It is understood that, according to actual needs, the insulating base 102 can have a power supply groove and terminals for connecting the electrodes, and the distance between the electrode mounting position and the outer edge of the insulating base 102 must ensure that the discharge is not affected.

[0041] In this invention, the plasma reactor further includes an inlet pipe connected to the gas nozzle 6 for supplying a raw material gas (e.g., at least one of hydrogen, nitrogen, and methane). It is understood that the inlet pipe can control the flow rate of the raw material gas; this is prior art and will not be elaborated upon here.

[0042] According to the present invention, preferably, the number of electrodes 3 is two or more. Preferably, each electrode 3 has the same positional relationship with the guide tube 2, and the plurality of electrodes 3 are evenly arranged along the circumferential direction of the reactor body 101.

[0043] Preferably, the electrodes 3 are arranged in pairs, with the two electrodes symmetrically distributed on opposite sides of the axis of the gas nozzle 6. The distance between the two electrodes gradually increases in the direction from the gas nozzle 6 to the reactant outlet 7, which facilitates better guidance of the raw material gas for reaction in the plasma region. It is understood that the electrodes 3 extend along the direction from the gas nozzle 6 to the reactant outlet 7.

[0044] In a preferred embodiment of the present invention, the maximum inner diameter D of the reactor body 101 is 70-100 mm, and the length is 150-300 mm; the minimum distance w between the two electrodes in the paired electrodes is 1-4 mm, and the shortest distance H between the electrode 3 and the gas nozzle 6 is 10-50 mm. This preferred embodiment facilitates the formation of a discharge arc between the two electrodes.

[0045] Preferably, the included angle α between the two electrodes in the paired electrodes is 30°-60°. In this invention, the included angle α between the two electrodes refers to the angle between the tangents on the inner surfaces of the two electrodes. For example, when the inner surfaces of the two electrodes are planes (which can be understood as straight lines), the included angle refers to the angle formed by extending the inner surfaces of the two electrodes. This preferred embodiment is more conducive to the formation of a larger sliding area of ​​the electric arc along the electrodes.

[0046] Preferably, within the same horizontal plane, the paired electrodes 3 are arranged in one or three pairs, and the one or three pairs of electrodes are evenly distributed along the circumference of the reactor body 101. When the paired electrodes 3 are one pair, the included angle between the two electrodes is 180°, and when the paired electrodes 3 are three pairs, the included angle between two adjacent electrodes is 60°.

[0047] According to the present invention, preferably, such as Figure 4 As shown, each electrode 3 is connected to an electrode post 303. The inner diameter of the guide tube 2 is d, the minimum distance between the two paired electrodes is w, and the distance between the two electrode posts connected to the two electrodes is W. The guide tube 2 satisfies: W > d > w. Under this preferred scheme, the raw material gas can be guided more effectively.

[0048] Preferably, the maximum inner diameter of the reactor body (101) is D, and the guide tube 2 satisfies: d = (0.1-0.9) × W, W = (0.5-0.9) × D.

[0049] In this invention, the guide tube 2 can have various specifications (i.e. different diameters) to meet the required inner diameter. Those skilled in the art can replace the guide tube 2 with different specifications according to their needs.

[0050] According to the present invention, those skilled in the art can freely choose the size relationship between the guide tube 2 and the reactor body 101 according to actual needs, as long as it is conducive to promoting the methane conversion rate and / or the selectivity of reaction products; preferably, the ratio of the inner diameter d of the guide tube 2 to the maximum inner diameter D of the reactor body 101 is 0.05-0.8:1, more preferably 0.3-0.6:1.

[0051] According to the present invention, the lower end of the guide tube 2 may extend to the lower part of the reactor body 101, or its lower end may not contact the lower part of the reactor body 101. Preferably, the lower end of the guide tube 2 is connected to the lower part of the reactor body 101. It is understood that the present invention does not limit the connection method, and those skilled in the art can freely choose; preferably, it is a detachable connection to facilitate the replacement of guide tubes 2 of different specifications.

[0052] According to a preferred embodiment of the present invention, a catalyst bed 8 filled with catalyst is provided at the lower part of the guide tube 2. In this preferred embodiment, the catalyst bed can also be heated by the heat generated by plasma, thereby performing hydrogenation or carbonylation reactions on the plasma exhaust gas (which can be understood to be a gas mixture after the discharge reaction) to finally obtain the target product (e.g., unsaturated hydrocarbons or acrylic acid).

[0053] Preferably, the lower part of the reactor body 101 is an inverted cone.

[0054] According to a preferred embodiment of the present invention, the plasma reactor further includes a jacket 4 for the flow of the heat exchange medium, the jacket 4 being disposed outside the reactor body 101. This preferred embodiment facilitates the recovery and utilization of heat generated by the discharge reaction occurring in the plasma region, while maintaining the temperature required for subsequent reactions, thereby further improving the methane conversion rate and reaction product selectivity based on heat recovery. It is understood that the jacket 4 and the reactor body 101 together form a heat exchange cavity 5.

[0055] Preferably, the lower end of the guide tube 2 passes through the lower end of the reactor body 101 and connects to the lower end of the jacket 4, so that the heat exchange medium surrounds the outside of the reactor body 101 and the lower end of the guide tube 2. In this preferred embodiment, the jacket 4 is located both outside the plasma region and outside the catalyst bed, so as to fully heat or extract heat from the catalyst catalytic reaction while exchanging heat for the discharge reaction.

[0056] According to the present invention, preferably, the plasma reactor further includes a heat exchange medium outlet 10 disposed on the upper part of the jacket 4 and a heat exchange medium inlet 9 disposed on the lower part of the jacket 4, thereby realizing convective heat exchange and achieving better heat exchange effect.

[0057] In this invention, the plasma reactor can be used in any field where a reaction can be carried out via a plasma reactor, and there are no limitations on this. For example, it is suitable for low-carbon alkanes, and particularly for methane conversion reactions. The detailed description of the plasma reactor above uses methane conversion as an example, but the invention is not limited thereto.

[0058] In this invention, the plasma reactor is used in methane conversion. On the one hand, it can be used to prepare unsaturated hydrocarbons (e.g., ethylene) or alkanes (e.g., ethane); on the other hand, it can also be used to prepare products such as olefins (it is understood that those skilled in the art can introduce the required raw materials according to the desired product).

[0059] A second aspect of the present invention provides a method for converting low-carbon alkane, the method comprising: introducing low-carbon alkane into a reactor for a discharge reaction; wherein the reactor is the plasma reactor described in the first aspect above.

[0060] In this invention, the low-carbon alkane can be C1-C4 alkane, including straight-chain or branched-chain C1-C4 alkane, and this invention does not limit this.

[0061] According to the present invention, preferably, the conditions for the discharge reaction include: a discharge voltage of 1-5 kV, a discharge frequency of 5-30 kHz, and a discharge input energy of 20-100 kJ / L low-carbon alkanes. It is understood that the discharge reaction is continuous.

[0062] According to the present invention, preferably, the discharge reaction is carried out in an environment with an oxygen content of less than 5% by volume, and more preferably in an oxygen-free environment. Under this preferred embodiment, no CO2 is generated, the yield of the target product is high, there is no risk of combustion or explosion, and the process is safe, green, and environmentally friendly.

[0063] More preferably, the method further includes: first introducing an oxygen-free gas (e.g., nitrogen) to replace the gas in the plasma reactor, and then introducing the low-carbon alkane to provide an oxygen-free environment.

[0064] According to a preferred embodiment of the present invention, the method further includes: filling or not filling the bottom of the guide tube 2 with a catalyst. For example, filling with a catalyst facilitates the conversion of low-carbon alkanes into corresponding olefins or alkenoic acids, while not filling with a catalyst facilitates the conversion of low-carbon alkanes into corresponding alkynes. Those skilled in the art can choose according to actual needs.

[0065] According to another preferred embodiment of the present invention, the method further includes: introducing or not introducing a heat exchange medium into a jacket 4 disposed outside the reactor body 101; more preferably, selecting the temperature of the heat exchange medium according to the target product requirements.

[0066] The heat exchange medium can be water (e.g., saturated water) or reaction raw materials, such as at least one of the following: raw material gas, boiling water, heat transfer oil, and cooling water. Using raw material gas for heat exchange can lower the temperature inside the reactor body 101 and effectively utilize the heat generated by the plasma, further reducing plasma energy consumption. Using boiling water for heat exchange can maintain a constant temperature in the reactor body 101, suitable for temperatures above 200°C, and can generate steam as a byproduct of the heat, improving the economic efficiency of the plasma process. Heat transfer oil is mainly used to cool or provide the catalyst with the temperature required for the reaction, suitable for reactions with temperatures above 100°C but below 200°C. Ordinary water can be used for temperature requirements below 100°C. Preferably, the heat exchange medium is at least one of boiling water, cooling water, reaction raw materials, and heat transfer oil.

[0067] According to a preferred embodiment of the present invention, the method further includes: first introducing a heat exchange medium into a jacket 4 disposed outside the reactor body 101, then filling a catalyst at the bottom of the guide tube 2, and then introducing the low-carbon alkane.

[0068] According to another preferred embodiment of the present invention, a catalyst is first loaded at the bottom of the guide tube 2, then the heat exchange medium is introduced into the jacket 4 located outside the reactor body 101, and then the low-carbon alkanes are introduced. This preferred scheme is beneficial for improving methane conversion and balancing the selectivity of the target product.

[0069] Further research by the inventors revealed that the above-mentioned method can be used to flexibly control the selectivity of the target product in the reactor provided by this invention, thereby meeting different market demands.

[0070] In this invention, there are no limitations on the catalyst used. Those skilled in the art can select existing catalysts according to their needs, such as hydrogenation catalysts or carbonylation catalysts, as long as they can achieve the purpose of hydrogenation or carbonylation reaction. Preferably, the catalyst is at least one of Pd-based catalysts, Ag-based catalysts, and Ni-based catalysts. The catalyst is preferably in particulate form, and more preferably, the particle size is 1-5 mm.

[0071] In this invention, those skilled in the art can select the heat exchange medium according to the reaction temperature required by the corresponding catalyst. For example, warm water can be used for heating or heat extraction in Pd-based catalysts, heat transfer oil can be used for heating in Ag-based high-temperature catalysts, and boiling water is required for heating in Ni-based catalysts.

[0072] According to a preferred embodiment of the present invention, the method further includes: performing a hydrogenation or carbonylation reaction after the discharge reaction.

[0073] Preferably, the conditions for the hydrogenation or carbonylation reaction include: a hydrogen feed flow rate to low-carbon alkane feed flow rate volume ratio of 0-1:1, and a hydrogenation reaction temperature of 30-200°C; optionally, the CO feed flow rate to low-carbon alkane feed flow rate volume ratio is 0.5-1.5:1, and the carbonylation reaction temperature is 50-250°C. The introduced CO is used for the carbonylation reaction to produce acrylic acid, and can be introduced through a gas nozzle or by adding a side-feed pipe to the plasma reactor (e.g., inserting a side-feed pipe between the electrode and the catalyst bed). The hydrogen introduced in the hydrogenation reaction can be introduced separately or together with methane into the reactor body 101.

[0074] More preferably, the hydrogenation reaction temperature is 50-150°C, or the carbonylation reaction temperature is 100-200°C.

[0075] This invention places no restrictions on the duration of the discharge reaction or the hydrogenation or carbonylation reaction; those skilled in the art can freely choose according to actual needs. Preferably, the duration of the hydrogenation or carbonylation reaction is the same as the duration of the discharge reaction. This is because the discharge reaction and the hydrogenation or carbonylation reaction occur respectively in the upper and lower parts of the reactor body 101. After the discharge reaction is completed, the products of the discharge reaction naturally flow to the catalyst bed for hydrogenation or carbonylation. In this invention, the hydrogenation or carbonylation reaction can proceed continuously and stably.

[0076] In this invention, the discharge reaction and the hydrogenation reaction or carbonylation reaction are both carried out in the guide tube. The temperature of the hydrogenation reaction or carbonylation reaction can be provided by the temperature provided by the discharge reaction, or it can be provided by the heat exchange medium in conjunction with the temperature provided by the discharge reaction. Those skilled in the art can choose freely according to actual needs.

[0077] In this invention, the hydrogenation or carbonylation reaction is preferably carried out in the presence of a reduced catalyst. There are no restrictions on the reduction conditions; conventional reduction conditions in the art can be used, as long as the catalyst can be reduced. Preferably, the catalyst reduction is carried out in a plasma reactor.

[0078] According to the present invention, preferably, the hydrogenation or carbonylation reaction is carried out in an environment with an oxygen content of less than 5 volumes, and more preferably in an oxygen-free environment. Under this preferred embodiment, no CO2 is generated, the yield of the target product is high, there is no risk of combustion or explosion, and the process is safe, green, and environmentally friendly.

[0079] According to a preferred embodiment of the present invention, such as Figure 1-3 As shown, the method for converting low-carbon alkane includes the following steps:

[0080] (1) In the aforementioned plasma reactor, select the required specifications of the guide tube 2 (i.e., select a guide tube with different inner diameter and height), and adjust the electrode structure to meet the required electrode structure parameters (e.g., the shortest distance H between the electrode 3 and the gas nozzle 6, and the minimum distance w between the two electrodes in a pair of electrodes).

[0081] (2) A catalyst is filled in the lower part of the reactor body 101 to form a catalyst bed 8;

[0082] (3) First, heat exchange medium is introduced into the jacket 4; then oxygen-free gas (e.g., inert gas, preferably nitrogen) is introduced into the reactor body 101 through the gas nozzle 6 to replace the oxygen in the reactor body 101 and obtain an oxygen-free environment.

[0083] (4) Then hydrogen (and an inert gas, preferably nitrogen, can be introduced at the same time) is introduced through gas nozzle 6 to reduce the catalyst;

[0084] (5) Next, raw material gas (preferably methane and hydrogen, to facilitate direct hydrogenation after methane conversion) is introduced through gas nozzle 6 to carry out a discharge reaction (when adjusting the discharge reaction parameters, it is preferable to first increase the voltage and then decrease the voltage to the required voltage value, the difference between the increased voltage value and the required voltage value being 0.5-1kV). The tail gas obtained from the discharge reaction naturally enters the catalyst bed 8 for hydrogenation or carbonylation reaction to obtain the target product. Under this preferred scheme, the selectivity of the target product is higher, the methane conversion rate is higher, and the carbon deposition is low or there is no obvious carbon deposition (generally, a carbon deposition of less than 1% is called no obvious carbon deposition).

[0085] The present invention will be described in detail below through embodiments. The formulas for calculating ethylene selectivity are: (molar amount of ethylene outlet) * 2 / (molar amount of methane inlet - molar amount of methane outlet); the formulas for calculating ethane selectivity are: (molar amount of ethane outlet) * 2 / (molar amount of methane inlet - molar amount of methane outlet); the formulas for calculating acetylene selectivity are: (molar amount of acetylene outlet) * 2 / (molar amount of methane inlet - molar amount of methane outlet); C3 + The formula for calculating selectivity is: Σ(C n (Export molar quantity) * n / (Methane import molar quantity - Methane export molar quantity), n = 3 - 5.

[0086] Example 1

[0087] This embodiment illustrates the plasma reactor and the method for converting low-carbon alkane according to the present invention.

[0088] (1) In Figure 1 In the plasma reactor shown, the inner diameter d of the guide tube 2 is 40 mm. The upper end of the guide tube 2 is connected to the electrode 3 (i.e., the height of the guide tube is equal to the height of the lower end of the gas nozzle 6). The lower end of the guide tube 2 passes through the lower end of the reactor body 101 and is connected to the lower end of the jacket 4. The maximum inner diameter D of the reactor body 101 is 70 mm, and the bottom of the reactor body 101 is inverted conical; where d:D = 0.7:1. The electrode 3 consists of two blade electrodes (the included angle α between the paired electrodes is 45°, the blade 301 is arc-shaped, and the distance between the two electrodes gradually increases in the direction from the gas nozzle 6 to the reactant outlet 7) and is horizontally symmetrically arranged. Figure 4 The positioning screw shown adjusts the structure of electrode 3 so that the shortest distance H between electrode 3 and gas nozzle 6 is 1cm, the minimum distance w between the two electrodes is 2mm, and the distance W between the two electrode posts 303 connected to the two electrodes is 60mm.

[0089] (2) A hydrogenation catalyst (specifically Pd-Ag / Al2O3, wherein, based on the total amount of catalyst and calculated as oxides, the content of Pd is 0.1 wt% and the content of Ag is 0.5 wt%) is packed into the lower part of the reactor body 101, approximately 60 g. The catalyst particle size is 3-5 mm.

[0090] (3) First, heat exchange medium water is introduced into the jacket 4 through the heat exchange medium inlet 9; then oxygen-free gas (nitrogen, inlet flow rate of 3L / min) is introduced into the reactor body 101 through the gas nozzle 6 for 30 minutes to replace the oxygen in the reactor body 101 and obtain an oxygen-free atmosphere.

[0091] (4) Then, hydrogen and nitrogen (2 L / min nitrogen and 1 L / min hydrogen) are introduced into the reactor body 101 through the gas nozzle 6. The power is turned on, and the voltage and frequency are adjusted. First, the voltage is increased to 2 kV and the frequency is adjusted to 25 kHz. Discharge is started, and the carbonylation catalyst is reduced for about 2 hours. The catalyst color turns basically black. The reduction is then ended, and the power is turned off.

[0092] (5) Next, the raw material gas (methane 1L / min, hydrogen 3L / min) is introduced into the reactor body 101 through the gas nozzle 6. The power is turned on, and the voltage and frequency are adjusted. First, the voltage is increased to 2kV, and the frequency is adjusted to 25kHz (i.e., the discharge frequency). Discharge begins, and the voltage is adjusted to the specified 1.2kV (i.e., the discharge voltage). At this time, the power is about 300W (i.e., the discharge power). The discharge reaction is carried out, and the temperature of the catalyst bed (i.e., the hydrogenation reaction temperature) packed in the lower part of the reactor body 101 is controlled between 50-150℃ by the heat exchange medium water. The product after discharge reaction and hydrogenation (hereinafter referred to as tail gas) is discharged from the reactant outlet 7.

[0093] After 8 hours, the tail gas was analyzed by gas chromatography. The results showed a methane conversion rate of 40%, ethylene selectivity of 90%, ethane selectivity of 2%, and C3... + 8%, with no obvious carbon buildup.

[0094] Example 2

[0095] The method is carried out according to Example 1, except that the voltage is adjusted to a specified 1.6kV.

[0096] Analysis of the exhaust gas revealed a methane conversion rate of 35%, an ethylene selectivity of 85%, an ethane selectivity of 5%, and a C3 conversion rate of [missing information]. + 10%, with no obvious carbon buildup.

[0097] Example 3

[0098] The method is carried out according to Example 1, except that the specifications of the guide tube are changed, and the inner diameter of the guide tube is 50mm.

[0099] Analysis of the exhaust gas revealed a methane conversion rate of 37%, an ethylene selectivity of 85%, an ethane selectivity of 5%, and a C3 conversion rate of [missing information]. + 10%, with no obvious carbon buildup.

[0100] Example 4

[0101] The method is carried out according to Example 1, except that the specifications of the guide tube are changed, the inner diameter of the guide tube is 30mm, and no heat exchange medium is introduced in step (3).

[0102] Analysis of the exhaust gas revealed a methane conversion rate of 43%, ethylene selectivity of 95%, ethane selectivity of 2%, and C3... + 3%, with no obvious carbon buildup.

[0103] Example 5

[0104] The procedure is carried out according to the method of Example 1, except that no catalyst is loaded in step (2) and step (4) is not performed.

[0105] Analysis of the exhaust gas showed a methane conversion rate of 40%, an acetylene selectivity of 95%, an ethylene selectivity of 5%, and no significant carbon deposits.

[0106] Example 6

[0107] The method is carried out according to Example 1, except that no heat exchange medium is introduced in step (3).

[0108] Analysis of the exhaust gas revealed a methane conversion rate of 41%, ethylene selectivity of 60%, ethane selectivity of 25%, and C3... + 5%, carbon deposits 10%.

[0109] Comparative Example 1

[0110] The procedure was carried out according to Example 1, except that the flow guide tube 2 was not set in the plasma reactor, H was 2cm, and the methane flow rate in step (5) was 1.5L / min. The rest was the same as in Example 1.

[0111] Analysis of the exhaust gas revealed a methane conversion rate of 35%, ethylene selectivity of 80%, ethane selectivity of 7%, and C3... + Selectivity 13%, no obvious carbon buildup.

[0112] Comparative Example 2

[0113] The procedure was carried out according to Example 1, except that the flow guide tube 2 was not installed in the plasma reactor; otherwise, it was the same as Example 1.

[0114] Analysis of the exhaust gas revealed a methane conversion rate of 30%, an ethylene selectivity of 65%, an ethane selectivity of 20%, and a C3 conversion rate of [missing information]. + 15%, with no obvious carbon buildup.

[0115] The above results demonstrate that the specific plasma reactor embodiments of the present invention exhibit high methane conversion rate and high selectivity for the target product. Furthermore, a comparison of Examples 1 and 5 shows that the method provided by the present invention allows for the control of the target product, and the high selectivity of the target product meets market demands.

[0116] Comparing Examples 1, 4, and 3, it is evident that the scheme employing the preferred guide tube structure of the present invention exhibits higher methane conversion rate and ethylene selectivity. Comparing Examples 1 and 6, it is evident that the scheme employing the preferred introduction of the heat exchange medium of the present invention, while maintaining a high methane conversion rate, also exhibits higher ethylene selectivity.

[0117] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A plasma reactor, comprising a reactor body (101) and at least one electrode (3) disposed within the reactor body (101), characterized in that, It also includes a guide tube (2) disposed in the reactor body (101), wherein the distance from the upper end of the guide tube (2) to the lower part of the reactor body (101) is greater than the distance from the lower end of at least one electrode (3) to the lower part of the reactor body (101), and the lower end of the guide tube (2) extends downstream in the direction of the flow of the reactant. At least one electrode (3) is arranged to intersect with the guide tube (2) or the curved surface where the guide tube (2) is located; The plasma reactor also includes a gas nozzle (6) and a reactant outlet (7), which are located at opposite ends of the reactor body (101); The electrodes (3) are arranged in pairs, and the two electrodes in the pair are symmetrically distributed on opposite sides of the axis of the gas nozzle (6). The distance between the two electrodes gradually increases in the direction from the gas nozzle (6) to the reactant outlet (7). The included angle α between the two electrodes in the pair is 30°-90°. Each electrode (3) is connected to an electrode post (303) above it. The inner diameter of the guide tube (2) is d. The minimum distance between the two electrodes in a pair is w. The distance between the two electrode posts connected to the two electrodes is W. The guide tube (2) satisfies: W>d>w.

2. The plasma reactor according to claim 1, characterized in that, The upper end of the guide tube (2) is located above the upper end of the electrode (3); or The upper end of the guide tube (2) is located between the upper and lower ends of the electrode (3), and the distances from the upper end of the guide tube (2) to the upper and lower ends of the electrode (3) are L1 and L2, respectively, with the ratio of L1 to L2 being 0.1-10:

1.

3. The plasma reactor according to claim 1 or 2, characterized in that, The guide tube (2) is provided with slots for the electrode (3) to move in the vertical and / or horizontal directions.

4. The plasma reactor according to claim 1, characterized in that, The distance from the upper end of the guide tube (2) to the lower part of the reactor body (101) is not greater than the distance from the lower end of the gas nozzle (6) to the lower part of the reactor body (101).

5. The plasma reactor according to claim 1, characterized in that, The plasma reactor also includes an insulating base (102) connected to the upper part of the reactor body (101), and the electrode (3) and the gas nozzle (6) are respectively disposed on the insulating base (102).

6. The plasma reactor according to claim 1, characterized in that, The reactor body (101) has a maximum inner diameter D of 70-100 mm and a length of 150-300 mm; the minimum distance w between the two electrodes in the paired electrodes is 1-4 mm; and the shortest distance H between the electrode (3) and the gas nozzle (6) is 10-50 mm. And / or, in the same horizontal plane, the paired electrodes (3) are one or three pairs, and the one or three pairs of electrodes are evenly arranged along the circumferential direction of the reactor body (101).

7. The plasma reactor according to claim 6, characterized in that, The maximum inner diameter of the reactor body (101) is D, and the guide tube (2) satisfies: d = (0.1-0.9) × W, W = (0.5-0.9) × D.

8. The plasma reactor according to claim 1, characterized in that, The ratio of the inner diameter d of the guide tube (2) to the maximum inner diameter D of the reactor body (101) is 0.05-0.8:

1.

9. The plasma reactor according to claim 8, characterized in that, The ratio of the inner diameter d of the guide tube (2) to the maximum inner diameter D of the reactor body (101) is 0.3-0.6:

1.

10. The plasma reactor according to claim 1, characterized in that, The lower end of the guide tube (2) is connected to the lower part of the reactor body (101).

11. The plasma reactor according to claim 1, characterized in that, The lower part of the reactor body (101) is an inverted cone.

12. The plasma reactor according to claim 1, characterized in that, The lower part of the guide tube (2) is provided with a catalyst bed (8) filled with catalyst.

13. The plasma reactor according to claim 1, characterized in that, The plasma reactor also includes a jacket (4) for the flow of heat exchange medium, the jacket (4) being disposed outside the reactor body (101).

14. The plasma reactor according to claim 13, characterized in that, The lower end of the guide tube (2) passes through the lower end of the reactor body (101) and connects to the lower end of the jacket (4) to allow the heat exchange medium to surround the outside of the reactor body (101) and the lower end of the guide tube (2).

15. A method for converting low-carbon alkane, the method comprising: Low-carbon alkanes are introduced into a reactor for a discharge reaction; wherein the reactor is a plasma reactor as described in any one of claims 1-14.

16. The method according to claim 15, wherein, The method further includes: filling the bottom of the guide tube (2) with a catalyst; And / or, the heat exchange medium is introduced into the jacket (4) located outside the reactor body (101), and the temperature of the heat exchange medium is selected according to the target product requirements.

17. The method according to claim 16, wherein, The method further includes: first introducing the heat exchange medium into the jacket (4) located outside the reactor body (101), then filling the bottom of the guide tube (2) with a catalyst, and then introducing the low-carbon alkane; And / or, first fill the bottom of the guide tube (2) with catalyst, then introduce the heat exchange medium into the jacket (4) set outside the reactor body (101), and then introduce the low carbon alkane.

18. The method according to claim 15, wherein, The conditions for the discharge reaction include: a discharge voltage of 1-5 kV, a discharge frequency of 5-30 kHz, and a discharge input energy of 20-100 kJ / L low-carbon alkanes; and / or The discharge reaction is carried out in an oxygen-free environment.

19. The method according to claim 15, wherein, The method further includes adding hydrogen after the discharge reaction.

20. The method according to claim 19, wherein, The hydrogenation conditions include: a volume ratio of hydrogen feed flow rate to low-carbon alkane feed flow rate of 0-1:1, and a hydrogenation reaction temperature of 30-200℃. And / or, the hydrogenation is carried out in an oxygen-free environment.

21. The method according to claim 15, wherein, The method further includes performing a carbonylation reaction after the discharge reaction.

22. The method according to claim 21, wherein, The conditions for the carbonylation reaction include: a volume ratio of CO feed flow rate to low-carbon alkane feed flow rate of 0.5-1.5:1, and a carbonylation reaction temperature of 50-250℃. And / or, the carbonylation reaction is carried out in an oxygen-free environment.

23. A method for converting low-carbon alkane, the method comprising: Low-carbon alkanes are introduced into a reactor for a discharge reaction; wherein the reactor is a plasma reactor as described in any one of claims 1-11.

24. The method according to claim 23, wherein, The method further includes: not filling the bottom of the guide tube (2) with a catalyst; And / or, the heat exchange medium is not introduced into the jacket (4) located outside the reactor body (101).

25. The method according to claim 23, wherein, The conditions for the discharge reaction include: a discharge voltage of 1-5 kV, a discharge frequency of 5-30 kHz, and a discharge input energy of 20-100 kJ / L low-carbon alkanes; and / or The discharge reaction is carried out in an oxygen-free environment.

26. The method according to claim 23, wherein, The method further includes adding hydrogen after the discharge reaction.

27. The method according to claim 26, wherein, The hydrogenation conditions include: a volume ratio of hydrogen feed flow rate to low-carbon alkane feed flow rate of 0-1:1, and a hydrogenation reaction temperature of 30-200℃. And / or, the hydrogenation is carried out in an oxygen-free environment.

28. The method according to claim 23, wherein, The method further includes performing a carbonylation reaction after the discharge reaction.

29. The method according to claim 28, wherein, The conditions for the carbonylation reaction include: a volume ratio of CO feed flow rate to low-carbon alkane feed flow rate of 0.5-1.5:1, and a carbonylation reaction temperature of 50-250℃. And / or, the carbonylation reaction is carried out in an oxygen-free environment.

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