Regeneration method and regeneration device for adsorbent

Abstract

One aspect of the present invention relates to a regeneration method for an adsorbent, the method comprising: heat-treating an adsorbent in a firing furnace at a temperature of 1500°C or lower in an inert gas; subjecting the gas discharged from the firing furnace to a combustion treatment in a secondary combustion furnace; and cooling the gas discharged from the secondary combustion furnace to 200°C or lower.

Description

Method and apparatus for regenerating adsorbent

[0001] This invention relates to a method and apparatus for regenerating adsorbent materials.

[0002] PFAS (perfluoroalkyl and polyfluoroalkyl substances), including PFOS (perfluorooctanesulfonate) and PFOA (perfluorooctanoic acid), as well as hundreds of other similar compounds, are chemically stable substances with excellent heat resistance and chemical resistance (e.g., acid resistance). Therefore, these persistent compounds are widely used as surfactants or industrial materials such as anti-reflective coatings in semiconductor manufacturing.

[0003] As a result, PFAS (protein-free phosphates) are accumulating in large quantities in nature. In recent years, it has become clear that PFAS pose a risk of adverse effects on human health and the environment. In response to this situation, among PFAS compounds, PFOA and PFOS are being voluntarily phased out. On the other hand, PFOA and PFOS are still known to persist in the environment. Furthermore, other PFAS compounds are still being used despite a limited understanding of their health risks. Currently, for example, the U.S. federal government has published Lifetime Health Advice regarding PFOA and PFOS, and in April 2024, announced that it would set the maximum contamination level (MCL) of these and other PFAS compounds in drinking water at 4 ng / L.

[0004] It is widely known that adsorbents such as activated carbon adsorb PFAS, but even at very dilute concentrations, there is a risk of accumulation in the human body and it may cause disease. Therefore, adsorbents used for PFAS adsorption in water treatment plants and other facilities need to be replaced more frequently, considering the possibility of PFAS re-leaching from the adsorbent. From the perspective of cost and the environment, it is desirable that PFAS adsorbents be recycled, and in recent years, recycling technologies for PFAS adsorbents have been investigated.

[0005] For example, Patent Document 1 describes a method for regenerating activated carbon that has adsorbed PFAS by contacting it with a solution containing alcohol and a base. Also, for example, Non-Patent Document 1 describes the results of observing the decomposition behavior of PFAS after heating activated carbon that has adsorbed PFAS.

[0006] However, the regeneration method described in Patent Document 1 uses an organic solvent to regenerate activated carbon for PFAS adsorption, but the use of an organic solvent is costly, and the removal rate of PFAS is not sufficient. Furthermore, the regeneration method described in Patent Document 1 does not describe the post-treatment of compounds removed from the activated carbon, and there is a risk of harmful substances being discharged into the environment, so the safety and environmental considerations have not been adequately addressed.

[0007] Furthermore, Non-Patent Document 1 describes a technique for heat treatment of activated carbon adsorbing PFAS, but activated carbon used for PFAS adsorption in water treatment plants and the like usually adsorbs chlorine compounds in addition to PFAS, and these chlorine compounds may react with organic matter during the heat treatment of the activated carbon, potentially generating organochlorine compounds such as dioxins. Non-Patent Document 1 only describes the results of observing the decomposition behavior of PFAS when activated carbon is heated, and makes no mention of organochlorine compounds such as dioxins that may be generated by the heat treatment.

[0008] Special Publication No. 2022-526919

[0009] Hideyuki Takemine, Mitsuyasu Takada, Shusaku Yamamoto, Nobuhisa Watanabe, Chisato Matsumura, Shigeho Fujii, Shuhei Tanaka, and Akira Kondo, "Behavior of Perfluoctanoic Acid Adsorbed on Granular Activated Carbon During Heating," BUNSEKI KAGAKU, Vol. 62, No. 2, pp. 107-113 (2013).

[0010] In view of the above situation, the present invention aims to provide a method and apparatus for regenerating an adsorbent that can safely regenerate the adsorbent by removing PFAS adsorbed on the adsorbent from the adsorbent, decomposing the PFAS removed from the adsorbent, and not releasing organochlorine compounds such as dioxins generated from chlorine compounds adsorbed on the adsorbent into the atmosphere.

[0011] As a result of various studies, the inventors have found that the above objective can be achieved by the following invention.

[0012] A method for regenerating an adsorbent according to one aspect of the present invention includes heat treatment of the adsorbent in a firing furnace at a temperature of 1500°C or lower under an inert gas, combustion treatment of the gas discharged from the firing furnace in a secondary combustion furnace, and cooling of the gas discharged from the secondary combustion furnace to 200°C or lower.

[0013] An adsorbent regeneration apparatus according to another aspect of the present invention comprises a firing furnace for heat-treating the adsorbent at a temperature of 1500°C or lower under an inert gas, a secondary combustion furnace for burning the gas discharged from the firing furnace, and a cooler for cooling the gas discharged from the secondary combustion furnace to 200°C or lower.

[0014] Figure 1 is a flowchart showing one embodiment of the adsorbent regeneration apparatus according to the present invention. Figure 2 is a flowchart showing another embodiment of the adsorbent regeneration apparatus according to the present invention. Figure 3 is a flowchart showing yet another embodiment of the adsorbent regeneration apparatus according to the present invention. Figure 4 is a flowchart showing yet another embodiment of the adsorbent regeneration apparatus according to the present invention.

[0015] The following describes specific embodiments for carrying out the present invention, but the present invention is not limited to these.

[0016] [Method for regenerating adsorbent] The method for regenerating the adsorbent in this embodiment includes heat treatment of the adsorbent in a firing furnace at a temperature of 1500°C or lower under an inert gas, combustion treatment of the gas discharged from the firing furnace in a secondary combustion furnace, and cooling of the gas discharged from the secondary combustion furnace to 200°C or lower.

[0017] According to the adsorbent regeneration method of this embodiment, first, the adsorbent is heat-treated in a firing furnace at a temperature of 1500°C or less under an inert gas, thereby decomposing or desorbing PFAS (perfluoroalkyl substances and polyfluoroalkyl substances) and chlorine compounds from the adsorbent and removing them. At this time, the thermal decomposition of the substances adsorbed on the adsorbent generates a gas containing organic chlorine compounds, hydrogen chloride, organic sulfur compounds, PFAS, aromatic hydrocarbons, hydrocarbons, hydrogen, carbon dioxide, carbon monoxide, and organic nitrogen compounds. In this embodiment, the compounds contained in this gas can be decomposed by burning it in a secondary combustion furnace. Specifically, this combustion treatment can, for example, mineralize fluorine and chlorine contained in the gas discharged from the firing furnace and convert them into hydrogen fluoride and hydrogen chloride, thereby suppressing the leakage of organic matter into the atmosphere. However, chlorine and carbon are suspended in the gas burned in the secondary combustion furnace, and these may generate dioxins through incomplete combustion in the air at approximately 250 to 400°C. In this embodiment, the generation of dioxins can be suppressed by cooling the gas discharged from the secondary combustion furnace to 200°C or below. Thus, according to the adsorbent regeneration method of this embodiment, PFAS adsorbed on the adsorbent is removed from the adsorbent, the PFAS removed from the adsorbent is decomposed, and organochlorine compounds such as dioxins generated from chlorine compounds adsorbed on the adsorbent are not discharged into the atmosphere, thus safely regenerating the adsorbent.

[0018] In other words, according to this embodiment, it is possible to provide a method and apparatus for regenerating an adsorbent that can safely regenerate the adsorbent by removing PFAS adsorbed on the adsorbent from the adsorbent, decomposing the PFAS removed from the adsorbent, and not releasing organochlorine compounds such as dioxins generated from chlorine compounds adsorbed on the adsorbent into the atmosphere.

[0019] In this embodiment, “perfluoroalkyl substances and polyfluoroalkyl substances” is commonly referred to as “PFAS.” When used herein, “PFAS” means the term “PFAS (perfluoroalkyl substances and polyfluoroalkyl substances),” specifically any perfluoroalkyl substance and polyfluoroalkyl substance, a mixture of such substances, or one or more derivatives of such substances. Examples of perfluoroalkyl and polyfluoroalkyl substances include perfluoroalkyl sulfonates, perfluoroalkanesulfonic acid (PFSA), N-butylperfluoroalkanesulfonamide (BuFASA), N-butylperfluoroalkanesulfonamideethanol (BuFASE), N-butylperfluoroalkanesulfonamideacetic acid (BuFASAA), N-ethylperfluoroalkanesulfonamide (EtFASA), N-ethylperfluoroalkanesulfonamideethanol (EtFASE), N-ethylperfluoroalkanesulfonamideacetic acid (EtFASAA), perfluoroalkanesulfonamide (FASA), and perfluoroalkanesulfonamideethanol. Examples include perfluoroalkanesulfonamide acetate (FASAA), N-methylperfluoroalkanesulfonamide (MeFASA), N-ethylperfluoroalkanesulfonamide acetate (EtFASAA), N-methylperfluoroalkanesulfonamide ethanol (MeFASA), perfluoroalkanesulfonyl fluoride (PASF), fluoroprotein (FP), fluorotelomer carboxylic acid (FTCA), fluorotelomer alcohol (FTOH), fluorotelomer sulfonate (FTS), fluorotelomer sulfonic acid (FTSA), perfluoroalkyl acid (PFAA), perfluoroalkyl sulfonamide ethanol (PFOSE), and their derivatives. Examples of perfluoroalkyl and polyfluoroalkyl substances include ammonium perfluorooctanoate (APFO) 4,8-Dioxa-3H-Perfluorononanoate ammonium, N-methylperfluorooctanesulfonamide (MeFOSA), perfluorooctanoic acid (PFOA), perfluorooctanesulfonic acid, perfluorooctanesulfonic acid (PFOS), 2,3,3,3-tetrafluoro-2-(heptafluoropropoxy)propanoate ammonium, 1,2,2,2-tetrafluoroethyl ether, 4:2-fluorotelomersulfonic acid (4:2 FtS), 6:2-fluorotelomersulfonic acid (6:2 FtS), 8:2-fluorotelomersulfonic acid (8:2 FtS), perfluorobutanoic acid (PFBA), perfluorobutanesulfonic acid, perfluorobutanesulfonic acid (PFBS), perfluorohexanesulfonic acid, perfluorohexanesulfonic acid (PFHxS), perfluorohexanoic acid, perfluorohexanoic acid (PFHxA), 4,8-Dioxa-3H-Perfluorononanoic acid, Ammonium perfluorooctanoate (APFO), N-Ethylperfluorooctanesulfonamide (EtFOSA), N-Ethylperfluorooctanesulfonamide ethanol (EtFOSE), Perfluorooctanesulfonamide (PFOSA), Perfluorooctanesulfonamide acetate (FOSAA), Perfluorooctanesulfonamide ethanol (FOSE), Perfluorobutanoic acid, Perfluorobutanoic acid, Perfluorobutyric acid, Perfluorobutyric acid, Perfluoroalkyl carboxylic acid, Perfluoroalkyl carboxylic acid (PFCA), Perfluorodecanoic acid, Perfluorodecanoic acid (PFDA), Perfluorododecanoic acid, Perfluorododecanoic acid (PFDoA), Perfluorododecanesulfonic acid (PFDoS), Perfluorododecanesulfonic acid (PFDoSA), Perfluorodecanesulfonic acid, Perfluorodecanesulfonic acid (PFDS), Perfluoroheptanoate, perfluoroheptanoic acid (PFHpA), perfluoroheptanesulfonic acid, perfluoroheptanesulfonic acid (PFHpS), perfluorononanoic acid, perfluorononanoic acid (PFNA), perfluorononanonesulfonic acid, perfluorononanonesulfonic acid (PFNS), perfluorooctanoic acid, perfluorophosphonic acid (PFPA), perfluoropentanoic acid, perfluoropentanesulfonic acid (PFPeA), perfluoro This includes lopentanesulfonic acid, perfluoropentanesulfonic acid (PFPeS), perfluorophosphinic acid (PFPiA), perfluorotetradecanoic acid (PFTeDA), perfluorotridecanoic acid (PFTrDA), perfluoroundecanoic acid, perfluoroundecanoic acid (PFUnA), perfluoroundecanesulfonic acid (PFUnS), perfluoroundecanesulfonic acid (PFUnSA), and polytetrafluoroethylene (PTFE). Furthermore, perfluoroalkyl and polyfluoroalkyl substances also include perfluoroalkyl, perfluoroalkyl, and polyfluoroalkyl substances obtained by decomposition and removal of functional groups, such as tetrafluoromethane, hexafluoroethylene, tetrafluoroethylene, octafluoropentane, and hexafluoropentene.

[0020] Furthermore, examples of "chlorine compounds" in this embodiment include chlorine, hydrogen chloride, sodium chloride, potassium chloride, magnesium chloride, calcium chloride and its salts, chloric acid and its salts such as hypochlorous acid, organochlorine compounds such as methylene chloride, chloroform, carbon tetrachloride, chloroethane, 1,2-dichloroethane, chlorobenzene, and dichlorobenzene, and chloroamines such as chloroamine, dichloroamine, and N-nitrosamine.

[0021] (Adsorbent) In this embodiment, the adsorbent can more reliably exhibit the effects described above if it is an adsorbent on which PFAS and chlorine compounds have been adsorbed. Preferably, the adsorbent is an adsorbent for PFAS adsorption (removal), and for example, an adsorbent for PFAS adsorption used in water purification applications can be used. Normally, in water purification plants, the water to be treated is disinfected with chlorine compounds, so in addition to PFAS, chlorine compounds are also adsorbed on the adsorbent used for PFAS adsorption. In other words, PFAS and chlorine compounds are adsorbed together on the adsorbent. The adsorption ratio is not particularly limited, and for example, any ratio in the range of PFAS:chlorine compound = 1:0.00001 to 0.00001:1 is acceptable.

[0022] The adsorbent material is not particularly limited, but it is preferably any material capable of adsorbing (removing) PFAS and chlorine compounds from a liquid or gas. Examples of adsorbents include activated carbon, natural and synthetic zeolites, silica, silica gel, sodium silicate, alumina, silica-alumina, zirconia, titania, bentonite, diatomaceous earth, MOF, ion exchange resin, calcium oxide, magnesium oxide, and iron oxide. Among these, activated carbon is preferred as the adsorbent. Using activated carbon as the adsorbent is preferable from the viewpoint that it can be recycled and maintains PFAS adsorption performance even after the heat treatment. Furthermore, using activated carbon as the adsorbent is preferable from the viewpoint of environmental advantages, such as the ability to safely regenerate the adsorbent, and from the viewpoint of low cost.

[0023] When the adsorbent is activated carbon, the raw materials are not particularly limited and include, for example, plant-based carbonaceous materials (e.g., wood, wood shavings, charcoal, fruit shells such as coconut shells and walnut shells, fruit seeds, pulp manufacturing by-products, lignin, molasses, and other plant-derived materials), mineral-based carbonaceous materials (e.g., peat, lignite, brown coal, bituminous coal, anthracite, coke, coal tar, coal pitch, petroleum distillation residue, petroleum pitch, and other mineral-derived materials), synthetic resin-based carbonaceous materials (e.g., synthetic resin-derived materials such as phenolic resin, polyvinylidene chloride, and acrylic resin), and natural fiber-based carbonaceous materials (e.g., natural fiber-derived materials such as cellulose and regenerated fiber such as rayon). These carbonaceous materials can be used individually or in combination of two or more types.

[0024] When the adsorbent is activated carbon, the activated carbon can be obtained, for example, by carbonizing and / or activating a carbonaceous material as described above. If carbonization is required, it can usually be carried out in a state where oxygen or air is blocked, for example, at 400 to 800°C, preferably 500 to 800°C, and more preferably 550 to 750°C. Either a gas activation method or a chemical activation method can be used as the activation method, and a combination of the gas activation method and the chemical activation method may also be used. In particular, when used for water purification, a gas activation method that leaves fewer impurities is preferred. The gas activation method can be carried out by reacting the carbonized carbonaceous material with an activation gas (for example, water vapor, carbon dioxide gas, etc.) at a temperature of, for example, 700 to 1100°C, preferably 800 to 980°C, and more preferably 850 to 950°C. Considering safety and reactivity, it is preferable to use a water vapor-containing gas containing 10 to 40% by volume of water vapor as the activation gas. The activation time and heating rate are not particularly limited and can be appropriately selected depending on the type, shape, and size of the carbonaceous material chosen.

[0025] The BET specific surface area of ​​the adsorbent is 400 to 2000 m². ２ It is preferably / g, and 800 to 1600m ２ It is more preferable that the amount is / g. The BET specific surface area of ​​the adsorbent is 400 to 2000 m². ２The value of / g ensures excellent adsorption performance of PFAS and guarantees the amount of adsorption. In this specification, the BET specific surface area of ​​the adsorbent (adsorbent before heat treatment) refers to the BET specific surface area of ​​the adsorbent before adsorption of PFAS and chlorine compounds. In this embodiment, the BET specific surface area of ​​the adsorbent can be measured by the method described in the examples later.

[0026] (Heat treatment of adsorbent) In the method for regenerating the adsorbent in this embodiment, first, the adsorbent is heat-treated in a firing furnace at a temperature of 1500°C or less under an inert gas. This heat treatment allows the PFAS and chlorine compounds adsorbed on the adsorbent to be decomposed or desorbed and removed.

[0027] By setting the heating temperature in the heat treatment to 1500°C or lower, PFAS in the adsorbent can be effectively removed. Preferably, the heating temperature is 1300°C or lower, and more preferably 1200°C or lower. On the other hand, preferably, the heating temperature is 400°C or higher, more preferably 700°C or higher, and even more preferably 800°C or higher. By setting the heating temperature to 400°C or higher, PFAS can be safely detached and decomposed from the adsorbent.

[0028] In this embodiment, the heating temperature in the heat treatment refers to the "ambient temperature inside the furnace" during the heat treatment. If the ambient temperature inside the furnace is not constant depending on the location, it refers to the "maximum ambient temperature inside the furnace." Specifically, for example, in the case of a continuous furnace, the ambient temperature tends to be higher in the area where the heat source is installed compared to the ambient temperature near the furnace inlet, and furthermore, even within the area where the heat source is installed, the ambient temperature tends to be higher towards the interior compared to the area near the furnace inlet. In such cases, the maximum ambient temperature in the area where the heat source is installed inside the furnace is used as the heating temperature for the heat treatment.

[0029] In the heat treatment described above, the heating time is preferably 1 minute to 3 hours, and more preferably 10 minutes to 2 hours. A heating time of 1 minute or more allows the adsorbed substance adsorbed on the adsorbent to decompose and the adsorbed substance to be sufficiently volatilized from the surface of the adsorbent. On the other hand, a heating time of 3 hours or less prevents excessive activation and deterioration of the activated carbon and maintains production (regeneration) efficiency.

[0030] In this embodiment, the heating time in the heat treatment refers to the time it takes for the adsorbent to pass through the heat source area within the furnace during the heat treatment, for example, when a continuous furnace is used. In this embodiment, the heat source area refers to a temperature range that is uniformly maintained at the heat treatment temperature, and if multiple heat sources are installed, it refers to the time it takes for the adsorbent to pass through all the heat source areas, from the heat source closest to the inlet to the heat source closest to the outlet. Even within the furnace, the time spent passing through areas other than the heat source area is not included in the heating time, and even if the adsorbent discharged from the furnace retains heat, that state is not included in the heating time.

[0031] Furthermore, when using a batch-type furnace, the heating time in the heat treatment refers to the time during which the material is heated to a predetermined maximum temperature by the heat source inside the furnace. In the case of a batch-type furnace, the time it takes to raise the temperature inside the furnace to a predetermined temperature (maximum temperature) is not included in the heating time. Also, even if heat remains inside the furnace or the adsorbent retains heat after heating to the predetermined temperature, this state is not included in the heating time.

[0032] By performing the heat treatment under an inert gas, the intrusion of oxygen from the outside to the inside of the furnace is suppressed, thereby preventing the combustion of the contents (adsorbent) inside the furnace. Examples of inert gases introduced into the firing furnace include nitrogen gas, argon gas, and helium gas. These gases may be used individually or as a mixed gas of two or more. Considering industrial use, nitrogen is usually used as the inert gas.

[0033] The heat treatment under the inert gas can be carried out, for example, by heating while flowing the inert gas through the firing furnace. In this case, it is preferable to supply the inert gas to the firing furnace in a countercurrent to the flow of the adsorbent passing through the furnace. This suppresses the re-adsorption of decomposition products generated by the heat treatment onto the adsorbent. Specifically, for example, when the adsorbent is introduced from the top of the firing furnace, it is preferable to supply the inert gas from the bottom of the firing furnace. Furthermore, the supply amount (flow rate) of the inert gas should be such that, for example, a volume of inert gas equal to 0.01 to 10 times, more preferably 0.05 to 5 times, the internal volume of the furnace is supplied into the furnace per minute. When the supply amount of inert gas is 0.01 to 10 times the internal volume of the furnace per minute, it is possible to more reliably suppress the re-adsorption of decomposition products generated during the heat treatment onto the adsorbent.

[0034] Furthermore, it is preferable to supply water into the furnace during the heat treatment. This improves the cooling effect, prevents oxidation of gases generated by the heat treatment, and improves the thermal conductivity inside the furnace by converting them into steam. The amount of water supplied (flow rate) should be, for example, such that a volume of water equal to 0.001 to 1 times, more preferably 0.002 to 0.05 times, of the furnace's internal volume is supplied into the furnace per minute. When the amount of water supplied per minute is 0.001 to 1 times the furnace's internal volume, a uniform cooling effect can be obtained, improving the efficiency and quality of the heat treatment process.

[0035] The type of firing furnace is not limited as long as it can raise the internal temperature to a temperature that effectively removes the PFAS from the adsorbent. In other words, any type of firing furnace is acceptable, such as multi-stage furnaces including multi-stage roasting paths, rotary kilns, belt kilns, mesh kilns, pusher furnaces, roller hearth kilns, and fluidized bed furnaces. Considering the versatility of the equipment, the use of a rotary kiln is preferred, and considering large-scale processing capacity, the use of a multi-stage roasting furnace is preferred. Furthermore, the firing furnace may be a batch processing type or a continuous processing type.

[0036] The heating method of the firing furnace is not particularly limited, and either an external heating method with a heat source provided outside the firing furnace and heating the inside by heat transfer or an internal combustion method with a fuel gas burned inside the firing furnace as a heat source may be used. By burning the decomposition products generated from the adsorbent, the decomposition of the decomposition products decomposed and volatilized from the adsorbent is further promoted, so the internal combustion method is preferred. Furthermore, it is more preferable to have a combustion device (heat source) on the inlet side where the adsorbent is introduced. In this case, since the temperature on the inlet side where the adsorbent is introduced becomes relatively high, the PFAS adsorbed on the adsorbent can be decomposed and removed more effectively.

[0037] As the heat source, those generally used conventionally may be used. For example, a gas burner, an oil burner, an electric heater, etc. can be used.

[0038] By performing the heat treatment described above, the PFAS present in the adsorbent can be removed. The removal of PFAS can be confirmed by comparing the PFAS concentration in the adsorbent after the heat treatment (regenerated adsorbent) with the PFAS concentration in the adsorbent before the heat treatment. By performing the heat treatment described above, for example, the PFAS concentration of the regenerated adsorbent can be reduced with respect to the PFAS concentration of the adsorbent before the heat treatment. For example, it is preferably reduced by 99.999 mass% or more, and more preferably reduced to a level where it is not detected. The PFAS concentration in the adsorbent can be measured, for example, by desorbing the PFAS remaining in the adsorbent into the extraction solution by extraction and using liquid chromatography-mass spectrometry (LC-MS), gas chromatography-mass spectrometry (GC-MS), etc.

[0039] By performing the heat treatment described above, it is possible to remove PFAS and chlorine compounds present in the adsorbent while maintaining the PFAS adsorption performance of the adsorbent. Therefore, the BET specific surface area of ​​the adsorbent obtained by the heat treatment described above (regenerated adsorbent) is preferably within ±20%, and more preferably within ±10%, of the BET specific surface area of ​​the adsorbent before heat treatment. If the BET specific surface area of ​​the recycled adsorbent is within ±20% of the BET specific surface area of ​​the adsorbent before heat treatment, the PFAS adsorption performance of the adsorbent will remain excellent even after heat treatment. Therefore, the recycled adsorbent can be suitably used as an adsorbent for PFAS adsorption. Specifically, the BET specific surface area of ​​the recycled adsorbent is, for example, 400 to 2500 m². ２ Preferably, it is 600 to 2200 m / g. ２ It is more preferable that the value is / g. In this embodiment, the BET specific surface area of ​​the adsorbent can be measured by the method described in the examples later.

[0040] (Combustion treatment of gas discharged from the firing furnace) Next, the gas discharged from the firing furnace is combusted in a secondary combustion furnace. During the heat treatment in the firing furnace, gas containing organic chlorine compounds, hydrogen chloride, organic sulfur compounds, PFAS, aromatic hydrocarbons, hydrogen, carbon dioxide, organic nitrogen compounds, carbon monoxide, hydrocarbons, and oxygen-containing organic compounds is generated by the thermal decomposition of substances adsorbed on the adsorbent. These compounds can be decomposed by combusting the gas discharged from the firing furnace in a secondary combustion furnace. Specifically, this combustion treatment can, for example, mineralize fluorine and chlorine contained in the gas discharged from the firing furnace and convert them into hydrogen fluoride and hydrogen chloride, thereby suppressing the leakage of organic matter into the atmosphere.

[0041] In the combustion treatment, the combustion temperature of the secondary combustion furnace is preferably 800 °C or higher, more preferably 900 °C or higher, and even more preferably 950 °C or higher. When the combustion temperature is 900 °C or higher, PFAS volatile components contained in the gas discharged from the firing furnace can be decomposed and mineralized. Further, the combustion temperature is preferably 1500 °C or lower, more preferably 1300 °C or lower, and even more preferably 1200 °C or lower. When the combustion temperature is 1500 °C or lower, a secondary combustion furnace can be constructed without using special heat-resistant materials.

[0042] Here, in the present embodiment, the combustion temperature in the secondary combustion furnace means the "atmospheric temperature in the furnace" at which the combustion treatment is performed. Also, when the atmospheric temperature in the furnace is not constant depending on the location, it shall mean the "highest atmospheric temperature in the furnace".

[0043] In the combustion treatment, the combustion time (gas residence time) is preferably 0.5 seconds to 1 minute, and more preferably 1 second to 30 seconds. When the combustion time is 0.5 seconds or longer, fluorine compounds contained in the gas discharged from the firing furnace can be more reliably mineralized, i.e., fluorine ionized, by complete combustion. Also, chlorine compounds contained in the gas coexisting with the fluorine compounds can be similarly mineralized, i.e., chlorine ionized. On the other hand, when the combustion time is 1 minute or shorter, enlargement of the production equipment can be suppressed, improvement of production efficiency and deterioration of equipment materials can be suppressed.

[0044] In the combustion treatment, it is preferable to perform combustion in an oxidizing atmosphere such as air. Thereby, in the process of the heat treatment, compounds generated by thermal decomposition of substances adsorbed on the adsorbent can be more reliably decomposed. The supply amount (flow rate) of the air may be, for example, such that air with a volume preferably 0.016 to 2 times, more preferably 0.02 to 1 times the volume of the furnace content per minute is supplied into the furnace. When the supply amount of the air is 0.016 to 2 times the volume of the furnace content per minute, combustion can be performed uniformly and gas treatment can be efficiently carried out.

[0045] The secondary combustion furnace may be a clean burn system, a catalytic system, or a flex-burn system. In the case of the catalytic system and the flex-burn system, there is a risk of reduced activity due to catalyst poisoning by fluorine and chlorine generated by decomposition; therefore, considering economic efficiency and long-term stability, a clean burn system is preferred. The secondary combustion furnace may be a batch processing type or a continuous processing type.

[0046] (Cooling of gas discharged from the secondary combustion furnace) Next, the gas discharged from the secondary combustion furnace is cooled to 200°C or below. This suppresses the generation of dioxins, which are produced when free chlorine and carbon in the discharged gas undergo incomplete combustion in the air at approximately 250 to 400°C. The gas discharged from the secondary combustion furnace is cooled to 200°C or below, and preferably to 150°C or below. The gas discharged from the secondary combustion furnace may also be cooled to room temperature (for example, 15 to 30°C), and from the viewpoint of improving thermal efficiency and equipment efficiency, it is preferable to cool it to 80°C or above, and more preferably to 100°C or above.

[0047] The method for cooling the gas discharged from the secondary combustion furnace is not particularly limited, but can be used, for example, with cooling water, cooling air, a heat exchanger, or a mist spray.

[0048] Furthermore, it is preferable to cool the gas discharged from the secondary combustion furnace (for example, 900 to 1300°C) to 200°C or below within one second. This makes it possible to more reliably suppress the generation of dioxins.

[0049] Furthermore, it is preferable to neutralize (clean) the cooled gas. This neutralizes and renders harmless acidic harmful gases (SOx, NOx, HCl, etc.) in the cooled gas. For the neutralization treatment, for example, a scrubber or an exhaust gas control system (RTO) can be used. The scrubber is preferably a wet scrubber or a dry scrubber. Moreover, a dry scrubber is even more preferable because it does not use water, thus not generating wastewater, and offers advantages in suppressing corrosion and scaling of the equipment, preventing white smoke (visible plume), reducing installation space, and enabling quick start-up and shutdown.

[0050] For wet scrubbers, alkaline aqueous solutions (e.g., sodium hydroxide aqueous solution), sodium hydroxide aqueous solution, sodium carbonate aqueous solution, sodium bicarbonate aqueous solution, calcium hydroxide slurry, etc., can be used. For dry scrubbers, sodium carbonate powder, sodium bicarbonate powder, calcium hydroxide or calcium oxide-containing absorbents, etc., can be used.

[0051] Furthermore, the cooling and neutralization of the gas discharged from the secondary combustion furnace may be performed simultaneously. For example, by pouring an alkaline aqueous solution (e.g., an aqueous sodium hydroxide solution) into the gas discharged from the secondary combustion furnace, the gas can be cooled to 200°C or below, and the chlorine components contained in the gas can be neutralized and absorbed.

[0052] Furthermore, it is preferable to introduce the cooled gas into the adsorption tower. This makes it possible to remove even trace amounts of substances remaining in the cooling gas, thereby ensuring an even higher level of safety. It is preferable that the adsorption tower is equipped with an adsorbent for adsorbing and removing residual substances. Specifically, a tank filled with an adsorbent can be used as the adsorption tower in this embodiment.

[0053] The adsorbent used in the adsorption tower is not particularly limited as long as it can adsorb residual substances in the gas. Specifically, for example, porous materials such as activated carbon, zeolite, and MOF (metal-organic frame), alkaline solids such as magnesium oxide, calcium oxide, calcium hydroxide, and calcium hydroxide, low-volatility organic solvents such as polyethylene glycol, glycerin, and liquid paraffin, water, alkaline water, and oxidizing aqueous solutions (e.g., hydrogen peroxide) can be used. Considering post-adsorption treatment and the size of the adsorption tower, it is preferable to use a porous adsorbent, and the use of activated carbon is particularly preferable.

[0054] Furthermore, it is preferable to introduce the cooled gas into the bag filter. Alternatively, the neutralized gas may be introduced into the bag filter. By introducing these gases into the bag filter and performing dust removal, environmental pollution can be minimized.

[0055] In the regeneration method of this embodiment, when using the scrubber, the adsorption tower, and / or the bag filter, it is preferable to process in the order of scrubber, adsorption tower, and bag filter.

[0056] According to the adsorbent regeneration method of this embodiment, PFAS adsorbed on the adsorbent can be removed from the adsorbent, the removed PFAS can be decomposed, and organochlorine compounds such as dioxins generated from chlorine compounds adsorbed on the adsorbent can be safely regenerated without releasing them into the atmosphere. Furthermore, PFAS and chlorine compounds present in the adsorbent can be removed while maintaining the PFAS adsorption performance of the adsorbent. For this reason, the regenerated adsorbent obtained by the adsorbent regeneration method of this embodiment can be suitably used as an adsorbent for PFAS adsorption.

[0057] [Adsorbent Regeneration Apparatus] The adsorbent regeneration apparatus in this embodiment comprises a firing furnace for heat-treating the adsorbent at a temperature of 1500°C or lower under an inert gas, a secondary combustion furnace for burning the gas discharged from the firing furnace, and a cooler for cooling the gas discharged from the secondary combustion furnace to 200°C or lower. With this configuration, PFAS adsorbed on the adsorbent can be removed from the adsorbent, the PFAS removed from the adsorbent can be decomposed, and organochlorine compounds such as dioxins generated from chlorine compounds adsorbed on the adsorbent can be safely regenerated without releasing them into the atmosphere.

[0058] Figure 1 is a flowchart illustrating an overview of one embodiment of the adsorbent regeneration apparatus in this embodiment. As shown in Figure 1, a secondary combustion furnace is connected to the firing furnace, and a cooler is continuously connected to the secondary combustion furnace. Each component will be described in detail below.

[0059] (Casturing Furnace) The casturing furnace in this embodiment is a device for heating the adsorbent to be processed in this embodiment. The adsorbent can be described in the same way as the "adsorbent" in the [Method for Regenerating Adsorbent] described above. The type of casturing furnace is not limited as long as it can raise the internal temperature to a temperature at which the PFAS in the adsorbent can be effectively removed. In other words, the casting furnace can be of any type, for example, a multi-stage furnace such as a multi-stage roasting path, a rotary kiln, a belt kiln, a mesh kiln, a pusher furnace, a tunnel furnace such as a roller hearth kiln, a fluidized bed furnace, etc. Considering the versatility of the device, the use of a rotary kiln is preferred, and considering large-scale processing capacity, the use of a multi-stage roasting furnace is preferred. The casting furnace may be a batch processing type or a continuous processing type.

[0060] The heating method of the firing furnace is not particularly limited, and it may be either an external heating method, which has a heat source outside the firing furnace and heats the inside by heat transfer, or an internal combustion method, which uses the combustion of fuel gas inside the firing furnace as the heat source. The internal combustion method is preferred because burning the decomposition products generated from the adsorbent further promotes the decomposition of the decomposition products that have decomposed and volatilized from the adsorbent. Furthermore, it is even more preferable to have a combustion device (heat source) on the inlet side into which the adsorbent is introduced. In this case, the temperature on the inlet side into which the adsorbent is introduced becomes relatively high, so the PFAS compound can be decomposed more effectively. As the heat source, conventionally used ones can be used, for example, a gas burner, an oil burner, and an electric heater.

[0061] An adsorbent supply device is provided on the inlet side of the firing furnace. On the other hand, an outlet is provided on the outlet side of the firing furnace for discharging the heat-treated adsorbent. This heat-treated adsorbent can be described in the same way as "heat-treated adsorbent (regenerated adsorbent)" in the [Method for regenerating adsorbent] described above. Furthermore, a secondary combustion furnace is provided on the exhaust side of the firing furnace for heating the gas generated in the firing furnace. The gas generated in the firing furnace contains organic chlorine compounds, hydrogen chloride, organic sulfur compounds, PFAS, aromatic hydrocarbons, hydrocarbons, hydrogen, carbon dioxide, carbon monoxide, and organic nitrogen compounds, which are produced by the thermal decomposition of substances adsorbed on the adsorbent.

[0062] Furthermore, the firing furnace has an inlet for introducing an inert gas into the furnace. The introduction of the inert gas may be counterflow or parallel flow relative to the introduction of the adsorbent, but counterflow is preferred. In other words, it is preferable that the inert gas is supplied so that the introduction position of the inert gas in the firing furnace is opposite (counterflow) to the flow of the adsorbent passing through the firing furnace. If this is done, it is possible to suppress the re-adsorption of decomposition products generated during heat treatment onto the adsorbent. Specifically, for example, there may be an inlet for introducing the adsorbent at the top of the firing furnace and an inlet for introducing the inert gas at the bottom of the firing furnace.

[0063] Furthermore, the firing furnace may have an inlet for introducing water into the furnace. This improves the cooling effect in the firing furnace, prevents oxidation of the gas generated by the heat treatment, and improves the thermal conductivity inside the furnace by converting it into steam.

[0064] With this configuration, first, the adsorbent is supplied to the firing furnace. Then, in the firing furnace, the adsorbent is heat-treated at a temperature of 1500°C or less under an inert gas atmosphere. Through the heat treatment in the firing furnace, the PFAS and chlorine compounds adsorbed on the adsorbent can be decomposed or desorbed and removed.

[0065] By setting the heating temperature to 1500°C or lower, PFAS in the adsorbent can be effectively removed. The heating temperature and heating time during the heat treatment of the adsorbent in the firing furnace can be explained in the same way as the heating temperature and heating time in the heat treatment described in the [Method for Regenerating Adsorbent] above.

[0066] Furthermore, by performing the heat treatment under an inert gas atmosphere, the intrusion of oxygen from the outside into the firing furnace is suppressed, thereby preventing the combustion of the contents (adsorbent) inside the firing furnace. Examples of inert gases introduced into the firing furnace include nitrogen gas, argon gas, and helium gas. These gases may be used individually or as a mixed gas of two or more. Considering industrial use, nitrogen is usually used as the inert gas. Furthermore, the supply rate (flow rate) of the inert gas should be such that, for example, a volume of inert gas equal to 0.01 to 10 times, more preferably 0.05 to 5 times, the internal volume of the furnace is supplied to the furnace per minute. When the supply rate of the inert gas is 0.01 to 10 times the internal volume of the furnace per minute, it is possible to more reliably suppress the re-adsorption of decomposition products generated during the heat treatment onto the adsorbent.

[0067] Furthermore, water may be supplied during the heat treatment, thereby improving the cooling effect, preventing the oxidation of gases generated by the heat treatment, and improving the thermal conductivity inside the furnace by converting them into steam. The amount of water supplied (flow rate) should be, for example, such that a volume of water equal to 0.001 to 1 times, more preferably 0.002 to 0.05 times, of the furnace internal volume is supplied into the furnace per minute. When the amount of water supplied per minute is 0.001 to 1 times the furnace internal volume, a uniform cooling effect can be obtained, improving the efficiency and quality of the heat treatment process.

[0068] The heat-treated adsorbent (regenerated adsorbent) is discharged from the outlet of the firing furnace. Meanwhile, the gas generated by the heat treatment is introduced into a secondary combustion furnace through the exhaust port of the firing furnace.

[0069] (Secondary Combustion Furnace) The type of secondary combustion furnace in this embodiment is not limited as long as it can burn the gas discharged from the firing furnace. The combustion method of the secondary combustion furnace may be a clean burn system, a catalytic system, or a flex burn system. In the case of the catalytic system and the flex burn system, there is a risk of reduced activity due to catalyst poisoning by fluorine and chlorine generated by decomposition, so a clean burn system is preferred when considering economy and long-term stability. The secondary combustion furnace may be a batch processing type or a continuous processing type.

[0070] A firing furnace is provided on the inlet side of the secondary combustion furnace. On the other hand, a cooler is provided on the outlet side of the secondary combustion furnace for cooling the gas generated in the secondary combustion furnace.

[0071] In this configuration, first, the gas discharged from the firing furnace is introduced into the secondary combustion furnace. Then, the gas discharged from the firing furnace is combusted in the secondary combustion furnace. During the heat treatment in the firing furnace, gases containing organic chlorine compounds, hydrogen chloride, organic sulfur compounds, PFAS, aromatic hydrocarbons, hydrocarbons, hydrogen, carbon dioxide, carbon monoxide, and organic nitrogen compounds are generated by the thermal decomposition of substances adsorbed on the adsorbent. These compounds can be decomposed by the combustion treatment in the secondary combustion furnace. Specifically, this combustion treatment can, for example, mineralize fluorine and chlorine contained in the gas discharged from the firing furnace and convert them into hydrogen fluoride and hydrogen chloride, thereby suppressing the leakage of organic matter into the atmosphere.

[0072] The combustion temperature and combustion time during the combustion treatment of the gas discharged from the firing furnace in the secondary combustion furnace can be explained in the same way as the combustion temperature and combustion time in the combustion treatment described in the [Method for Regenerating Adsorbent] above. Furthermore, the combustion treatment of the gas discharged from the firing furnace in the secondary combustion furnace is preferably carried out under an oxidizing atmosphere such as air, which would allow for more reliable decomposition of compounds generated by the thermal decomposition of substances adsorbed on the adsorbent during the heat treatment process. The amount of air supplied (flow rate) should, for example, be such that an amount of air is supplied into the furnace per minute that is preferably 0.016 to 2 times, more preferably 0.02 to 1 time, of the furnace internal volume. When the amount of air supplied per minute is 0.016 to 2 times the furnace internal volume, uniform combustion is possible, and gas treatment can be carried out efficiently.

[0073] The gas generated by the combustion process in the secondary combustion furnace is introduced into the cooler through the exhaust port on the outlet side of the secondary combustion furnace.

[0074] (Cooler) The cooler in this embodiment is not particularly limited in type, as long as it can cool the temperature of the gas discharged from the secondary combustion furnace to 200°C or below. For example, an air-cooled cooler, a water-cooled cooler, or an air-water combined cooler can be used. The cooling method is also not particularly limited, but examples include a cooler using cooling water, cooling air, or a cooler using a refrigerant such as propane.

[0075] The secondary combustion furnace is provided on the inlet side of the cooler. On the other hand, the outlet side of the cooler is provided for discharging the cooled gas into the atmosphere.

[0076] With this configuration, first, the gas discharged from the secondary combustion furnace is introduced into the cooler. The gas discharged from the secondary combustion furnace is then cooled to below 200°C. This suppresses the generation of dioxins, which are produced when free chlorine and carbon in the gas discharged from the secondary combustion furnace undergo incomplete combustion in the air at approximately 250 to 400°C. The gas cooled by the cooler is then discharged into the atmosphere in a harmless state.

[0077] Furthermore, regarding the cooling temperature and cooling time of the gas discharged from the secondary combustion furnace in the cooling of the gas using the cooler, the same explanation as for the cooling temperature and cooling time of the gas discharged from the secondary combustion furnace described above in the [Method for Regenerating Adsorbent] can be given.

[0078] The adsorbent regeneration device in this embodiment preferably further includes a scrubber or exhaust gas treatment (RTO) for neutralizing the cooled gas. This neutralizes the gas cooled by the cooler, ensuring that the gas is more reliably rendered harmless before being discharged into the atmosphere. The scrubber is preferably a wet scrubber or a dry scrubber. A dry scrubber is more preferably used. The cooler and scrubber may be installed in the same device, or they may be in separate devices, as shown in Figure 2. When the cooler and scrubber are installed in the same device, for example, by pouring an alkaline aqueous solution (e.g., an aqueous sodium hydroxide solution) into the gas discharged from the secondary combustion furnace, the gas can be cooled to 200°C or below, and the chlorine components contained in the gas can be neutralized and absorbed.

[0079] The adsorbent regeneration apparatus in this embodiment preferably further comprises an adsorption tower into which the cooled gas is introduced. The adsorption tower is preferably provided after the scrubber, as shown in Figure 3. The adsorption tower can be the same as the adsorption tower described in the [Adsorbent Regeneration Method] above. By providing such an adsorption tower, even trace amounts of substances remaining in the cooling gas can be removed, thereby ensuring an even higher level of safety.

[0080] In this embodiment, the adsorbent regeneration device preferably further includes a bag filter into which the cooled gas is introduced. When a bag filter is included, as shown in Figure 4, the adsorbent regeneration device may also include a bag filter into which the neutralized gas is introduced after passing through the adsorption tower. By further including a bag filter in the adsorbent regeneration device in this embodiment, these gases are subjected to dust removal treatment, and gases that have been more reliably rendered harmless are discharged into the atmosphere. Therefore, environmental pollution can be minimized.

[0081] As described above, this specification discloses various aspects of technology, the main technologies among them are summarized below.

[0082] A method for regenerating an adsorbent according to a first aspect of the present invention includes heat treatment of the adsorbent in a firing furnace at a temperature of 1500°C or lower under an inert gas, combustion treatment of the gas discharged from the firing furnace in a secondary combustion furnace, and cooling of the gas discharged from the secondary combustion furnace to 200°C or lower.

[0083] A second aspect of the present invention relates to a method for regenerating an adsorbent, wherein the adsorbent is an adsorbent that has adsorbed perfluoroalkyl substances, polyfluoroalkyl substances, and chlorine compounds, in the method for regenerating an adsorbent according to the first aspect.

[0084] A third aspect of the present invention relates to a method for regenerating an adsorbent, in which, in the method for regenerating an adsorbent according to the first or second aspect, the inert gas is supplied to the firing furnace in a manner that is opposite (countercurrent) to the flow of the adsorbent passing through the firing furnace.

[0085] A method for regenerating an adsorbent according to a fourth aspect of the present invention includes neutralizing the cooled gas using a wet or dry scrubber, in a method for regenerating an adsorbent according to any of the first to third aspects.

[0086] A fifth aspect of the present invention relates to a method for regenerating an adsorbent, which includes introducing the cooled gas into an adsorption tower, in a method for regenerating an adsorbent according to any of the first to fourth aspects.

[0087] A method for regenerating an adsorbent according to a sixth aspect of the present invention includes introducing the cooled gas into a bag filter, in a method for regenerating an adsorbent according to any of the first to fifth aspects.

[0088] A method for regenerating an adsorbent according to the seventh aspect of the present invention is a method for regenerating an adsorbent according to any of the first to sixth aspects, wherein the adsorbent is activated carbon.

[0089] An adsorbent regeneration apparatus according to the eighth aspect of the present invention comprises a firing furnace for heat-treating the adsorbent at a temperature of 1500°C or lower under an inert gas, a secondary combustion furnace for burning the gas discharged from the firing furnace, and a cooler for cooling the gas discharged from the secondary combustion furnace to 200°C or lower.

[0090] The adsorbent regeneration apparatus according to the ninth aspect of the present invention is an adsorbent regeneration apparatus according to the eighth aspect, wherein the adsorbent is an adsorbent that has adsorbed perfluoroalkyl substances, polyfluoroalkyl substances, and chlorine compounds.

[0091] An adsorbent regeneration apparatus according to the tenth aspect of the present invention is an adsorbent regeneration apparatus according to the eighth or ninth aspect, wherein the inert gas is supplied such that the introduction position of the inert gas in the firing furnace is opposite (countercurrent) to the flow of the adsorbent passing through the firing furnace.

[0092] An adsorbent regeneration apparatus according to the eleventh aspect of the present invention is an adsorbent regeneration apparatus according to any eighth to tenth aspect, further comprising a scrubber for neutralizing the cooled gas, wherein the scrubber is wet or dry.

[0093] An adsorbent regeneration apparatus according to the twelfth aspect of the present invention is an adsorbent regeneration apparatus according to any eighth to eleventh aspect, further comprising an adsorption tower for removing residual substances in the cooled gas by adsorption.

[0094] An adsorbent regeneration apparatus according to the thirteenth aspect of the present invention is an adsorbent regeneration apparatus according to any eighth to twelfth aspect, further comprising a bag filter into which the cooled gas is introduced.

[0095] The adsorbent regeneration apparatus according to the 14th aspect of the present invention is an adsorbent regeneration apparatus according to any of the 8th to 13th aspects, wherein the adsorbent is activated carbon.

[0096] An adsorbent regeneration apparatus according to the 15th aspect of the present invention is an adsorbent regeneration apparatus according to the 12th aspect, wherein the adsorption tower comprises a porous adsorbent containing activated carbon.

[0097] The present invention will be described in more detail below with reference to examples, but the present invention is not limited in any way by these examples.

[0098] First, in the following tests, the BET specific surface area of ​​activated carbon was measured as follows.

[0099] (Method for measuring specific surface area using the BET method) Using a BELSORP-mini manufactured by Nippon Bell Co., Ltd., activated carbon was heated at 300°C for 3 hours under a nitrogen gas flow (nitrogen flow rate: 50 mL / min), and then the nitrogen adsorption isotherm of the activated carbon at 77.4 K was measured. From the obtained nitrogen adsorption isotherms, multipoint analysis was performed using the BET formula, and the specific surface area was calculated from the straight line in the relative pressure P / P0 region of the obtained curve between 0.01 and 0.1.

[0100] (Example 1) 10 g of activated carbon (PGW, manufactured by Kuraray Co., Ltd.) on which 4000 ppm of chloroform as a chlorine compound and 5000 ppm of polyfluorooctanoic acid as PFAS were adsorbed was placed on a ceramic board and placed in a 40 mmφ ceramic tubular furnace. 1300 ml / min of nitrogen and 0.44 g / min of water were introduced into the tubular furnace and heat treatment was performed at 900°C for 1 hour.

[0101] Following the aforementioned heat treatment, the gas discharged from the tubular furnace was introduced into a secondary combustion furnace (tube diameter 40 mmφ, heating length 500 mm, combustion time (gas residence time) approximately 2.5 seconds). While introducing 1200 ml / min of air into the secondary combustion furnace, the gas discharged from the tubular furnace was heated to 1200°C for approximately 2.5 seconds.

[0102] The gas discharged from the secondary combustion furnace was cooled to 25°C within 0.5 seconds of discharge. A wet scrubber (1 L of 0.1 N sodium hydroxide aqueous solution) was used for cooling, and the components contained in the gas were neutralized simultaneously with the cooling process.

[0103] To measure the organic carbon content, the gas emitted from the secondary combustion furnace was absorbed with a 0.1N sodium hydroxide aqueous solution, then its acidity was adjusted (pH 3 or less), and it was analyzed using a total organic carbon analysis system (Shimadzu Corporation, TOC-L). As a result, no organic carbon content was detected. In other words, it was confirmed that all organic matter removed from the activated carbon was mineralized.

[0104] The specific surface area of ​​the activated carbon used in the above example, measured by the BET method, was 1024 m² before adsorption of chloroform and polyfluorooctanoic acid. ２ The concentration is / g, and after adsorbing 4000 ppm chloroform and 5000 ppm polyfluorooctanoic acid, it is 856 m ２ / g. Also, the specific surface area of the activated carbon (regenerated activated carbon) from which chloroform and polyfluorooctanoic acid were removed by performing the above playback process was 1102 m ２ / g. Therefore, it was confirmed that the activated carbon used in the examples maintained its PFAS adsorption performance even after the above regeneration treatment.

[0105] (Example 2) 10 g of activated carbon (PGW, manufactured by Kuraray Co., Ltd.) adsorbed with 4000 ppm of chloroform as a chlorine compound and 5000 ppm of polyfluorooctanoic acid as PFAS was placed on a ceramic board and placed in a 40 mmφ ceramic tubular furnace. Nitrogen 1300 ml / min and water 0.44 g / min were introduced into the tubular furnace, and heat treatment was performed at 900 °C for 1 hour.

[0106] The gas discharged from the tubular furnace by the heat treatment was introduced into a secondary combustion furnace (pipe diameter 40 mmφ, heating length 500 mm, combustion time (gas residence time) about 2.5 seconds). While introducing 1200 ml / min of air into the secondary combustion furnace, the gas discharged from the tubular furnace was heated at 1200 °C for about 2.5 seconds.

[0107] The gas discharged from the secondary combustion furnace was cooled to 40 °C within 0.5 seconds after being discharged from the secondary combustion furnace. For cooling, a wet scrubber (1 L of 0.1 N aqueous sodium hydroxide solution) was used, and the components contained in the gas were neutralized simultaneously with cooling.

[0108] For the measurement of organic carbon content, the gas discharged from the secondary combustion furnace was absorbed with a 0.1 N aqueous sodium hydroxide solution, and then the acidity was adjusted (pH 3 or less), and analyzed with a total organic carbon analysis system (TOC-L, manufactured by Shimadzu Corporation). As a result, no organic carbon content was detected. That is, it was confirmed that all the organic substances removed from the activated carbon were mineralized.

[0109] The specific surface area of the activated carbon used in the above example by the BET method was 1024 m before adsorbing chloroform and polyfluorooctanoic acid. ２ / g, and after adsorbing 4000 ppm of chloroform and 5000 ppm of polyfluorooctanoic acid, it was 856 m ２The value was / g. Furthermore, the specific surface area of ​​the activated carbon (regenerated activated carbon) from which the above regeneration treatment was performed and chloroform and polyfluorooctanoic acid were removed was 1116 m². ２ The result was / g. Therefore, it was confirmed that the activated carbon used in the example maintained its PFAS adsorption performance even after the above regeneration treatment. The BET specific surface area of ​​the activated carbon was measured as follows.

[0110] (Example 3) 10 g of activated carbon (PGW, manufactured by Kuraray Co., Ltd.) on which 4000 ppm of chloroform as a chlorine compound and 5000 ppm of polyfluorooctanoic acid as PFAS were adsorbed was placed on a ceramic board and placed in a 40 mmφ ceramic tubular furnace. 1300 ml / min of nitrogen and 0.44 g / min of water were introduced into the tubular furnace and heat treatment was performed at 900°C for 1 hour.

[0111] Following the aforementioned heat treatment, the gas discharged from the tubular furnace was introduced into a secondary combustion furnace (tube diameter 40 mmφ, heating length 500 mm, combustion time (gas residence time) approximately 2.5 seconds). While introducing 1200 ml / min of air into the secondary combustion furnace, the gas discharged from the tubular furnace was heated to 1200°C for approximately 2.5 seconds.

[0112] The gas discharged from the secondary combustion furnace was cooled to 25°C within 0.5 seconds of discharge. For cooling, after a 15°C cooling shower, the exhaust gas was passed through a dry scrubber (containing sodium carbonate powder), which simultaneously cooled the gas and neutralized its components.

[0113] To measure the organic carbon content, the gas emitted from the secondary combustion furnace was absorbed with a 0.1N sodium hydroxide aqueous solution, then its acidity was adjusted (pH 3 or less), and it was analyzed using a total organic carbon analysis system (Shimadzu Corporation, TOC-L). As a result, no organic carbon content was detected. In other words, it was confirmed that all organic matter removed from the activated carbon was mineralized.

[0114] The specific surface area of ​​the activated carbon used in the above example, measured by the BET method, was 1024 m² before adsorption of chloroform and polyfluorooctanoic acid. ２ The concentration is / g, and after adsorbing 4000 ppm chloroform and 5000 ppm polyfluorooctanoic acid, it is 856 m ２The value was / g. Furthermore, the specific surface area of ​​the activated carbon (regenerated activated carbon) from which the above regeneration treatment was performed and chloroform and polyfluorooctanoic acid were removed was 1008 m². ２ The result was / g. Therefore, it was confirmed that the activated carbon used in the example maintained its PFAS adsorption performance even after the above regeneration treatment. The BET specific surface area of ​​the activated carbon was measured as follows.

[0115] In the above-described embodiment, activated carbon was heat-treated at a temperature of 1500°C or lower under an inert gas, the gas generated by the heat treatment was combusted, and the combusted gas was cooled to 200°C or lower. It was confirmed that the gas generated by the heat treatment was mineralized, and that organochlorine compounds such as dioxins were below the detection limit. Furthermore, it was confirmed that the activated carbon after heat treatment (regenerated activated carbon) had the same specific surface area as the activated carbon before heat treatment.

[0116] This application is based on Japanese Patent Application No. 2025-26703, filed on 21 February 2025, the contents of which are included in this application.

[0117] In order to express the present invention, the invention has been adequately and sufficiently described above through embodiments with reference to specific examples and drawings, etc. However, those skilled in the art should recognize that it is easy to modify and / or improve the embodiments described above. Therefore, unless the modifications or improvements implemented by those skilled in the art fall outside the scope of the claims described in the claims, such modifications or improvements shall be interpreted as being included within the scope of the claims.

[0118] The present invention has broad industrial applicability in the technical field relating to activated carbon, methods for regenerating the same, and apparatus for regenerating the same.

Claims

1. A method for regenerating an adsorbent, comprising: heat-treating the adsorbent in a firing furnace at a temperature of 1500°C or less under an inert gas; burning the gas discharged from the firing furnace in a secondary combustion furnace; and cooling the gas discharged from the secondary combustion furnace to 200°C or less.

2. The method for regenerating an adsorbent according to claim 1, wherein the adsorbent is an adsorbent that has adsorbed perfluoroalkyl substances, polyfluoroalkyl substances, and chlorine compounds.

3. The method for regenerating an adsorbent according to claim 1, wherein the inert gas is supplied to the firing furnace in a manner opposite to (counter-flow of) the flow of the adsorbent passing through the firing furnace.

4. A method for regenerating an adsorbent according to claim 1, comprising neutralizing the cooled gas using a wet or dry scrubber.

5. A method for regenerating an adsorbent according to claim 1, comprising introducing the cooled gas into an adsorption tower.

6. A method for regenerating an adsorbent according to claim 1, comprising introducing the cooled gas into a bag filter.

7. The method for regenerating an adsorbent according to claim 1, wherein the adsorbent is activated carbon.

8. An adsorbent regeneration apparatus comprising a firing furnace for heat-treating the adsorbent at a temperature of 1500°C or less under an inert gas, a secondary combustion furnace for burning the gas discharged from the firing furnace, and a cooler for cooling the gas discharged from the secondary combustion furnace to 200°C or less.

9. The adsorbent regeneration apparatus according to claim 8, wherein the adsorbent is an adsorbent that has adsorbed perfluoroalkyl substances, polyfluoroalkyl substances, and chlorine compounds.

10. The adsorbent regeneration apparatus according to claim 8, wherein the introduction position of the inert gas in the firing furnace is arranged such that the inert gas is supplied in a countercurrent manner to the flow of the adsorbent passing through the firing furnace.

11. The adsorbent regeneration apparatus according to claim 8, further comprising a scrubber for neutralizing the cooled gas, wherein the scrubber is wet or dry.

12. The adsorbent regeneration apparatus according to claim 8, further comprising an adsorption tower for removing residual substances in the cooled gas by adsorption.

13. The adsorbent regeneration apparatus according to claim 8, further comprising a bag filter into which the cooled gas is introduced.

14. The adsorbent regeneration apparatus according to claim 8, wherein the adsorbent is activated carbon.

15. The adsorption tower comprises a porous adsorbent containing activated carbon, the adsorption regeneration apparatus according to claim 12.

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