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. An exhaust gas treatment method for treating exhaust gas containing chlorine gas and a perfluorinated compound, the method comprising: a chlorine gas decomposition step in which chlorine gas in the exhaust gas is reacted with water by heat to decompose 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 both the chlorine concentration and the perfluorocompound concentration of the gas low.

[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 through heat; 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 bringing the gas that has undergone the chlorine decomposition step into contact with water and dissolving the hydrogen chloride in the water.

[0011] [4] The exhaust gas treatment method according to any one of [1] to [3], wherein the decomposition reaction of the chlorine gas in the chlorine gas decomposition step is carried out at a temperature of 700 °C or higher and 850 °C or lower.

[0012] [5] The exhaust gas treatment method according to any one of [1] to [4], 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.

[0013] [6] An exhaust gas treatment device for treating exhaust gas containing chlorine gas and perfluorinated compounds, comprising a chlorine gas decomposition unit, a hydrogen chloride removal unit, and a perfluorinated compound decomposition unit,

[0014] The chlorine gas decomposition unit decomposes the chlorine gas in the exhaust gas by reacting it with water through heat.

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

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

[0017] [7] The exhaust gas treatment device according to [6], wherein the perfluorinated compound decomposition unit further comprises a chlorine gas decomposition catalyst in addition to the perfluorinated compound decomposition catalyst, decomposes the perfluorinated compound in the gas after the hydrogen chloride is removed by the hydrogen chloride removal unit by reacting it in the presence of the perfluorinated compound decomposition catalyst, and decomposes the chlorine gas in the gas after the hydrogen chloride is removed by the hydrogen chloride removal unit by reacting it in the presence of the chlorine gas decomposition catalyst.

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

[0019] [9] The exhaust gas treatment device according to any one of [6] to [8], wherein the chlorine gas decomposition unit carries out the decomposition reaction of the chlorine gas at a temperature of 700 °C or higher and 850 °C or lower.

[0020]

[10] The exhaust gas treatment device according to any one of [6] to [9], wherein the perfluorinated compound decomposition unit 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 of 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 through heat; 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 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 decomposes chlorine in the exhaust gas by reacting with water through heat. 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 equipped 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 in the presence of the perfluorinated compound decomposition catalyst.

[0026] If chlorine (Cl2) reacts with water (H2O) to undergo hydrolysis, as shown in 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 regeneration of chlorine and make the chlorine concentration in the gas low, 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 step is carried out after the chlorine decomposition step, the re-generation of chlorine is not likely to occur after the hydrogen chloride removal step. Moreover, through the perfluorinated compound decomposition step after the hydrogen chloride removal step, 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 concentrations.

[0030] In addition, the exhaust gas treatment device of this embodiment has a hydrogen chloride removal section that removes hydrogen chloride from the gas after chlorine has been partially decomposed by the chlorine decomposition section. Therefore, the re-generation of chlorine is not likely to occur in the gas after hydrogen chloride has been removed by the hydrogen chloride removal section. Moreover, the exhaust gas treatment device of this embodiment has a perfluorinated compound decomposition section. Therefore, both the chlorine concentration and the perfluorinated compound concentration in the gas can be made low concentrations.

[0031] For example, the chlorine concentration of the gas after the decomposition of perfluorinated compounds is preferably 1.0 volume ppm or less with respect to the chlorine concentration of the exhaust gas of 100 to 10,000 volume ppm, and the perfluorinated compound concentration of the gas after the decomposition of perfluorinated compounds is preferably 50 volume ppm or less with respect to the perfluorinated compound concentration of the exhaust gas of 1,000 to 10,000 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 both preferably 0.01% by volume or more and 10% by volume or less, more preferably 0.1% by volume or more and 1% by volume or less. In addition, the total concentration of chlorine and perfluorinated compounds is preferably 1% by volume or less.

[0036] Examples of the exhaust gas include the gas discharged during the manufacturing process of compounds and the gas discharged in various industrial processes. More specific examples of the exhaust gas include 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). 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), and nitrogen trifluoride (NF3) can be cited.

[0040] [Chlorine decomposition process, chlorine decomposition section]

[0041] As an example of the chlorine decomposition section that performs the decomposition reaction of chlorine, a reactor can be cited. As long as the exhaust gas is introduced into the high-temperature reactor and the exhaust gas is heated, the chlorine decomposition process can be implemented.

[0042] The material of the reactor is preferably a material that is inert or lacks reactivity with respect to chlorine or 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.

[0043] The decomposition reaction of chlorine is a reaction in which chlorine in the exhaust gas reacts with water by heat 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.

[0044] When the exhaust gas sufficiently contains water, the chlorine decomposition process can be directly carried out on the exhaust gas. However, when the exhaust gas completely does not contain water, 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.

[0045] In addition, when the exhaust gas does not sufficiently contain water and the water concentration of the exhaust gas is low, it is preferable to carry out the chlorine decomposition process 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 has a water supply section for adding water to the exhaust gas.

[0046] 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 implementing the chlorine decomposition process, it is preferable to add water to the exhaust gas so that the water concentration of the exhaust gas becomes higher than the lower limit value of the above numerical range.

[0047] The temperature conditions and pressure conditions of the chlorine decomposition process are not particularly limited as long as the decomposition of chlorine can be carried out. The temperature conditions are preferably 700 °C or more and 900 °C or less, more preferably 700 °C or more and 850 °C or less.

[0048] The pressure conditions are preferably normal pressure or a pressurized state, more preferably normal pressure.

[0049] By implementing such a chlorine decomposition process on the exhaust gas, chlorine is decomposed, so that the chlorine concentration of the gas passing through the chlorine decomposition process can be 300 ppm by volume or less.

[0050] Furthermore, before implementing the chlorine decomposition process, a treatment of bringing water into contact with the exhaust gas can also be carried out. For example, a treatment of bringing water into gas-liquid contact with the exhaust gas can also be carried out using a wet gas cleaning device (water scrubber). In this way, water-soluble gases can be removed from the exhaust gas.

[0051] [Hydrogen chloride removal process, hydrogen chloride removal section]

[0052] The gas that has decomposed chlorine through the chlorine decomposition process 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 process through the hydrogen chloride removal process.

[0053] The method for removing hydrogen chloride is not particularly limited, but preferably the hydrogen chloride removal process is a process of bringing the gas passing through the chlorine decomposition process 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 section and a treatment of bringing water into gas-liquid contact with the gas passing through the chlorine decomposition process is carried out, then since hydrogen chloride dissolves in water, hydrogen chloride can be removed from the gas passing through the chlorine decomposition process.

[0054] In addition, hydrogen chloride can also be removed from the gas passing through the chlorine decomposition process by a method of adsorbing hydrogen chloride with an adsorbent such as activated carbon. For example, using an adsorption tower filled with an adsorbent as the hydrogen chloride removal section, 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.

[0055] The conditions for removing hydrogen chloride from the exhaust gas using a water scrubber are described. To increase the contact frequency between the exhaust gas and water, it is preferable to have a large supply amount of water to the water scrubber, and the supply amount of water to the water scrubber is preferably 2.5% or more of the exhaust gas flow rate. For example, when the exhaust gas flow rate is 400 L / minute, the supply rate of water is preferably 10 L / minute or more.

[0056] 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.

[0057] To suppress clogging of the piping through which the water discharged from the water scrubber flows, water with a low metal ion concentration is preferably used as the water supplied to the water scrubber. If the water contains metal ions such as magnesium ions and calcium ions, the metal ions may react with hydrogen chloride to form metal salts that can cause clogging of the piping.

[0058] [Perfluorinated compound decomposition catalyst]

[0059] 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.

[0060] 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).

[0061] When the perfluorinated compound decomposition catalyst is a metal oxide, since it also functions as a chlorine decomposition catalyst, it can decompose the chlorine remaining in the gas that has passed through the chlorine decomposition process during the perfluorinated compound decomposition process.

[0062] The 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.

[0063] The shape and size of the carrier are not particularly limited. For example, a structure such as a bead shape, pellet shape, powder shape, granular shape, or monolithic shape is preferred, and a pellet shape is particularly preferred.

[0064] 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 cm2 Less than / g.

[0065] The material of the carrier is preferably a material that is inert or lacks reactivity with respect to chlorine and hydrogen chloride. Examples thereof include alumina (Al2O3), silica (SiO2), cordierite, zeolite, etc., and alumina is preferred.

[0066] The average particle diameter (diameter) of the carrier can be 1 mm or more and 10 mm or less, or can be 2 mm or more and 5 mm or less.

[0067] [Perfluorinated compound decomposition process, perfluorinated compound decomposition section]

[0068] 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.

[0069] The material of the reactor is preferably a material that is inert or lacks reactivity with respect to chlorine and hydrogen chloride. Examples thereof include nickel alloys, and as specific examples of nickel alloys, Inconel (registered trademark) 600, Inconel (registered trademark) 601, and Inconel (registered trademark) 625 can be cited.

[0070] The type of the decomposition reaction of perfluorinated compounds is not particularly limited as long as the perfluorinated compounds in the gas that has undergone the hydrogen chloride removal process are decomposed. For example, it can be a thermal decomposition reaction or a reaction of hydrolysis with water. Examples of the hydrolysis reaction of perfluorinated compounds are shown below.

[0071] C n F m +H2O→nCO2+mHF

[0072] SF6+xH2O→SO x +6HF

[0073] NF3+xH2O→NO x +3HF

[0074] 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.

[0075] When the gas after the hydrogen chloride removal step contains sufficient water, the perfluorinated compound decomposition step can be directly performed on the gas after the hydrogen chloride removal step. When the gas after the hydrogen chloride removal step does not contain any water, it is necessary to perform the perfluorinated compound decomposition step after adding water to the gas after the hydrogen chloride removal step, or 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 needs to be equipped with a water supply unit for adding water to the gas after the hydrogen chloride removal step.

[0076] In addition, when the gas after the hydrogen chloride removal step does not contain sufficient water and the water concentration of the gas after the hydrogen chloride removal step is low, it is preferable to perform the perfluorinated compound decomposition step after adding water to the gas after the hydrogen chloride removal step to increase the water concentration, or 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 for adding water to the gas after the hydrogen chloride removal step.

[0077] 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 performing 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.

[0078] 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.

[0079] 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.

[0080] By performing 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 50 vol ppm or less with respect to the perfluorinated compound concentration of 1000 - 10000 vol ppm after the hydrogen chloride removal step.

[0081] Furthermore, the gas after the hydrogen chloride removal process sometimes contains unreacted chlorine in the chlorine decomposition process, and depending on the type of perfluorinated compound decomposition catalyst, the unreacted chlorine can be decomposed in the perfluorinated compound decomposition process. 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 perfluorinated compound decomposition catalysts, the perfluorinated compound and chlorine are decomposed in the perfluorinated compound decomposition process. When decomposing chlorine in the perfluorinated compound decomposition process, the chlorine concentration in the gas after the perfluorinated compound decomposition process can be set to 1.0 volume ppm or less relative to the chlorine concentration of 10 to 100 volume ppm after the hydrogen chloride removal process.

[0082] As described above, the gas after the hydrogen chloride removal process sometimes contains unreacted chlorine in the chlorine decomposition process. 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 process. That is, the perfluorinated compound decomposition section may also include a chlorine decomposition catalyst in addition to the perfluorinated compound decomposition catalyst.

[0083] When a chlorine decomposition catalyst is used together with the perfluorinated compound decomposition catalyst in the perfluorinated compound decomposition process, the perfluorinated compound decomposition process becomes the following process: reacting and decomposing the perfluorinated compound in the gas after the hydrogen chloride removal process in the presence of the perfluorinated compound decomposition catalyst, and reacting and decomposing the chlorine in the gas after the hydrogen chloride removal process in the presence of the chlorine decomposition catalyst.

[0084] 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 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 hydrogen chloride is removed by the hydrogen chloride removal section reacts and decomposes in the presence of the chlorine decomposition catalyst.

[0085] If a perfluorinated compound decomposition catalyst and a chlorine decomposition catalyst are used in the perfluorinated compound decomposition process, the unreacted chlorine in the chlorine decomposition process can be decomposed in the perfluorinated compound decomposition process. Therefore, the chlorine concentration in the gas can be made lower.

[0086] [Chlorine decomposition catalyst]

[0087] 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).

[0088] 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. Examples of other types of metal oxides include 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). Furthermore, the mass ratio of the component elements of the chlorine decomposition catalyst is preferably (cerium):(cobalt):(copper):(aluminum):(oxygen) = (5 to 15):(5 to 15):(0.1 to 0.5):(25 to 45):(40 to 50).

[0089] Moreover, in addition to containing at least one of cerium oxide and cobalt oxide, the chlorine decomposition catalyst may contain a composite oxide of cerium (Ce) and other metals. Examples of other metals constituting the composite oxide include at least one of magnesium (Mg), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), and zirconium (Zr).

[0090] 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.

[0091] 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 in a state not supported on a carrier. Regarding the carrier, it is the same as in the case of the perfluorinated compound decomposition catalyst, so detailed description is omitted.

[0092] After implementing the perfluorinated compound decomposition process, a treatment of bringing the gas that has undergone the perfluorinated compound decomposition process 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 undergone the perfluorinated compound decomposition process into gas-liquid contact with water, hydrogen chloride and hydrogen fluoride can be removed from the gas that has undergone the perfluorinated compound decomposition process. This hydrogen fluoride is generated by the decomposition of the perfluorinated compound. When removing hydrogen chloride and hydrogen fluoride from the gas that has undergone the perfluorinated compound decomposition process, the main component of the harmless gas discharged from the gas cleaning device after the perfluorinated compound decomposition process 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] Using an exhaust gas treatment device, the exhaust gas containing chlorine gas and perfluorinated compounds was treated to render the exhaust gas harmless. Referring to Figure 1 the schematic conceptual diagram of

[0097] Figure 1 the exhaust gas treatment device used in Example 1 will be described.

[0098] The chlorine gas decomposition unit 10 is a reactor made of Inconel (registered trademark) (with a capacity of 70 mL). Moreover, no catalyst is disposed inside the reactor, and the thermal decomposition reaction of chlorine gas occurs inside the reactor.

[0099] The hydrogen chloride removal unit 20 is a water scrubber.

[0100] The perfluorinated compound decomposition unit 30 is a reactor made of Inconel (registered trademark) (with a capacity of 90 mL), and 80 g of catalyst in the shape of pellets with a diameter of 3 mm and a length of 10 mm is filled inside it. 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 constituent elements is nickel:aluminum:oxygen = 23:37:40.

[0101] In Figure 1 the exhaust gas treatment device, the exhaust gas is introduced into the chlorine gas decomposition unit 10, and the chlorine gas decomposition process is carried out, and the chlorine gas in the exhaust gas is thermally decomposed. The gas passing through the chlorine gas decomposition process is discharged from the chlorine gas decomposition unit 10 and introduced into the hydrogen chloride removal unit 20.

[0102] Then, the hydrogen chloride removal process is carried out in the hydrogen chloride removal unit 20, and the hydrogen chloride in the gas passing through the chlorine gas decomposition process is removed.

[0103] The gas passing 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, the perfluorinated compound decomposition process is carried out in the perfluorinated compound decomposition unit 30, and the perfluorinated compounds and chlorine gas in the gas passing through the hydrogen chloride removal process are hydrolyzed. The gas from which chlorine gas and perfluorinated compounds have been removed is discharged as harmless gas from the perfluorinated compound decomposition unit 30.

[0104] Using Figure 1The composition of the exhaust gas treated by the exhaust gas treatment device shown below is as follows. That is, the exhaust gas is a mixed gas of chlorine, octafluorocyclobutane, nitrogen, water vapor, and oxygen, and the volume ratio is chlorine:octafluorocyclobutane: nitrogen:water vapor:oxygen = 0.5:0.5:82:15:2.

[0105] Specifically, the volumes of chlorine, octafluorocyclobutane, nitrogen, and air are adjusted with mass flow controllers and mixed at the above volume ratio, and then introduced into the chlorine decomposition unit 10 at 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 decomposition unit 10 in such a manner that the composition of the mixed gas of chlorine, octafluorocyclobutane, nitrogen, water vapor, and oxygen reaches the above volume ratio. Furthermore, the supply rate of the mixed gas of chlorine, octafluorocyclobutane, nitrogen, water vapor, and oxygen to the chlorine decomposition unit 10 is 5 L / min in terms of standard state (0 °C, 1.01×10 5 Pa).

[0106] As described above, the mixed gas (exhaust gas) is supplied to the chlorine decomposition unit 10, and the decomposition reaction of chlorine is carried out at 750 °C in the chlorine decomposition unit 10. Then, at the time point when the decomposition reaction of chlorine has been carried out for 1 hour, the mixed gas (exhaust gas) supplied to the chlorine decomposition unit 10 and the gas discharged from the chlorine decomposition unit 10 are respectively prepared, and the concentrations of chlorine, 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".

[0107]

[0108] The method for measuring the chlorine concentration in the gas is as follows. The gas (the exhaust gas supplied to the chlorine decomposition unit 10 or the gas discharged from the chlorine 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 in the gas.

[0109] The method for measuring the octafluorocyclobutane concentration in the gas is as follows. That is, 1 cm 3 of the gas to be analyzed is sampled with a syringe and injected into a gas chromatograph (manufactured by Shimadzu Corporation, GC-14B, detector: TCD) that has been pre-input with various factors in such a manner that the concentration of the gas to be analyzed can be quantitatively analyzed, and the concentration is measured.

[0110] The method for measuring the hydrogen chloride concentration in the gas includes the cases of the gas after the chlorine decomposition process and the gas after the hydrogen chloride decomposition process described later, and there are the following two types.

[0111] First, in the case where the gas to be analyzed does not contain chlorine, the concentration of hydrogen chloride in the gas was measured using a detector tube type gas detector composed of a hydrogen chloride detector tube (manufactured by Gastec Corporation, hydrogen chloride 14L) and a gas generator (manufactured by Gastec Corporation, GV-100 type). That is, a certain volume (500 mL) of gas was aspirated with the detector tube type gas detector, and the concentration of hydrogen chloride was measured based on the discolored length of the detector tube through which the gas passed (hereinafter referred to as "Method A").

[0112] On the other hand, in the case where the gas to be analyzed 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 concentration of hydrogen chloride was calculated (hereinafter referred to as "Method B").

[0113] Since the gas to be analyzed contains chlorine, the concentration of hydrogen chloride in the gas after the chlorine decomposition process was measured by Method B.

[0114] The concentration of hydrogen chloride in the gas after the hydrogen chloride removal process was calculated by multiplying the concentration of hydrogen chloride in the gas after the chlorine decomposition process by the reduction ratio of the concentration of hydrogen chloride when the hydrogen chloride removal process was carried out on a gas composed only of hydrogen chloride and nitrogen, which was measured by Method A.

[0115] 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.

[0116] Then, at the time point when the removal of hydrogen chloride was carried out for 1 hour, the gas discharged from the hydrogen chloride removal unit 20 was produced, 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 of chlorine, octafluorocyclobutane, and hydrogen chloride are the same as those described above.

[0117] Next, the gas discharged from the hydrogen chloride removal unit 20 was supplied to the perfluorinated compound decomposition unit 30, and the perfluorinated compound and chlorine were decomposed at 750°C in the perfluorinated compound decomposition unit 30.

[0118] Then, at the time point when the decomposition reaction of the perfluorinated compound and chlorine was carried out for 1 hour, the harmless gas discharged from the perfluorinated compound decomposition unit 30 was produced, 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 of chlorine, octafluorocyclobutane, and hydrogen chloride are the same as those described above.

[0119] In addition, the measurement result of the chlorine concentration of the harmless gas is substituted into the following formula to calculate the harmless rate of chlorine. For octafluorocyclobutane, the harmless rate is calculated in the same manner as for chlorine. The results are shown in Table 1.

[0120] Harmless rate (%) = { (0.5 - chlorine concentration of the harmless gas (vol%)) / 0.5} × 100

[0121] (Example 2)

[0122] Inside the perfluorinated compound decomposition section 30, 11 g of chlorine decomposition catalyst in the form of a pellet with a diameter of 3.2 mm and a length of 10 mm and 64 g of the same type of perfluorinated compound decomposition catalyst as used in Example 1 were filled. Other than this, the exhaust gas treatment was carried out in the same manner as in Example 1. The results are shown in Table 1.

[0123] Furthermore, the chlorine decomposition catalyst was 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.

[0124] (Example 3)

[0125] The temperature for the decomposition reaction of chlorine in the chlorine decomposition section 10 was 850 °C, and other than this, the exhaust gas treatment was carried out in the same manner as in Example 1. The results are shown in Table 1.

[0126] (Comparative Example 1)

[0127] The exhaust gas treatment device did not have the hydrogen chloride removal section 20, and the gas discharged from the chlorine decomposition section 10 was supplied to the perfluorinated compound decomposition section 30. Other than this, the exhaust gas treatment was carried out in the same manner as in Example 2. From Table 1, it can be seen that in Comparative Example 1 compared with Examples 1 and 2, the chlorine concentration of the harmless gas could not be made low enough.

[0128] (Comparative Example 2)

[0129] The exhaust gas treatment device did not have the hydrogen chloride removal section 20 and the perfluorinated compound decomposition section 30 and only had the chlorine decomposition section 10. Other than this, the exhaust gas treatment was carried out in the same manner as in Example 1. That is, the exhaust gas was supplied to the chlorine decomposition section 10, and the thermal decomposition of chlorine was carried out at 750 °C in the chlorine decomposition section 10.

[0130] Then, at the time point of performing the decomposition reaction of chlorine for 1 hour, the gas discharged from the chlorine decomposition unit 10 was produced as a harmless gas, and the concentrations of chlorine, perfluorocyclobutane, and hydrogen chloride in the gas were measured respectively. The results are shown in Table 1. The measurement methods of chlorine, perfluorocyclobutane, and hydrogen chloride are the same as those described above.

[0131] As can be seen from Table 1, compared with Comparative Example 2 and Examples 1 and 2, the chlorine concentration of the harmless gas could not be made low enough.

[0132] Description of reference numerals

[0133] 10 Chlorine decomposition unit

[0134] 20 Hydrogen chloride removal unit

[0135] 30 Perfluorinated compound decomposition unit

Claims

1. An exhaust gas treatment method is a method for treating exhaust gas containing chlorine and perfluorinated compounds, having: a chlorine decomposition step of decomposing the chlorine in the exhaust gas by reaction with heat and water; 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 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 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 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 700 °C or higher and 850 °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, having a chlorine decomposition section, a hydrogen chloride removal section, and a perfluorinated compound decomposition section, wherein the chlorine decomposition section decomposes the chlorine in the exhaust gas by reaction with heat and water, the hydrogen chloride removal section removes hydrogen chloride from the gas after the chlorine has been decomposed by the chlorine decomposition section, and 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 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 includes 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 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 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 700 °C or higher and 850 °C or lower.

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

Images