Exhaust gas treatment method and exhaust gas treatment device

Abstract

Provided is an exhaust gas treatment method with which it is possible to decompose chlorine gas and perfluorinated compounds in exhaust gas containing chlorine gas and perfluorinated compounds, and to reduce both the chlorine gas concentration and the perfluorinated compound concentration in the gas. This exhaust gas treatment method treats exhaust gas containing chlorine gas and a perfluorinated compound, and comprises: a chlorine gas decomposition step for reacting chlorine gas in the exhaust gas with water in the presence of a chlorine gas decomposition catalyst and decomposing the chlorine gas; a hydrogen chloride removal step for removing hydrogen chloride from the gas subjected to the chlorine gas decomposition step; and a perfluorinated compound decomposition step in which the perfluorinated compound in the gas that has undergone the hydrogen chloride removal step is reacted and decomposed in the presence of a perfluorinated compound decomposition catalyst.

Description

Technical Field

[0001] The present invention relates to an exhaust gas treatment method and an exhaust gas treatment apparatus. Background Art

[0002] When manufacturing semiconductors, exhaust gas containing chlorine and perfluorocompounds (PFCs) is sometimes discharged. Therefore, a treatment method for decomposing both chlorine and perfluorocompounds in the exhaust gas into low concentrations is required. For example, Patent Document 1 discloses a treatment apparatus that introduces exhaust gas into a reactor filled with both a chlorine decomposition catalyst and a perfluorocompound decomposition catalyst to decompose both chlorine and perfluorocompounds simultaneously.

[0003] Prior Art Documents

[0004] Patent Document 1: International Publication No. 2022 / 138850 Summary of the Invention

[0005] However, there is a demand for further improving the removal efficiency of decomposing and removing chlorine from the exhaust gas.

[0006] An object of the present invention is to provide an exhaust gas treatment method and an exhaust gas treatment apparatus that can decompose chlorine and perfluorocompounds in exhaust gas containing chlorine and perfluorocompounds to make the concentrations of chlorine and perfluorocompounds in the gas both low concentrations.

[0007] To solve the foregoing problems, one aspect of the present invention is as described in the following [1] to

[10] .

[0008] [1] An exhaust gas treatment method for treating exhaust gas containing chlorine and perfluorocompounds, comprising: a chlorine decomposition step of decomposing the chlorine in the exhaust gas by reacting it with water in the presence of a chlorine decomposition catalyst; a hydrogen chloride removal step of removing hydrogen chloride from the gas that has undergone the chlorine decomposition step; and a perfluorocompound decomposition step of decomposing the perfluorocompounds in the gas that has undergone the hydrogen chloride removal step by reacting them in the presence of a perfluorocompound decomposition catalyst.

[0009] [2] The exhaust gas treatment method according to [1], wherein the perfluorocompound decomposition step is a step of decomposing the perfluorocompounds in the gas that has undergone the hydrogen chloride removal step by reacting them in the presence of a perfluorocompound decomposition catalyst, and decomposing the chlorine in the gas that has undergone the hydrogen chloride removal step by reacting it in the presence of a chlorine decomposition catalyst.

[0010] [3] The exhaust gas treatment method according to [1] or [2], wherein the hydrogen chloride removal step is a step of removing the hydrogen chloride by dissolving it in water by bringing the gas that has undergone the chlorine decomposition step into contact with water.

[0011] [4] The decomposition reaction of the chlorine in the chlorine decomposition step is carried out at a temperature of 500 °C or higher and 800 °C or lower according to the exhaust gas treatment method described in any one of [1] to [3].

[0012] [5] The decomposition reaction of the perfluorinated compound in the perfluorinated compound decomposition step is carried out at a temperature of 500 °C or higher and 800 °C or lower according to the exhaust gas treatment method described in any one of [1] to [4].

[0013] [6] An exhaust gas treatment device is a device for treating exhaust gas containing chlorine and perfluorinated compounds, and has a chlorine decomposition section, a hydrogen chloride removal section, and a perfluorinated compound decomposition section.

[0014] The chlorine decomposition section is provided with a chlorine decomposition catalyst, and the chlorine in the exhaust gas reacts with water in the presence of the chlorine decomposition catalyst to decompose.

[0015] The hydrogen chloride removal section removes hydrogen chloride from the gas after the chlorine is decomposed by the chlorine decomposition section.

[0016] The perfluorinated compound decomposition section is provided with a perfluorinated compound decomposition catalyst, and the perfluorinated compound in the gas after the hydrogen chloride is removed by the hydrogen chloride removal section reacts and decomposes in the presence of the perfluorinated compound decomposition catalyst.

[0017] [7] According to the exhaust gas treatment device described in [6], the perfluorinated compound decomposition section further has a chlorine decomposition catalyst in addition to the perfluorinated compound decomposition catalyst, and the perfluorinated compound in the gas after the hydrogen chloride is removed by the hydrogen chloride removal section reacts and decomposes in the presence of the perfluorinated compound decomposition catalyst, and the chlorine in the gas after the hydrogen chloride is removed by the hydrogen chloride removal section reacts and decomposes in the presence of the chlorine decomposition catalyst.

[0018] [8] According to the exhaust gas treatment device described in [6] or [7], the hydrogen chloride removal section removes the hydrogen chloride by bringing the gas after the chlorine is decomposed by the chlorine decomposition section into contact with water and dissolving the hydrogen chloride in the water.

[0019] [9] According to the exhaust gas treatment device described in any one of [6] to [8], the chlorine decomposition section carries out the decomposition reaction of the chlorine at a temperature of 500 °C or higher and 800 °C or lower.

[0020]

[10] According to the exhaust gas treatment device described in any one of [6] to [9], the perfluorinated compound decomposition section carries out the decomposition reaction of the perfluorinated compound at a temperature of 500 °C or higher and 800 °C or lower.

[0021] According to the present invention, chlorine and perfluorinated compounds in the exhaust gas containing chlorine and perfluorinated compounds can be decomposed, so that both the chlorine concentration and the perfluorinated compound concentration in the gas become low concentrations. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a schematic conceptual diagram showing an example of an exhaust gas treatment apparatus for implementing the exhaust gas treatment method of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0023] Hereinafter, an embodiment of the present invention will be described. Furthermore, this embodiment shows an example of the present invention, and the present invention is not limited to this embodiment. In addition, various changes or improvements can be made to this embodiment, and such modified or improved embodiments are also included in the present invention.

[0024] The exhaust gas treatment method of this embodiment is a method for treating exhaust gas containing chlorine and perfluorinated compounds, and has: a chlorine decomposition step of decomposing chlorine in the exhaust gas by reacting with water in the presence of a chlorine decomposition catalyst; a hydrogen chloride removal step of removing hydrogen chloride from the gas that has passed through the chlorine decomposition step; and a perfluorinated compound decomposition step of decomposing the perfluorinated compounds in the gas that has passed through the hydrogen chloride removal step by reacting in the presence of a perfluorinated compound decomposition catalyst.

[0025] The exhaust gas treatment apparatus of this embodiment is an apparatus for treating exhaust gas containing chlorine and perfluorinated compounds, and has a chlorine decomposition section, a hydrogen chloride removal section, and a perfluorinated compound decomposition section. The chlorine decomposition section is provided with a chlorine decomposition catalyst and decomposes chlorine in the exhaust gas by reacting with water in the presence of the chlorine decomposition catalyst. The hydrogen chloride removal section removes hydrogen chloride from the gas after the chlorine is decomposed by the chlorine decomposition section. The perfluorinated compound decomposition section is provided with a perfluorinated compound decomposition catalyst and decomposes the perfluorinated compounds in the gas after the hydrogen chloride is removed by the hydrogen chloride removal section by reacting in the presence of the perfluorinated compound decomposition catalyst.

[0026] If chlorine (Cl2) reacts with water (H2O) to undergo hydrolysis, as shown by the following reaction formula, hydrogen chloride (HCl) and oxygen (O2) are generated.

[0027] Cl2 + H2O → 2HCl + 1 / 2O2

[0028] Since this reaction is an equilibrium reaction, if the concentration of hydrogen chloride becomes high, a reaction opposite to the hydrolysis reaction occurs, and chlorine is regenerated again by the oxidation of hydrogen chloride. Therefore, in order to suppress the re-generation of chlorine and make the chlorine concentration in the gas a low concentration, it is necessary to remove the hydrogen chloride generated by the hydrolysis of chlorine.

[0029] In the exhaust gas treatment method of this embodiment, since the hydrogen chloride removal process is carried out after the chlorine decomposition process, it is not easy for chlorine to be regenerated again after the hydrogen chloride removal process. Moreover, through the perfluorinated compound decomposition process after the hydrogen chloride removal process, the perfluorinated compounds are removed from the gas from which hydrogen chloride has been removed. Therefore, both the chlorine concentration and the perfluorinated compound concentration in the gas can be made low.

[0030] In addition, the exhaust gas treatment device of this embodiment has a hydrogen chloride removal unit that removes hydrogen chloride from the gas after chlorine is decomposed by the chlorine decomposition part. Therefore, it is not easy for chlorine to be regenerated again in the gas after hydrogen chloride is removed by the hydrogen chloride removal unit. Moreover, the exhaust gas treatment device of this embodiment has a perfluorinated compound decomposition unit. Therefore, both the chlorine concentration and the perfluorinated compound concentration in the gas can be made low.

[0031] For example, the chlorine concentration of the gas after the decomposition of the perfluorinated compound can be made 0.5 volume ppm or less relative to the chlorine concentration of the exhaust gas of 100 - 10000 volume ppm, and the perfluorinated compound concentration of the gas after the decomposition of the perfluorinated compound can be made 100 volume ppm or less relative to the perfluorinated compound concentration of the exhaust gas of 1000 - 10000 volume ppm.

[0032] Hereinafter, the exhaust gas treatment method and the exhaust gas treatment device of this embodiment will be described in more detail.

[0033] [Exhaust gas]

[0034] In the exhaust gas treatment method and the exhaust gas treatment device of this embodiment, the type of exhaust gas that can be treated is not particularly limited, as long as it is a gas containing chlorine and perfluorinated compounds. The exhaust gas may contain other components in addition to chlorine and perfluorinated compounds. For example, it may also contain at least one of argon (Ar), nitrogen (N2), oxygen, and water.

[0035] The chlorine concentration and the perfluorinated compound concentration of the exhaust gas before treatment are not particularly limited, but are preferably both 0.01 volume % or more and 10 volume % or less, more preferably 0.1 volume % or more and 1 volume % or less. In addition, the total concentration of chlorine and perfluorinated compounds is preferably 1 volume % or less.

[0036] As an example of the exhaust gas, the gas discharged during the manufacturing process of compounds and the gas discharged in various industrial processes can be cited. As a more specific example of the exhaust gas, the etching gas used in the manufacturing process of semiconductors and the manufacturing process of liquid crystal display elements, and the cleaning gas used in a chemical vapor deposition apparatus (CVD apparatus) can be cited. These exhaust gases sometimes contain chlorine and perfluorinated compounds.

[0037] [Perfluorinated compounds]

[0038] Perfluorinated compounds refer to compounds that do not have chlorine atoms and are compounds composed of carbon atoms and fluorine atoms; compounds composed of carbon atoms, hydrogen atoms and fluorine atoms; compounds composed of sulfur atoms and fluorine atoms; and compounds composed of nitrogen atoms and fluorine atoms in general.

[0039] As specific examples of perfluorinated compounds, carbon tetrafluoride (CF4), trifluoromethane (CHF3), hexafluoroethane (C2F6), 1,1-difluoroethylene (CH2F2)), cis-1,2-difluoroethylene (CH2F2), trans-1,2-difluoroethylene (CH2F2), octafluoropropane (C3F8), octafluorocyclobutane (C4F8), octafluorocyclopentene (C5F8), sulfur hexafluoride (SF6), nitrogen trifluoride (NF3) can be cited.

[0040] [Chlorine decomposition catalyst]

[0041] The chlorine decomposition catalyst is not particularly limited as long as it is a catalyst that promotes the hydrolysis reaction of chlorine, but preferably contains at least one of cerium oxide (CeO2) and cobalt oxide (CoO, Co2O3).

[0042] In addition to containing at least one of cerium oxide and cobalt oxide, the chlorine decomposition catalyst may further contain other types of metal oxides. As other types of metal oxides, at least one of aluminum oxide (Al2O3), magnesium oxide (MgO), chromium oxide (CrO, Cr2O3, CrO2, CrO3), manganese oxide (MnO, Mn2O3, MnO2, MnO3, Mn2O7), iron oxide (FeO, Fe2O3), nickel oxide (NiO), copper oxide (Cu2O, CuO) and zirconium oxide (ZrO2) can be cited. Furthermore, the mass ratio of the component elements of the chlorine decomposition catalyst is preferably (cerium):(cobalt):(copper):(aluminum):(oxygen)=(5-15):(5-15):(0.1-0.5):(25-45):(40-50).

[0043] Moreover, in addition to containing at least one of cerium oxide and cobalt oxide, the chlorine decomposition catalyst may further contain a composite oxide of cerium (Ce) and other metals. As other metals constituting the composite oxide, at least one of magnesium (Mg), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu) and zirconium (Zr) can be cited.

[0044] Moreover, the chlorine decomposition catalyst may also contain at least one of cerium oxide and cobalt oxide, at least one of the above-mentioned other types of metal oxides, and at least one of the above-mentioned composite oxides.

[0045] The chlorine decomposition catalyst can be used for the decomposition of chlorine in a state supported on a carrier, or can be directly used for the decomposition of chlorine without being supported on a carrier.

[0046] The shape and size of the carrier are not particularly limited. For example, preferred are structural bodies such as bead shape, pellet shape, powder shape, granular shape, monolithic shape, etc., and pellet shape is particularly preferred.

[0047] In addition, the carrier is preferably composed of a porous material, and the specific surface area measured by the BET method can be 100 cm 2 / g or more and 500 cm 2 / g or less, or can also be 100 cm 2 / g or more and 300 cm 2 / g or less.

[0048] The material of the carrier is preferably a material that is inert or lacks reactivity with respect to chlorine and hydrogen chloride. Examples include alumina (Al2O3), silica (SiO2), cordierite, zeolite, etc., and alumina is preferred.

[0049] The average particle size (diameter) of the carrier can be 1 mm or more and 10 mm or less, or can also be 2 mm or more and 5 mm or less.

[0050] [Chlorine decomposition process, chlorine decomposition section]

[0051] As an example of the chlorine decomposition section for carrying out the chlorine decomposition reaction, a reactor can be cited. If exhaust gas is introduced into a reactor equipped with a chlorine decomposition catalyst inside, the chlorine decomposition process can be carried out.

[0052] The material of the reactor is preferably a material that is inert or lacks reactivity with respect to chlorine and hydrogen chloride. Examples include nickel alloys, and as specific examples of nickel alloys, Inconel (registered trademark) 600, Inconel (registered trademark) 601, Inconel (registered trademark) 625 can be cited.

[0053] The chlorine decomposition reaction is a reaction in which chlorine in the exhaust gas reacts with water in the presence of a chlorine decomposition catalyst and hydrolyzes, so it needs to be carried out in the presence of water. As long as the water can contact the chlorine in the exhaust gas, it can be either liquid water or gaseous water (water vapor), but usually it is water vapor.

[0054] When the exhaust gas contains sufficient water, the chlorine decomposition process can be directly carried out on the exhaust gas. However, when the exhaust gas contains no water at all, it is necessary to carry out the chlorine decomposition process after adding water to the exhaust gas or while adding water to the exhaust gas. Therefore, in this case, the exhaust gas treatment device of the present embodiment needs to be equipped with a water supply section for adding water to the exhaust gas.

[0055] In addition, when the exhaust gas is not sufficiently exhausted and contains water, resulting in a low water concentration in the exhaust gas, it is preferable to carry out the chlorine decomposition step after adding water to the exhaust gas to increase the water concentration or while adding water to the exhaust gas. Therefore, in this case, the exhaust gas treatment device of the present embodiment preferably includes a water supply unit for adding water to the exhaust gas.

[0056] The water concentration in the exhaust gas is preferably 1% by volume or more and 40% by volume or less, more preferably 10% by volume or more and 25% by volume or less. When the water concentration in the exhaust gas is lower than the lower limit value of the above numerical range, when carrying out the chlorine decomposition step, it is preferable to add water to the exhaust gas so that the water concentration in the exhaust gas becomes higher than the lower limit value of the above numerical range.

[0057] The temperature condition and pressure condition of the chlorine decomposition step are not particularly limited as long as the decomposition of chlorine can be carried out. The temperature condition is preferably 300 °C or more and 1000 °C or less, more preferably 400 °C or more and 800 °C or less, and further preferably 500 °C or more and 800 °C or less.

[0058] The pressure condition is preferably normal pressure or a pressurized state, more preferably normal pressure.

[0059] By carrying out such a chlorine decomposition step on the exhaust gas, chlorine is decomposed, and thus the chlorine concentration of the gas passing through the chlorine decomposition step can be made 300 ppm by volume or less.

[0060] Furthermore, before carrying out the chlorine decomposition step, a treatment of bringing water into contact with the exhaust gas may also be carried out. For example, a treatment of bringing water into gas-liquid contact with the exhaust gas may be carried out using a wet gas cleaning device (water scrubber). In this way, water-soluble gases can be removed from the exhaust gas.

[0061] [Hydrogen chloride removal step, hydrogen chloride removal unit]

[0062] The gas obtained by decomposing chlorine through the chlorine decomposition step contains hydrogen chloride. As described above, since chlorine may be regenerated by the oxidation of hydrogen chloride, it is necessary to remove hydrogen chloride from the gas passing through the chlorine decomposition step through the hydrogen chloride removal step.

[0063] The method for removing hydrogen chloride is not particularly limited, but preferably the hydrogen chloride removal step is a step of bringing the gas passing through the chlorine decomposition step into contact with water and removing hydrogen chloride by dissolving hydrogen chloride in water. For example, if a wet gas cleaning device (water scrubber) is used as the hydrogen chloride removal unit and a treatment of bringing water into gas-liquid contact with the gas passing through the chlorine decomposition step is carried out, then since hydrogen chloride dissolves in water, hydrogen chloride can be removed from the gas passing through the chlorine decomposition step.

[0064] Alternatively, hydrogen chloride can also be removed from the gas passing through the chlorine decomposition process by adsorbing hydrogen chloride with an adsorbent such as activated carbon. For example, an adsorption tower filled with an adsorbent is used as the hydrogen chloride removal section, and by introducing the gas passing through the chlorine decomposition process into the adsorption tower, hydrogen chloride can be removed from the gas passing through the chlorine decomposition process.

[0065] The conditions for removing hydrogen chloride from the exhaust gas using a water scrubber will be described. In order to increase the contact frequency between the exhaust gas and water, it is preferable that the supply amount of water to the water scrubbing device is large, and it is preferable that the supply amount of water to the water scrubbing device is 2.5% or more of the exhaust gas flow rate. For example, when the flow rate of the exhaust gas is 400 L / min, the supply rate of water is preferably 10 L / min or more.

[0066] In order to increase the solubility of hydrogen chloride in water, it is preferable that the temperature of the water supplied to the water scrubber is low, preferably 25°C or lower.

[0067] In order to prevent the piping for discharging water from the water scrubber from being blocked, it is preferable to use water with a low metal ion concentration as the water supplied to the water scrubber. If the water contains metal ions such as magnesium ions and calcium ions, the metal ions react with hydrogen chloride, and metal salts that may cause piping blockage may be generated.

[0068] [Perfluorinated compound decomposition catalyst]

[0069] The perfluorinated compound decomposition catalyst is not particularly limited as long as it is a catalyst that promotes the decomposition reaction of perfluorinated compounds. For example, it preferably contains nickel oxide (NiO), alumina (Al2O3), or a mixture thereof. In addition, the perfluorinated compound decomposition catalyst preferably contains the following composite oxide, which has at least one element selected from aluminum (Al), tungsten (W), titanium (Ti), and zirconium in addition to nickel.

[0070] Furthermore, the mass ratio of the component elements of the perfluorinated compound decomposition catalyst is preferably (nickel):(aluminum):(oxygen)=(20-30):(30-40):(30-50).

[0071] When the perfluorinated compound decomposition catalyst is a metal oxide, since it also functions as a chlorine decomposition catalyst, chlorine remaining in the gas passing through the chlorine decomposition process can be decomposed in the perfluorinated compound decomposition process.

[0072] This perfluorinated compound decomposition catalyst can be used for the decomposition of perfluorinated compounds in a state supported on a carrier, or can be directly used for the decomposition of perfluorinated compounds in a state not supported on a carrier. Regarding the carrier, it is the same as in the case of the chlorine decomposition catalyst, so detailed description is omitted.

[0073] [Perfluorinated compound decomposition process, perfluorinated compound decomposition section]

[0074] As an example of the perfluorinated compound decomposition section for performing the decomposition reaction of perfluorinated compounds, a reactor can be cited. If a gas that has undergone the hydrogen chloride removal process is introduced into a reactor equipped with a perfluorinated compound decomposition catalyst inside, the perfluorinated compound decomposition process can be carried out.

[0075] The material of the reactor is preferably a material that is inert or lacks reactivity with respect to chlorine gas and hydrogen chloride. For example, nickel alloys can be cited, and as specific examples of nickel alloys, Inconel (registered trademark) 600, Inconel (registered trademark) 601, and Inconel (registered trademark) 625 can be cited.

[0076] The type of the decomposition reaction of perfluorinated compounds is not particularly limited as long as it is the decomposition of perfluorinated compounds in the gas that has undergone the hydrogen chloride removal process. For example, it can be a thermal decomposition reaction or a hydrolysis reaction with water. Examples of the hydrolysis reaction of perfluorinated compounds are shown below.

[0077] C n F m +H2O→nCO2+mHF

[0078] SF6+xH2O→SO x +6HF

[0079] NF3+xH2O→NO x +3HF

[0080] When the decomposition reaction of perfluorinated compounds is a hydrolysis reaction, the decomposition reaction of perfluorinated compounds needs to be carried out in the presence of water. As long as water can contact the perfluorinated compounds in the gas that has undergone the hydrogen chloride removal process, it can be either liquid water or gaseous water (water vapor), but usually it is water vapor.

[0081] When the gas that has undergone the hydrogen chloride removal process contains sufficient water, the perfluorinated compound decomposition process can be directly carried out on the gas that has undergone the hydrogen chloride removal process. When the gas that has undergone the hydrogen chloride removal process does not contain any water, it is necessary to carry out the perfluorinated compound decomposition process after adding water to the gas that has undergone the hydrogen chloride removal process or while adding water to the gas that has undergone the hydrogen chloride removal process. Therefore, in this case, the exhaust gas treatment device of the present embodiment needs to be equipped with a water supply section for adding water to the gas that has undergone the hydrogen chloride removal process.

[0082] In addition, when the gas after the hydrogen chloride removal step does not sufficiently contain water and thus the water concentration of the gas after the hydrogen chloride removal step is low, it is preferable to add water to the gas after the hydrogen chloride removal step to increase the water concentration or to carry out the perfluorinated compound decomposition step while adding water to the gas after the hydrogen chloride removal step. Therefore, in this case, the exhaust gas treatment device of the present embodiment preferably includes a water supply unit that adds water to the gas after the hydrogen chloride removal step.

[0083] The water concentration of the gas after the hydrogen chloride removal step is preferably 1 vol% or more and 40 vol% or less, more preferably 10 vol% or more and 25 vol% or less. When the water concentration of the gas after the hydrogen chloride removal step is lower than the lower limit value of the above numerical range, when carrying out the perfluorinated compound decomposition step, it is preferable to add water to the gas after the hydrogen chloride removal step so that the water concentration of the gas after the hydrogen chloride removal step becomes higher than the lower limit value of the above numerical range.

[0084] The temperature conditions and pressure conditions of the perfluorinated compound decomposition step are not particularly limited as long as the decomposition of the perfluorinated compound proceeds. When the perfluorinated compound decomposition reaction is a thermal decomposition reaction or a hydrolysis reaction, the temperature conditions are both preferably 300°C or more and 1000°C or less, more preferably 400°C or more and 800°C or less, and further preferably 500°C or more and 800°C or less.

[0085] When the perfluorinated compound decomposition reaction is a thermal decomposition reaction or a hydrolysis reaction, the pressure conditions are both preferably normal pressure or a pressurized state, more preferably normal pressure.

[0086] By carrying out such a perfluorinated compound decomposition step on the gas after the hydrogen chloride removal step, the perfluorinated compound is decomposed at a high decomposition rate of 99% or more. Therefore, the perfluorinated compound concentration of the gas after the perfluorinated compound decomposition step can be set to 100 vol ppm or less with respect to the perfluorinated compound concentration of 1000 - 10000 vol ppm after the hydrogen chloride removal step.

[0087] Furthermore, in the gas after the hydrogen chloride removal step, unreacted chlorine in the chlorine decomposition step may be contained. Depending on the type of the perfluorinated compound decomposition catalyst, the unreacted chlorine can be decomposed in the perfluorinated compound decomposition step. For example, since metal oxides such as nickel oxide also act as chlorine decomposition catalysts, when metal oxides such as nickel oxide are used as the perfluorinated compound decomposition catalyst, the perfluorinated compound and chlorine are decomposed in the perfluorinated compound decomposition step. When decomposing chlorine in the perfluorinated compound decomposition step, the chlorine concentration of the gas after the perfluorinated compound decomposition step can be set to 0.5 vol ppm or less with respect to the chlorine concentration of 10 - 100 vol ppm after the hydrogen chloride removal step.

[0088] As described above, in the gas after the hydrogen chloride removal step, chlorine that has not been decomposed in the chlorine decomposition step is sometimes contained. Therefore, regardless of whether the perfluorinated compound decomposition catalyst is effective for decomposing chlorine, a chlorine decomposition catalyst can also be used together with the perfluorinated compound decomposition catalyst in the perfluorinated compound decomposition step. That is, the perfluorinated compound decomposition section can also include a perfluorinated compound decomposition catalyst and a chlorine decomposition catalyst.

[0089] When a chlorine decomposition catalyst is used together with the perfluorinated compound decomposition catalyst in the perfluorinated compound decomposition step, the perfluorinated compound decomposition step becomes the following steps: decomposing the perfluorinated compound in the gas that has passed through the hydrogen chloride removal step in the presence of the perfluorinated compound decomposition catalyst, and decomposing the chlorine in the gas that has passed through the hydrogen chloride removal step in the presence of the chlorine decomposition catalyst.

[0090] In addition, when the perfluorinated compound decomposition section includes a chlorine decomposition catalyst in addition to the perfluorinated compound decomposition catalyst, in the perfluorinated compound decomposition section, the perfluorinated compound in the gas after the hydrogen chloride has been removed by the hydrogen chloride removal section reacts and decomposes in the presence of the perfluorinated compound decomposition catalyst, and the chlorine in the gas after the hydrogen chloride has been removed by the hydrogen chloride removal section reacts and decomposes in the presence of the chlorine decomposition catalyst.

[0091] If a perfluorinated compound decomposition catalyst and a chlorine decomposition catalyst are used in the perfluorinated compound decomposition step, the chlorine that has not been decomposed in the chlorine decomposition step can be decomposed in the perfluorinated compound decomposition step. Thus, the chlorine concentration in the gas can be made lower.

[0092] In addition, after the perfluorinated compound decomposition step is implemented, a treatment of bringing the gas that has passed through the perfluorinated compound decomposition step into contact with water can also be implemented. For example, if a wet gas cleaning device (water scrubber) is used to implement a treatment of bringing the gas that has passed through the perfluorinated compound decomposition step into gas-liquid contact with water, hydrogen chloride and hydrogen fluoride can be removed from the gas that has passed through the perfluorinated compound decomposition step. This hydrogen fluoride is generated by the decomposition of the perfluorinated compound. When hydrogen chloride and hydrogen fluoride are removed from the gas that has passed through the perfluorinated compound decomposition step, the main component of the harmless gas discharged from the gas cleaning device after the perfluorinated compound decomposition step is carbon dioxide (CO2).

[0093] Examples

[0094] Examples and comparative examples are shown below to more specifically illustrate the present invention.

[0095] (Example 1)

[0096] An exhaust gas treatment device was used to treat the exhaust gas containing chlorine and perfluorinated compounds to render the exhaust gas harmless. Refer toFigure 1 Schematic conceptual diagram for explaining the structure of the exhaust gas treatment device used in Example 1.

[0097] Figure 1 The exhaust gas treatment device has a chlorine decomposition section 10, a hydrogen chloride removal section 20, and a perfluorinated compound decomposition section 30. The chlorine decomposition section 10 performs a chlorine decomposition process in which chlorine in the exhaust gas reacts with water in the presence of a chlorine decomposition catalyst and decomposes. The hydrogen chloride removal section 20 performs a hydrogen chloride removal process for removing hydrogen chloride from the gas that has undergone the chlorine decomposition process. The perfluorinated compound decomposition section 30 performs a perfluorinated compound decomposition process in which perfluorinated compounds in the gas that has undergone the hydrogen chloride removal process react and decompose in the presence of a perfluorinated compound decomposition catalyst.

[0098] The chlorine decomposition section 10 is a reactor made of Inconel (registered trademark) (with a capacity of 70 mL), and inside it is filled with 65 g (with a volume of 70 mL) of chlorine decomposition catalyst in the shape of tablets with a diameter of 3.2 mm and a length of 10 mm. This chlorine decomposition catalyst is obtained by kneading cerium nitrate, cobalt nitrate, copper nitrate, and boehmite, extrusion molding, and sintering. Moreover, this chlorine decomposition catalyst is a mixture of cerium oxide (CeO2), cobalt oxide (CoO), copper oxide (CuO), and aluminum oxide (Al2O3), and the mass ratio of its component elements is cerium: cobalt: copper: aluminum: oxygen = 11.8: 7.5: 0.2: 36.0: 44.5.

[0099] The hydrogen chloride removal section 20 is a water scrubber. The perfluorinated compound decomposition section 30 is a reactor made of Inconel (registered trademark) (with a capacity of 70 mL), and inside it is filled with 60 g (with a volume of 70 mL) of perfluorinated compound decomposition catalyst in the shape of tablets with a diameter of 3 mm and a length of 10 mm. This perfluorinated compound decomposition catalyst is obtained by kneading nickel nitrate and boehmite, extrusion molding, and sintering. Moreover, this perfluorinated compound decomposition catalyst is a mixture of nickel oxide (NiO) and aluminum oxide (Al2O3), and the mass ratio of its component elements is nickel: aluminum: oxygen = 23: 37: 40.

[0100] In Figure 1 the exhaust gas treatment device, the exhaust gas is introduced into the chlorine decomposition section 10, and the chlorine decomposition process is performed, and the chlorine in the exhaust gas is hydrolyzed. The gas that has undergone the chlorine decomposition process is discharged from the chlorine decomposition section 10 and introduced into the hydrogen chloride removal section 20.

[0101] Then, the hydrogen chloride removal process is performed in the hydrogen chloride removal section 20, and the hydrogen chloride in the gas that has undergone the chlorine decomposition process is removed.

[0102] The gas that has passed through the hydrogen chloride removal process is discharged from the hydrogen chloride removal unit 20 and introduced into the perfluorinated compound decomposition unit 30. Then, in the perfluorinated compound decomposition unit 30, a perfluorinated compound decomposition process is carried out, and the perfluorinated compounds and chlorine gas in the gas that has passed through the hydrogen chloride removal process are hydrolyzed. The gas from which chlorine gas and perfluorinated compounds have been removed is discharged from the perfluorinated compound decomposition unit 30 as a harmless gas.

[0103] The Figure 1 composition of the exhaust gas treated by the exhaust gas treatment device shown is as follows. That is, this exhaust gas is a mixed gas of chlorine gas, octafluorocyclobutane, nitrogen gas, water vapor, and oxygen gas, and its volume ratio is chlorine gas: octafluorocyclobutane: nitrogen gas: water vapor: oxygen gas = 0.5: 0.5: 82: 15: 2.

[0104] Specifically, the volumes of chlorine gas, octafluorocyclobutane, nitrogen gas, and air are adjusted with mass flow controllers and mixed at the above volume ratio, and then introduced into the chlorine gas decomposition unit 10 under normal pressure. On the other hand, pure water at room temperature is introduced into a preheating unit (not shown), vaporized at 400 °C, and the resulting water vapor is introduced into the chlorine gas decomposition unit 10 in such a way that the composition of the mixed gas of chlorine gas, octafluorocyclobutane, nitrogen gas, water vapor, and oxygen gas reaches the above volume ratio. Furthermore, the supply rate of the mixed gas of chlorine gas, octafluorocyclobutane, nitrogen gas, water vapor, and oxygen gas to the chlorine gas decomposition unit 10 is converted to 5 L / min at standard conditions (0 °C, 1.01×10 5 Pa).

[0105] As described above, the mixed gas (exhaust gas) is supplied to the chlorine gas decomposition unit 10, and the decomposition reaction of chlorine gas is carried out at 525 °C in the chlorine gas decomposition unit 10. Then, at the time point when the decomposition reaction of chlorine gas has been carried out for 1 hour, the mixed gas (exhaust gas) supplied to the chlorine gas decomposition unit 10 and the gas discharged from the chlorine gas decomposition unit 10 are respectively prepared, and the concentrations of chlorine gas, octafluorocyclobutane, and hydrogen chloride in each gas are measured. The results are shown in Table 1. Furthermore, in Table 1, octafluorocyclobutane is denoted as "PFC".

[0106]

[0107] The method for measuring the chlorine gas concentration in the gas is as follows. The gas (the exhaust gas supplied to the chlorine gas decomposition unit 10 or the gas discharged from the chlorine gas decomposition unit 10) is passed through 100 g of an aqueous potassium iodide solution with a concentration of 1.0 mass% for 15 minutes. Then, based on the iodine titration method, the aqueous potassium iodide solution after the gas has passed through is titrated to calculate the amount of chlorine gas in the gas.

[0108] The method for measuring the octafluorocyclobutane concentration in the gas is as follows. That is, a syringe is used to take 1 cm 3The target gas for analysis was sampled and injected into a gas chromatograph (manufactured by Shimadzu Corporation, GC-14B, detector: TCD) that had been pre-input with various factors in a manner capable of quantitatively analyzing the concentration of the target gas for analysis, and the concentration was measured.

[0109] The methods for measuring the hydrogen chloride concentration in the gas include the cases of the gas after the chlorine decomposition process and the gas after the hydrogen chloride decomposition process described later, and are the following two types.

[0110] First, in the case where the target gas for analysis does not contain chlorine, a detector tube-type gas detector composed of a hydrogen chloride detector tube (manufactured by Gastec Corporation, hydrogen chloride 14L) and a gas sampler (manufactured by Gastec Corporation, GV-100 type) was used to measure the hydrogen chloride concentration in the gas. That is, a certain volume (500 mL) of gas was aspirated with the detector tube-type gas detector, and the hydrogen chloride concentration was measured based on the discolored length of the detector tube through which the gas had passed (hereinafter referred to as "Method A").

[0111] On the other hand, in the case where the target gas for analysis contains chlorine, since chlorine affects the detection of hydrogen chloride, Method A cannot be used. Therefore, the iodine titration method was used to measure the chlorine concentration, and it was regarded as converting the difference between the chlorine concentration before the process and the chlorine concentration after the process into hydrogen chloride, and the hydrogen chloride concentration was calculated (hereinafter referred to as "Method B").

[0112] Since the target gas for analysis contains chlorine, the hydrogen chloride concentration in the gas after the chlorine decomposition process was measured by Method B.

[0113] The hydrogen chloride concentration in the gas after the hydrogen chloride removal process was calculated by multiplying the hydrogen chloride concentration in the gas after the chlorine decomposition process by the reduction ratio of the hydrogen chloride concentration when the hydrogen chloride removal process was performed on a gas composed only of hydrogen chloride and nitrogen, which was measured by Method A.

[0114] Next, the gas discharged from the chlorine decomposition unit 10 was supplied to the hydrogen chloride removal unit 20 (water scrubber), and hydrogen chloride was removed in the hydrogen chloride removal unit 20. The supply rate of the gas discharged from the chlorine decomposition unit 10 to the hydrogen chloride removal unit 20 was 5 L / min in terms of standard state, and the supply rate of water was 0.5 mL / min. In addition, the temperature of the water supplied to the hydrogen chloride removal unit 20 was 25°C.

[0115] Then, at the time point when the removal of hydrogen chloride had been carried out for 1 hour, the gas discharged from the hydrogen chloride removal unit 20 was sampled, and the concentrations of chlorine, octafluorocyclobutane, and hydrogen chloride in the gas were measured respectively. The results are shown in Table 1. The measurement methods for chlorine, octafluorocyclobutane, and hydrogen chloride are the same as those described above.

[0116] Next, the gas discharged from the hydrogen chloride removal section 20 was supplied to the perfluorinated compound decomposition section 30, and the perfluorinated compound and chlorine gas were decomposed at 750 °C in the perfluorinated compound decomposition section 30.

[0117] Then, at the time point when the decomposition reaction of the perfluorinated compound and chlorine gas was carried out for 1 hour, harmless gas discharged from the perfluorinated compound decomposition section 30 was produced, and the concentrations of chlorine gas, octafluorocyclobutane, and hydrogen chloride in the gas were measured respectively. The results are shown in Table 1. The measuring methods of chlorine gas, octafluorocyclobutane, and hydrogen chloride are the same as those described above.

[0118] In addition, the measured result of the chlorine gas concentration of the harmless gas was substituted into the following formula to calculate the harmless rate of chlorine gas. For octafluorocyclobutane, the harmless rate was calculated in the same way as for chlorine gas. The results are shown in Table 1.

[0119] Harmless rate (%) = { (0.5 - chlorine gas concentration of harmless gas (volume %)) / 0.5} × 100

[0120] (Example 2)

[0121] The temperature of the decomposition reaction of chlorine gas in the chlorine gas decomposition section 10 was 750 °C, and the exhaust gas was treated in the same manner as in Example 1 except for this. The results are shown in Table 1.

[0122] (Comparative Example 1)

[0123] The exhaust gas treatment device did not have the hydrogen chloride removal section 20, and the gas discharged from the chlorine gas decomposition section 10 was supplied to the perfluorinated compound decomposition section 30, and the exhaust gas was treated in the same manner as in Example 1 except for this. As can be seen from Table 1, compared with Example 1, in Comparative Example 1, the chlorine gas concentration of the harmless gas could not be made low enough.

[0124] (Comparative Example 2)

[0125] The exhaust gas treatment device did not have the chlorine gas decomposition section 10 and the hydrogen chloride removal section 20, and both a chlorine gas decomposition catalyst and a perfluorinated compound decomposition catalyst were filled in the perfluorinated compound decomposition section 30, and the exhaust gas was treated in the same manner as in Example 1 except for this. That is, the exhaust gas was supplied to the perfluorinated compound decomposition section 30, and the perfluorinated compound and chlorine gas were decomposed at 750 °C in the perfluorinated compound decomposition section 30.

[0126] The perfluorinated compound decomposition section 30 was a reactor made of Inconel (registered trademark) (capacity: 105 mL), and 11 g of the same type of chlorine gas decomposition catalyst as that used in Example 1 and 80 g of the same type of perfluorinated compound decomposition catalyst as that used in Example 1 were filled therein.

[0127] Then, at the time point when the decomposition reaction of the perfluorinated compound and chlorine gas was carried out for 1 hour, the harmless gas discharged from the perfluorinated compound decomposition section 30 was produced, and the concentrations of chlorine gas, octafluorocyclobutane, and hydrogen chloride in the gas were measured respectively. The results are shown in Table 1. The measuring methods of chlorine gas, octafluorocyclobutane, and hydrogen chloride were the same as those described above. Furthermore, the concentration of hydrogen chloride in the harmless gas was not recorded in Table 1, and it was 9935 volume ppm.

[0128] As can be seen from Table 1, compared with Example 1, in Comparative Example 2, the chlorine gas concentration of the harmless gas could not be made low enough.

[0129] Explanation of reference numerals

[0130] 10 Chlorine gas decomposition section

[0131] 20 Hydrogen chloride removal section

[0132] 30 Perfluorinated compound decomposition section

Claims

1. An exhaust gas treatment method is a method for treating exhaust gas containing chlorine and perfluorinated compounds, comprising: a chlorine decomposition step of decomposing the chlorine in the exhaust gas by reacting it with water in the presence of a chlorine decomposition catalyst; a hydrogen chloride removal step of removing hydrogen chloride from the gas that has passed through the chlorine decomposition step; and a perfluorinated compound decomposition step of decomposing the perfluorinated compound in the gas that has passed through the hydrogen chloride removal step by reacting it in the presence of a perfluorinated compound decomposition catalyst.

2. The exhaust gas treatment method according to claim 1, wherein the perfluorinated compound decomposition step is a step of decomposing the perfluorinated compound in the gas that has passed through the hydrogen chloride removal step by reacting it in the presence of the perfluorinated compound decomposition catalyst, and decomposing the chlorine in the gas that has passed through the hydrogen chloride removal step by reacting it in the presence of a chlorine decomposition catalyst.

3. The exhaust gas treatment method according to claim 1 or 2, wherein the hydrogen chloride removal step is a step of removing the hydrogen chloride by dissolving it in water by bringing the gas that has passed through the chlorine decomposition step into contact with water.

4. The exhaust gas treatment method according to claim 1 or 2, wherein the decomposition reaction of the chlorine in the chlorine decomposition step is carried out at a temperature of 500 °C or higher and 800 °C or lower.

5. The exhaust gas treatment method according to claim 1 or 2, wherein the decomposition reaction of the perfluorinated compound in the perfluorinated compound decomposition step is carried out at a temperature of 500 °C or higher and 800 °C or lower.

6. An exhaust gas treatment apparatus is an apparatus for treating exhaust gas containing chlorine and perfluorinated compounds, comprising a chlorine decomposition section, a hydrogen chloride removal section, and a perfluorinated compound decomposition section. The chlorine decomposition section is provided with a chlorine decomposition catalyst and decomposes the chlorine in the exhaust gas by reacting it with water in the presence of the chlorine decomposition catalyst. The hydrogen chloride removal section removes hydrogen chloride from the gas after the chlorine has been decomposed by the chlorine decomposition section. The perfluorinated compound decomposition section is provided with a perfluorinated compound decomposition catalyst and decomposes the perfluorinated compound in the gas after the hydrogen chloride has been removed by the hydrogen chloride removal section by reacting it in the presence of the perfluorinated compound decomposition catalyst.

7. The exhaust gas treatment apparatus according to claim 6, wherein the perfluorinated compound decomposition section further comprises a chlorine decomposition catalyst in addition to the perfluorinated compound decomposition catalyst, decomposes the perfluorinated compound in the gas after the hydrogen chloride has been removed by the hydrogen chloride removal section by reacting it in the presence of the perfluorinated compound decomposition catalyst, and decomposes the chlorine in the gas after the hydrogen chloride has been removed by the hydrogen chloride removal section by reacting it in the presence of the chlorine decomposition catalyst.

8. The exhaust gas treatment apparatus according to claim 6 or 7, wherein the hydrogen chloride removal section removes the hydrogen chloride by dissolving it in water by bringing the gas after the chlorine has been decomposed by the chlorine decomposition section into contact with water.

9. The exhaust gas treatment apparatus according to claim 6 or 7, wherein the chlorine decomposition section carries out the decomposition reaction of the chlorine at a temperature of 500 °C or higher and 800 °C or lower.

10. The exhaust gas treatment device according to claim 6 or 7, wherein the perfluorinated compound decomposition section performs the decomposition reaction of the perfluorinated compound at a temperature of 500°C or higher and 800°C or lower.

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