JP5146730B2 - Method and apparatus for reducing carbon dioxide in gas - Google Patents

Description

  The present invention relates to a method and a carbon dioxide reduction device for reducing carbon dioxide by setting an oxygen concentration in a mixed gas containing carbon dioxide to an extremely low oxygen partial pressure and heating and reducing the gas.

  In recent years, the effects of greenhouse gases have been pointed out as one of the causes of global warming, and in particular, attempts to prevent the global warming by reducing greenhouse gases such as carbon dioxide are global. Has been made. To date, various immobilization and effective utilization have been proposed for the reduction of carbon dioxide.

  Carbon dioxide fixation, effective utilization methods include geological storage, marine sequestration, ground sequestration by plantation, and separation and recovery using physical and chemical methods, followed by decomposition into carbon and chemical products. The method of converting and using it effectively is mentioned.

  On the other hand, decomposition into carbon and conversion to chemicals using chemical reactions are still at the basic research stage, but it is possible to extract carbon by using reactions with metals and methane, and by using catalysts. Conversion to a chemical product is performed by a method utilizing a reaction, electrochemical reduction, or photochemical reduction.

  Sequestration by underground storage requires compression and liquefaction energy at the time of injection, there are still many unclear points about whether carbon dioxide has been stably sequestered in the long term. However, there is a problem that adverse effects on the environment, such as effects on living things, are unknown.

Ground sequestration by planting uses biological photosynthesis, so a considerable amount of carbon dioxide can be expected. It also helps protect tropical forests and prevent desertification. However, planting and planting also requires vast land, and it takes many years to grow.

  Although it is very attractive to directly decompose carbon dioxide into carbon by using a reaction with metal or methane, the current technology reduces the carbon dioxide, and in order to decompose it into carbon, a reaction is required. There are problems such as requiring metal to wake up and a large amount of heat energy.

  As electrochemical reduction, a method is known in which carbon dioxide in an electrolytic solution is decomposed using a special electrode to produce formic acid, methane, etc. at room temperature, but a large-scale reaction tank is required. In order to promote the reaction, it is necessary to supply a large amount of electric energy.

  Photochemical reduction is reduction by a photoelectrode reaction using a semiconductor, and obtains energy necessary for reduction from sunlight. This is one in which a photoelectrode is placed in an aqueous solution in which carbon dioxide is dissolved, and light is irradiated to oxidize water at one electrode to obtain oxygen, and at the other electrode to reduce carbon dioxide to obtain carbon monoxide. Are known. However, the performance of the photoelectrode is not sufficient, and there is a problem in the stability of the reaction.

As the reduction of carbon dioxide using a catalytic reaction, means for converting carbon dioxide into carbon monoxide, methanol or the like and using the same are known. Patent Document 1 discloses a mixture of carbon dioxide and hydrogen. A method of generating methanol by decomposing carbon dioxide on the catalyst surface by irradiating microwaves in the presence of the catalyst and heating the catalyst with microwaves has been proposed. There is danger and there is a problem in the handling.
Japanese Patent Application No. 2004-332797

  The carbon dioxide reduction method of the present invention includes a step of generating a mixed gas containing carbon dioxide gas, and an extremely low oxygen partial pressure in which the oxygen concentration in the mixed gas is 10 minus 20th atmospheric pressure or less, 10 or less minus 35th atmospheric pressure or more. And a reduction step of reducing the carbon dioxide in the mixed gas by reducing the carbon dioxide in the mixed gas to carbon by heating the mixed gas.

  In addition, the carbon dioxide reduction method of the present invention further includes a step of discharging the mixed gas from which the carbon dioxide has been removed to the atmosphere.

  The mixed gas containing carbon dioxide includes one or more of nitrogen, oxygen, argon, neon, and helium.

  The extremely low oxygen partial pressure uses oxygen ion conductivity of a solid electrolyte body.

  The heating temperature in the reducing device is 300 ° C. or higher and 3000 ° C. or lower.

  The carbon dioxide reduction device of the present invention includes a mixed gas generation device that generates a mixed gas containing carbon dioxide gas, and an oxygen concentration in the mixed gas of 10 minus 20th atmospheric pressure or less and 10 minus 35th atmospheric pressure or more oxygen content. An oxygen molecule discharging device that generates pressure, and a reducing device that heats the mixed gas having the partial pressure of oxygen to reduce carbon dioxide in the mixed gas to carbon.

  The carbon dioxide reduction device of the present invention includes a mixed gas generation device that generates a mixed gas containing carbon dioxide gas, and an oxygen concentration in the mixed gas of 10 minus 20th atmospheric pressure or less and 10 minus 35th atmospheric pressure or more. An oxygen molecule discharging device that generates oxygen partial pressure; and a reducing device that heats the mixed gas having the oxygen partial pressure to reduce carbon dioxide in the mixed gas to carbon, the reducing device generating the mixed gas A device is provided.

  Furthermore, the carbon dioxide reduction device of the present invention further includes a discharge device that discharges the mixed gas from which the carbon dioxide has been removed to the atmosphere.

  The mixed gas containing carbon dioxide includes one or more of nitrogen, oxygen, argon, neon, and helium.

  The oxygen molecule discharging apparatus uses oxygen ion conductivity of a solid electrolyte body.

  The heating temperature is 300 ° C. or higher and 3000 ° C. or lower.

  According to the present invention, by utilizing extremely low oxygen gas, carbon dioxide can be effectively efficiently reduced directly from carbon dioxide to carbon without using other materials such as electrodes, catalysts, and water. It can be reduced well.

Carbon dioxide is reduced to carbon at an extremely low partial pressure of oxygen, in which the oxygen concentration in the mixed gas is an extremely low oxygen partial pressure of 10 minus 20th atmospheric pressure or less and 10 minus 35th atmospheric pressure or more.
The chemical formula associated with the reduction is as follows.
CO ₂ (gas) = C + O ₂ (gas)
In FIG. 1, the horizontal axis represents temperature, and the vertical axis represents oxygen partial pressure. FIG. 1 is a correlation diagram obtained from a chemical formula and thermodynamic calculation, and shows that the reduction region changes depending on the relationship between temperature and oxygen partial pressure. That is, the higher the temperature and the lower the oxygen partial pressure, the more the reduction reaction proceeds. The arrow (T) in the figure indicates that when the CO ₂ concentration is 50%, when the oxygen partial pressure is 10 minus 30 atm, the reduction starts at about 400 ° C. and the reduction starts. Further, when the CO ₂ concentration in the system changes, the reduction boundary line changes as shown in the figure. That is, when the CO ₂ concentration is 100 ppm, the reduction starts from about 500 ° C. when the oxygen partial pressure is 10 minus 30 atm. According to the present invention, the carbon dioxide content 50% in the mixed gas can be reduced to 5% or less.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 2 is a schematic diagram showing the carbon dioxide reduction device 10. The carbon dioxide reduction device 10 includes a gas mixer 12 that mixes a process gas and carbon dioxide, and an extremely low extremely low oxygen content in which the oxygen concentration in the mixed gas is 10 minus 20th atmospheric pressure or less and 10 minus 35th atmospheric pressure or more. An oxygen molecule discharging device 14 that generates pressure is provided, and a reducing device 16 that reduces carbon dioxide to carbon. As the mixed gas containing carbon dioxide, a gas containing one or more of nitrogen, oxygen, argon, neon, and helium is used as a process gas. The heating temperature in the reducing device is 300 ° C. or higher and 3000 ° C. or lower.

  A mixed gas containing carbon dioxide gas is introduced into the oxygen molecule discharging device 14 via a circulation pump 17. The oxygen partial pressure of the oxygen concentration of the oxygen molecule discharging device is controlled by the oxygen partial pressure control device 18.

  As shown in FIG. 3, the carbon dioxide and the process gas may be mixed by providing a gas mixer 12 in the reduction device and mixing the carbon dioxide and the process gas in the reduction device 16.

  Further, in FIG. 2, in addition to removing carbon dioxide by fixing carbon to the surface of a dialuminum trioxide crucible provided in the reducing device 16, a mixed gas not containing carbon dioxide is directly discharged to the atmosphere. You may do it.

The oxygen molecule discharging device 14 includes a solid electrolyte body having oxygen ion conductivity, and net-like electrodes made of gold or platinum and disposed on both the inner and outer surfaces of the solid electrolyte body. FIG. 4 shows a schematic diagram of an oxygen molecule discharging apparatus. 4 includes a zirconia solid electrolyte body 21 having oxygen ion conductivity, and net-like electrodes 22 and 23 made of gold or platinum, which are disposed on the inner and outer surfaces of the solid electrolyte body 21. Prepare. The zirconia solid electrolyte body 21 is fixed to the metal tube body 20 made of a Kovar material at both ends by silver brazing. The electrode and tube of the solid electrolyte body constitute an inner electrode. The internal pressure of the oxygen partial pressure discharge apparatus is 3 kg / cm ² or less, is usually 0.1~1.0kg / cm ^2.

When a current I is passed from the DC power source E between the inner surface electrode 22 and the outer surface electrode 23, oxygen molecules (O ₂ ) are electrically reduced and ionized (O ²⁻ ) at the inner surface electrode 22, and the solid electrolyte 21. The electrons are taken away by the outer electrode 23 and converted into oxygen molecules again. By exhausting oxygen molecules released to the outside of the sealed container using an auxiliary gas such as air as a carrier gas, the oxygen molecules in the mixed gas supplied to the sealed container can be removed and the oxygen partial pressure can be controlled. . In this way, one of H ₂ and O ₂ produced by thermal decomposition of H ₂ O, O ₂ is removed by oxygen molecules discharge device 14. Therefore, the chemical equilibrium of H ₂ O << H ₂ + (1/2) O ₂ continuously proceeds to the right side, and moisture is decomposed and removed.

  As described above, the oxygen molecule discharge device 14 discharges oxygen molecules in the mixed gas to the outside air while the gas introduced into the solid electrolyte body 21 passes through the solid electrolyte body 21 to generate an extremely low oxygen partial pressure. To do. In FIG. 4, ● is an inert gas, OO is an oxygen molecule, and ◯ is an oxygen ion.

The solid electrolyte constituting the solid electrolyte body is, for example, a general formula (ZrO ₂ ) _1-xy (In ₂ O ₃ ) _x (Y ₂ O ₃ ) _y (0 <x <0.20, 0 <y <020, 0.08 < A zirconia system represented by x + y <0.20) can be used. Among them, 0 <x <0.20 and y = 0 are preferable, and 0.06 <x <0.12 and y = 0 are more preferable.

In addition to those exemplified above, the solid electrolyte is, for example, a composite Ba oxide containing Ba and In, in which a part of Ba of this composite oxide is replaced by solid solution with La, in particular the atomic ratio. {La / (Ba + La)} is set to 0.3 or more, a part of In is further substituted with Ga, and the general formula {Ln _1−x Sr _x Ga _{1− (y + z)} Mg _y Co _z O ₃ , wherein one or two of Ln = La and Nd, x = 0.05 to 0.3, y = 0 to 0.29, z = 0.01 to 0.3, y + z = 0.025 to 0.3}, formula _{{Ln (1-x) a} x Ga (1-yz) B1 y B2 z O 3-δ, however, Ln = La, Ce, Pr , Nd, 1 or more kinds of Sm, a = Sr , One or more of Ca, Ba, one or more of B1 = Mg, Al, In, B2 = one or more of Co, Fe, Ni, Cu} The or general formula _{{Ln 2-x M x Ge} 1-y LyO 5, however, Ln = La, Ce, Pr , Sm, Nd, Gd, Yd, Y, Sc, M = Li, Na, K, Rb , Ca, Sr, Ba, or one or more, L = Mg, Al, Ga, In, Mn, Cr, Cu, or Zn, or a general formula {La _(1-x) Sr _x Ga _(1-yz) Mg _y Al _z O ₃ , where 0 <x ≦ 0.2, 0 <y ≦ 0.2, 0 <z <0.4}, and the general formula {La _(1-x) A _x Ga _{( 1-yz)} B1 _y B2 _z O ₃ , where Ln = La, Ce, Pr, Sm, Nd, one or more, A = Sr, Ca, Ba, one or more, B1 = Mg , One or more of Al, In, one or more of B2 = Co, Fe, Ni, Cu, x = 0.05 to 0.3, y = 0 to 0.29, z = 0.01 to 0.3, y + z = 0.025 to 0.3} etc. That.

  The oxygen partial pressure control device 18 that sets the oxygen partial pressure value to a predetermined value is a discharge side that measures the oxygen partial pressure of the extremely low oxygen partial pressure gas that is discharged from the oxygen partial pressure setting unit and the immobilization device. It comprises an oxygen partial pressure sensor, and includes an oxygen partial pressure control unit based on a PID control system that controls the oxygen partial pressure of the gas delivered from the oxygen pump portion to a predetermined value by comparing the monitor value of the sensor with the oxygen partial pressure set value.

  A reduction device that reduces carbon dioxide to carbon reduces carbon dioxide to carbon at a relatively high temperature. When the temperature is raised, the following known heating method is applied. Examples thereof include a resistance heating method, a high frequency induction heating method, an arc discharge method, an electron beam heating method, infrared heating, and laser beam heating. In the resistance heating, high frequency induction heating method, and arc discharge method, all use crucibles, Joule heat generated when current is passed through the resistance, metal due to high frequency, heat generation due to induction current in carbon crucible, crucible and electrode The sintered body in the crucible is heated by the heating by the arc discharge. On the other hand, the electron beam heating method, infrared condensing heating, and laser beam heating are methods for heating an object to be heated by concentrating or condensing electron beam flow, infrared rays, and laser, respectively.

  In terms of reducing carbon dioxide gas to carbon and collecting the carbon, methods such as resistance heating, high-frequency induction heating, and arc discharge methods are desirable for heating, such as heating in a crucible. In the sense that carbon can be used, resistance heating and high frequency induction heating are more preferable.

  Along with the heating operation, in the first stage, the generation of oxygen is detected under the influence of oxygen generated from the surface of the heated sintered body. Along with this, the amount of oxygen in the processing apparatus increases slightly. Thereafter, the oxygen partial pressure decreases again, but when the temperature exceeds the temperature at which carbon dioxide is reduced, the oxygen concentration value of the oxygen concentration meter of the oxygen partial pressure control device rises again, and the generation of oxygen can be confirmed. When further heated, the oxygen partial pressure becomes stable, and the reduction is performed by continuing the heating.

  A crucible made of dialuminum trioxide is placed in a reducing apparatus consisting of a resistance heating furnace, and the inside of the system is a mixed gas of argon gas and carbon dioxide at 1 atm. After the oxygen partial pressure was changed to an atmosphere of minus 30 to atmospheric pressure of 3.2 × 10 using the oxygen molecule discharging device, the temperature of the reducing device was set to 1100 ° C. and held for 72 hours. As a result, the surface of the crucible made of dialuminum trioxide that had been placed in the reducing device turned black. FIG. 5 shows the surface of the crucible before and after the treatment when the alumina turns black due to carbon. FIG. 6 is a spectrum showing the result of analysis by EDX, and a peak of carbon was confirmed in addition to oxygen and aluminum constituting dialuminum trioxide.

  In addition, a silicon wafer was placed in a reduction apparatus consisting of a resistance heating furnace, and the inside of the system was a mixed gas of argon gas and carbon dioxide at 1 atm. After the oxygen partial pressure was changed to an oxygen partial pressure of 7.5 × 10 minus 30th atmospheric pressure by the oxygen molecule discharging apparatus, the temperature of the reducing apparatus was set to 1100 ° C. and held for 48 hours. As a result, a thickness of 3 to 6 μm of carbon reduced on the silicon wafer was confirmed. As shown in the SEM photograph of FIG. 7, a black particle-like object appeared on the surface of the silicon wafer that had been put in the reducing apparatus. When this particle was analyzed by EDX, it was confirmed that it was a carbon peak (FIG. 8).

  The present invention can effectively use a large amount of waste heat generated from blast furnaces, garbage incinerators, etc. in steelworks, and can reduce carbon dioxide, which is a greenhouse gas that causes global warming. Can be reduced. Moreover, if electric power obtained by solar power, wind power, or geothermal power generation is used, the possibility of being used as a carbon dioxide reduction plant can be expected. Furthermore, the carbon produced by this invention can be reused in industry.

It is a figure which shows the relationship between oxygen partial pressure and temperature. It is the schematic which shows the carbon dioxide reduction apparatus which concerns on this invention. It is the schematic which shows the other carbon dioxide reduction apparatus which concerns on this invention. It is the schematic which shows the oxygen molecule discharge apparatus of the carbon dioxide reduction apparatus which concerns on this invention. A crucible made of dialuminum trioxide that turns black with carbon. EDX spectrum of dialuminum trioxide, which turned black with carbon. An electron micrograph of the silicon wafer surface. EDX spectrum of a silicon wafer that has turned black.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10; Carbon dioxide reduction device 12; Gas mixer 14; Oxygen molecule discharge device 16; Reduction device 18; Oxygen partial pressure control device 20; Tube 21;

Claims (11)

  A step of generating a mixed gas containing carbon dioxide gas, a step of generating an oxygen concentration in the mixed gas at an extremely low oxygen partial pressure of 10 minus 20th atmospheric pressure or less, 10 minus 35th atmospheric pressure or more, and the mixed gas. And a reduction step of reducing carbon dioxide by reducing carbon dioxide in the mixed gas to carbon by heating the mixed gas.   The carbon dioxide reduction method according to claim 1, further comprising a step of discharging the mixed gas from which the carbon dioxide has been removed to the atmosphere.   2. The carbon dioxide reduction method according to claim 1, wherein the mixed gas containing carbon dioxide includes one or more of nitrogen, oxygen, argon, neon, and helium. 2. The carbon dioxide according to claim 1, wherein the extremely low oxygen partial pressure is generated by discharging oxygen molecules in the mixed gas to the outside air using oxygen ion conductivity of a solid electrolyte body. Reduction method. The carbon dioxide reduction method according to claim 1, wherein the heating temperature in the reduction step is 300 ° C or higher and 3000 ° C or lower.   A mixed gas generating device that generates a mixed gas containing carbon dioxide gas; and an oxygen molecule discharging device that generates an oxygen concentration in the mixed gas to an oxygen partial pressure of 10 minus 20th atmospheric pressure or less and 10 minus 35th atmospheric pressure or more. A carbon dioxide reduction device comprising: a reduction device that heats the mixed gas having the oxygen partial pressure to reduce carbon dioxide in the mixed gas to carbon.   A mixed gas generating device that generates a mixed gas containing carbon dioxide gas; and an oxygen molecule discharging device that generates an oxygen concentration in the mixed gas to an oxygen partial pressure of 10 minus 20th atmospheric pressure or less and 10 minus 35th atmospheric pressure or more. A reduction device that heats the mixed gas having a partial pressure of oxygen to reduce carbon dioxide in the mixed gas to carbon, and the reduction device includes the mixed gas generation device.   The carbon dioxide reduction device according to claim 6 or 7, further comprising a discharge device that discharges the mixed gas from which the carbon dioxide has been removed to the atmosphere.   The carbon dioxide reduction device according to claim 6 or 7, wherein the mixed gas containing carbon dioxide contains one kind or plural kinds of nitrogen, oxygen, argon, neon, and helium. The oxygen molecule discharging apparatus discharges oxygen molecules in the mixed gas to the outside of the oxygen molecule discharging apparatus by utilizing oxygen ion conductivity of a solid electrolyte body. Carbon reduction device.   The carbon dioxide reduction device according to claim 6 or 7, wherein the heating temperature is not less than 300 ° C and not more than 3000 ° C.

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