JP6334947B2 - Decomposition method of carbon dioxide by microwave nonequilibrium plasma - Google Patents

Description

  The present invention relates to a method capable of decomposing carbon dioxide with non-equilibrium plasma and obtaining carbon monoxide useful as an industrial raw material as a product after decomposition at a high decomposition rate.

  Carbon dioxide is generated when burning fossil fuels such as coal, oil, and natural gas, and petroleum products such as plastics and chemical fibers. As the concentration of carbon dioxide in the atmosphere increases, some of the infrared radiation emitted from the surface is absorbed, resulting in a greenhouse effect. This greenhouse effect is considered to be the main cause of global warming in recent years.

  In order to prevent this global warming, there is an international cry for the need to reduce carbon dioxide emissions, but in Japan we will reduce greenhouse gas emissions by 60 to 80% by 2050. We set goals and are leading the world toward the realization of a low-carbon society.

  On the other hand, the nuclear power plant accident caused by the Tohoku-Pacific Ocean Earthquake that occurred in March 2011 resulted in the shutdown of nuclear power plants nationwide, causing a shortage of power supply as a practical problem.

  Therefore, measures have been taken to compensate for the shortage of power supply by utilizing thermal power plants that have been suspended until now. However, since fossil fuels are used in thermal power plants, the amount of carbon dioxide generated increases. End up.

  Under such circumstances, various methods have been proposed as carbon dioxide treatment techniques. For example, a carbon dioxide capture and storage (CCS) method that efficiently collects carbon dioxide from an emission source such as a thermal power plant or factory, and a non-thermal plasma atmosphere as described in Patent Document 1 below. A method for decomposing carbon dioxide into carbon and oxygen, a method for converting carbon dioxide into a combustible gas by a plasma gas phase reaction described in Patent Document 2 below, and a dielectric barrier as described in Patent Document 3 below A method of decomposing carbon dioxide using electric discharge has been proposed.

Special table 2011-500309 JP2003-27241 JP2013-147411A

  The above-mentioned method of burying carbon dioxide in the ground is based on the idea that carbon dioxide is a very stable substance and its decomposition is very difficult, so it is buried deeply in the ground without being decomposed. However, this method does not fundamentally reduce the amount of carbon dioxide, and the processing cost is enormous.

  In addition, the method of decomposing carbon dioxide into carbon and oxygen in non-thermal plasma and the method of converting carbon dioxide to combustible gas by plasma gas phase reaction can fundamentally reduce the amount of carbon dioxide. Catalysts and gasifying agents are required for carbon decomposition, which complicates the equipment structure and increases equipment costs.

  On the other hand, the method of decomposing carbon dioxide using dielectric barrier discharge has the advantage that it can fundamentally reduce the amount of carbon dioxide and does not require a catalyst or gasifying agent to decompose carbon dioxide. There is a problem that the decomposition rate is as low as 46% at the maximum.

  Therefore, the present invention provides a carbon dioxide decomposition method that can decompose carbon dioxide at a high decomposition rate without using a catalyst or a gasifying agent.

The invention according to claim 1 irradiates a microwave into a system whose pressure is reduced to less than 1000 [Pa], and introduces carbon dioxide alone at the irradiation position of the microwave without using a catalyst or a gasifying agent. The carbon dioxide charged is ionized to obtain carbon monoxide at a conversion rate of at least 46% .

According to a second aspect of the present invention, in the first aspect of the invention, when the microwave is output at 700 [W], the pressure in the system is reduced to 200 [Pa], and the microwave is reduced from 700 [W]. When the output is made lower, the pressure in the system is further reduced from 200 [Pa] .

According to the first aspect of the present invention, it is possible to decompose carbon dioxide at a high decomposition rate without using any catalyst or gasifying agent by simply irradiating the system with a pressure reduced to less than 1000 [Pa]. It becomes possible.

According to the second aspect of the present invention, when the microwave output is 700 [W], the inside of the system is depressurized to 200 [Pa], thereby ionizing carbon dioxide alone to carbon monoxide with high efficiency. In the case where the microwave output is set lower than 700 [W] and the power consumption is suppressed, the decomposition rate of carbon dioxide can be further increased by further reducing the pressure in the system from 200 [Pa].

It is a whole block diagram which shows the processing apparatus for implement | achieving the decomposition method of the carbon dioxide by this invention.

  Hereinafter, an embodiment of the present invention will be described with reference to FIG. FIG. 1 shows a processing apparatus A for realizing the carbon dioxide decomposition method according to the present invention.

  The processing apparatus A includes a microwave oscillator 1, a microwave waveguide 2, a carbon dioxide supply tube 3, a reaction tube 4 that generates plasma therein, and a vacuum pump 5 that adjusts the atmospheric pressure in the reaction tube 4. The pressure gauge 6 for measuring the atmospheric pressure in the reaction tube 4 is generally configured.

  The microwave waveguide 2 absorbs the reflection of the microwave oscillated by the microwave oscillator 1 and prevents the microwave from returning into the oscillator 1, a power monitor 8 for examining the intensity of the microwave, A stub tuner 9 for focusing the microwave on the plasma forming part X in the reaction tube 4 by resonating the microwave is provided.

  The carbon dioxide supply pipe 3 includes a mass flow controller 10 that adjusts the amount of carbon dioxide supplied into the reaction pipe 4.

  The reaction tube 4 is formed of a transparent hollow quartz tube that allows microwaves guided by the microwave waveguide 2 to pass therethrough. An upper sealing plug 11 that shuts off the outside air is attached.

  At the lower end of the reaction tube 4, a lower end sealing plug 13 connected only to the pressure adjusting tube 12 connected to the vacuum pump 5 is attached, and on the outer periphery of the reaction tube 4, the micro-tube irradiated in the reaction tube 4 is attached. A microwave leakage prevention network 14 for preventing waves from leaking outside the reaction tube 4 is attached.

  A switching valve 17 for switching the gas (oxygen or carbon monoxide) in the reaction tube 4 to the sampling port 15 or the exhaust pipe 16 and discharging it is attached to the rear stage of the vacuum pump 5.

  Next, a method for decomposing carbon dioxide using the processing apparatus A configured as described above will be described. When carbon dioxide is decomposed, carbon dioxide alone is supplied from the supply pipe 3 shown in FIG. The supply amount of carbon dioxide is adjusted by the mass flow controller 10, and the carbon dioxide adjusted to the predetermined supply amount is supplied into the reaction tube 4 through the supply tube 3 penetrating the upper sealing plug 11.

  Next, the vacuum pump 5 is started, and the inside of the reaction tube 4 is evacuated and depressurized via the atmospheric pressure adjusting tube 12 connected to the lower sealing plug 13. At this time, the atmospheric pressure in the reaction tube 4 is adjusted to less than 1000 [Pa] (for example, 200 [Pa]) using the pressure gauge 6.

  Subsequently, when the microwave oscillator 1 is started and a microwave having a predetermined output (for example, 700 [W]) is output, the microwave propagates from the waveguide 2 to the power monitor 8 via the isolator 7, and the power monitor. The incident power is detected by 8. At this time, the isolator 7 absorbs the reflected microwave and protects the microwave oscillator 1 as described above. The power of the reflected microwave is detected by the power monitor 8.

  The microwave that has passed through the waveguide 2 is resonated by the stub tuner 9, and is irradiated to the reaction tube 4 so that the maximum amount of microwave is consumed in the plasma forming portion X of the reaction tube 4.

  The irradiated microwave passes through the reaction tube 4 made of a transparent quartz tube, enters the reaction tube 4, and is irradiated to the carbon dioxide supplied into the reaction tube 4. Carbon dioxide is ionized in the plasma forming part X in the reaction tube 4 to be converted into plasma.

  The plasma generated at this time is generated by glow discharge because the pressure in the reaction tube 4 is reduced to less than 1000 [Pa]. Glow discharge is a more stable discharge in a wider range than corona discharge, and can be generated with lower energy than arc discharge.

  By converting carbon dioxide into plasma in this way, carbon dioxide is decomposed into oxygen and carbon monoxide. The conversion rate to carbon monoxide at this time can maintain a high numerical value as long as the pressure in the reaction tube 4 is reduced to less than 1000 [Pa] as described above.

  In particular, when the microwave output is set to 700 [W] and the pressure in the reaction tube 4 is reduced to 200 [Pa], the decomposition rate of carbon dioxide is 95%, and a very high decomposition rate can be realized. Even if the microwave output is lowered, the decomposition rate can be further increased by further reducing the pressure in the reaction tube 4.

  The decomposed oxygen and carbon monoxide are discharged from the reaction tube 4 through the pressure adjusting tube 12 and are collected from the sampling port 15 by operating the switching valve 17 to analyze the gas properties. Or it can take out from the exhaust pipe 16 and can utilize it as an industrial raw material. In particular, carbon monoxide can be used as a raw material for producing alcohol, glycols, carboxylic acids (formic acid, acetic acid, etc.), and the like.

  Further, there is almost no precipitation of carbon or the like in the decomposition process of carbon dioxide, and there is no problem that soot adheres to the inner peripheral surface of the reaction tube 4 and prevents the incidence of microwaves.

  Furthermore, since no rare gas is required as a reactive gas for the formation of plasma, decomposition of carbon dioxide can be realized at low cost.

  As described above, the method for decomposing carbon dioxide using microwave non-equilibrium plasma according to the present invention does not require any catalyst or gasifying agent at the time of decomposition, so that the equipment structure of the processing apparatus is prevented from becoming complicated. Cost can be reduced.

  Further, the decomposition rate of carbon dioxide (conversion rate to carbon monoxide) can be very high as compared with the conventional decomposition method, which is very effective.

  It can be used for carbon dioxide decomposition.

DESCRIPTION OF SYMBOLS 1 Microwave oscillator 2 Microwave waveguide 3 Carbon dioxide supply pipe 4 Reaction pipe 5 Vacuum pump 6 Pressure gauge 7 Isolator 8 Power monitor 9 Stub tuner 10 Mass flow controller 11 Upper sealing plug 12 Atmospheric pressure adjustment pipe 13 Lower sealing plug 14 Microwave leakage prevention network 15 Sampling port 16 Exhaust pipe 17 Switching valve A Processing device X Plasma formation part

Claims (2)

By irradiating microwaves into a system whose pressure is reduced to less than 1000 [Pa] and introducing carbon dioxide alone at the microwave irradiation position, the introduced carbon dioxide is ionized without using a catalyst or a gasifying agent. A method of decomposing carbon dioxide with a microwave nonequilibrium plasma, characterized in that carbon monoxide is obtained at a conversion rate of at least 46% .   When the microwave is output at 700 [W], the inside of the system is depressurized to 200 [Pa], and when the microwave is output below 700 [W], the inside of the system is started from 200 [Pa]. 2. The method for decomposing carbon dioxide with microwave nonequilibrium plasma according to claim 1, wherein the pressure is further reduced.

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