Activated carbon regeneration method and activated carbon regeneration apparatus

Abstract

An activated carbon regeneration method comprising a microwave irradiation step that involves heating activated carbon to which an organic fluorine compound has adhered to a temperature higher than 800°C via a microwave irradiation treatment.

Description

Method for regenerating activated carbon and apparatus for regenerating activated carbon

[0001] The present disclosure relates to, for example, a method for regenerating activated carbon and an apparatus for regenerating activated carbon.

[0002] Activated carbon is used for adsorption treatment in fields such as wastewater treatment, exhaust gas treatment, or deodorization treatment. The activated carbon used for adsorption treatment has a reduced adsorption capacity. In order to repeatedly use activated carbon, it is necessary to restore its adsorption capacity. From such a situation, a method for regenerating activated carbon that regenerates activated carbon from used activated carbon has been studied (see, for example, Patent Documents 1 to 4).

[0003] Activated carbon used for adsorption treatment such as an aqueous solution containing an organic fluorine compound is usually discarded as industrial waste without undergoing a regeneration process. When a regeneration process is performed on used activated carbon, there is a risk that the organic fluorine compound attached to the activated carbon will not be decomposed and will migrate into the exhaust gas and diffuse into the atmosphere. In addition, some organic fluorine compounds are classified as hardly decomposable substances. Such organic fluorine compounds may exist in water, soil, or the atmospheric environment without being decomposed for many years.

[0004] Japanese Patent No. 3974929, JP-A-2010-131478, JP-A-2021-137805, JP-T-2022-526919

[0005] In a conventional method for regenerating an adsorbent from a used adsorbent on which a normal organic compound is adsorbed, the used activated carbon is subjected to a heat treatment in a regeneration furnace. For example, a multi-stage furnace type regeneration furnace for large furnaces using an external heating method with heavy oil or gas, a rotary kiln type regeneration furnace for medium-sized furnaces, and a direct current energization superheating type regeneration furnace for small furnaces heated by electrode energization are known.

[0006] Most organic compounds decompose at the operating temperature of the regeneration furnace described above. However, organofluorine compounds may not decompose sufficiently at this temperature. As a result, there is a concern that a large amount of organofluorine compounds detached from spent activated carbon will be contained in the exhaust gas discharged from the regeneration furnace, and that these organofluorine compounds will diffuse into the atmosphere. Due to this concern, spent activated carbon on which organofluorine compounds have been adsorbed is often disposed of without undergoing regeneration treatment.

[0007] The purpose of this disclosure is to provide a method for regenerating activated carbon, which involves decomposing the organic fluorine compounds attached to the activated carbon to regenerate the activated carbon.

[0008] One embodiment of the activated carbon regeneration method of the present disclosure includes a microwave irradiation step, which involves heating activated carbon to which an organofluorine compound is attached to a temperature exceeding 800°C by microwave irradiation treatment.

[0009] According to this disclosure, a method for regenerating activated carbon is provided, which involves decomposing the organic fluorine compounds attached to the activated carbon to regenerate the activated carbon.

[0010] Figure 1 is a schematic block diagram showing one embodiment of the regeneration device of the present disclosure. Figure 2 is a schematic block diagram showing one embodiment of the regeneration device of the present disclosure.

[0011] In this specification, the numerical range N1 to N2 means N1 or greater and N2 or less. In this specification, if the units of the numbers before and after the "~" indicating a numerical range are the same, the unit of the number before the "~" may be omitted.

[0012] [Method for regenerating activated carbon] The method for regenerating activated carbon according to the present disclosure includes a microwave irradiation step, which involves heating activated carbon to which an organofluorine compound is attached to a temperature exceeding 800°C by microwave irradiation treatment.

[0013] Activated carbon can be regenerated by using the regeneration method of this disclosure. In this specification, "regeneration of activated carbon" means at least partially restoring the original adsorption capacity of activated carbon, or enhancing the adsorption capacity of activated carbon, by removing organofluorine compounds attached to the activated carbon. Furthermore, activated carbon with restored adsorption capacity can be produced by using the regeneration method of this disclosure.

[0014] In this specification, "removing a substance from activated carbon" means removing at least a portion of the substance from the activated carbon. "Removal" includes not only the decomposition of the substance but also its detachment from the activated carbon. "Detaching" means that the substance separates from the activated carbon by volatilization or other means. The substance in question is, for example, an organofluorine compound.

[0015] Hereinafter, "activated carbon with organic fluorine compounds attached" will also be referred to as "activated carbon (A)". Activated carbon (A) includes activated carbon and organic fluorine compounds attached to the activated carbon by adsorption or other means. Activated carbon (A) may contain one or more types of activated carbon. Activated carbon (A) may contain one or more types of organic fluorine compounds. Activated carbon (A) is, for example, used activated carbon.

[0016] Examples of activated carbon include powdered activated carbon and granular activated carbon. The regeneration method of this disclosure can be applied to the regeneration of either powdered or granular activated carbon. Granular activated carbon has a larger particle size than powdered activated carbon. Specifically, examples of activated carbon include mineral-based activated carbon such as coal-based activated carbon and petroleum-based activated carbon; and plant-based activated carbon such as wood-based activated carbon and coconut shell-based activated carbon.

[0017] Examples of organofluorine compounds include perfluoroalkyl compounds having a perfluoroalkyl group and polyfluoroalkyl compounds having a polyfluoroalkyl group.

[0018] Examples of perfluoroalkyl compounds include perfluoroalkyl sulfonic acid and its derivatives, perfluoroalkyl carboxylic acid and its derivatives, perfluoroalkyl ethers such as perfluoro(2-butyl-tetrahydrofuran), perfluoroalkanes, perfluoroalkyl sulfides, perfluoroalkyl iodides, perfluoroalkylamines such as perfluorotributylamine, perfluoroalkyl phosphate esters, perfluoroalkylsilane compounds, and salts thereof.

[0019] Examples of polyfluoroalkyl compounds include polyfluoroalkyl sulfonic acids and their derivatives, polyfluoroalkyl carboxylic acids and their derivatives, polyfluoroalkyl ethers, polyfluoroalkanes, polyfluoroalkyl sulfides, polyfluoroalkyl iodides, polyfluoroalkylamines, polyfluoroalkyl phosphate esters, polyfluoroalkylsilane compounds, and salts thereof.

[0020] Examples of organofluorine compounds include perfluorobutanesulfonic acid, perfluoro(2-ethoxyethane)sulfonic acid, perfluoropentanesulfonic acid, perfluoro-1,3-propanedisulfonic acid, 1H,1H,2H,2H-perfluorohexanesulfonic acid, perfluorohexanesulfonic acid (PFHxS), perfluoroheptanesulfonic acid, 1H,1H,2H,2H-perfluorooctanesulfonic acid, 9-chlorohexadecafluoro-3-oxanonanane-1-sulfonic acid, and perfluoroocta Perfluorooctanesulfonic acid (PFOS), perfluorooctanesulfonic acid fluoride, perfluorooctanesulfonic acid amide, perfluorononanesulfonic acid, 11-chloroicosafluoro-3-oxaundecane-1-sulfonic acid, 1H,1H,2H,2H-perfluorodecanesulfonic acid, perfluorodecanesulfonic acid, N-ethylperfluorooctanesulfonamide acetate, N-methylperfluorooctanesulfonamide acetate, perfluoroundecanesulfonic acid, perfluorododecanesulfonic acid, perfluoro Tridecanesulfonic acid, perfluoropropionic acid, perfluorobutanoic acid, perfluoro-3-methoxypropanoic acid, nonafluoro-3,6-dioxaheptanoic acid, perfluoro-4-methoxybutanoic acid, perfluoropentanoic acid, hexafluoropropylene oxide dimer acid, perfluorohexanoic acid, 4,8-dioxa-3H-perfluorononanoic acid, perfluoroheptanoic acid, perfluorooctanoic acid (PFOA), perfluorononanoic acid, perfluorodecanoic acid, perfluoroundecanoic acid, perfluoro Examples include rhododecanoic acid, perfluorotridecanoic acid, perfluorotetradecanoic acid, perfluorohexadecanoic acid, perfluorobutane, perfluoropentane, perfluorohexane, perfluorooctane, perfluorodecane, perfluorododecane, perfluorotetradecane, perfluorohexadecane, perfluorobutyl ethyl sulfide, perfluorohexyl ethyl sulfide, perfluorooctyl ethyl sulfide, perfluorooctyl iodide, and perfluorodecyl iodide.

[0021] Among organofluorine compounds, at least one selected from the group consisting of perfluorooctanesulfonic acid (PFOS), perfluorohexanesulfonic acid (PFHxS), and perfluorooctanoic acid (PFOA) is preferred.

[0022] Examples of the above derivatives include esters, amides, and halides. Examples of the above salts include alkali metal salts such as lithium salts, sodium salts, and potassium salts; amine salts such as alkanolamine salts such as monoethanolamine salts, diethanolamine salts, and triethanolamine salts; and ammonium salts.

[0023] The number of carbon atoms in the organofluorine compound is preferably 20 or less, more preferably 18 or less, even more preferably 16 or less, and particularly preferably 14 or less. The boiling point of the organofluorine compound at 1 atmosphere is preferably 120 to 800°C, more preferably 120 to 500°C, even more preferably 120 to 400°C, and particularly preferably 120 to 300°C.

[0024] Activated carbon (A) may contain two or more organofluorine compounds.

[0025] <Microwave Irradiation Process> In conventional regeneration furnaces, the used activated carbon inside the furnace is heated by heat transfer. Conventional regeneration methods using conventional furnaces tend to be difficult to operate at high temperatures due to the heat resistance of the materials that make up the furnace. Therefore, conventional regeneration furnaces tend to be difficult to fully decompose the organic fluorine compounds attached to the activated carbon.

[0026] On the other hand, in the regeneration method of this disclosure, activated carbon (A) is heated by irradiating it with microwaves. Microwave heating is a so-called internal heating method in which microwaves directly act on the activated carbon (A) and directly heat the activated carbon itself, thereby heating the organofluorine compounds attached to the activated carbon as well. For this reason, the temperature around the activated carbon (A) does not rise in the same way as the temperature of the activated carbon (A) rises. Only the components in contact with the activated carbon (A) are indirectly heated by heat transfer due to the rising temperature of the activated carbon, and the regeneration furnace itself is hardly heated. In other words, microwave heating can solve the heat resistance limitations of the material of the activated carbon regeneration furnace. Furthermore, unlike the heat transfer method of conventional activated carbon regeneration furnaces, the microwave heating device can directly raise the temperature of the activated carbon by an internal heating method, so the microwave heating device itself is hardly heated, resulting in excellent thermal efficiency and reduced CO2 generation.

[0027] In the regeneration method of this disclosure, organofluorine compounds attached to activated carbon can be sufficiently decomposed by adjusting the heating temperature by microwave irradiation. While some desorption of organofluorine compounds from the activated carbon may occur along with the decomposition of organofluorine compounds on the activated carbon, it is preferable to perform microwave irradiation under conditions in which the decomposition of organofluorine compounds proceeds primarily, from the viewpoint of suppressing the gasification of organofluorine compounds.

[0028] Therefore, by applying the regeneration method of this disclosure to activated carbon that has adsorbed organic fluorine compounds such as so-called PFAS (for example, used activated carbon) and regenerating the activated carbon, used activated carbon can be reused as activated carbon without disposal treatment such as landfill disposal or incineration, and without diffusing and releasing large amounts of organic fluorine compounds into the atmosphere.

[0029] The microwave irradiation step includes irradiating the activated carbon with microwaves to maintain the activated carbon at a temperature above 800°C. The temperature of the activated carbon irradiated with microwaves (hereinafter also referred to as the "heating temperature of the activated carbon") is preferably 820°C or higher, more preferably 850°C or higher, even more preferably 900°C or higher, even more preferably 950°C or higher, particularly preferably 980°C or higher, preferably 1500°C or lower, more preferably 1300°C or lower, even more preferably 1200°C or lower, for example, between 800°C and 1500°C, preferably 820 to 1500°C, more preferably 850 to 1300°C, and even more preferably 900 to 1200°C. At such temperatures, organic fluorine compounds attached to the activated carbon tend to be sufficiently decomposed. The temperature of the activated carbon can be measured by an infrared thermographic camera.

[0030] In the microwave irradiation process, for example, the activated carbon is irradiated with microwaves in a heating container equipped with a microwave irradiation unit capable of irradiating microwaves. The heating container is not particularly limited as long as it can withstand microwave irradiation, but for example, it is a steel container such as a stainless steel (SUS) container. In the microwave irradiation process, the activated carbon may be irradiated with microwaves continuously or intermittently.

[0031] In the microwave irradiation step, the temperature of the activated carbon can be maintained at over 800°C (preferably the heating temperature of the activated carbon described above) for at least one second, ensuring the residence time necessary for the decomposition of the organofluorine compound. The time for maintaining the temperature of the activated carbon above 800°C is, for example, at least one second, preferably at least one second to ten minutes, more preferably at least one second to five minutes, and even more preferably at least one second to three minutes, and may be at least two seconds, five seconds, ten seconds, twenty seconds, or thirty seconds. Under these conditions, the organofluorine compound can be sufficiently decomposed.

[0032] Considering the penetration depth and attenuation of microwaves into the activated carbon described above, it is preferable that the activated carbon aggregate irradiated with microwaves be in a layered structure. The thickness of the activated carbon layer irradiated with microwaves is preferably 1 to 100 mm, more preferably 2 to 80 mm, even more preferably 3 to 50 mm, and particularly preferably 5 to 30 mm.

[0033] The microwave frequency is preferably 0.3 to 30 GHz, more preferably 0.5 to 28 GHz, even more preferably 1 to 26 GHz, even more preferably 1 to 15 GHz, and particularly preferably 1 to 8 GHz. The microwave output is preferably 10 W to 10,000 kW, more preferably 50 W to 8,000 kW, and even more preferably 100 W to 6,000 kW.

[0034] In the microwave irradiation step, the activated carbon may be heated by microwave irradiation starting from a temperature of 800°C or lower (hereinafter also referred to as the "starting temperature") and rising to over 800°C (preferably the heating temperature of the activated carbon as described above). The starting temperature is preferably 100°C or lower, more preferably 0 to 80°C, even more preferably 3 to 60°C, even more preferably 5 to 40°C, and particularly preferably room temperature. The heating rate of the activated carbon is preferably 20°C / second or higher, more preferably 30°C / second or higher, even more preferably 40°C / second or higher, and particularly preferably 45 to 100°C / second. Such a heating rate can be achieved by microwave irradiation. By heating the activated carbon at such a heating rate, the decomposition of the organofluorine compound can be promoted well while suppressing the desorption and gasification of the organofluorine compound from the activated carbon, and in some cases, the decomposition can proceed to HF.

[0035] If moisture is attached to the activated carbon (if activated carbon (A) contains moisture), microwave irradiation will cause the moisture attached to the activated carbon to volatilize. In the microwave irradiation process, it is preferable to heat the activated carbon to, for example, 100°C or more but less than 150°C by microwave irradiation, and then heat it to 150°C or higher by microwave irradiation. In this manner, the organic fluorine compounds can be removed after the moisture attached to the activated carbon has been volatilized and removed. For example, by primarily volatilizing the moisture attached to the activated carbon first and then removing the organic fluorine compounds, it is possible to achieve efficient energy use and uniform heating.

[0036] In the microwave irradiation process, external heating may be performed simultaneously with microwave irradiation. External heating can be performed, for example, by contact between the activated carbon and heated steam (hereinafter also referred to as "heated steam") or hot air, or by using an electric heater. Microwave irradiation and external heating do not have to be performed simultaneously.

[0037] In addition to irradiating the activated carbon with microwaves, contact between the activated carbon and heated steam may also be performed. For example, the activated carbon may be irradiated with microwaves in an atmosphere containing heated steam. Trace amounts of carbides may remain on the activated carbon after microwave irradiation (e.g., inside the pores). These carbides can be gasified and removed from the activated carbon by a water gasification reaction by contacting the activated carbon with heated steam. In the gasification reaction, gases such as hydrogen and carbon monoxide may be generated. The heated steam can also function as a heat source for removing organofluorine compounds from the activated carbon (A). The temperature of the heated steam contacted with the activated carbon is preferably 600 to 1200°C, more preferably 650 to 1100°C, even more preferably 700 to 1000°C, and particularly preferably 750 to 900°C, from the viewpoint of enabling the water gasification reaction to proceed smoothly and suppressing the deterioration of the activated carbon itself.

[0038] In the microwave irradiation process, the activated carbon may be heated to a temperature exceeding 800°C (preferably the heating temperature of the activated carbon described above) by microwave irradiation, and then heated to a temperature of, for example, 500 to 800°C by microwave irradiation. At this time, heated steam may be brought into contact with the activated carbon along with the microwave irradiation. The performance of the activated carbon can be adjusted by such processing.

[0039] In the microwave irradiation step, the activated carbon after microwave irradiation may be brought into contact with heated steam. The carbides can be gasified and removed from the activated carbon by the water gasification reaction that occurs when the activated carbon is brought into contact with heated steam. The temperature of the heated steam brought into contact with the activated carbon is preferably 600 to 1200°C, more preferably 650 to 1100°C, even more preferably 700 to 1000°C, and particularly preferably 750 to 900°C, from the viewpoint of enabling the water gasification reaction to proceed well and suppressing the deterioration of the activated carbon itself.

[0040] As described above, the regeneration method of this disclosure may involve bringing heated steam into contact with the activated carbon during and after microwave irradiation of the activated carbon, at least one step selected from the group consisting of during and after microwave irradiation of the activated carbon.

[0041] The oxygen gas concentration in the atmosphere in which the microwave irradiation process is carried out is preferably 10% by volume or less, more preferably 6% by volume or less, even more preferably 4% by volume or less, and particularly preferably 2% by volume or less. In the microwave irradiation process, the activated carbon may be irradiated with microwaves under an inert gas atmosphere, a water vapor atmosphere, or a mixed gas atmosphere of an inert gas and water vapor. Examples of inert gases include nitrogen and argon. The water vapor may be heated water vapor. This allows the irradiation process to be carried out in an atmosphere with a low oxygen gas concentration. Therefore, this regeneration method can suppress the deterioration of the quality of the activated carbon itself.

[0042] <Cooling Step> The regeneration method of this disclosure may further include a cooling step (including cooling by heat dissipation) of the activated carbon after the microwave irradiation step. In the cooling step, it is preferable to gradually lower the temperature so that the activated carbon does not become extremely brittle.

[0043] The cooling temperature is not particularly limited, but is preferably less than 100°C, more preferably 80°C or lower, even more preferably 60°C or lower, even more preferably 40°C or lower, and especially preferably 30°C or lower, for example, 0°C or higher.

[0044] <Removal Step> In one embodiment, a gas containing a compound derived from an organic fluorine compound, for example, a decomposition product of an organic fluorine compound, is obtained by a microwave irradiation step. The regeneration method of the present disclosure may further include a removal step of removing the compound derived from the organic fluorine compound from the gas obtained in the microwave irradiation step. The gas may, for example, contain a trace amount of the organic fluorine compound desorbed from activated carbon. When at least one gas component selected from the group consisting of water vapor and an inert gas is used in the gas, the gas also contains the gas component.

[0045] By providing a removal step, a compound (for example, an inorganic fluorine compound such as hydrogen fluoride) generated by decomposition of an organic fluorine compound in the microwave irradiation step or an organic fluorine compound that may be contained in trace amounts in the gas without being decomposed in the microwave irradiation step can be removed from the gas and recovered without being released into the atmosphere.

[0046] In the removal step, it is preferable to subject the gas to wet scrubber treatment. By subjecting the gas to wet scrubber treatment, the compound derived from the organic fluorine compound in the gas can be dissolved or trapped in water. For example, the gas and liquid water may be brought into countercurrent contact. Specifically, the gas may be blown in from the bottom into a wet scrubber treatment apparatus equipped with a packing material, and liquid water (for example, pure water, tap water or industrial water) may be sprayed from the top, and the gas and water may be brought into sufficient contact in the process of passing through the packing material.

[0047] The aqueous solution obtained by wet scrubber treatment (hereinafter also referred to as "scrubber treatment liquid") may be treated as waste liquid by a conventionally known method. For example, the obtained scrubber treatment liquid may be subjected to adsorption treatment using activated carbon. For example, when the obtained scrubber treatment liquid contains an organic fluorine compound such as so-called PFAS, the treatment liquid is subjected to adsorption treatment with activated carbon, and the activated carbon after this treatment is treated again using the regeneration method of the present disclosure, whereby the organic fluorine compound can be sufficiently decomposed.

[0048] [Activated Carbon Regeneration Device] The activated carbon regeneration device of the present disclosure includes a container (hereinafter also referred to as a "heating container") that contains activated carbon (activated carbon (A)) to which an organic fluorine compound is attached or through which the activated carbon (A) can pass, a microwave irradiation unit provided in the container that can irradiate the activated carbon with microwaves, and a gas discharge line through which the gas discharged from the container flows.

[0049] The heating container contains the activated carbon or the activated carbon passes through the heating container. The heating container, for example, has a layer of the activated carbon (activated carbon layer). The activated carbon layer may be, for example, a fixed bed or a fluidized bed. The thickness of the activated carbon layer in the case of a fixed bed is as described above.

[0050] The heating container is not particularly limited as long as it can withstand microwave irradiation. For example, it is a steel container such as a stainless steel (SUS) container. Since the SUS material basically reflects microwaves, the temperature of the SUS container hardly rises due to microwave irradiation itself, and the temperature rise due to heat transfer from the activated carbon is mainly involved. Therefore, in microwave irradiation, the activated carbon can be heated under the condition that, for example, the temperature of the SUS material does not rise until it reaches the melting point.

[0051] The installation location of the microwave irradiation unit in the heating container is not particularly limited. The microwave irradiation unit may be provided on the ceiling surface of the heating container or on the side wall of the heating container. From the viewpoint of enhancing the irradiation efficiency of microwaves on the activated carbon, the heating container may include a metal plate (for example, a propeller) that reflects microwaves.

[0052] Microwaves are generated, for example, by a microwave oscillator. The microwave irradiation unit may include a microwave oscillator. Alternatively, the regeneration device may include a microwave oscillator located outside the heating container and a waveguide for introducing microwaves into the heating container (microwave irradiation unit). Examples of microwave oscillators include magnetrons, klystrons, and Gunn diodes, with magnetrons being preferred among these. The microwave conditions and heating temperature are as described above. The heating container may further include a temperature sensor for measuring the temperature of the activated carbon. An example of a temperature sensor is an infrared thermographic camera.

[0053] The gas discharge line carries the gas discharged from the heating vessel. The heating vessel is usually equipped with a gas outlet. The gas discharge line is connected to the gas outlet of the heating vessel. Gas containing compounds derived from the above-mentioned organofluorine compounds is discharged from the gas outlet. If at least one gas component selected from the group consisting of water vapor and inert gases is used, this gas also contains that gas component. A blower for drawing in the above gas may be provided on the gas discharge line.

[0054] The above-described regeneration apparatus may further include a conveying device for transporting the activated carbon so that it passes through the heating container. Examples of conveying devices include belt conveyors and mobile roller plates. In this case, the heating container has an inlet and an outlet for the conveying device. The activated carbon (A) may be transported, for example, by being placed on the conveying device and introduced into the heating container. In this case, microwaves are irradiated onto the activated carbon (A) on the conveying device inside the heating container. The transport speed of the activated carbon (A) in the conveying device is not particularly limited and can be set appropriately according to the heating temperature and heating time of the activated carbon, as well as the amount of activated carbon supplied.

[0055] The above regeneration apparatus may further include an activated carbon supply device that supplies activated carbon (A) onto a conveying device before it enters the heating container. Examples of the activated carbon supply device include a hopper and a screw feeder. The above regeneration apparatus may further include an activated carbon recovery device that recovers the regenerated activated carbon from the conveying device after it has left the heating container.

[0056] The above regeneration device may further include a steam generator for generating steam and a steam supply line connecting the steam generator and the heating container. In this case, the heating container further includes a steam inlet. The steam supply line is connected to the steam inlet. The above regeneration device may also include a heating section capable of adjusting the steam temperature at one or more locations selected from the group consisting of the steam generator, the steam supply line, and the heating container.

[0057] Examples of heating devices for heating steam include direct heating devices such as cartridge heaters, flange heaters, infrared heaters, tape heaters, and ceramic heaters; and indirect heating devices such as induction heaters, dielectric heaters, and microwave heaters. The temperature of the steam heated in the heating device is the same as the temperature described in the [Activated Carbon Regeneration Method] section. The regeneration device may further include a temperature sensor for measuring the temperature of the steam.

[0058] The heating container may be equipped with the heating section described above. This heating section heats the steam introduced into the heating container. When the steam is heated in the heating container and brought into contact with the activated carbon (A), it is not necessary to preheat the steam in the steam supply line, nor is it necessary to provide a heating section for heating the steam on the steam supply line.

[0059] The steam generator may include the heating unit described above. The heating unit may be provided on the steam supply line. This heating unit heats the steam flowing through the steam supply line. The heating unit can be installed anywhere on the steam supply line as long as it can heat the steam, but it is preferable to install it in a location close to the heating container in order to minimize heat loss from the steam.

[0060] The above regeneration device may further include an inert gas supply device and an inert gas supply line connecting the inert gas supply device and the heating container. In this case, the heating container further includes an inert gas inlet. The inert gas supply line is connected to the inert gas inlet.

[0061] The locations of the steam inlet and inert gas inlet in the heating vessel are not particularly limited. The inlets may, for example, be provided within the activated carbon layer of the heating vessel, or they may be provided above or below the activated carbon layer in the direction of gravity. The inlets may, for example, be provided at the top (or apex) or bottom (or base) of the heating vessel. The locations of the gas outlet in the heating vessel are not particularly limited. The gas outlet may, for example, be provided below or above the activated carbon layer in the direction of gravity. The gas outlet may, for example, be provided at the bottom (or base) or top (or apex) of the heating vessel.

[0062] The heating container may be an upward flow type in which a gas component such as water vapor or an inert gas is introduced from the bottom (or base) of the heating container and the gas is removed from the top (or top), or a downward flow type in which a gas component such as water vapor or an inert gas is introduced from the top (or top) of the heating container and the gas is removed from the bottom (or base).

[0063] The steam supply line and / or inert gas supply line may be equipped with at least one selected from the group consisting of a pressure regulating valve, a flow meter, and a pressure sensor. The pressure regulating valve is a valve that adjusts the supply pressure of the steam or inert gas supplied from the above device to the heating vessel. The flow meter is a device that measures the flow rate of steam or inert gas flowing through the steam supply line or inert gas supply line. The flow meter may be electrically connected to the control device. The control device acquires flow rate information of steam or inert gas based on the measurement value of the flow meter. The pressure sensor is a device that measures the supply pressure of steam or inert gas. The pressure sensor may be electrically connected to the control device. The control device acquires pressure information based on the measurement value of the pressure sensor.

[0064] Each line is composed of, for example, piping.

[0065] The above-described regeneration apparatus may further include a steam heating container in addition to the heating container, and may further include a conveying device for conveying the activated carbon so that it passes through the heating container and the steam heating container. Examples of conveying devices include belt conveyors and conveyors such as movable roller plates. In this case, the steam heating container may be located upstream or downstream of the heating container in the flow direction of the conveying device. Inside the steam heating container, the activated carbon is heated by superheated steam. A steam generator may be connected to the steam heating container via a steam supply line. A heating section capable of adjusting the steam temperature may be provided at one or more locations selected from the group consisting of the steam generator, the steam supply line, and the steam heating container.

[0066] The above regeneration device preferably further includes a scrubber treatment device for wet scrubbing the gas discharged from the heating vessel. In this case, the gas discharge line connects the heating vessel and the scrubber treatment device.

[0067] Hereinafter, embodiments of the regeneration apparatus of this disclosure will be described with reference to the drawings. The regeneration apparatus 1 shown in Figure 1 comprises a heating container 10, a steam generator 20, an inert gas supply device 30, a wet scrubber processing device 40, a gas discharge line L1 connecting the heating container 10 and the wet scrubber processing device 40, a steam supply line L2 connecting the steam generator 20 and the heating container 10, an inert gas supply line L3 connecting the inert gas supply device 30 and the heating container 10, and a treated gas discharge line L4 through which the gas discharged from the wet scrubber processing device 40 flows.

[0068] The regeneration device 1 comprises a microwave irradiation unit 11, a base 12, and an activated carbon layer AC placed on the base 12, each located within the heating container 10. The heating container 10 further comprises a gas outlet 13, a steam inlet 14, and an inert gas inlet 15. The wet scrubber processing device 40 comprises a gas inlet 41 and a treated gas outlet 42.

[0069] The gas discharge line L1 has one end connected to the gas outlet 13 and the other end connected to the gas inlet 41. The steam supply line L2 is connected to the steam inlet 14. The inert gas supply line L3 is connected to the inert gas inlet 15. The treated gas discharge line L4 is connected to the treated gas outlet 42. A heating unit (not shown) is provided on the steam supply line L2.

[0070] The regeneration apparatus 1 shown in Figure 2 comprises a heating container 10, a wet scrubber processing device 40, a gas discharge line L1 connecting the container 10 and the device 40, a treated gas discharge line L4 through which the gas discharged from the device 40 flows, and a conveying device 50. The regeneration apparatus 1 includes a microwave irradiation unit 11 located inside the heating container 10. The heating container 10 further includes a gas outlet 13, and an inlet 16 and an outlet 17 for the conveying device 50.

[0071] The wet scrubber apparatus 40 comprises a water tank 43 (and water) located at the bottom of the apparatus 40, a water spraying unit 44 (e.g., a spray nozzle) located at the top of the apparatus 40, a mist catcher 45 (e.g., a packing material), a gas inlet 41 into which gas discharged from the heating container 10 in the microwave irradiation process is introduced, a treated gas outlet 42 into which the gas treated by the wet scrubber is discharged, a circulation line L5 connecting the lower water tank 43 and the water spraying unit 44, and a circulation pump 46 provided on the circulation line L5.

[0072] The water in the lower tank 43 is drawn in by the circulation pump 46 and supplied to the water spraying unit 44 through the circulation line L5. The water sprayed from the water spraying unit 44 falls back into the lower tank 43. The gas discharged from the heating container 10 during the microwave irradiation process is introduced into the wet scrubber treatment device 40 through the gas discharge line L1 from the gas outlet 13 of the heating container 10 and through the gas inlet 41. The gas comes into contact with the water sprayed from the water spraying unit 44, and after the water-soluble components are dissolved or captured in the water, it is discharged from the treated gas outlet 42. The water in the lower tank 43 is taken out via lines (piping) not shown and sent to wastewater treatment equipment not shown for treatment.

[0073] [Method for purifying a fluid] The method for purifying a fluid according to the present disclosure comprises a step of bringing a fluid containing an organofluorine compound into contact with activated carbon to cause the organofluorine compound to adhere to the activated carbon (hereinafter also referred to as the "adsorption step"), and a step of regenerating the activated carbon by the regeneration method of the present disclosure described above (hereinafter also referred to as the "regeneration step").

[0074] The fluid containing organofluorine compounds that is to be treated is also referred to as the "fluid to be treated" below. Examples of fluids include liquids and gases. Examples of liquids include aqueous solutions containing organofluorine compounds (e.g., drinking water, wastewater, effluent, and groundwater). Examples of gases include gases containing organofluorine compounds (e.g., exhaust gas from incineration facilities). Details of organofluorine compounds and activated carbon are as described above. Details of the regeneration method are as described above.

[0075] According to the purification method of this disclosure, it is possible to purify fluids containing organic fluorine compounds and to regenerate activated carbon whose adsorption capacity has decreased as a result of this purification treatment.

[0076] [Fluid purification apparatus] The regeneration apparatus of this disclosure may be incorporated into a fluid purification apparatus for purifying fluids containing organofluorine compounds. The purification apparatus also functions as an activated carbon regeneration apparatus.

[0077] [Examples of Embodiments] This disclosure relates, for example, to the following [1] to

[14] . [1] A method for regenerating activated carbon, comprising a microwave irradiation step of heating activated carbon to a temperature exceeding 800°C by microwave irradiation treatment. [2] The method for regenerating activated carbon according to [1], wherein the microwave irradiation step includes raising the temperature of the activated carbon to over 800°C by microwave irradiation and maintaining the temperature of the activated carbon at over 800°C for 1 second or more. [3] The method for regenerating activated carbon according to [1] or [2], wherein the microwave irradiation step includes raising the temperature of the activated carbon at a rate of 20°C / second or more by microwave irradiation. [4] The method for regenerating activated carbon according to any one of [1] to [3], wherein in the microwave irradiation step, the activated carbon is irradiated with microwaves in an atmosphere with an oxygen gas concentration of 2 volume% or less. [5] A method for regenerating activated carbon according to any one of [1] to [4], wherein the microwave irradiation step is performed in a SUS container containing the activated carbon. [6] A method for regenerating activated carbon according to any one of [1] to [5], comprising contacting the activated carbon with heated steam at at least one step selected from the group consisting of during and after the microwave irradiation of the activated carbon. [7] A method for regenerating activated carbon according to any one of [1] to [6], wherein in the microwave irradiation step, a gas containing a compound derived from the organofluorine compound is obtained, and the regeneration method further comprises a removal step of removing the compound from the gas. [8] A method for regenerating activated carbon according to [7], wherein the removal step comprises wet scrubbing the gas. [9] A method for producing activated carbon, comprising the step of producing activated carbon using the method for regenerating activated carbon according to any one of [1] to [8].

[10] A method for purifying a fluid, comprising the steps of: contacting a fluid containing an organofluorine compound with activated carbon to cause the organofluorine compound to adhere to the activated carbon; and regenerating the activated carbon by the activated carbon regeneration method described in any of [1] to [8].

[11] An activated carbon regeneration apparatus comprising: a container containing activated carbon to which an organofluorine compound is attached, or a container through which the activated carbon can pass; a microwave irradiation unit provided inside the container capable of irradiating the activated carbon with microwaves; and a gas discharge line through which gas discharged from the container flows.

[12] The activated carbon regeneration apparatus according to

[11] , wherein the regeneration apparatus further comprises a scrubber treatment device for wet scrubbing the gas discharged from the container, and the gas discharge line connects the container and the scrubber treatment device.

[13] The activated carbon regeneration apparatus according to

[11] or

[12] , wherein the regeneration apparatus further comprises a steam generator for generating steam, and a steam supply line connecting the steam generator and the container.

[14] The activated carbon regeneration apparatus according to

[13] , wherein the regeneration apparatus comprises a heating unit capable of adjusting the temperature of the steam, located in one or more locations selected from the group consisting of the steam generator, the steam supply line, and the container.

[0078] The method for regenerating activated carbon according to this disclosure will be described based on examples. However, the above regeneration method is not limited to the following examples.

[0079] [Preparation of Activated Carbon with Adsorbed PFOA] In a polypropylene (PP) bottle, 20 mg of perfluorooctanoic acid (PFOA) standard (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was dissolved in ultrapure water to prepare 500 mL of a 10,000 ng-PFOA / L aqueous solution. 50 g of coal-based activated carbon (Klicol WG-765, mesh size (8-32 mesh), manufactured by Kurita Water Industries Ltd.) was added thereto, and the PP bottle was shaken for 5 days. After that, the contents of the PP bottle were filtered through glass fiber filter paper (Merck, no adhesive used, pore size 0.7 μm, 90 mm diameter) to recover the PFOA-adsorbed activated carbon on the filter paper.

[0080] [Example 1] An experimental apparatus was prepared. The experimental apparatus consisted of a stainless steel container (400 mm x 400 mm x 400 mm in size) with a gas outlet, a turntable-type base and a microwave irradiation device provided inside the container, a gas outlet line connected to the gas outlet, and activated carbon for gas trapping (Kuraray Co., Ltd.) provided on the gas outlet line. 10 g-dry PFOA-adsorbing activated carbon was placed on the base to a thickness of 10 mm. To simplify calculations, the same amount of activated carbon for gas trapping (10 g-dry) as the PFOA-adsorbing activated carbon was used. Inside the experimental apparatus, the PFOA-adsorbing activated carbon was heated from 25°C to 1000°C in about 20 seconds by irradiating it with microwaves (frequency: 2.45 GHz, output: 500-4000 kW), and the PFOA-adsorbing activated carbon was maintained at 1000°C for 1 minute (heat treatment). The PFOA content of activated carbon after heat treatment, activated carbon before heat treatment, and activated carbon for gas traps after heat treatment were analyzed using the method described below. The analysis results are shown in Table 1.

[0081] [Comparative Example 1] The procedure was the same as in Example 1, except that the PFOA-adsorbing activated carbon was heated from 25°C to 800°C in about 16 seconds and maintained at 800°C for 1 minute. The PFOA content of the activated carbon after heat treatment, the activated carbon before heat treatment, and the activated carbon for gas traps after heat treatment were analyzed by the method described below. The analysis results are shown in Table 1.

[0082] [Analysis Method 1] Method for analyzing the PFOA content in activated carbon 0.2 g-dry activated carbon was accurately weighed into a centrifuge tube, 20 mL of methanol was added to it, and then 50 μL of a 100 ng / mL standard solution was added and mixed thoroughly to obtain test solution 1. Test solution 1 was subjected to sonication at 25°C for 20 minutes.

[0083] Test solution 1, after the above sonication treatment, was subjected to sonication at 50°C for 15 minutes, followed by centrifugation at 3000 rpm for 10 minutes. Methanol was collected by decantation and placed in a 500 mL PP volumetric flask. 20 mL of 0.5% ammonia / methanol was added to the remaining activated carbon to obtain test solution 2. Test solution 2 was similarly subjected to sonication at 25°C for 20 minutes, followed by centrifugation at 3000 rpm for 10 minutes. Methanol was collected by decantation and placed in the same 500 mL PP volumetric flask. This procedure was repeated one more time, for a total of three times. Then, ultrapure water was added to the 500 mL PP volumetric flask to make up to 500 mL, and the liquid in the PP volumetric flask was stirred. Subsequently, the PFOA concentration was measured according to the testing method for water quality management target setting items, attached to Health Water Bureau Notification No. 1010001, dated October 10, 2003. The PFOA content in the activated carbon was determined by multiplying the PFOA concentration of the obtained liquid by 500 mL and the dry mass of the activated carbon.

[0084] [Analysis Method 2] Method for Analyzing PFOA Concentration in Exhaust Gas If the mass of the PFOA-adsorbing activated carbon used in the test is the same as the mass of the activated carbon used for the gas trap from which the gas was collected, the PFOA content of the activated carbon used for the gas trap after the test / PFOA content of the PFOA-adsorbing activated carbon used in the test × 100 (%) will be the percentage of PFOA that did not decompose and transferred to the gas. If the total amount including other PFAS is less than 1% by mass, it can be considered that 99% or more by mass has decomposed.

[0085] [Analysis Method 3] Method for analyzing inorganic fluorine: 5 g-dry activated carbon and 10 mL of ultrapure water were placed in a 50 mL plastic bottle, and the bottle was shaken for 1 hour. The contents of the plastic bottle were filtered through glass fiber filter paper (Merck, no adhesive used, pore size 0.7 μm, 90 mm diameter), and the filtrate was subjected to inorganic fluorine analysis. Inorganic fluorine analysis was performed by flow injection (detection limit 0.1 mg / L).

[0086]

[0087] As shown in Table 1, in Example 1, it can be seen that the amount of PFOA decreased by more than 99.9% by mass. The inorganic fluorine content increased by 60 μg / g, and this value is 87% by mass compared to the theoretical value of 69 μg / g. Therefore, it is considered that the PFOA was almost completely decomposed, rather than decreasing due to volatilization. Almost no PFOA was detected in the activated carbon for the gas trap, but inorganic fluorine was detected, suggesting that the PFOA decomposed into hydrofluoric acid, and some of it was gasified.

[0088] As shown in Table 1, in Comparative Example 1, it can be seen that the amount of PFOA decreased by 70% by mass. Since the inorganic fluorine content did not increase, it is thought that PFOA did not decompose and that the decrease was due to volatilization. Since PFOA was detected in the activated carbon for the gas trap, and inorganic fluorine was hardly detected, it is thought that PFOA did not decompose and that some of it was gasified.

[0089] 1...Regeneration device, 10...Heating container, 11...Microwave irradiation unit, 12...Base, 13...Gas outlet, 14...Steam inlet, 15...Inert gas inlet, 16...Inlet of conveying device, 17...Outlet of conveying device, 20...Steam generator, 30...Inert gas supply device, 40...Wet scrubber treatment device, 41...Gas inlet, 42...Treatment gas outlet, 43...Water tank, 44...Water spraying unit, 45...Mist catcher, 46...Circulation pump, 50...Conveying device, L1...Gas discharge line, L2...Steam supply line, L3...Inert gas supply line, L4...Treatment gas discharge line, L5...Circulation line, AC...Activated carbon layer

Claims

1. A method for regenerating activated carbon, comprising a microwave irradiation step, which includes heating activated carbon to a temperature exceeding 800°C by microwave irradiation treatment, on which an organofluorine compound is attached.

2. The method for regenerating activated carbon according to claim 1, wherein the microwave irradiation step includes raising the temperature of the activated carbon to over 800°C by microwave irradiation and maintaining the temperature of the activated carbon at over 800°C for 1 second or more.

3. The method for regenerating activated carbon according to claim 1, wherein the microwave irradiation step includes raising the temperature of the activated carbon at a rate of 20°C / second or more by irradiation with microwaves.

4. The method for regenerating activated carbon according to claim 1, wherein in the microwave irradiation step, the activated carbon is irradiated with microwaves in an atmosphere in which the oxygen gas concentration is 2 volume percent or less.

5. The method for regenerating activated carbon according to claim 1, wherein the microwave irradiation step is performed inside a stainless steel container containing the activated carbon.

6. A method for regenerating activated carbon according to claim 1, comprising contacting heated steam with the activated carbon in at least one step selected from the group consisting of during and after microwave irradiation of the activated carbon.

7. The method for regenerating activated carbon according to claim 1, wherein in the microwave irradiation step, a gas containing a compound derived from the organofluorine compound is obtained, and the regeneration method further comprises a removal step of removing the compound from the gas.

8. The method for regenerating activated carbon according to claim 7, wherein the removal step includes treating the gas with a wet scrubber.

9. A method for producing activated carbon, comprising the step of producing activated carbon using the activated carbon regeneration method described in any one of claims 1 to 8.

10. A method for purifying a fluid, comprising the steps of: contacting a fluid containing an organofluorine compound with activated carbon to cause the organofluorine compound to adhere to the activated carbon; and regenerating the activated carbon by the activated carbon regeneration method described in any one of claims 1 to 8.

11. An activated carbon regeneration apparatus comprising: a container containing activated carbon to which an organofluorine compound is attached, or a container through which the activated carbon can pass; a microwave irradiation unit provided inside the container and capable of irradiating the activated carbon with microwaves; and a gas discharge line through which gas discharged from the container flows.

12. The activated carbon regeneration apparatus according to claim 11, wherein the regeneration apparatus further comprises a scrubber treatment apparatus for wet scrubbing the gas discharged from the container, and the gas discharge line connects the container and the scrubber treatment apparatus.

13. The activated carbon regeneration apparatus according to claim 11 or 12, further comprising: a steam generator for generating steam; and a steam supply line connecting the steam generator and the container.

14. The activated carbon regeneration apparatus according to claim 13, wherein the regeneration apparatus is provided with a heating unit capable of adjusting the temperature of the steam in one or more locations selected from the group consisting of the steam generator, the steam supply line, and the container.

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