Gas decomposition method, gas decomposition device, and gas decomposition system

Abstract

Provided is a method for decomposing a treatment target gas, the method involving decomposing dinitrogen monoxide while suppressing emission of NOx.　This method is for decomposing a treatment target gas, the method comprising decomposing dinitrogen monoxide in the treatment target gas by providing, to the treatment target gas, energy for exciting a gas contained in the treatment target gas. The treatment target gas contains at least dinitrogen monoxide and carbon dioxide. The gas concentration of the carbon dioxide contained in the treatment target gas is higher than the concentration of each gas contained in the treatment target gas excluding the carbon dioxide.

Description

Gas decomposition method, gas decomposition device, and gas decomposition system

[0001] The present invention relates to a method for decomposing a gas to be treated, a gas decomposition apparatus, and a gas decomposition system.

[0002] Since the Industrial Revolution, the average temperature of the Earth has been rising, making measures to combat global warming an urgent issue. Greenhouse gases known to cause global warming include carbon dioxide, methane, nitrous oxide, and chlorofluorocarbons. Of these gases, carbon dioxide is the most widely emitted, followed by methane, and then nitrous oxide.

[0003] Meanwhile, in terms of global warming potential (GWP), it has been reported that the GWP of methane is 25 times that of carbon dioxide, and that of nitrous oxide is 298 times that of carbon dioxide. For these reasons, the impact of nitrous oxide emissions on global warming cannot be ignored.

[0004] Nitrous oxide is emitted not only during the disposal of human and livestock waste and agricultural activities, but also during industrial activities such as the manufacture of chemical products and the burning of waste. In order to curb global warming, it is necessary to prevent the release of nitrous oxide into the atmosphere.

[0005] Nitrous oxide is decomposed to prevent it from being released into the atmosphere. High-temperature combustion and catalytic methods have been used to decompose nitrous oxide. However, high-temperature combustion requires a large amount of energy to burn the gas. Using fossil fuels to secure large amounts of energy increases carbon dioxide emissions, making it undesirable as a measure against global warming. Catalytic methods also require the gas to be heated to high temperatures. Furthermore, ammonia must be procured for use as a catalyst and reducing agent, and there are also issues with wastewater treatment after treatment. Therefore, catalytic methods are also undesirable as a measure against global warming.

[0006] Another method for decomposing nitrous oxide is to use light (see Patent Documents 1 and 2).

[0007] JP 2024-022455 A JP 2024-021127 A

[0008] Nitrous oxide (hereinafter referred to as "N ２ When light is irradiated onto a gas containing N, ２ O can be decomposed into nitrogen gas and oxygen gas, but N ２ In this specification, NOx refers to nitrogen monoxide (hereinafter sometimes referred to as "NO"), nitrogen dioxide (hereinafter sometimes referred to as "NO"), and the like. ２ "), nitrogen trioxide (hereinafter referred to as "NO ３ "), and dinitrogen pentoxide (hereinafter referred to as "N ２ O ５ " is an expression that includes the following:

[0009] NOx has adverse effects on humans and animals, so ２ In order to neutralize the NOx generated during the decomposition process of O, nitric acid (hereinafter referred to as "HNO ３ ". You can consider converting it to "N". ２ O to HNO ３ To obtain N ２ The advantage of this method is that it can fix O without releasing it into the atmosphere. ２ Nitric acid is a useful substance in various industrial fields, including the chemical industry, so N ２ Obtaining nitric acid from O has high business value. ２ When nitric acid can be obtained by decomposing O, the amount of nitric acid produced for the purpose of producing nitric acid itself can also be reduced. ２ Since it emits O, it is necessary to reduce the N that was previously emitted when producing nitric acid itself. ２ O emissions can also be reduced.

[0010] N ２ Decomposes O to HNO ３ The chemical reaction that produces N will be described in detail later. ２ Decomposes O to HNO ３The reaction pathway leading to the production of N is complex. ２ The decomposition of O stops midway through the reaction pathway, and HNO ３ As mentioned above, NOx has adverse effects on humans and animals, so it is necessary to suppress NOx emissions as much as possible.

[0011] Therefore, the present invention is a method for reducing NOx emissions while ２ The present invention aims to provide a method for decomposing a gas to be treated, a decomposition device, and a decomposition system that appropriately decompose O.

[0012] In the method for decomposing a gas to be treated disclosed in this specification, the gas to be treated contains at least nitrous oxide and carbon dioxide, the gas concentration of carbon dioxide contained in the gas to be treated is higher than the concentrations of all gases contained in the gas to be treated other than carbon dioxide, and the nitrous oxide in the gas to be treated is decomposed by providing the gas to be treated with energy for exciting the gas contained in the gas to be treated.

[0013] The details will be described later, but the background to the above decomposition method will be briefly explained. ２ When the temperature in the decomposition reactor for decomposing O is high, N ２ O to HNO ３ It was noticed that the reaction stopped midway through the reaction pathway leading to the production of ozone (hereinafter referred to as "O"), making it more likely for NOx to remain. ３ ") is converted into an oxygen molecule (O ２ ) and oxygen atom O( ３ P) in the decomposition reactor. ３ decreases. ３ is N ２ The NO produced by decomposition of O is treated as HNO ３ It is a substance necessary to convert it to O( ３ P) is the ground state oxygen atom, called "triplet oxygen." ３ When decreases, HNO ３ The NOx is more likely to remain in the atmosphere.

[0014] Based on the above observation, the inventor ２ The gas to be treated from which O is discharged is carbon dioxide (hereinafter referred to as "CO ２ In this method, N ２ CO at higher concentrations than O ２ This provides the gas to be treated containing the above with energy for exciting the gas.

[0015] The energy ２ From this, a large amount of CO and oxygen atoms O ( １ D) or O( ３ P) is generated (see equations (24) and (25) below). １ D) is a highly reactive excited state of oxygen atom called "singlet oxygen." ２ When the temperature in the decomposition reactor for decomposing O is high, the O ３ is insufficient, and N ２ The reaction is likely to stop with NO produced from O. However, CO ２ The large amount of CO produced from ２ Also, CO ２ A large amount of oxygen atoms O( ３ P) says NO to NO ２ This is then oxidized to nitrate by hydroxyl radicals, which will be described later. In this way, the remaining NOx is reduced.

[0016] On the other hand, N ２ When the temperature inside the decomposition reactor for decomposing O is low, the reduction of NO by CO becomes difficult. ３ promotes the nitration of NO. ３ By complementing the differences in the properties of N and CO, the reaction field in the decomposition reactor can be kept at a high or low temperature. ２ The reaction can proceed without being stopped by NO produced from O. ２ O and CO ２ This can be said to be a synergistic effect of the mixed gas to be treated.

[0017] The gas to be treated may further contain water vapor. Hydroxy radicals generated from water vapor are converted into NO ２ When it acts on the nitrate, it produces nitric acid. ２ From NO ３ Through N ２ O ５ When this is generated, N can be produced without relying on water vapor. ２ O ５ Therefore, nitric acid can be generated even if the gas to be treated does not contain water vapor.

[0018] The energy may be light energy having a main emission wavelength of 160 nm or more and less than 200 nm.

[0019] The energy may be electron energy generated by converting the gas to be treated into plasma.

[0020] The gas to be treated may be brought into contact with a catalyst.

[0021] The catalyst may be a three-way catalyst used to promote the reduction of nitric oxide produced by the decomposition of nitrous oxide.

[0022] The catalyst may be a two-way catalyst used to promote oxidation of at least one of nitric oxide produced by decomposition of dinitrogen monoxide and carbon monoxide produced from carbon dioxide.

[0023] A gas containing oxygen may be additionally supplied to the gas to be treated after the energy is applied.

[0024] The decomposition device for a gas to be treated disclosed in this specification comprises: a gas supply port that introduces the gas to be treated into the decomposition device, the gas containing at least nitrous oxide and carbon dioxide, wherein the gas concentration of carbon dioxide contained in the gas to be treated is higher than the concentrations of any other gases contained in the gas to be treated except for carbon dioxide; and an energy source that provides energy to the gas to be treated introduced from the gas supply port into the decomposition device, for exciting gases contained in the gas to be treated, in order to decompose the nitrous oxide in the gas to be treated.

[0025] The decomposition device may be provided with a gas concentration adjusting unit connected to the gas supply port that adjusts the amount of gas components contained in the gas to be treated so that the gas concentration of carbon dioxide contained in the gas to be treated is higher than the concentration of any other gas other than carbon dioxide contained in the gas to be treated.

[0026] The energy may be light energy having a main emission wavelength of 160 nm or more and less than 200 nm, and the energy source may be a light source that radiates the light energy. The light source may be an excimer lamp. The main wavelength may be 172 nm or near 172 nm.

[0027] The energy may be electron energy that converts the gas to be treated into plasma, and the energy source may be an electrode that supplies the electron energy.

[0028] The decomposition device may include a three-way catalyst that promotes the reduction of nitric oxide produced by the decomposition of nitrous oxide.

[0029] The decomposition device may be provided with a two-way catalyst used to promote oxidation of at least one of nitric oxide produced by decomposition of the dinitrogen monoxide and carbon monoxide produced from the carbon dioxide.

[0030] The decomposition device may include an oxygen supply port for adding an oxygen-containing gas to the gas to be treated after the energy has been applied, and the two-way catalyst may be positioned so as to come into contact with the gas to be treated to which the oxygen-containing gas has been added.

[0031] The decomposition system for a gas to be treated disclosed in this specification includes the above-mentioned decomposition device for a gas to be treated, and a gas supply source connected to the gas supply port and supplying the gas to be treated into the decomposition device.

[0032] This allows N to be released regardless of the temperature of the reaction field inside the decomposition reactor. ２ As a result, NOx emissions are suppressed while N ２ It is possible to provide a method, apparatus, and system for decomposing a gas to be treated that appropriately decomposes O. Providing such a method, apparatus, and system for decomposing a gas will greatly contribute to achieving Goal 13 of the Sustainable Development Goals (SDGs) led by the United Nations, which is to "take urgent action to combat climate change and its impacts."

[0033] 1A is a diagram showing a first embodiment of a gas decomposition device. FIG. 1B is a cross-sectional view taken along line S1-S1 in FIG. ２ 1 is a diagram showing the mechanism of O decomposition. ２ O and CO ２ 8A. FIG. 8A is a cross-sectional view taken along line S6-S6 of FIG. 9A. FIG. 9A is a cross-sectional view taken along line S7-S7 of FIG. 10A. FIG. 10B is a cross-sectional view taken along line S7-S7 of FIG. 10A. FIG. 10C is a cross-sectional view taken along line S7-S7 of FIG. 10A. FIG. 10D is a cross-sectional view taken along line S7-S7 of FIG. 10A.

[0034] The embodiments will be described with reference to the drawings as appropriate. Note that all drawings, except for graphs, are schematic illustrations, and the dimensional ratios in the drawings do not necessarily correspond to the actual dimensional ratios, and the dimensional ratios between the drawings do not necessarily correspond to the actual dimensional ratios.

[0035] First Embodiment [Outline of Gas Decomposition Apparatus] The gas decomposition apparatus has a gas supply port for introducing a gas to be treated into the decomposition apparatus, and an energy source for imparting energy to a gas contained in the gas to be treated. ２ O gas and CO ２ The gas mixture includes a gas.

[0036] A first embodiment of a gas decomposition apparatus is shown in Figure 1A. Figure 1B is a cross-sectional view taken along line S1-S1 in Figure 1A. In gas decomposition apparatus 10 shown as the first embodiment, the energy source that provides energy for exciting gases contained in gas G1 is light source 1 that emits ultraviolet light L1.

[0037] The gas decomposition device 10 has a decomposition reactor 2. The light source 1 is disposed within the decomposition reactor 2. The decomposition reactor 2 has a gas supply port 3i and a gas exhaust port 3o. The gas supply port 3i and the gas exhaust port 3o are disposed to face each other with the light source 1 in between. In this specification, the light L1 emitted from the light source 1 is illustrated by a solid arrow pointing outward from the light source 1.

[0038] Gas G1 is supplied into the decomposition reactor 2 from the gas supply port 3i. Light L1 emitted from the light source 1 is irradiated onto the gas G1 in the decomposition reactor 2. The light L1 acts as a trigger, and a chain reaction of chemical reactions, which will be described later, occurs within the decomposition reactor 2 as a reaction field, resulting in the decomposition of N ２ The gas G2 after the chemical reaction due to the light irradiation is discharged from the gas outlet 3o. By performing these steps continuously, the N contained in the gas G1 is decomposed. ２ O can be decomposed continuously.

[0039] The light source 1 is electrically connected to the control unit 5, and when power is supplied from the control unit 5 to the light source 1, the light source 1 is turned on. Details of the light source 1 will be described later. ２The light intensity of the light source 1 may be set taking into consideration the degree of decomposition of O.

[0040] From the viewpoint of increasing the decomposition efficiency, it is more preferable to design the decomposition reactor 2 so that the light L1 reaches sufficiently into the decomposition reactor 2. Therefore, the distance D1 (see FIG. 1A or FIG. 1B) between the surface of the light source 1 and the inner wall of the decomposition reactor 2 is relatively narrow. The distance D1 may be, for example, 500 mm or less, and preferably 300 mm or less. The distance D1 is set to an appropriate distance so that the light is not excessively attenuated. This can reduce the amount of gas that passes through the decomposition reactor 2 without being irradiated with the light L1.

[0041] A catalyst 8 is supported on the inner wall of the decomposition reactor 2. The catalyst 8 may be a three-way catalyst or a two-way catalyst. Both a three-way catalyst and a two-way catalyst may be used. Details of the catalyst 8 will be described later.

[0042] [N ２ 2, the N decomposition mechanism of the light L1 ２ The gas decomposition mechanism of N is explained below. ２ The decomposition mechanism when light energy is used to decompose O will be explained, but the decomposition mechanism when the gas to be processed is converted into plasma is basically the same. ２ The decomposition method for O is N using ultraviolet light. ２ Direct decomposition of O and UV-generated O ( １ D) N ２ There is an indirect decomposition of O.

[0043] UV light N ２ The direct decomposition of O is illustrated in chemical reaction R1 in Figure 2. Ultraviolet light with a wavelength of 340 nm or less is used to decompose N ２ When irradiated to O, N is generated according to the following formula (1): ２ O is decomposed to N ２ and O ( １ D). ２ O+hν(≦340nm) → N ２ +O( １ D) ... (1)

[0044] In this specification, the notation "hν (≦Wnm)" (where "W" represents a number) represents the energy of light with a wavelength of W (nm) or less. For example, the decomposition reaction of formula (1) indicates that it occurs with ultraviolet light with a wavelength of 340 nm or less. Looking at formula (1) alone, it would be sufficient to use ultraviolet light with a wavelength of 340 nm or less, but the N ２ The absorption cross section for O is small. To make the decomposition reaction of formula (1) more efficient, it is advisable to use light having a wavelength of less than 200 nm, which has a relatively large absorption cross section. This also applies to other light-induced decomposition reactions described below.

[0045] UV-generated O( １ D) N ２ The indirect decomposition of O will be explained. ２ O( １ D) by N ２ The chemical reaction for decomposing O is shown as chemical reaction R2 in Figure 2. O( １ D) is N ２ When it comes into contact with O, NO is produced according to the following formula (2): ２ O+O( １ D) → 2NO...(2)

[0046] Also, O( １ D) is an oxygen molecule (O ２ ) and nitrogen molecules (N ２ ) may be generated. ２ O+O( １ D) → O ２ +N ２ ...(3) The main part of formula (3) is shown as chemical reaction R3 in FIG.

[0047] O ( required for the reactions of formulas (2) and (3) １ D) is calculated by equation (1) ２ However, in the reaction field, there is O generated by the formula (3) ２ There is O contained originally in the gas G1 itself. ２ or O generated by the reaction described below３ In such a case, the following equations (4) and (5) can also be used to calculate O( １ D) is produced. ２ +hν(≦175nm) → O( ３ P) + O( １ D) ...(4) O ３ +hν(≦411nm) → O( １ D) + O ２ ...(5) Equation (4) is shown as chemical reaction R4 and chemical reaction R5 in Fig. 2. The main part of equation (5) is shown as chemical reaction R6 in Fig. 2.

[0048] O required for the reaction of formula (5) ３ can be produced through the reactions of the following formulas (1), (4), (6), (7), and (8) (formulas (1) and (4) are shown again). In this specification, "M" included in the chemical reaction formula represents a third body. ２ O+hν(≦340nm) → N ２ +O( １ D) ...(1) O ２ +hν(≦175nm) → O( ３ P) + O( １ D) ...(4) O ２ +hν(≦242nm) → O( ３ P) + O( ３ P) ...(6) O( １ D) + M → O ( ３ P) + M ... (7) O ２ +O( ３ P) + M → O ３ +M ... (8) Formula (6) is shown as chemical reaction R5 in Figure 2. Chemical reaction R5 corresponds to formula (4) or formula (6) depending on the wavelength of the ultraviolet light. A key part of formula (7) is shown as chemical reaction R7 in Figure 2. A key part of formula (8) is shown as chemical reaction R8 in Figure 2. As shown in Figure 2, the arrow (broken line) of chemical reaction R17, which is the reverse reaction of chemical reaction R8, indicates that O ３ From O ２ and O ( ３There may also be a reaction in which the compound is decomposed into O (P). Regarding chemical reaction R17, see the later section, "O due to a high-temperature reaction field." ３ More details are provided in the section on "Shortage of

[0049] Thus, N due to the ultraviolet light energy hν ２ Direct decomposition of O and UV-generated O ( １ D) N ２ Indirect decomposition of O has been described. Usually, both direct and indirect decomposition occur. The ratio of direct and indirect decomposition varies depending on the gas composition of gas G1.

[0050] The NO produced by the chemical reaction R2 of formula (2) is converted into O ( ３ P) causes the reaction of formula (9) to produce nitrogen dioxide (hereinafter referred to as "NO ２ ") is produced. NO + O ( ３ P) → NO ２ (9) The main part of formula (9) is included in chemical reaction R9 in FIG.

[0051] In addition, when a hydroxyl radical (hereinafter sometimes referred to as "OH") is present in the reaction field, NO is converted to NO via the formulas (10) and (11). ２ is produced. NO + OH → HNO ２ ...(10) HNO ２ +OH → NO ２ +H ２ O 2 (11) Equation (10) is shown as chemical reaction R10 in Fig. 2. Equation (11) is shown as chemical reaction R11 in Fig. 2.

[0052] OH in the reaction field is generated from water. That is, the gas G1 contains water (water vapor or mist, etc.). ２ When H is included, it is generated in the decomposition reactor 2 according to formula (12). ２ O+hν(≦242nm) → OH+H...(12)

[0053] In addition, when ozone is present in the reaction field, NO is converted to NO via the reaction of formula (13). ２is produced. NO + O ３ +M → NO ２ +O ２ +M (13) The essential part of formula (13) is included in chemical reaction R9 in FIG.

[0054] NO ２ is the reaction field O( ３ P) causes the reaction of formula (14), and NO ３ When ozone is present in the reaction field, NO ２ The reaction of formula (15) occurs with ozone, and NO ３ Generates NO ２ +O( ３ P) + M → NO ３ +M...(14) NO ２ +O ３ +M → NO ３ +O ２ +M (15) The main part of the reactions of formulas (14) and (15) is shown as chemical reaction R12 in FIG.

[0055] NO produced by chemical reaction R12 ３ and NO present in the reaction field ２ The reaction of equation (16) occurs, and N ２ O ５ Generates NO ３ +NO ２ → N ２ O ５ ...(16) The reaction of formula (16) is shown as chemical reaction R13 in FIG.

[0056] In addition, NO produced by chemical reaction R12 ３ is NO or O ( ３ P) to produce the reaction of formula (17) or (18), and NO ２ Sometimes it goes back to ３ +NO → NO ２ +NO ２ ...(17) NO ３ +O( ３ P) → NO ２ +O ２The reactions of formulas (17) and (18) are shown as chemical reaction R14 in FIG.

[0057] N ２ O ５ together with the water vapor or water mist present in the reaction field, the reaction of formula (19) occurs, and HNO ３ Generate N ２ O ５ +H ２ O → 2HNO ３ ...(19) The reaction of formula (19) is shown as chemical reaction R15 in FIG. ２ O ５ By bubbling gas containing N in water, ２ O ５ and water to induce the reaction of formula (19).

[0058] When OH is present in the reaction field, NO is reacted as shown in formula (20). ２ However, nitric acid can be obtained without going through the chemical reactions R12, R13, and R15. ２ +OH → HNO ３ ...(20) The reaction of formula (20) is shown as chemical reaction R16 in FIG.

[0059] As mentioned above, N ２ The series of reactions that convert O to nitric acid requires sufficient O ３ It is assumed that there is sufficient O in the reaction field. ３ In the absence of NOx, nitration does not occur, and NOx, especially NO and NO ２ will remain in the reaction field. ３ There are several factors that contribute to this shortage, which are explained below.

[0060] [O by NOx cycle ３ The NOx cycle reaction will be explained. According to the formulas (9) and (13) shown below, NO is converted into NO ２ On the other hand, NO ２reacts with oxygen atoms O according to the following formula (21) or (22), or is photodecomposed according to formula (23) to produce NO. ３ P) → NO ２ ...(9) NO+O ３ +M → NO ２ +O ２ +M...(13) NO ２ +O( １ D) → NO + O ２ ...(21) NO ２ +O( ３ P) → NO+O ２ ...(22) NO ２ +hν(≦398nm) → NO+O( ３ P) ... (23)

[0061] NO to NO shown in the previous paragraph ２ and a reaction to produce NO ２ The reaction that produces NO from O can be repeated. This is called the NOx cycle reaction. ３ Continue to consume. ３ By consuming ３ When the reaction rate decreases, the reactions of formulas (13) and (15) become slower. This means that the chemical reaction between R9 and R12 becomes difficult to occur, and NO and NO are present in the reaction field. ２ remains.

[0062] [O due to high temperature reaction field ３ Only the occurrence of NOx cycle reactions is ３ The inventors have found that N ２ It was discovered that if the temperature in the decomposition reactor for decomposing O is high, the reaction stops midway through the complex reaction pathway leading to nitric acid. In detail, if the temperature of the reaction field is high, O ３ GA O ２ and O ( ３ P) is decomposed into O ３ As mentioned above, O ３ is converted from NO to NO using equation (13). ２or by equation (15) NO ２ No ３ Because it is an essential substance for converting ３ decreases, NO becomes HNO ３ This does not result in an increase in NOx emissions.

[0063] [CO ２ The present inventors have ３ As a measure to counter the residual NOx caused by the reduction of CO ２ I realized that using CO is effective. ２ is a compound obtained by combining CO and an oxygen atom (O( ３ P) or O( １ D)) is produced. ２ +hν(≦166nm) → CO+O( １ D) ...(24) CO ２ +hν(≦227nm) → CO+O( ３ P) ... (25)

[0064] The CO produced by the reactions (24) and (25) undergoes the reaction (26) in the presence of a three-way catalyst: 2NO + 2CO → N ２ +2CO ２ ...(26)

[0065] The reaction of formula (26) is a reaction that reduces NO to nitrogen. The reaction of formula (26) converts the NO remaining in the reaction field into nitrogen gas. In addition, when NO decreases, the reactions of formulas (9) and (13) decrease, so NO ２ The reduction in NO also reduces the NOx cycle reaction, and O ３ The shortage will be alleviated.

[0066] Incidentally, the reaction of formula (26) occurs more easily as the temperature of the reaction field increases. This is because the higher the temperature of the reaction field, the more easily O ３ This effectively combines with the phenomenon of a decrease in O ３ is difficult to decrease, ２The "O decomposition mechanism" promotes the production of nitric acid. ３ However, the reduction of NO by CO shown in formula (26) occurs, and the amount of residual NOx decreases. ２ In a reaction field containing a large amount of NOx, NOx can be reduced regardless of the temperature.

[0067] The reactions of formulas (24) and (25) occur due to the partial reaction of CO ２ Therefore, the CO ２ The higher the concentration, the better. ２ The gas concentration of CO contained in the gas G1 to be treated ２ In this case, the concentration of CO ２ The concentration is N ２ This means that the concentration is higher than the O concentration.

[0068] In equations (24) and (25), CO ２ from oxygen atom (O( １ D) or O( ３ P)) is also produced, but oxygen atoms (O( ３ P)) also contributes to the production of ozone through chemical reactions R7 and R8 (see equations (7) and (8)), and NO through chemical reaction R9. ２ (see equation (9)), and NO by chemical reaction R ３ contributes to the production of (see formula (14)). １ D)) also involves the reaction of N by chemical reaction R2 and chemical reaction R3. ２ contributes to the decomposition of O (see formulas (2) and (3)). ２ The significance of using CO ２ Not only does it reduce NOx by utilizing the reduction action of CO generated from ２ Another way is to use the oxygen atoms produced by the nitrification to promote nitration.

[0069] [Light Source] The light source 1 of this embodiment preferably emits light L1 having a main emission wavelength of 160 nm or more and less than 200 nm. FIG. 3 shows the absorption spectrum of light in a medium. The horizontal axis represents wavelength, and the vertical axis represents absorption cross section (unit: cm ２ ・molecule －１ In FIG. 3, the curve C1 represents N ２ curve C1 shows the absorption cross section of CO ２ The absorption cross section of

[0070] Curve C2 shows high absorption below 200 nm. ２ In order to generate oxygen atoms from N, it is preferable that the wavelength of light is 200 nm or less. In the curve C1, light is absorbed even at wavelengths exceeding 200 nm, and N ２ Although O is decomposed into nitrogen and oxygen atoms (see formula (1) above), this shows that the decomposition is accelerated below 200 nm. ２ Since there is a risk that the absorption of O light may be hindered, a wavelength of 165 nm or more is preferred, at which point the absorption of curve C2 does not become too high.

[0071] The light source 1 of this embodiment uses a xenon excimer lamp that emits excimer light with a peak wavelength or main emission wavelength of 172 nm or near 172 nm. When the wavelength is 172 nm, the curve C1 (N ２ The absorption of light by CO ２ 3, ΔA is the difference between the light absorption of the curve C1 and the light absorption of the curve C2, which is about 10 times higher than that of the curve C2. ２ While sufficiently decomposing O, a large amount of CO ２ This results in light of a preferred wavelength that can decompose the desired amount.

[0072] In this specification, "near 172 nm" refers to a region within the range of 172 nm ± 5 nm. In this specification, "main emission wavelength" refers to a wavelength λi in a wavelength range Z(λi) that shows an integrated intensity of 40% or more of the total integrated intensity in the emission spectrum, when a wavelength range Z(λ) of ± 10 nm from a certain wavelength λ is defined on the emission spectrum. When the light source that emits light of the "main wavelength" has an extremely narrow half-width and shows high light intensity only at a specific wavelength, such as a xenon excimer lamp, the wavelength with the relatively highest light intensity (peak wavelength) can usually be considered to be the main wavelength.

[0073] As shown in FIG. 1B , light source 1 has a cylindrical arc tube, and xenon gas is sealed inside 1i of the arc tube. Excimer lamps are light sources that can be mass-produced stably and have a significant cost-reduction effect. The shape of the arc tube is not limited to a cylindrical shape, and light source 1 is not limited to a xenon excimer lamp but may be, for example, a low-pressure mercury lamp. Light source 1 may also be an excimer lamp in which a gas other than xenon is sealed. Light source 1 may also be a solid-state light source such as an LED or LD.

[0074] [Gas to be processed] The gas to be processed will be described in detail. As described above, the gas G1 to be processed supplied from the gas supply port 3i is N ２ O and CO ２ The gas G1 may also contain water, oxygen gas, nitrogen gas, air, or saturated hydrocarbons (particularly, alkanes having 10 or less, 6 or less, or 4 or less carbon atoms).

[0075] A case where the gas G1 contains water will be described. In this specification, water is a concept that includes water vapor, which is a gas, and atomized water, which is a liquid. When the gas G1 contains water, the water is irradiated with light L1, and hydroxyl radicals are generated according to formula (27). H ２ O+hν(≦242nm) → H+OH...(27)

[0076] Furthermore, water reacts with O( １ D) produces hydroxyl radicals.２ O+O( １ D) → 2OH...(28)

[0077] OH is the OH-containing compound that converts NO to NO in the above-mentioned chemical reactions R10 and R11 (see Equations (10) and (11)). ２ In addition, OH promotes the conversion of NO to NO in the above-mentioned chemical reaction R16 (see formula (20)). ２ Equations (10), (11) and (20) are shown again: NO + OH → HNO ２ ...(10) HNO ２ +OH → NO ２ +H ２ O...(11) NO ２ +OH → HNO ３ ...(20)

[0078] As shown in FIG. 2, R10, R11 and R16 are N ２ O to HNO ３ However, the formation of additional reaction pathways for producing OH and H is not essential for nitration. ２ This indicates that O may not be contained.

[0079] In the chemical reaction R15, as shown in formula (19), N ２ O ５ From HNO ３ To generate H ２ O is essential, but this H ２ As mentioned above, O is N ２ O ５ The gas G1 itself supplied from the gas supply port 3i contains H. ２ Chemical reaction R15 can be realized without including O. Equation (19) is shown again. ２ O ５ +H ２ O → HNO ３ +HNO ３ ...(19)

[0080] Gas G1 contains oxygen gas (O ２ As described above, the case where the gas G1 itself contains O ２ The gas G1 itself supplied from the gas supply port 3i may contain O. ２ By including more O( １ D) and O( ３ P) is generated. ３ P) through chemical reaction R8 to O ３ As mentioned above, O( ３ P) and O ３ is N ２ It is an important substance in the nitration of O.

[0081] Gas G1 contains nitrogen gas (N ２ ) will be described. Nitrogen gas itself does not directly contribute to the series of chemical reactions shown in FIG. 2, but it does not significantly impede the series of chemical reactions. Therefore, gas G1 may contain nitrogen gas. Furthermore, gas G1 may contain an inert gas other than nitrogen gas.

[0082] As can be seen from the fact that the gas G1 may contain water vapor, oxygen gas, and nitrogen gas, the gas G1 supplied from the gas supply port 3i may contain air. This air may be CDA (Clean Dry Air) or atmospheric air containing water vapor.

[0083] The saturated hydrocarbons that may be contained in the gas G1 supplied from the gas supply port 3i will be described. The saturated hydrocarbons are O( １ D), O( ３ The saturated hydrocarbon may be an alkane. The number of carbon atoms in the alkane may be 10 or less, 6 or less, or 4 or less. The saturated hydrocarbon may be methane. Methane is a hydrocarbon that is decomposed by N ２ Like O, N is a greenhouse gas. ２ It is preferable from the viewpoint of environmental conservation that methane can be decomposed simultaneously with O. The gas G1 may contain a plurality of saturated hydrocarbons.

[0084] [Method for Treating Nitric Acid] Figure 4 shows an example of a method for treating nitric acid. In Figure 4, gas G2 containing nitric acid produced in the gas decomposition device 10 and discharged from the decomposition reactor 2 passes through an exhaust pipe 11 connected to the gas exhaust port 3o and comes into contact with water W1 in a container 12, whereby the nitric acid contained in the gas G2 dissolves in the water W1 to form an aqueous nitric acid solution, thereby trapping the nitric acid. Nitric acid is a raw material for ammonium nitrate and is a useful substance in the chemical industry, agriculture, and other fields. Therefore, the aqueous nitric acid solution in the container 12 may be recovered. Furthermore, if the concentration of the aqueous nitric acid solution is low enough to be discharged, it may be discharged into a sewer without being recovered. The nitric acid discharged into the sewer is biodegraded to NOx. ３ － After that, finally N ２ Although Fig. 4 shows a method of recovering the nitric acid by dissolving it in water W1, it is also possible to recover the nitric acid by simply cooling the gas G2. Since the boiling point of nitric acid is approximately 83°C, when the gas is cooled, the nitric acid is liquefied from the gas.

[0085] [Catalyst] The catalyst 8 will be described in detail below. As described above, the catalyst 8 may be a three-way catalyst or a two-way catalyst.

[0086] The three-way catalyst will be described. The three-way catalyst promotes the reduction of nitrogen oxides by using carbon monoxide contained in the gas G1. The gas G1 contains N ２ Along with O, high concentrations of CO ２ Therefore, the light L1 causes N ２ NO is produced from O, and CO ２ CO is produced from the gas G1, and the gas G2 reduces NO to N by using CO according to equation (29). ２ At the same time, CO is oxidized to CO ２ The three-way catalyst promotes the reaction of equation (29), in which oxidation and reduction occur simultaneously: 2NO + 2CO → N ２ +2CO ２ ...(29)

[0087] The reaction of formula (29) occurs more easily as the temperature of the reaction field increases. ２If the temperature of the reaction field where O is decomposed is high, O ３ is insufficient, and N ２ The reaction stops when NO is generated from O, but the reaction of equation (29) becomes more active and CO ２ The CO produced from the reduction of NO to N ２ This reduces NO that is not converted to nitrate even when the temperature of the reaction field is high. Furthermore, CO is also harmful to the human body, and the three-way catalyst reduces CO ２ Since the gas G1 can be converted into the three-way catalyst, the three-way catalyst contributes to making the gas G1 harmless.

[0088] On the other hand, N ２ When the temperature in the decomposition reactor for decomposing O is low, ３ This allows the decomposition reactor to be used in both high-temperature and low-temperature reaction zones. ２ Without stopping the reaction with NO produced from O, nitric acid or N ２ As a result, NOx can be reduced.

[0089] Examples of materials that can be used for the three-way catalyst include rhodium, ruthenium, iridium, palladium, and platinum. It is also preferable to use a catalyst made of an iron-cobalt composite oxide or a tungsten-substituted vanadium oxide catalyst in which tungsten atoms are dispersed in vanadium oxide, because these catalysts exhibit catalytic performance even in a relatively low-temperature environment of around 150°C.

[0090] The two-way catalyst will be described. The two-way catalyst is an oxidation catalyst that promotes the oxidation of both substances contained in the gas G1. When the gas G1 contains at least one of nitrogen oxides and carbon monoxide, the two-way catalyst promotes the oxidation of at least one of nitrogen oxides and carbon monoxide using oxygen in the gas G1. ２ NO is produced from O, and CO ２ When CO is produced from the reaction, the two-way catalyst promotes the reactions of formulas (30) and (31). ２ → 2CO ２ ...(30) 2NO+O ２ → 2NO ２...(31)

[0091] For nitrogen oxides, NO is converted to NO by equation (31). ２ If the conversion can be performed up to 1000kJ / kg, nitration becomes possible even without ozone in the reaction field as long as there are hydroxyl radicals. Therefore, the binary catalyst contributes to the nitration of NO. In addition, CO, which is harmful to humans and animals, can be converted to CO. ２ It can be neutralized by converting it to

[0092] Possible materials for the binary catalyst include, for example, iron, platinum, and platinum.

[0093] [Method of Using the Gas Decomposition Apparatus] A method of using the gas decomposition apparatus 10 will be described. Nitrous oxide is emitted, for example, from soil at agricultural and livestock farms, waste management areas and septic tanks, sewage systems and sewage treatment facilities, garbage disposal plants, biomass factories, and chemical plants. The same is true for carbon dioxide. Carbon dioxide itself is emitted simply by burning carbon and hydrocarbons. However, it is unlikely that a mixed gas containing a high concentration of carbon dioxide, for example, a mixed gas in which carbon dioxide is the highest gas concentration, would be directly emitted from equipment (including transportation equipment such as automobiles) that burns carbon and hydrocarbons with oxygen contained in air. Therefore, it is desirable to adjust the concentration of carbon dioxide contained in the gas G1 to a high level. For example, a gas decomposition system may be constructed that includes equipment that emits gas at a high concentration of carbon dioxide or a gas supply source that supplies high-concentration carbon dioxide.

[0094] In order to provide the gas to be treated with energy for exciting the gas, the wavelength, the amount of light, and the irradiation time are selected, and N ２ The gas decomposition device 10 is connected to the gas supply port 3i and is configured to decompose the CO contained in the gas G1. ２ The gas concentration of CO contained in the gas G1 ２ The gas concentration adjusting unit may be configured to adjust the amount of each gas component contained in the gas G1 so that the concentration of each gas component is higher than the concentration of any other gas except for the above.

[0095] Second Embodiment A second embodiment of a gas decomposition apparatus will be described. The following description will focus on differences from the first embodiment, and descriptions of commonalities with the first embodiment will be omitted. The same applies to the third and subsequent embodiments described below.

[0096] 5A does not have a catalyst in the decomposition reactor 2. Instead, it has a catalyst unit 21 downstream of the decomposition reactor 2. The catalyst unit 21 incorporates a catalyst contact section 25 in a widened portion of a pipe 29. Gas G2 discharged from a gas outlet 3o of the decomposition reactor 2 flows into the catalyst contact section 25.

[0097] 5B is a cross-sectional view taken along line S2-S2 in FIG. 5A. The catalytic contact section 25 has a large number of cells inside a pipe 29. Each cell 27 is surrounded by a ceramic wall. Each cell 27 is elongated in the gas flow direction and is arranged side by side along the cross section of the pipe 29.

[0098] 5C is an enlarged view of the P1 region in FIG. 5B. Ceramic walls 23 are arranged in a lattice pattern. A space 24 is provided in the center of each cell 27, and the space 24 functions as a passageway for the gas G2. A catalyst 8 is arranged outside the space 24 and inside the ceramic wall 23. The above-mentioned three-way catalyst and two-way catalyst can be used as the catalyst 8. The role of the catalyst contact portion 25 will be explained. When a three-way catalyst is used as the catalyst, it reduces NO and converts it into nitrogen gas, thereby reducing NOx, and when a two-way catalyst is used, it oxidizes CO and converts it into CO ２ The goal is to convert it into

[0099] In this embodiment, in order to increase the contact area between the catalyst 8 and the gas G2, the catalyst contact portion 25 is arranged in the widened portion of the pipe 29, and the catalyst 8 is installed on the wall surfaces of the numerous cells 27. However, the catalyst contact portion 25 may not have numerous cells 27. Furthermore, even when the catalyst contact portion 25 having numerous cells 27 is employed, the cross-sectional shape of the ceramic walls (cell shape) may be any shape. For example, in FIG. 5C , the ceramic walls 23 are arranged in a rectangular lattice pattern, but the ceramic walls 23 may be arranged to form a honeycomb structure.

[0100] [Modified Embodiment] A modified embodiment of the second embodiment will be described with reference to Fig. 6. The modified embodiment will be described mainly focusing on the differences between the modified embodiment and the second embodiment. A two-way catalyst is used in the catalytic contact section 25. An oxygen gas supply pipe 41 is connected between the gas decomposition device 20 and the catalytic contact section 25 shown in Fig. 6, and oxygen gas is supplied from an oxygen gas supply port 42 provided in the pipe 29 to the upstream of the catalytic contact section 25. When either NO or CO remains in the gas G2 discharged from the gas discharge port 3o, oxygen gas is supplied from the oxygen gas supply pipe 41, and the CO is oxidized in the catalytic contact section 25 to produce CO. ２ This promotes the conversion of NOx into CO2, thereby reducing NOx and improving safety for humans and animals.

[0101] The second embodiment and its modified example have been described above. In the above description, instead of providing the catalyst 8 inside the gas decomposition apparatus 20, the catalyst 8 is arranged inside the piping 29 downstream of the gas decomposition apparatus 20. However, it is also possible to arrange the catalyst 8 inside the gas decomposition apparatus 20 as in the first embodiment, and also arrange the catalyst 8 inside the piping 29 downstream of the gas decomposition apparatus 20 as in the second embodiment.

[0102] 7A , an energy source in a gas decomposition apparatus 30 according to the third embodiment is an energy source that provides electron energy for exciting gas contained in the gas to be treated to generate plasma, and the electron energy is provided by applying a high-frequency voltage between electrodes that sandwich the gas to be treated.

[0103] 7A , the closed cylindrical tubular body 33 has two openings, which correspond to a gas supply port 3i and a gas exhaust port 3o. The gas supply port 3i is an opening for introducing gas G1, which is a gas to be treated, into the inside of the tubular body 33. The gas exhaust port 3o is an opening for discharging treated gas G2. The gas exhaust port 3o is located at a position separated from the gas supply port 3i in the tube axis direction d1. In this embodiment, the gas exhaust port 3o is located at a position separated from the gas supply port 3i in the tube axis direction d1 across the region where the outer electrode 35a is formed.

[0104] The two electrodes (35a, 35b) of the gas decomposition device 30 will be described. The outer electrode 35a is a mesh-like electrode provided along the outer wall surface of the tubular body 33. The inner electrode 35b is a rod-like electrode that extends linearly inside the tubular body 33 along the axial direction d1 of the tubular body 33. The inner electrode 35b is disposed so as to penetrate the tubular body 33 from the outside to the inside of the tubular body 33. Both electrodes (35a, 35b) are electrically connected to the power source 6.

[0105] Figure 7B is a cross-sectional view taken along the line S3-S3 in Figure 7A. As shown in Figure 7B, a space SP1 is formed inside the tube 33 located between the two electrodes (35a, 35b). When a voltage is applied between the two electrodes (35a, 35b), a dielectric barrier discharge occurs inside the tube 33, and an atmospheric pressure plasma space is formed in the space SP1.

[0106] The applied voltage supplied from the power supply 6 may be in any range that can generate a dielectric barrier discharge within the tube body 3 by applying a voltage between the electrodes (35a, 35b). Specifically, the applied voltage supplied from the power supply 6 is preferably in the range of 3 kVpp or more and 50 kVpp or less. The frequency of the applied voltage supplied from the power supply 6 is preferably in the range of 1 kHz or more and 1000 kHz or less, and more preferably in the range of 1 kHz or more and 150 kHz or less. The reason why the upper limit is preferably 150 kHz is that the frequency detected by the noise terminal voltage in the EMC standard is 150 kHz or more. In this way, a high-frequency voltage is applied between the electrodes (35a, 35b) from the power supply 6.

[0107] It is preferable that the power supply 6 applies a voltage so that the outer electrode 35a is at ground voltage and the inner electrode 35b is at high voltage, thereby reducing the risk of electric shock caused by the electrode exposed to the outside being at high voltage.

[0108] As described above, the decomposition mechanism of the gas decomposition device of this embodiment is basically the same as the decomposition mechanism when light energy is used. ２ O molecules are decomposed in the atmospheric pressure plasma space by a mechanism similar to the decomposition mechanism described above, and converted into nitrates.

[0109] The tube 33 is made of a dielectric material such as quartz glass or ceramics. The electrodes (5a, 5b) are made of a metal material such as stainless steel, aluminum, copper, tungsten, or nickel. While the tube 33 is cylindrical, it is not limited to a cylindrical shape. The tube 33 may be rectangular or, in particular, flat. While the outer electrode 35a is a mesh-like electrode provided along the outer wall surface of the tube 33, it is not limited to this shape. The outer electrode 35a may be, for example, a metal sheet or metal film provided along the outer wall surface of the tube 33, or may be a block-like electrode located outside the tube 33. The outer electrode 35a does not necessarily need to completely cover the wall surface of the tube 33 in the circumferential direction and may be configured to only partially cover the wall surface of the tube 33. Similarly, the shape of the inner electrode 35b is not limited to the above-described shape.

[0110] [Modification] A modification of the third embodiment will be described. In the gas decomposition apparatus 40 shown in FIG. 8A, the tubular body 3 has a double-tube structure. FIG. 8B is a cross-sectional view taken along line S4-S4 in FIG. 8A. More specifically, as shown in FIG. 8A, the tubular body 33 includes an outer tube 33a having a cylindrical shape and located on the outside, and an inner tube 33b having a cylindrical shape and a smaller inner diameter than the outer tube 33a, which is arranged coaxially with the outer tube 33a inside the outer tube 33a. The end of the inner tube 33b may be open to allow the same gas as the atmosphere in which the gas decomposition apparatus 40 is placed to flow into the inner tube 33b, or the end of the inner tube 33b may be sealed to allow a gas different from the atmosphere to flow into the inner tube 33b.

[0111] A rod-shaped inner electrode 35b extending linearly along the tube axis direction d1 of the tube body 33 is inserted inside the inner tube 33b. Another outer electrode 35a is provided outside the outer tube 33a. A space SP1 having an annular shape (here, a circular ring shape) when viewed from the tube axis direction d1 is formed between the outer tube 33a and the inner tube 33b. The gas supply port 3i and the gas exhaust port 3o communicate with the space SP1 located outside the inner tube 33b. That is, the gas G1 flows into the space SP1 through the gas supply port 3i.

[0112] <Fourth embodiment> Fig. 9A shows a gas decomposition apparatus 50 according to a fourth embodiment. Fig. 9B is a cross-sectional view taken along line S6-S6 in Fig. 9A. In gas decomposition apparatus 50, the energy used to excite gases contained in a mixed gas is both ultraviolet light and plasma generated by a high-frequency voltage.

[0113] 9A and 9B, gas decomposition apparatus 50 has a double-pipe structure in which inner pipe 54 is disposed inside outer pipe 53. Inside inner pipe 54 is gas flow path 52 through which gas G1, which is the gas to be treated, flows along the direction in which the double pipe extends.

[0114] An outer electrode 55a is disposed outside the outer wall of the outer tube 53, and an inner electrode 55b is disposed inside the inner wall of the inner tube 54. The inner electrode 55b and the outer electrode 55a preferably have a mesh-like structure. The outer tube 53 is shorter than the inner tube 54, and both ends of the outer tube 53 are sealed. A space 58 between the outer tube 53 and the inner tube 54 is filled with a light-emitting gas such as xenon gas. By applying a voltage between the outer electrode 55a and the inner electrode 55b, the space 58 becomes a discharge space, generating light L1 which is radiated into the gas G1 flowing through the gas flow path 52 (see FIG. 9A ).

[0115] When a voltage is applied between the inner electrode 55b and the outer electrode 55a, atmospheric pressure plasma AP is generated in the gap between the inner wall of the inner tube 54 and the inner electrode 55b. When gas G1 flows through this gap, the gas molecules contained in the gas G1 are excited by the atmospheric pressure plasma AP. In this way, the gas molecules constituting the gas G1 are excited by the plasma formed by the ultraviolet light and the high-frequency voltage.

[0116] The inner tube 54 is made of a material that transmits the luminous gas, such as quartz. The luminous gas passes through the inner tube 54 and reaches the inner gas flow passage 52. The gas decomposition device 50 has a gas supply port 3i at one end of the inner gas flow passage 52 and a gas exhaust port 3o at the other end of the inner gas flow passage 52. Gas G1 is supplied from the gas supply port 3i to the inner gas flow passage 52, light L1 emitted from the light source 1 is irradiated onto the gas G1 to be processed, and the gas G2 after light irradiation is continuously discharged from the gas exhaust port 3o. As a result, N in the gas G1 is decomposed. ２ O and CO ２ The decomposition can be carried out continuously.

[0117] The outer tube 53 is made of, for example, quartz. In the gas decomposition device 50, a reflective film that reflects the light L1 may be formed on the inner wall surface of the outer tube 53. The light-emitting gas is emitted toward the outside of the outer tube 53, and if a reflective film is formed on the inner wall surface of the outer tube 53, the light L1 that would otherwise be directed toward the outside of the outer tube 53 is reflected back inside, thereby increasing the light intensity in the inner gas flow path 52.

[0118] [First Modification] FIG. 10A shows a gas decomposition apparatus 60 according to a first modification of the fourth embodiment. FIG. 10B is a cross-sectional view taken along line S7-S7 in FIG. 10A. The gas decomposition apparatus 60 has a triple-tube structure in which an intermediate tube 73 is disposed within an outer tube 71, and an inner tube 54 is disposed within the intermediate tube 73. There are multiple gas flow paths. First, there is a gas flow path 52 formed within the inner tube 54, as in the gas decomposition apparatus 50. Second, there is a gas flow path 72 formed between the outer tube 71 and the intermediate tube 73, which is not present in the gas decomposition apparatus 50. Because the gas flow path 72 is located outside the gas flow path 52, the gas flow path 72 is sometimes referred to as the "outer gas flow path 72," and the gas flow path 52 is sometimes referred to as the "inner gas flow path." Light L1 is also irradiated onto the gas G1 flowing through the outer gas flow path 72.

[0119] There is a gap not only between the inner electrode 55b and the inner tube 54, but also between the outer electrode 55a and the intermediate tube 73. Therefore, the atmospheric pressure plasma AP acts not only between the inner electrode 55b and the inner tube 54, but also between the outer electrode 55a and the intermediate tube 73, exciting gas molecules contained in the gas G1 flowing through the outer gas flow passage 72. In this way, the gas molecules flowing through each gas flow passage (52, 72) are excited by ultraviolet light and high-frequency voltage. Since the gas G1 can be treated in each gas flow passage (52, 72), a large amount of gas can be treated, improving the utilization efficiency of the light L1 and the atmospheric pressure plasma AP.

[0120] 11 shows a gas decomposition apparatus 70 according to a second modified embodiment of the fourth embodiment. The gas decomposition apparatus 70 differs from the gas decomposition apparatus 60 according to the first modified embodiment of the fourth embodiment in that the inner gas flow passage 52 formed within the inner tube 54 is connected to an outer gas flow passage 72. The gas G2 processed in the inner gas flow passage 52 turns back and passes through the outer gas flow passage 72, where it is processed again. This allows the gas to be processed to be processed more effectively, improving the utilization efficiency of the light L1.

[0121] In this modified embodiment, the gas first passes through the inner gas flow passage 52 and then the outer gas flow passage 72, but it may also be configured so that the gas first passes through the outer gas flow passage 72 and then the inner gas flow passage 52.

[0122] The above describes various embodiments of the gas decomposition method and gas decomposition apparatus, as well as appropriate variations thereof. The above-described embodiments and variations thereof are merely examples of the present invention, and the present invention is not limited to the above-described embodiments. Various changes or modifications can be made to the above-described embodiments, and the above-described embodiments or variations can be combined, without departing from the spirit of the present invention.

[0123] DESCRIPTION OF SYMBOLS 1: Light source 2: Decomposition reactor 3: Tube body 3a: Outer tube 3b: Inner tube 3i, 4i: Gas supply port 3o, 4o: Gas exhaust port 5: Control unit 5a, 5b: Electrode 6: Power source 8: Catalyst 10, 20, 30, 40, 50, 60, 70: Gas decomposition device 11: Exhaust pipe 12: Container 21: Catalyst unit 23: Wall 24: Space 25: Catalyst contact portion 29: Pipe 31: Gas supply port 32: Gas exhaust port 33: Tube body 33a, 53, 71: Outer tube 33b, 54: Inner tube 35a, 55a: Outer electrode 35b, 55b: Inner electrode 41: Supply pipe for oxygen-containing gas 42: Supply port for oxygen-containing gas 52, 72: Gas flow path 57: Reflection film 58: Space 73: Intermediate tube L1: Light AP: Atmospheric pressure plasma SP1: Space

Claims

1. A method for decomposing a gas to be treated, wherein the gas to be treated contains at least nitrous oxide and carbon dioxide, the gas concentration of carbon dioxide contained in the gas to be treated is higher than the concentrations of all gases contained in the gas to be treated other than carbon dioxide, and the nitrous oxide in the gas to be treated is decomposed by providing the gas to be treated with energy for exciting the gas contained in the gas to be treated.

2. The decomposition method according to claim 1, wherein the gas to be treated further contains water vapor.

3. The decomposition method according to claim 1, wherein the energy is light energy having a main emission wavelength of 160 nm or more but less than 200 nm.

4. The decomposition method according to claim 1, wherein the energy is electron energy obtained by converting the gas to be treated into plasma.

5. The decomposition method according to any one of claims 1 to 4, characterized in that the gas to be treated is brought into contact with a catalyst.

6. The decomposition method according to claim 5, wherein the catalyst is a three-way catalyst used to promote the reduction of nitric oxide produced by the decomposition of nitrous oxide.

7. The decomposition method according to claim 5, wherein the catalyst is a two-way catalyst used to promote the oxidation of at least one of the nitric oxide produced by the decomposition of nitrous oxide and the carbon monoxide produced from the carbon dioxide.

8. The decomposition method according to claim 7, wherein a gas containing oxygen is additionally supplied to the gas to be treated after the energy has been applied.

9. A decomposition device for a gas to be treated, comprising: a gas supply port that introduces the gas to be treated into the decomposition device, the gas containing at least nitrous oxide and carbon dioxide, the gas concentration of carbon dioxide being higher than the concentrations of any other gases contained in the gas to be treated except for carbon dioxide; and an energy source that provides energy to the gas to be treated introduced from the gas supply port into the decomposition device, for exciting gases contained in the gas to be treated, in order to decompose the nitrous oxide in the gas to be treated.

10. The decomposition device described in claim 9, characterized in that it is provided with a gas concentration adjusting unit connected to the gas supply port and adjusting the amount of gas components contained in the gas to be treated so that the gas concentration of carbon dioxide contained in the gas to be treated is higher than the concentration of any other gas other than carbon dioxide contained in the gas to be treated.

11. The decomposition device according to claim 9, wherein the energy is light energy having a main emission wavelength of 160 nm or more and less than 200 nm, and the energy source is a light source that radiates the light.

12. The decomposition apparatus according to claim 9, wherein the energy is electron energy generated by converting the gas to be treated into plasma, and the energy source is an electrode that supplies the electron energy.

13. The decomposition device according to any one of claims 9 to 12, characterized in that the decomposition device is equipped with a three-way catalyst that promotes the reduction of nitric oxide produced by the decomposition of nitrous oxide.

14. The decomposition device according to any one of claims 9 to 12, characterized in that it is equipped with a two-way catalyst used to promote the oxidation of at least one of the nitric oxide produced by the decomposition of the dinitrogen monoxide and the carbon monoxide produced from the carbon dioxide.

15. The decomposition device according to claim 14, characterized in that the decomposition device is provided with an oxygen supply port for adding an oxygen-containing gas to the gas to be treated after the energy has been applied, and the two-way catalyst is arranged so as to come into contact with the gas to be treated to which the oxygen-containing gas has been added.

16. A system for decomposing a gas to be treated, comprising: the decomposition device according to any one of claims 9, 11 and 12; and a gas supply source connected to the gas supply port and supplying the gas to be treated into the decomposition device.

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