Production system, production apparatus and production method for unsaturated hydrocarbon

Abstract

To provide a system, an apparatus and a method for producing an unsaturated hydrocarbon, capable of making reaction conditions mild and improving the selectivity of a product.SOLUTION: The system for producing an unsaturated hydrocarbon includes a methane supply unit that supplies methane to a reaction field, a plasma generation unit that generates plasma in the reaction field to convert methane into a hydrocarbon having 2 or more carbon atoms, and an electrochemical cell including an anode, an electrolyte exhibiting proton conductivity in which the anode is disposed, and a cathode disposed in the electrolyte, in which the electrochemical cell electrolyzes the hydrocarbon in contact with the anode to convert the hydrocarbon into the unsaturated hydrocarbon.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a system, a production apparatus and a production method for producing unsaturated hydrocarbons from methane. [Background technology]

[0002] As a technique for converting methane, there is a prior art technique disclosed in Patent Document 1 in which ethylene (unsaturated hydrocarbon) is produced by oxidative coupling. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Special Publication No. 2015-529230 Summary of the Invention [Problem to be solved by the invention]

[0004] The prior art requires high temperature conditions of 700°C or more for oxidative coupling, and furthermore, the unsaturated hydrocarbons produced are successively oxidized, resulting in a significant decrease in selectivity.

[0005] The present invention has been made to solve this problem, and an object of the present invention is to provide a system, an apparatus and a method for producing unsaturated hydrocarbons that can make the reaction conditions milder and further improve the selectivity of the products. [Means for solving the problem]

[0006] A first aspect for achieving this object is a system for producing unsaturated hydrocarbons, comprising: a methane supply unit that supplies methane to a reaction field; a plasma generation unit that generates plasma in the reaction field and converts the methane into hydrocarbons having two or more carbon atoms; and an electrochemical cell including an anode, a proton-conductive electrolyte in which the anode is disposed, and a cathode disposed in the electrolyte, wherein the electrochemical cell electrolyzes hydrocarbons in contact with the anode and converts them into unsaturated hydrocarbons.

[0007] In the second aspect, in the first aspect, the plasma generating unit comprises a columnar or cylindrical first electrode and a cylindrical second electrode arranged outside the first electrode and providing a reaction field between the first electrode and the second electrode; the electrochemical cell is cylindrical with an anode arranged inside a cylindrical electrolyte and a cathode arranged outside the electrolyte; and the second electrode is arranged inside the electrolyte alongside the anode.

[0008] In the third aspect, in the second aspect, the first electrode is cylindrical with an internal space, the methane supply unit supplies methane to the space, and the first electrode has a plurality of holes on its side that connect the space to the reaction field.

[0009] A fourth aspect is any one of the first to third aspects, further comprising a conversion unit that recovers waste heat from the electrochemical cell and converts it into thermoelectric power, and the electric power converted by the conversion unit is supplied to the plasma generation unit.

[0010] A fifth aspect is any of the first to third aspects, further comprising a conversion unit that recovers waste heat from the electrochemical cell and converts it into thermoelectric power, and a purification unit that separates the product from impurities, and the electricity converted in the conversion unit is supplied to the purification unit.

[0011] A sixth aspect is an apparatus for producing unsaturated hydrocarbons, comprising: a methane supply unit that supplies methane to a reaction field; a plasma generation unit that has an electrode facing the reaction field and generates plasma in the reaction field; an electrochemical cell that includes an anode located downstream of the plasma generation unit and facing the reaction field; a proton-conductive electrolyte in which the anode is disposed; and a cathode that is disposed in the electrolyte and positioned outside the reaction field.

[0012] A seventh aspect is a method for producing unsaturated hydrocarbons, which includes the steps of generating plasma in a reaction field to which methane is supplied and converting the methane into hydrocarbons having two or more carbon atoms, and electrolyzing the hydrocarbons in an electrochemical cell containing a proton-conductive electrolyte to convert them into unsaturated hydrocarbons. [Effects of the Invention]

[0013] According to the present invention, methane supplied to a reaction field is converted by plasma into hydrocarbons with two or more carbon atoms, and the hydrocarbons are electrolyzed in an electrochemical cell to produce unsaturated hydrocarbons. The proton-conducting electrochemical cell operates at a low temperature, for example, below 400°C, making it possible to keep the reaction conditions mild. Furthermore, unsaturated hydrocarbons are produced by a reaction that does not involve oxygen, preventing oxidative decomposition of the products, thereby improving product selectivity. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a block diagram of a system for producing unsaturated hydrocarbons according to a first embodiment. [Figure 2] FIG. 1 is a schematic cross-sectional view of a reactor. [Figure 3] FIG. 10 is a schematic cross-sectional view of a reaction device in a second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0015] Preferred embodiments of the present invention will now be described with reference to the accompanying drawings. FIG. 1 is a block diagram of a system 10 for producing unsaturated hydrocarbons in a first embodiment. The production system 10 includes a reactor 11 that converts methane to produce unsaturated hydrocarbons, and a methane supply unit 26 that supplies methane to the reactor 11. Unsaturated hydrocarbons have a carbon chain with two or more carbon atoms. Examples of unsaturated hydrocarbons include ethylene and propylene. The reactor 11 includes a plasma generation unit 12 that generates plasma, and an electrochemical cell 18.

[0016] FIG. 2 is a schematic cross-sectional view of a reaction apparatus 11. The plasma generating unit 12 generates reactive plasma, so-called atmospheric pressure plasma, in a high-density medium at atmospheric pressure or higher. The plasma generating unit 12 includes an electrode member 13 including a first electrode 14, and a power supply 17 that applies a voltage between the first electrode 14 and a second electrode 16. In this embodiment, the plasma generating unit 12 has a so-called coaxial cylindrical shape, in which the first electrode 14 is rod-shaped and the second electrode 16 is cylindrical and surrounds the first electrode 14. The electrode member 13 includes a dielectric 15 disposed on the first electrode 14.

[0017] Examples of materials for the first electrode 14 and the second electrode 16 include metal and carbon. When the electrodes 14, 16 are made of a metal, they contain one or more elements selected from Groups 4 to 14 of the periodic table based on the IUPAC 1990 Recommendations. Examples of elements include Al, Ti, Cr, Fe, Ni, Co, Cu, Zn, Ru, Ag, Pd, Pt, and Au.

[0018] The dielectric 15 prevents arc discharge caused by a large current flowing locally between the first electrode 14 and the second electrode 16. Because electric charge accumulates in the dielectric 15, when the direction of the voltage changes after the initial discharge, a discharge can occur at a lower voltage than the initial discharge. Therefore, plasma can be generated with a small input energy. Examples of the dielectric 15 include a membrane, film, or cylinder made of a material selected from glass, ceramics, synthetic resin, etc.

[0019] The power supply 17 is a device that applies an AC voltage between the first electrode 14 and the second electrode 16. The AC voltage may be, for example, a sine wave, a triangular wave, a sawtooth wave, or a pulse wave of about 50 Hz to 100 MHz.

[0020] The electrochemical cell 18 includes an electrolyte 19, an anode 20, and a cathode 21 that are separated from each other by the electrolyte 19. In this embodiment, the electrolyte 19 is cylindrical, with the anode 20 disposed on the inner periphery of the electrolyte 19 and the cathode 21 disposed on the outer periphery of the electrolyte 19. The electrochemical cell 18 is a so-called cylindrical vertical stripe cell. A second electrode 16 is disposed on the inner periphery of the electrolyte 19. The second electrode 16 is disposed on the inner periphery of the electrolyte 19, axially aligned with the anode 20. The cathode 21 is disposed on the back side of the electrolyte 19, excluding the area where the first electrode 14 is projected radially outward.

[0021] The material of the electrolyte 19 can be a substance that exhibits proton conductivity under the operating conditions of the electrochemical cell 18. Examples of the substance that exhibits proton conductivity include perovskite-type oxides (ceramics) such as BaZrO3 in which the B site is substituted with trivalent metal ions such as Y or In.

[0022] The material of the anode 20 is a perovskite oxide, La 1-X Sr X MnO 3-δ ,La 1-X Sr X CoO 3-δ ,La 1-X Sr X Co 1-Y Fe Y O 3-δ ,Pr 1-X Sr X MnO 3-δ Examples of the material for the anode 20 include a composite material of one or more oxides selected from these perovskite oxides and a material that can form the electrolyte 19.

[0023] The cathode 21 may be made of a cermet containing an electron-conducting metal catalyst and a proton-conducting oxide. Examples of the metal catalyst include Cr, Fe, Co, Cu, Ru, Pd, Ag, Pt, Au, and Ni. Examples of the oxide include perovskite-type oxides such as BaZrO3, in which the B site is substituted with a trivalent metal ion such as Y or In.

[0024] A power supply 22 applies a DC voltage between the anode 20 and the cathode 21. A heater 23 is disposed outside the electrolyte 19 at a distance from the cathode 21. The heater 23 is a device that heats the electrochemical cell 18 to an operating temperature (for example, about 400°C).

[0025] In the reactor 11, a cylindrical reaction field 24 is provided between the electrode member 13 of the plasma generating unit 12 and the second electrode 16, and a space 25 is provided inside the portion where the cathode 21 of the electrochemical cell 18 is provided. The space 25 is connected to the reaction field 24. A methane supply unit 26 supplies methane to the reaction field 24.

[0026] The apparatus for producing unsaturated hydrocarbons includes a methane supply unit (26) that supplies methane to a reaction field (24), a plasma generation unit (12) that has an electrode (14) facing the reaction field (24) and generates plasma in the reaction field (24), an electrochemical cell (18) that includes an anode (20) located downstream of the plasma generation unit (12) and facing the reaction field (24), a proton-conductive electrolyte (19) in which the anode (20) is disposed, and a cathode (21) that is disposed in the electrolyte (19) and located outside the reaction field (24).

[0027] An AC voltage is applied between the first electrode 14 and the second electrode 16 of the plasma generating unit 12. When the voltage reaches a discharge inception voltage, the gas in the reaction field 24 undergoes dielectric breakdown, generating a dielectric barrier discharge in the reaction field 24. Methane is converted by the dielectric barrier discharge into saturated hydrocarbons such as ethane, propane, and butane. Some methane is converted into unsaturated hydrocarbons such as ethylene and acetylene. That is, in the reaction field 24, methane is converted into hydrocarbons other than methane.

[0028] The hydrocarbons present in the reaction field 24 are pushed out by the methane supplied to the reaction field 24 by the methane supply unit 26, reach the space 25, and are supplied to the anode 20 in the space 25. At the anode 20, hydrogen is converted from the hydrocarbons into protons (H +) are separated. This allows, for example, ethylene to be synthesized from ethane, and propylene to be synthesized from propane. That is, the reactor 11 converts saturated hydrocarbons into unsaturated hydrocarbons at the anode 20, producing unsaturated hydrocarbons.

[0029] Protons generated at the anode 20 pass through the electrolyte 19 to reach the cathode 21, where they are reduced, generating hydrogen. Therefore, the reactor 11 produces hydrogen in addition to unsaturated hydrocarbons. The operating temperature of the electrochemical cell 18 is, for example, about 400°C, which is lower than the reaction conditions for oxidative coupling, allowing for milder reaction conditions. Furthermore, unlike oxidative coupling, this reaction does not involve oxygen, so oxidative decomposition of the product does not occur, improving product selectivity.

[0030] In the reactor 11, a reaction field 24 is provided upstream of the flow of methane supplied by a methane supply unit 26, and a space 25 is provided downstream of the reaction field 24, with the reaction field 24 and the space 25 being connected together. This allows the device to be made more compact than a device that separately provides a plasma generation unit 12 that irradiates methane with plasma and an electrochemical cell 18 that electrolyzes hydrocarbons.

[0031] A second electrode 16 is provided on an electrolyte 19 provided with a cathode 21 and an anode 20, and the second electrode 16 and the anode 20 are aligned in the direction of the flow of the methane-containing gas. Because the second electrode 16 is supported by the electrolyte 19 in which the anode 20 is disposed, the number of parts can be reduced compared to when a separate member for supporting the second electrode 16 is provided.

[0032] The heater 23 heats not only the portion of the electrolyte 19 where the cathode 21 is disposed, but also the portion where the second electrode 16 is disposed, so the temperature difference in the axial direction of the electrolyte 19 can be reduced compared to when the heater 23 heats only the portion where the cathode 21 is disposed. This reduces thermal strain generated in the electrolyte 19, and reduces damage to the electrolyte 19.

[0033] Returning to Figure 1, the production system 10 includes a methane supply unit 26 that supplies methane to the reactor 11, a purification unit 27 that separates the unsaturated hydrocarbons (products) produced by the reactor 11 from impurities, and a conversion unit 34 that recovers waste heat from the electrochemical cell 18 and converts it into thermoelectric power.

[0034] The purification section 27 separates the product from impurities by equilibrium separation operations such as distillation, adsorption, and extraction, or membrane separation. The impurities include unreacted materials and by-products other than the target product. In this embodiment, the purification section 27 includes a first cooler 28 and a first separation section 29 that cool the gas (excluding hydrogen) discharged from the reaction device 11 to separate propylene, and a second cooler 30 and a second separation section 31 that cool the gas to separate ethylene.

[0035] The first cooler 28 and the first separation section 29 are exemplified by those which cool the propylene to about −48° C. at atmospheric pressure to liquefy the propylene. The second cooler 30 and the second separation section 31 are exemplified by those which cool the ethylene to about −105° C. at atmospheric pressure to liquefy the ethylene. The impurities separated from the ethylene in the second separation section 31 are supplied to the reaction device 11 and used as a raw material for unsaturated hydrocarbons. This reduces waste of the raw material (methane).

[0036] The conversion unit 34 includes a thermoelectric conversion element that recovers waste heat from the electrochemical cell 18 and converts the recovered waste heat into electricity. The conversion unit 34 supplies power to one or more of the power supply 17 of the plasma generation unit 12, the power supply 22 of the electrochemical cell 18, the first cooler 28, and the second cooler 30. The manufacturing system 10 can improve energy efficiency by utilizing the waste heat recovered by the conversion unit 34 as electricity.

[0037] A second embodiment will be described with reference to Fig. 3. In the first embodiment, a manufacturing system 10 including a so-called coaxial cylindrical plasma generation unit 12 was described. In the second embodiment, a manufacturing system 10 including a so-called coaxial double cylindrical plasma generation unit 41 will be described. The same parts as those described in the first embodiment are designated by the same reference numerals, and the following description will be omitted.

[0038] 3 is a schematic cross-sectional view of a reaction device 40 of a production system 10 in the second embodiment. The reaction device 40 is provided in the production system 10 in place of the reaction device 11 in the first embodiment. The reaction device 40 includes a plasma generation unit 41 and an electrochemical cell 18. The plasma generation unit 41 is a device that generates atmospheric pressure plasma.

[0039] The plasma generating unit 41 includes an electrode member 42 including a first electrode 43, and an AC voltage is applied between the first electrode 43 and the second electrode 16. The electrode member 42 is cylindrical and includes a dielectric 44 disposed on the first electrode 43. The materials of the first electrode 43 and the dielectric 44 are the same as the materials of the first electrode 14 and the dielectric 15 in the first embodiment.

[0040] The unsaturated hydrocarbon production apparatus includes a methane supply unit (26) that supplies methane to a reaction field (24), a plasma generation unit (41) that has an electrode (43) facing the reaction field (24) and generates plasma in the reaction field (24), an electrochemical cell (18) that includes an anode (20) located downstream of the plasma generation unit (41) and facing the reaction field (24), a proton-conductive electrolyte (19) in which the anode (20) is disposed, and a cathode (21) that is disposed in the electrolyte (19) and located outside the reaction field (24).

[0041] The electrode member 42 has holes 45. The holes 45 connect the space 46 inside the electrode member 42 to the reaction field 24. A plurality of the holes 45 are scattered around. The size of the holes 45 is smaller than the diameter of the space 46. The holes 45 may be formed in the electrode member 42a using a tool such as a drill or laser processing. Alternatively, the first electrode 43 and the dielectric 44 may be made of a material such as a mesh or fiber, and the holes 45 may be formed between the fibers or at openings in the mesh.

[0042] The electrode member 42 is a cylindrical member with a closed end and a closed space 46. The methane supply unit 26 supplies methane to the space 46 inside the electrode member 42. The methane is dispersed from the space 46 through the holes 45 and supplied to the reaction field 24, where it is converted by the plasma into hydrocarbons other than methane. The hydrocarbons are electrolyzed in the electrochemical cell 18 to produce unsaturated hydrocarbons.

[0043] The present invention has been described above based on the embodiments, but the present invention is not limited to the above embodiments, and it can be easily inferred that various improvements and modifications are possible within the scope of the present invention.

[0044] Although not described in the embodiment, it is naturally possible for the reactors 11, 40 and the purification unit 27 to utilize the waste heat recovered by the conversion unit 34. For example, the waste heat may be utilized to heat the electrochemical cells 18 of the reactors 11, 40 to their operating temperatures. Furthermore, the waste heat may be utilized to heat the gas when the purification unit 27 purifies the product by distillation.

[0045] In the embodiment, the reactors 11 and 40 are described as having a so-called cylindrical vertical stripe type electrochemical cell 18, but the present invention is not necessarily limited to this. It is of course possible to adopt various types of electrochemical cells, such as flat plate type, cylindrical horizontal stripe type, and metal-supported flat plate type.

[0046] In the embodiment, the anode 20 of the electrochemical cell 18 and the second electrode 16 of the plasma generating unit 12, 41 are electrically connected, but this is not necessarily limited to this. It is of course possible to insulate the anode 20 from the second electrode 16. The arrangement of the first electrode 14, 43 and the second electrode 16 of the plasma generating unit 12, 41 is not limited to a coaxial cylindrical shape or a coaxial double cylindrical shape, and a so-called parallel plate shape in which a plate-shaped first electrode and a plate-shaped second electrode face each other may also be employed.

[0047] In the embodiments, the reactors 11 and 40 have been described as using a dielectric barrier discharge, but the present invention is not limited to this. It is naturally possible to use other plasmas. Examples of other plasmas include corona discharge, surface discharge, atmospheric pressure glow discharge, and microwave discharge. It is naturally possible to combine multiple plasmas.

[0048] In the embodiment, the proton-conductive electrolyte 19 has been described as including a perovskite oxide such as BaZrO3, but is not necessarily limited to this. It is of course possible to use a perfluorocarbon or hydrocarbon polymer electrolyte or a glass electrolyte such as phosphate glass for the electrolyte 19. Examples of perfluorocarbon proton conductors include Nafion (registered trademark) and Aquivion (registered trademark), in which a sulfo group is linked to a perfluoroalkyl polymer. To improve the properties of the proton conductor, a polymer and inorganic particles may be combined.

[0049] Examples of hydrocarbon-based proton conductors include polymers in which sulfo groups or phosphate groups are linked to aromatic hydrocarbon-based engineering plastics. Examples of hydrocarbon-based proton conductors include polymers (SPEEK) in which sulfo groups are introduced into the main chain of polyether ether ketone. To improve the properties of proton conductors, hetero elements such as fluorine, sulfur, nitrogen, and phosphorus, or units containing these elements, may be introduced.

[0050] When a polymer electrolyte is used for the electrolyte 19, the anode 20 and the cathode 21 can be made of porous carbon carrying a catalyst such as Pt or Pt—Ru. The operating temperature of the electrochemical cell 18 containing the polymer electrolyte in the electrolyte 19 is 120° C. or less, and therefore the temperature of the space 25 can be lowered accordingly.

[0051] Although not described in the embodiment, the temperature of the reaction field 24 is set appropriately within a range from room temperature to 500°C, for example. The pressure of the reaction field 24 is set appropriately within a range from 101 kPa to 1000 kPa, for example. The temperature and pressure of the reaction field 24 and the flow rate of methane supplied to the reaction field 24 are set appropriately depending on the type of target product.

[0052] Although not described in the embodiment, it is possible to place a catalyst in the reaction field 24. There are no particular limitations on the catalyst as long as it is present in the reaction field 24. For example, the catalyst can be attached to the surface of the dielectric 15, 44 that contacts the reaction field 24. Examples of the shape of the catalyst attached to the dielectric 15, 44 include a mesh, plate, and film. The catalyst contains one or more elements selected from Groups 4 to 14 of the Periodic Table based on the IUPAC 1990 Recommendations. Examples of elements include Al, Ti, Cr, Fe, Ni, Co, Cu, Zn, Ru, Ag, Pd, Pt, and Au.

[0053] A catalyst may be filled in the reaction field 24. When the catalyst is filled in the reaction field 24, an example of the catalyst is one in which a skeleton with a three-dimensional network structure made of a porous body made of an oxide such as alumina or zirconia supports the catalyst.

[0054] In the second embodiment, the electrode member 42 is described as having holes 45 penetrating both the first electrode 43 and the dielectric 44, but this is not necessarily limited to this. Another example of the electrode member 42 is one in which the first electrodes 43 are arranged in a vertical or horizontal stripe pattern on the inner surface of a cylindrical dielectric 44 having holes 45 formed therein. The first electrodes 43 arranged at intervals in a horizontal or vertical stripe pattern are electrically connected to each other. In this case, too, gas flows between the space 46 and the reaction field 24 through the gaps between the first electrodes 43 arranged in a stripe pattern and through the holes 45, thereby achieving the same effects as in this embodiment.

[0055] In the second embodiment, a case has been described in which the hole 45 is provided in the electrode member 42 of the so-called coaxial double cylindrical plasma generating unit 41 in which the cylindrical electrode member 42 and the cylindrical second electrode 16 are coaxially arranged, but this is not necessarily limited to this. It is of course possible to omit the hole 45 in the electrode member 42. In this case, the end of the electrode member 42 does not need to be closed, and the methane supply unit 26 supplies methane to the reaction field 24 between the electrode member 42 and the second electrode 16. [Explanation of symbols]

[0056] 10 Manufacturing Systems 12,41 Plasma generating unit 14,43 First electrode 16 Second electrode 18 Electrochemical Cell 19 Electrolytes 20 anodes 21 Cathode 24 Reaction Field 26 Methane supply section 27 Refining Department 34 Conversion unit 45 holes 46 Space

Claims

1. 1. A system for producing unsaturated hydrocarbons, comprising: a methane supply unit that supplies methane to the reaction field; a plasma generating unit that generates plasma in the reaction field and converts methane into hydrocarbons having two or more carbon atoms; an electrochemical cell including an anode, a proton-conducting electrolyte in which the anode is disposed, and a cathode disposed in the electrolyte; The electrochemical cell is a production system that electrolyzes hydrocarbons in contact with the anode and converts them into unsaturated hydrocarbons.

2. the plasma generation unit includes a columnar or cylindrical first electrode and a cylindrical second electrode that is disposed outside the first electrode and provides the reaction field between the first electrode and the second electrode; the electrochemical cell is cylindrical, with the anode disposed inside the cylindrical electrolyte and the cathode disposed outside the electrolyte; The manufacturing system according to claim 1 , wherein the second electrode is disposed inside the electrolyte alongside the anode.

3. the first electrode is cylindrical and has an internal space; the methane supply unit supplies methane to the space; The manufacturing system according to claim 2 , wherein the first electrode has a plurality of holes formed on a side surface thereof, the holes connecting the space and the reaction field.

4. a conversion unit that recovers waste heat from the electrochemical cell and converts it into thermoelectric power, The manufacturing system according to claim 1 , wherein the plasma generating unit is supplied with power converted by the converting unit.

5. a conversion unit that recovers waste heat from the electrochemical cell and converts it into thermoelectric power; a purification section that separates the product from impurities, The manufacturing system according to claim 1 , wherein the refining unit is supplied with electric power converted by the conversion unit.

6. An apparatus for producing unsaturated hydrocarbons, comprising: a methane supply unit that supplies methane to the reaction field; a plasma generating unit that has an electrode facing the reaction field and generates plasma in the reaction field; a manufacturing apparatus comprising an electrochemical cell including: an anode located downstream of the plasma generating unit and facing the reaction field; a proton-conductive electrolyte in which the anode is disposed; and a cathode located in the electrolyte and outside the reaction field.

7. generating plasma in a reaction field to which methane is supplied and converting the methane into hydrocarbons having two or more carbon atoms; and converting the hydrocarbon into an unsaturated hydrocarbon by electrolysis in an electrochemical cell containing a proton-conducting electrolyte.

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