Method for regenerating activated carbon and apparatus for regenerating activated carbon

Abstract

This invention provides a method for regenerating activated carbon by decomposing the organic fluorine compounds attached to the activated carbon, thereby regenerating the activated carbon. [Solution] 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.

Description

Technical Field

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

Background Art

[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 reuse activated carbon, it is necessary to restore its adsorption capacity. In view of 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. If a regeneration process is performed on used activated carbon, there is a risk that the organic fluorine compound adhering 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.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0005] In conventional methods for regenerating adsorbents from used adsorbents that have adsorbed ordinary organic compounds, the used activated carbon is subjected to heat treatment in a regeneration furnace. For example, there are known multi-stage furnace regeneration furnaces suitable for large furnaces that use an external heating method with heavy oil or gas, rotary kiln regeneration furnaces suitable for medium-sized furnaces, and direct current superheating regeneration furnaces suitable for small furnaces that are heated by the application of current to electrodes.

[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. [Means for solving the problem]

[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. [Effects of the Invention]

[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. [Brief explanation of the drawing]

[0010] [Figure 1] Figure 1 is a block diagram schematically showing one embodiment of the regeneration device of the present disclosure. [Figure 2] Figure 2 is a block diagram schematically showing one embodiment of the regeneration device of the present disclosure. [Modes for carrying out the invention]

[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] [How to regenerate activated carbon] The activated carbon regeneration method of this 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] Hereafter, "activated carbon with organic fluorine compounds attached" will also be referred to as "activated carbon (A)". Activated carbon (A) comprises activated carbon and an organofluorine compound adhering 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 organofluorine compounds. Activated carbon (A) is, for example, used activated carbon.

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

[0017] Examples of the organic fluorine compound include perfluoroalkyl compounds having a perfluoroalkyl group and polyfluoroalkyl compounds having a polyfluoroalkyl group.

[0018] Examples of the perfluoroalkyl compound 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, perfluoroalkyl amines such as perfluorotributylamine, perfluoroalkyl phosphate esters, perfluoroalkyl silane compounds, and salts thereof.

[0019] Examples of the polyfluoroalkyl compound include polyfluoroalkyl sulfonic acid and its derivatives, polyfluoroalkyl carboxylic acid and its derivatives, polyfluoroalkyl ethers, polyfluoroalkanes, polyfluoroalkyl sulfides, polyfluoroalkyl iodides, polyfluoroalkyl amines, polyfluoroalkyl phosphate esters, polyfluoroalkyl silane compounds, and salts thereof.

[0020] Specific examples of the organic fluorine compound 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-oxanonane-1-sulfonic acid, perfluorooctanesulfonic acid (PFOS), perfluorooctanesulfonic acid fluoride, perfluorooctanesulfonic acid amide, perfluorononanesulfonic acid, 11-chloroeicosadecafluoro-3-oxaundecane-1-sulfonic acid, 1H,1H,2H,2H-perfluorodecanesulfonic acid, perfluorodecanesulfonic acid, N-ethylperfluorooctanesulfonamidoacetic acid, N-methylperfluorooctanesulfonamidoacetic acid, perfluoroundecanesulfonic acid, perfluorododecanesulfonic acid, perfluorotridecanesulfonic acid, perfluoropropionic acid, perfluorobutyric acid, perfluoro-3-methoxypropionic acid, nonafluoro-3,6-dioxaheptanoic acid, perfluoro-4-methoxybutyric 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, perfluorododecanoic acid, perfluorotridecanoic acid, perfluorotetradecanoic acid, perfluorohexadecanoic acid, perfluorobutane, perfluoropentane, perfluorohexane, perfluorooctane, perfluorodecane, perfluorododecane, perfluorotetradecane, perfluorohexadecane, perfluorobutylethyl sulfide, perfluorohexyethyl sulfide, perfluorooctylethyl 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 organofluorine compounds 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. However, conventional regeneration methods tend to have difficulty operating at high temperatures due to the heat resistance of the materials that make up the furnace. Therefore, conventional regeneration furnaces tend to have difficulty adequately decomposing 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 emissions.

[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 methods 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 820-1500°C, more preferably 850-1300°C, and even more preferably 900-1200°C. At such temperatures, organic fluorine compounds attached to the activated carbon tend to be sufficiently decomposed. The temperature of the activated carbon mentioned above can be measured using 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 2 seconds or more, 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, 1 second or more, preferably 1 second to 10 minutes, more preferably 1 second to 5 minutes, and even more preferably 1 second to 3 minutes, and may be, for example, 2 seconds or more, 5 seconds or more, 10 seconds or more, 20 seconds or more, or 30 seconds or more. 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 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, decomposition can proceed to HF.

[0035] If moisture is present on 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 first 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 leads to 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 the microwave irradiation of the activated carbon described above, 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 caused by contacting the activated carbon with heated steam. In the gasification process, gases such as hydrogen and carbon monoxide may be generated. Furthermore, heated steam can also function as a heat source for removing organofluorine compounds from activated carbon (A). 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 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, 500-800°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 contacting the activated carbon with heated steam 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 steam. 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 process> The regeneration method of this disclosure may further include a cooling step of cooling the activated carbon after the microwave irradiation step (including cooling by heat dissipation). 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 process> In one embodiment, the microwave irradiation step yields a gas containing compounds derived from organofluorine compounds, such as decomposition products of organofluorine compounds. The regeneration method of this disclosure may further include a removal step to remove the compounds derived from organofluorine compounds from the gas obtained in the microwave irradiation step. The gas may contain, for example, trace amounts of organofluorine compounds desorbed from activated carbon. If at least one gas component selected from the group consisting of water vapor and inert gases is used, the gas may also include that gas component.

[0045] By providing a removal step, compounds produced by the decomposition of organofluorine compounds in the microwave irradiation step (for example, inorganic fluorine compounds such as hydrogen fluoride), as well as organofluorine compounds that may be present 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 process, it is preferable to treat the gas with a wet scrubber. By treating the gas with a wet scrubber, compounds derived from the organofluorine compounds in the gas can be dissolved or captured in water. For example, the gas and liquid water may be brought into countercurrent contact. Specifically, the gas may be blown into a wet scrubber apparatus equipped with a packing material from below, and liquid water (e.g., pure water, tap water, or industrial water) may be sprayed from above, allowing the gas and water to come into sufficient contact as they pass through the packing material.

[0047] The aqueous solution obtained by wet scrubbing (hereinafter also referred to as "scrubber treatment solution") may be treated as wastewater by conventionally known methods. For example, the obtained scrubber treatment solution may be treated with adsorption using activated carbon. For example, if the obtained scrubber treatment solution contains organic fluorine compounds such as so-called PFAS, the organic fluorine compounds can be sufficiently decomposed by adsorbing the solution with activated carbon and then treating the activated carbon again using the regeneration method of this disclosure.

[0048] [Activated carbon regeneration device] The activated carbon regeneration apparatus of this disclosure is A container containing activated carbon (activated carbon (A)) to which an organofluorine compound is attached, or a container through which activated carbon (A) can pass (hereinafter also referred to as the "heating container"), A microwave irradiation unit is provided inside the above container and capable of irradiating the activated carbon with microwaves, A gas discharge line through which the gas discharged from the above container flows, It is equipped with.

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

[0050] The heating container is not particularly limited as long as it can withstand microwave irradiation, but examples include steel containers such as stainless steel (SUS) containers. Since SUS material basically reflects microwaves, there is almost no temperature rise in the SUS container due to microwave irradiation itself, and the temperature rise is mainly due to heat transfer from the activated carbon. For this reason, the activated carbon can be heated under conditions where, for example, the temperature of the SUS material does not rise to its melting point when irradiated with microwaves.

[0051] The location of the microwave irradiation unit within 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 increasing the efficiency of microwave irradiation to activated carbon, the heating container may be equipped with a metal plate (e.g., 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 temperatures 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-mentioned gas may be provided on the gas discharge line.

[0054] The above 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-described regeneration apparatus may further include an activated carbon recovery device for recovering the regenerated activated carbon that has been transported out of 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 above regeneration device may further include a temperature sensor for measuring the temperature of the water vapor.

[0058] The heating container may be equipped with the above-mentioned heating unit. This heating unit 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 unit for heating the steam on the steam supply line.

[0059] The steam generator may also include the heating section described above. The heating unit described above 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 location of the gas outlet in the heating vessel is not particularly limited. The gas outlet may be located, for example, below or above the activated carbon layer in the direction of gravity. The gas outlet may be located, for example, 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 vessel, the activated carbon is heated by superheated steam. A steam generator may be connected to the steam heating vessel 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 vessel.

[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 treatment 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 apparatus 40, a treated gas discharge line L4 through which the gas discharged from the apparatus 40 flows, and a conveying device 50. The regeneration device 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 a wastewater treatment facility not shown for treatment.

[0073] [Methods for purifying fluids] The fluid purification method of this 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 this disclosure described above (hereinafter also referred to as the "regeneration step").

[0074] The fluid containing organofluorine compounds that is subject to purification treatment will also be 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, etc.). Details regarding the organofluorine compounds and activated carbon are as described above. Details of the playback method are as described above.

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

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

[0077] [Example of behavior] This disclosure relates, for example, to the following [1] to

[14] . [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 [1], wherein the microwave irradiation step includes raising the temperature of the activated carbon to over 800°C by irradiation with microwaves 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 irradiation with microwaves. [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 in which the oxygen gas concentration is 2 volume% or less. [5] The method for regenerating activated carbon according to any one of [1] to [4], wherein the microwave irradiation step is performed inside 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 during and after microwave irradiation of the activated carbon in at least one step selected from the group consisting of microwave irradiation and microwave irradiation of the activated carbon. [7] The 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] The method for regenerating activated carbon according to [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 of [1] to [8] above.

[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] above.

[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

[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

[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

[13] , wherein the regeneration apparatus comprises 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. [Examples]

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

[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 to this solution, 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 (400mm x 400mm x 400mm) with a gas outlet, a turntable-type base and a microwave irradiation device installed inside the container, a gas outlet line connected to the gas outlet, and activated carbon for gas trapping (Kuraray Co., Ltd.) placed on the gas outlet line. 10g-dry PFOA-adsorbing activated carbon was placed on the base to a thickness of 10mm. To simplify calculations, the same amount of 10g-dry activated carbon as the PFOA-adsorbing activated carbon was used for the gas trapping. In the experimental apparatus, PFOA-adsorbing activated carbon was heated from 25°C to 1000°C in approximately 20 seconds by irradiating it with microwaves (frequency: 2.45 GHz, output: 500-4000 kW), and maintained at 1000°C for 1 minute (heat treatment). 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 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 approximately 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 using the method described below. The analysis results are shown in Table 1.

[0082] [Analysis Method 1] Method for analyzing 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 the volume 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 gas trap from which the gas was collected, the percentage of PFOA that did not decompose and transferred to the gas is calculated as: PFOA content of the gas trap activated carbon after the test / PFOA content of the PFOA-adsorbing activated carbon used in the test × 100 (%). If the total amount including other PFAS is less than 1% by mass, it can be considered that 99% or more by mass has been decomposed.

[0085] [Analysis Method 3] Analysis Method for 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] [Table 1]

[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, 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. PFOA was detected in the activated carbon for the gas trap, and almost no inorganic fluorine was detected, suggesting that PFOA did not decompose and that some of it was gasified. [Explanation of Symbols]

[0089] 1...Playback device 10...Heating container 11...Microwave irradiation section 12…Pedestal 13...Gas outlet 14... Steam inlet 15...Inert gas inlet 16... Entrance to the conveying device 17… Exit of the conveying device 20...Steam generator 30...Inert gas supply device 40...Wet scrubber processing equipment 41...Gas inlet 42...Treated gas outlet 43... Aquarium 44... Sprinkler unit 45…Mist catcher 46…Circulation pump 50…Conveyor device L1…Gas discharge line L2…Water vapor supply line L3...Inert gas supply line L4…Treated 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 one 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 the activated carbon with heated steam during and after microwave irradiation of 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 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, A step of regenerating activated carbon by the activated carbon regeneration method described in any one of claims 1 to 8, A method for purifying a fluid, comprising [a specific characteristic].

11. 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 is provided inside the container and capable of irradiating the activated carbon with microwaves, A gas discharge line through which the gas discharged from the aforementioned container flows, A regeneration device for activated carbon, equipped with the following features.

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 aforementioned regeneration device A steam generator that produces steam, A steam supply line connecting the steam generator and the container, Furthermore, The activated carbon regeneration apparatus according to claim 11 or 12.

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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