Activated carbon, and water treatment method and water treatment device using said activated carbon

Abstract

One aspect of the present invention relates to activated carbon in which at least one of a perfluoroalkyl compound and a polyfluoroalkyl compound is adsorbed onto the activated carbon, and a relaxation time T1(α) derived from fluorine at the α-position of C4-C8 perfluorocarboxylic acid is 1.1 seconds or less, the relaxation time T1(α) being measured at 80.0°C or less and being obtained by solid-state 19F-NMR.

Description

Activated carbon, and a water treatment method and water treatment apparatus using the activated carbon.

[0001] The present invention relates to activated carbon, and to a water treatment method and water treatment apparatus using the activated carbon.

[0002] Fluorine-containing organic compounds possess unique properties that cannot be achieved with other substances (such as excellent heat and chemical resistance, usability under harsh conditions, and lack of light absorption), and have therefore been used in a variety of applications, including surfactants, emulsifiers, water repellents, fire extinguishing agents, waxes, carpet cleaners, and coatings. Recently, their use as functional materials, such as surface treatment agents for semiconductors and fuel cell components, has been increasing.

[0003] However, in recent years, researchers, primarily in the United States and Canada, have begun reporting that some fluorine-containing organic compounds are accumulating in environmental water and in the bodies of wildlife. A typical example is perfluorooctanoic acid (PFOA:C). ７ F １５ Perfluorocarboxylic acids, such as COOH, and perfluorooctanesulfonic acid (PFOS:C) ８ F １７ SO ３ These are perfluorosulfonic acids, exemplified by H), and as researchers in Europe and Japan subsequently entered the field of environmental analysis, it became clear that these compounds exist in the environment globally, including in Japan. In response to this situation, efforts have begun to reduce the environmental risks of fluorine-containing organic compounds (PFCs).

[0004] For example, Patent Document 1 discloses a method for recovering PFOA using granular activated carbon.

[0005] However, in the treatment of PFOA and the like, the treatment method using activated carbon, as described in Patent Document 1, has significant economic advantages, but the treatment efficiency was insufficient.

[0006] In view of the above situation, the present invention aims to provide activated carbon that can efficiently remove fluorine-containing organic compounds from liquids or gases, as well as a water treatment method and water treatment apparatus that use this activated carbon to treat water containing fluorine-containing organic compounds.

[0007] United States Patent Application Publication No. 2005 / 0000904

[0008] As a result of various studies, the inventors of the present invention have found that the above object is achieved by the invention described below.

[0009] The activated carbon according to one aspect of the present invention is obtained by causing activated carbon to adsorb at least one selected from a perfluoroalkyl compound and a polyfluoroalkyl compound, and is a solid measured at 80.0°C or lower １９ characterized in that the relaxation time T1(α) derived from fluorine at the α-position of perfluorocarboxylic acids having 4 to 8 carbon atoms, which is determined from ¹⁹F-NMR, is 1.1 seconds or less.

[0010] A water treatment method according to another aspect of the present invention is characterized by comprising bringing the activated carbon into contact with water to be treated that contains a fluorine-containing organic compound, to obtain treated water having a fluorine-containing organic compound content of 0.1 ppb or less.

[0011] Hereinafter, modes for carrying out the present invention will be specifically described, but the present invention is not limited to these.

[0012] <Activated Carbon> The activated carbon in the present embodiment is obtained by causing activated carbon to adsorb at least one selected from a perfluoroalkyl compound and a polyfluoroalkyl compound, and is a solid measured at 80.0°C or lower １９ The relaxation time T1(α) derived from fluorine at the α-position of perfluorocarboxylic acids having 4 to 8 carbon atoms, which is determined from ¹⁹F-NMR, is 1.1 seconds or less. With such a configuration, activated carbon that can efficiently remove fluorine-containing organic compounds from liquid or gas can be obtained.

[0013] According to such a configuration, activated carbon that can efficiently remove fluorine-containing organic compounds from liquid or gas can be provided. Furthermore, by using this activated carbon, a water treatment method and a water treatment apparatus that efficiently treat water containing fluorine-containing organic compounds can be provided.

[0014] In this embodiment, the relaxation time T1(α) refers to the relaxation time derived from the fluorine at the α-position of perfluorocarboxylic acids with 4 to 8 carbon atoms, which is obtained from １９ 19F-NMR in activated carbon that has adsorbed at least one of perfluoroalkyl compounds and polyfluoroalkyl compounds.

[0015] Here, the fluorine-containing organic compounds have unique properties that cannot be achieved by other substances (excellent heat resistance and chemical resistance, can be used even under harsh conditions, no light absorption ability, etc.), so they are used in various applications. On the other hand, some fluorine-containing organic compounds (for example, perfluorocarboxylic acids represented by perfluorooctanoic acid (PFOA: C ７ F １５ COOH) and perfluorosulfonic acids represented by perfluorooctanesulfonic acid (PFOS: C ８ F １７ SO ３ H)) have been found to accumulate in the bodies of wild animals, and subsequent various studies have revealed that they exist in the environment on a global scale. Under such circumstances, reducing the content of fluorine-containing organic compounds in water (to 0.1 ppb or less) contributes to the reduction of environmental risks.

[0016] As a result of intensive studies by the present inventors, it was found that when the concentration of fluorine-containing organic compounds contained in the water to be treated is low, there is a limit to the reduction of fluorine-containing organic compounds even if a large amount of activated carbon is added when using conventional activated carbon to reduce fluorine-containing organic compounds. In contrast, the present inventors found that by using the specific activated carbon of this embodiment, treated water from which fluorine-containing organic compounds have been removed can be obtained with extremely high efficiency from the target water containing fluorine-containing organic compounds.

[0017] It is generally well known that the performance of activated carbon depends on its specific surface area. However, the inventors have found that the treatment efficiency of aqueous solutions with low concentrations of fluorine-containing organic compounds does not clearly correlate with the specific surface area of ​​the activated carbon, but rather depends largely on the affinity of the activated carbon for the fluorine-containing organic compounds. Furthermore, it was found that the relaxation time T1(α) changes significantly depending on the properties of the activated carbon, and that a shorter relaxation time T1(α) indicates a higher affinity between the fluorine-containing organic compounds and the activated carbon.

[0018] In other words, the activated carbon in this embodiment has a relaxation time T1(α) of 1.1 seconds or less at any measurement temperature below 80.0°C, which is determined by measurement at 80.0°C or below. As a result, fluorine-containing organic compounds can be efficiently removed from the liquid or gas, and by using such activated carbon, treated water that contains almost no fluorine-containing organic compounds (for example, water with a fluorine-containing organic compound content of 0.1 ppb or less) can be obtained. Here, "measured at 80.0°C or below" refers to the activated carbon on which at least one of perfluoroalkyl compounds and polyfluoroalkyl compounds has been adsorbed, and the solid １９ This means that the measurement temperature when performing F-NMR measurement is 80.0°C or lower. Specifically, examples of the measurement temperature include 80.0°C, 42.0°C, 60.0°C, 10.0°C, etc. The lower limit of the measurement temperature is not particularly limited, but may be 10.0°C or higher, for example.

[0019] The relaxation time T1(α) measured at 80.0°C or below is preferably 1.08 seconds or less, more preferably 1.06 seconds or less, even more preferably 1.05 seconds or less, especially preferably 1.00 seconds or less, particularly preferably 0.90 seconds or less, even more preferably 0.80 seconds or less, and most preferably 0.70 seconds or less. On the other hand, the relaxation time T1(α) measured at 80.0°C or below is preferably 0.01 seconds or more, as this suppresses the influence on substances other than fluorine-containing organic compounds and allows for effective removal of fluorine-containing organic compounds. The relaxation time T1(α) measured at 80.0°C or below is more preferably 0.015 seconds or more, even more preferably 0.02 seconds or more, especially preferably 0.03 seconds or more, particularly preferably 0.04 seconds or more, and even more preferably 0.05 seconds or more.

[0020] In this embodiment, it is preferable that the absolute difference between the relaxation time T1(α) measured at 10.0°C and the relaxation time T1(α) measured at 80.0°C is 0.8 seconds or less. A small difference in the relaxation time T1(α) at ​​different measurement temperatures indicates a small difference in adsorption capacity due to temperature. Therefore, by having an absolute difference of 0.8 seconds or less between the relaxation time T1(α) measured at 10.0°C and the relaxation time T1(α) measured at 80.0°C, fluorine-containing organic compounds can be removed more reliably and efficiently from liquids or gases. When determining the absolute difference between the relaxation time T1(α) measured at 10.0°C and the relaxation time T1(α) measured at 80.0°C, the solid １９ Although the temperature conditions in F-NMR measurements differ, the conditions for adsorbing at least one of perfluoroalkyl compounds and polyfluoroalkyl compounds onto activated carbon, and the solid １９All measurement conditions other than temperature in F-NMR measurements (resonance frequency, probe, measurement mode, rotation speed, and line width broadening factor (BF), etc.) will be kept the same.

[0021] The absolute value of the difference between the relaxation time T1(α) measured at 10.0°C and the relaxation time T1(α) measured at 80.0°C is more preferably 0.75 seconds or less, even more preferably 0.60 seconds or less, particularly preferably 0.55 seconds or less, especially preferably 0.50 seconds or less, even more preferably 0.45 seconds or less, and most preferably 0.40 seconds or less. On the other hand, considering the molecular mobility of adsorption and desorption, the absolute value of the difference between the relaxation time T1(α) measured at 10.0°C and the relaxation time T1(α) measured at 80.0°C is preferably 0.01 seconds or more, more preferably 0.02 seconds or more, and especially preferably 0.03 seconds or more.

[0022] In this embodiment, the activated carbon is measured at a temperature of 10.0°C to 80.0°C to determine the relaxation time T1(α), and at least one of a perfluoroalkyl compound and a polyfluoroalkyl compound is adsorbed onto the activated carbon, and the result is measured under the same temperature conditions as the relaxation time T1(α), and is a solid. １９ It is preferable that the absolute value of the difference between the relaxation time T1(α) and the relaxation time T1(β) derived from the fluorine at the β-position of the C4-C8 perfluorocarboxylic acid, as determined by F-NMR, is 0.8 seconds or less at all temperatures. If the difference in relaxation time due to the position of fluorine in the C4-C8 perfluorocarboxylic acid is small, it can be said that the difference in molecular adsorption force due to the length of the carbon chain is small. Therefore, by having the absolute value of the difference between the relaxation time T1(α) and the relaxation time T1(β) be 0.8 seconds or less, fluorine-containing organic compounds can be removed more reliably and efficiently from liquids and gases. When determining the absolute value of the difference between the relaxation time T1(α) and the relaxation time T1(β), the conditions for adsorbing at least one of the perfluoroalkyl compounds and polyfluoroalkyl compounds onto the activated carbon, and the solid １９The measurement conditions in F-NMR measurement (resonance frequency, probe, measurement mode, rotation speed, measurement temperature, and line width broadening factor (BF), etc.) should be the same. Specifically, for example, it is preferable to compare the relaxation time T1(α) obtained by measurement at 10.0°C with the relaxation time T1(β) obtained by measurement at 10.0°C, determine the absolute value of the difference between them, and that value is 0.8 seconds or less. Also, for example, it is preferable to compare the relaxation time T1(α) obtained by measurement at 80.0°C with the relaxation time T1(β) obtained by measurement at 80.0°C, determine the absolute value of the difference between them, and that value is 0.8 seconds or less. Furthermore, for example, as shown in the examples described later, the absolute value of the difference between relaxation time T1(α) and relaxation time T1(β) obtained under the same measurement conditions can be determined.

[0023] The absolute value of the difference between the relaxation time T1(α) and the relaxation time T1(β), measured under the same temperature conditions between 10.0°C and 80.0°C, is more preferably 0.25 seconds or less, even more preferably 0.20 seconds or less, particularly preferably 0.15 seconds or less, and especially preferably 0.10 seconds or less, at any temperature. On the other hand, the absolute value of the difference between the relaxation time T1(α) and the relaxation time T1(β), measured under the same temperature conditions between 10.0°C and 80.0°C, is preferably 0.005 seconds or more, and more preferably 0.01 seconds or more, at any temperature, taking into account the molecular mobility of adsorption and desorption.

[0024] The method for determining the relaxation time T1(α) and the relaxation time T1(β) in this embodiment is as follows.

[0025] First, 1 g of activated carbon is dispersed in 100 g of methanol, and a total of 0.01 g of perfluoroalkyl compounds and polyfluoroalkyl compounds (PFAS) are added. The mixture is shaken in a shaker at room temperature for 1 hour, filtered, and then dried in a hot air dryer at 80°C for 3 hours. Examples of perfluoroalkyl compounds and polyfluoroalkyl compounds (PFAS) include perfluorooctanoic acid (PFOA), perfluorooctanesulfonic acid (PFOS), perfluorobutanoic acid (PFBA), perfluorobutanesulfonic acid (PFBS), and similar compounds.

[0026] The activated carbon on which PFAS has been adsorbed in this manner was subjected to the following measurement conditions: １９ F-NMR measurement is performed. At this time, the activated carbon on which PFAS has been adsorbed is solid. １９ In F-NMR measurements １９ A peak originating from F is observed between -20 and -220 ppm.

[0027] (Measurement conditions) ・Measurement items: １９ F • Resonance frequency: 470 MHz • Probe: 3.2 mm diameter • Measurement mode: MAS (Relaxation Delay = 10 s) • Rotation speed: 14 kHz • Measurement temperature: 80.0°C or less • Line width broadening factor (BF): 20 Hz

[0028] Note: solid １９ F-NMR measurements can be performed using any NMR instrument capable of acquiring NMR spectra of solid samples by nuclear magnetic resonance (NMR) spectroscopy, without any particular limitations. Examples of NMR instruments that can be used include the "ECZ-500R" (manufactured by JEOL Ltd.).

[0029] Next, the relaxation time T1(T1(α) and T1(β)) is determined using the NMR measurement software Delta ver5 manufactured by JEOL Ltd. Specifically, the signal intensity is read out by applying a 180° pulse using the Saturation Recovery method. Then, the longitudinal magnetization that recovers (recovery time τ) is read out as the signal intensity by applying a subsequent 90° pulse (continuous measurement). Finally, the relaxation time T1(T1(α) and T1(β)) can be determined by performing fitting based on the following equation (1).

[0030]

[0031] Here, Mz(τ) is the signal intensity, and M ０ τ is the maximum signal intensity. τ is the recovery time, and T1 is the relaxation time for each peak.

[0032] In this embodiment, the average particle size of the activated carbon is preferably 0.001 mm to 10 mm, more preferably 0.002 mm to 8 mm, and even more preferably 0.005 mm to 7 mm. An average particle size of 0.001 mm or more is preferable because the activated carbon has a sufficient surface area to adsorb and retain fluorine-containing organic compounds. On the other hand, an average particle size of 10 mm or less is preferable because the adsorption performance is fully exhibited even inside the particles. In this specification, the average particle size of the activated carbon refers to the average particle diameter measured according to JIS K1474.

[0033] In this embodiment, the activated carbon has a specific surface area (BET specific surface area) of 500 m² calculated by the BET method (multipoint method) on the nitrogen adsorption isotherm obtained from the nitrogen adsorption amount at 77 K. ２ / g to 2000m ２ It is preferable that it be / g, and 550m ２ / g to 1900m ２ It is more preferable that it be / g, 600m ２ / g ~ 1700m ２It is even more preferable that the value is / g. When it is within the above range, the activated carbon is reliably superior in its ability to remove (adsorb) fluorine-containing organic compounds and also superior in mechanical strength. The BET specific surface area can be measured by the method described in the examples below.

[0034] In this embodiment, the activated carbon preferably has a carbon content of 95% or more. When the carbon content is 95% or more, the influence of impurities is reduced, and the carbon can exhibit its inherent adsorption properties. The activated carbon is more preferably 97% or more in carbon content. On the other hand, from the viewpoint of economic efficiency and availability of raw materials, the carbon content of the activated carbon is preferably 99.8% or less, and more preferably 99.6% or less. In this specification, the carbon content is a value measured by simultaneous thermogravimetric and differential thermal analysis (TG-DTA), and can be measured by the method described in the examples below.

[0035] In this embodiment, the activated carbon preferably has an iodine adsorption capacity of 900 mg / g to 1200 mg / g. The iodine adsorption capacity serves as an indicator of the volume of pores with a diameter smaller than 1 μm. When the iodine adsorption capacity is within the above range, it is possible to achieve a more sufficient adsorption amount of fluorine-containing organic compounds while maintaining strength. The iodine adsorption capacity is more preferably 920 mg / g to 1180 mg / g. In this specification, the iodine adsorption capacity can be measured by the method described in the examples later.

[0036] Examples of raw materials for the activated carbon in this embodiment include 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., coal-based materials such as peat, lignite, brown coal, bituminous coal, anthracite, coke, coal tar, and coal pitch; mineral-derived materials such as petroleum distillation residues and petroleum pitch), 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. It is known that organofluorine compounds are adsorbed onto activated carbon through hydrophobic interactions. From the viewpoint of balancing high specific surface area and hydrophobicity, and from the viewpoint of mechanical strength when subjected to heat treatment, it is preferable to use mineral-based carbonaceous materials, and in particular, it is preferable to use activated carbon derived from bituminous coal.

[0037] The activated carbon of this embodiment can be produced, for example, by dry mixing a carbonaceous material having weak cohesiveness or better and a carbonaceous material with slight cohesiveness from among the carbonaceous materials described above, followed by heat treatment and activation. Here, a carbonaceous material having weak cohesiveness or better is a carbonaceous material with a button index greater than 1. Slight cohesiveness refers to a carbonaceous material with a button index of 1 or less, and the button index may even be 0. The button index is measured in accordance with the crucible expansion test method of JIS M 8801 6, by placing the sample in a predetermined crucible and heating it under predetermined conditions, and comparing the resulting residue with a standard contour.

[0038] Carbonaceous materials having weaker or greater cohesiveness include plant-based, fruit shell-based, and mineral-based materials, but mineral-based carbonaceous materials are preferred, and among mineral-based materials, coal-based carbonaceous materials are preferred for the reasons mentioned above. As such carbonaceous materials, weakly cohesive coal with a button index greater than 1 and less than or equal to 4 is preferably used, but if the cohesiveness is insufficient and the moldability is poor, strongly cohesive coal with a button index greater than 4 and pitch can be mixed in an appropriate proportion.

[0039] As the slightly cohesive carbonaceous material, mineral-based carbonaceous materials are preferred, and among them, coal-based carbonaceous materials are preferred. Furthermore, it is preferable that the slightly cohesive carbonaceous material contains at least one of alkali metals and alkaline earth metals. Examples of alkali metals include potassium and sodium. Examples of alkaline earth metals include calcium. In the slightly cohesive carbonaceous material containing alkali metals and / or alkaline earth metals, the total amount of alkali metals and alkaline earth metals is preferably 300 ppm to 1100 ppm. Among alkali metals and alkaline earth metals, calcium is particularly preferred, and it is more preferable from the viewpoint of hardness and moldability to use a carbonaceous material with a calcium content of 300 ppm to 1000 ppm.

[0040] In the method for producing activated carbon in this embodiment, it is preferable to use a raw material in which at least one of alkali metals and alkaline earth metals is homogeneously and highly dispersed within the structure of the carbonaceous material. Compared to the method of adding a specific amount of metal compound to the carbonaceous material and then activating it, localization of pore formation is less likely to occur, resulting in homogeneous pore formation, which allows for an appropriate pore distribution and higher hardness.

[0041] To produce the activated carbon in this embodiment, first, a carbonaceous material having weak or greater cohesive properties (hereinafter sometimes referred to as Material 1) and a carbonaceous material with slight cohesive properties (hereinafter sometimes referred to as Material 2, preferably containing alkali metals and / or alkaline earth metals) are dry-mixed and pulverized. In addition to these carbonaceous materials 1 and 2, strong carbon or pitch may be added as long as it does not hinder the effects of the present invention. The dry-mixing and pulverizing method is not particularly limited as long as the ratio of the two carbonaceous materials is kept approximately constant, but it can be easily carried out using a jaw crusher, bucket crusher, cone crusher, single-roll crusher, double-roll crusher, impact crusher, ball mill, lot mill, or high-speed mixer.

[0042] The mixing ratio of material 1 and material 2 can be determined according to the carbonaceous material used as the raw material, the ability to remove the target fluorine-containing organic compound, and the desired hardness. However, if the ratio of material 1 is too high, the hardness will increase, but the formation of voids with a pore diameter of 500 nm or more will be suppressed, and the ability to remove fluorine-containing organic compounds will tend to decrease. Also, if the ratio of material 1 is too low, the moldability will decrease and the hardness will tend to decrease. Therefore, it is preferable to mix material 1 and material 2 in a weight ratio of preferably 1:9 to 9:1, and more preferably 2:8 to 6:4.

[0043] In the molding process, material 1 and material 2 are dry-mixed and pulverized, and then molded by pressure molding. The pressure used during pressure molding is 140 kg / cm². ２ ~600 kg / cm ２ Preferably, 140 kg / cm² ２ ~400 kg / cm ２ More preferably, 180 kg / cm² ２ ~360 kg / cm ２ A pressure of 140 kg / cm² is even more preferable. ２ With the above conditions, materials 1 and 2 can be sufficiently compounded during the subsequent grinding process without reverting to separate materials, and suitable void formation can be achieved. Also, the pressure is 600 kg / cm². ２ The following conditions allow for the creation of appropriate voids during the activated carbon production process. The equipment for pressure molding is not particularly limited; for example, roll press type, disc type pelletizer type, ring type pelletizer type, and extrusion type molding equipment can be used. Furthermore, the pressure and shape of the molded product are not particularly limited and can be appropriately determined according to the purpose, such as cylindrical, cylindrical, pellet, spherical, or sheet shape. The size of these products is also not particularly limited.

[0044] The resulting molded material is crushed using a known crusher, such as a jaw crusher, roll crusher, ball mill, lot mill, or high-speed mixer. The crushed material is sized to a predetermined size, such as 8 / 30 mesh, but it is practical to size it so that the particle size range for activated carbon is preferably about 0.01 to 5.0 mm, more preferably about 0.05 to 3.0 mm, and the average particle size is preferably about 0.3 to 3.0 mm, more preferably about 0.5 to 1.0 mm. The sized crushed material (granules) is subjected to heat treatment. The heat treatment can be carried out by heating to 550 to 750°C in a reducing gas atmosphere. To obtain a higher performance and higher strength carbide or activated carbon, a two-stage heat treatment is preferable, for example, heating to 200 to 400°C at a rate of 5 to 30°C / min in an oxidizing gas atmosphere, and then further heating to 550 to 750°C at a rate of 5 to 30°C / min in a reducing gas atmosphere.

[0045] The heat-treated (carbonized) pulverized material is further activated to become activated carbon. While there are no particular limitations as long as the above-described activated carbon can be obtained, for example, the above-described activated carbon can be obtained by performing the following activation treatments. As for activation, gas activation carried out at 400 to 1200°C in an atmosphere of oxidizing gas such as water vapor, carbon dioxide, air, propane combustion exhaust gas, LPG, or a mixture thereof; and chemical activation carried out at about 400 to 800°C in the presence of chemicals such as zinc chloride, phosphoric acid, calcium chloride, and potassium sulfide can be employed. In particular, it is preferable to employ combustion gas activation carried out at 400 to 1200°C, preferably 600 to 1150°C, and even more preferably 700 to 1100°C, in the flow of combustion gas derived from the combustion of a mixture gas in the ratio of air to LPG in the range of 1:0.001 to 1:0.20, preferably 1:0.01 to 1:0.10, and more preferably 1:0.03 to 1:0.06. The activation time is in the range of 10 to 180 minutes, preferably 15 to 160 minutes, and more preferably 20 to 150 minutes. The activation yield can be appropriately determined as needed based on the relationship between the ability to remove fluorine-containing organic compounds and hardness.

[0046] After activation, the resulting activated carbon can be obtained by washing it with acid water such as dilute hydrochloric acid to adjust the pH to between 5.0 and 7.0. The pH of the activated carbon referred to here is the pH measured in accordance with JIS K1474.

[0047] Depending on the application, the activated carbon of this embodiment may be subjected to post-treatment such as chemical modification of the surface or physical loading of functional substances onto the surface. Examples of such surface modifications include impregnation of metal salts or oxides such as silver and iron, mineral acids, and treatments to make the surface acidic.

[0048] The activated carbon of this embodiment is preferably activated carbon that removes fluorine-containing organic compounds from a liquid or gas. Using the activated carbon of this embodiment has the excellent advantage of reducing the fluorine-containing organic compound content in the treated water. Using the activated carbon of this embodiment, the concentration of fluorine-containing organic compounds in the resulting treated water is preferably 0.1 ppb or less, more preferably 0.01 ppb or less, and even more preferably 0.005 ppb or less. In this specification, the concentration of fluorine-containing organic compounds can be measured using a liquid chromatograph-tandem mass spectrometer (LC / MS / MS) manufactured by Waters Corporation under the following conditions. This is a particularly useful measurement method for concentrations of 100 ppb or less.

[0049] (Measurement conditions) ・HPLC system main unit: 2695 separation module ・Mobile phase solvent: acetonitrile 45 vol% / 0.15% acetic acid aqueous solution 55 vol% ・HPLC column: Atlantis dC18 3 μm 2.1 × 30 mm ・Tandem quadrupole mass spectrometer: Quattro micro API

[0050] In this embodiment, examples of fluorine-containing organic compounds to be removed (adsorbed) by the activated carbon include perfluoroalkane carboxylic acids, perfluoroalkyl sulfonic acids, and amphiphilic perfluoroalkane derivatives such as 1H,1H,2H,2H-perfluoroalkyl alcohols. Perfluoroalkane carboxylic acids include perfluorobutanoic acid, perfluoropentanoic acid, perfluorohexanoic acid, perfluoroheptanoic acid, perfluorooctanoic acid, perfluorononanoic acid, perfluorodecanoic acid, perfluoroundecanoic acid, and perfluorododecanoic acid. Perfluoroalkyl sulfonic acids include perfluorobutanesulfonic acid, perfluorohexanesulfonic acid, and perfluorooctanesulfonic acid. In particular, the activated carbon of this embodiment has excellent adsorption (removal) ability for perfluoropentanoic acid, perfluorohexanoic acid, perfluoroheptanoic acid, perfluorooctanoic acid, perfluorooctanesulfonic acid, and especially perfluorooctanoic acid. Furthermore, it exhibits excellent adsorption (removal) capacity for polyfluoroalkyl compounds having 2 to 12 carbon atoms.

[0051] As described above, the activated carbon in this embodiment can efficiently and long-term adsorb fluorine-containing organic compounds, and is therefore suitable for use as a fluorine-containing organic compound removal material. Accordingly, the present invention also includes a fluorine-containing organic compound removal material made of the activated carbon described above.

[0052] <Water Treatment Method> Another aspect of the present invention is a water treatment method comprising contacting the activated carbon described above with water to be treated containing a fluorine-containing organic compound to obtain treated water having a fluorine-containing organic compound content of 0.1 ppb or less. According to the water treatment method of this embodiment, treated water from which the fluorine-containing organic compound has been removed from water to be treated containing a fluorine-containing organic compound can be obtained with extremely high efficiency.

[0053] In this water treatment method, at least one of a perfluoroalkyl compound and a polyfluoroalkyl compound is adsorbed onto activated carbon, and the solid is measured at a temperature of 80°C or below. １９By using activated carbon that exhibits a certain level of relaxation time T1(α) derived from fluorine at the α-position of perfluorocarboxylic acids with 4 to 8 carbon atoms, as determined by F-NMR, fluorine-containing organic compounds can be efficiently removed, and treated water that contains almost no fluorine-containing organic compounds (fluorine-containing organic compound content of 0.1 ppb or less) can be obtained.

[0054] In the water treatment method of this embodiment, a fluorine-containing organic compound removal material made of specific activated carbon is brought into contact with the water to be treated, which contains fluorine-containing organic compounds. The concentration of fluorine-containing organic compounds in the water to be treated is not particularly limited, as it varies depending on the location where the water is collected, and is usually in the range of 0.1 to 1000 ppb. The water treatment method of this embodiment can remove fluorine-containing organic compounds with high efficiency even when the concentration of fluorine-containing organic compounds in the water to be treated is 1000 ppb or less, or even 100 ppb or less. The concentration of fluorine-containing organic compounds can be measured by the method described above in the section on <activated carbon>.

[0055] The contact between the water to be treated and the activated carbon may be a batch-type contact in which the activated carbon is added to the water to be treated, or a continuous-type contact in which the water to be treated is passed through a column packed with the activated carbon. Furthermore, the treatment may be performed multiple times using the batch-type contact, multiple times using the continuous-type contact, or a combination of batch-type and continuous-type contact may be used. In the case of continuous-type contact, the packed column may be a moving-bed type, a fixed-bed type, or a fluidized-bed type.

[0056] In batch-type contact, the contact time between the water to be treated and the activated carbon can be appropriately set according to the amount of activated carbon used, the concentration of fluorine-containing organic compounds in the water to be treated, etc., but from the viewpoint of ensuring a sufficient removal rate, it is preferable to have a contact time of 60 minutes or more.

[0057] From the viewpoint of ensuring sufficient treatment efficiency, the amount of activated carbon relative to the water to be treated is preferably 0.015% by mass or more, more preferably 0.05% by mass or more, and even more preferably 0.10% by mass or more. Furthermore, from the viewpoint of volumetric efficiency, the amount of activated carbon relative to the water to be treated is preferably 20% by mass or less, more preferably 10% by mass or less, and even more preferably 5% by mass or less.

[0058] The water treatment method of this embodiment obtains treated water in which the concentration of fluorine-containing organic compounds is 0.1 ppb or less. More preferably, the concentration of fluorine-containing organic compounds in the obtained treated water is 0.01 ppb or less, and even more preferably 0.005 ppb or less.

[0059] The water treatment method of this embodiment may further include a step to remove activated carbon if the treated water contains activated carbon. The method for removing activated carbon is not particularly limited, but known methods such as filtration, sedimentation separation, centrifugation, and separation with a coagulant can be employed.

[0060] <Water Treatment Apparatus> Yet another aspect of the present invention is a water treatment apparatus comprising the activated carbon of this embodiment. The activated carbon of the water treatment apparatus may be contained in a treatment tank through which the water to be treated is treated, or it may be provided as an activated carbon packed column through which the water to be treated passes, and its form is not limited as long as it is provided in a manner that allows the water to be treated and the activated carbon to come into appropriate contact. Furthermore, the method of contacting the water to be treated and the activated carbon in the water treatment apparatus may be batch type or continuous type. In continuous contact, the packed column may be a moving bed type, a fixed bed type, or a fluidized bed type.

[0061] As described above, this specification discloses various aspects of technology, the main technologies among them are summarized below.

[0062] The activated carbon according to the first aspect of the present invention is a solid carbon in which at least one of a perfluoroalkyl compound and a polyfluoroalkyl compound is adsorbed onto the activated carbon and measured at 80.0°C or below. １９The relaxation time T1(α) derived from the fluorine at the α-position of perfluorocarboxylic acids having 4 to 8 carbon atoms, as determined by F-NMR, is 1.1 seconds or less.

[0063] The activated carbon according to the second aspect of the present invention is characterized in that, in the activated carbon according to the first aspect, the absolute value of the difference between the relaxation time T1(α) measured at 10.0°C and the relaxation time T1(α) measured at 80.0°C is 0.8 seconds or less.

[0064] The activated carbon according to the third aspect of the present invention is an activated carbon according to the first or second aspect, wherein at least one of a perfluoroalkyl compound and a polyfluoroalkyl compound is adsorbed onto the activated carbon, and measured under the same temperature conditions between 10.0°C and 80.0°C, the solid １９ The absolute difference between the relaxation time T1(β) derived from the fluorine at the β-position of the perfluorocarboxylic acid having 4 to 8 carbon atoms, as determined from F-NMR, and the relaxation time T1(α) is 0.8 seconds or less in both cases.

[0065] The activated carbon according to the fourth aspect of the present invention is an activated carbon according to any of the first to third aspects that removes fluorine-containing organic compounds from a liquid or gas.

[0066] The activated carbon according to the fifth aspect of the present invention is an activated carbon according to any of the first to fourth aspects, wherein the average particle size is 0.001 to 10 mm and the specific surface area is 500 m². ２ It is 1 / g or more, and has a carbon content of 95% or more.

[0067] The activated carbon according to the sixth aspect of the present invention is the activated carbon according to the fourth aspect, wherein the fluorine-containing organic compound is a polyfluoroalkyl compound having 2 to 12 carbon atoms.

[0068] A water treatment apparatus according to the seventh aspect of the present invention comprises activated carbon according to any of the first to sixth aspects.

[0069] A water treatment method according to the eighth aspect of the present invention includes contacting activated carbon according to any of the first to sixth aspects with water to be treated containing a fluorine-containing organic compound to obtain treated water having a fluorine-containing organic compound content of 0.1 ppb or less.

[0070] 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.

[0071] First, we will describe the activated carbon prepared in each example shown in Table 1.

[0072] [Example 1] As material 1, a weakly cohesive bituminous coal (button index 3) with a fixed carbon content of 59.5% by weight and an ash content of 0.7% by weight was used, and as material 2, a slightly cohesive bituminous coal (button index 0.5) with a fixed carbon content of 48.3% by weight or more, an ash content of 0.7% by weight, and containing 45 ppm sodium and 200 ppm calcium was used. These materials 1 and 2 were mixed and ground using a ball mill in a weight ratio of 3:7, and the resulting powder was filled into a container with a diameter of 40 mm and a length of 150 mm using a roll press type pressure molding machine manufactured by Yamamoto Hydraulic Engineering Co., Ltd., and heated at 100°C and 280 kg / cm². ２ It was molded under pressure. Then it was crushed with a pin mill and sized into granules with a particle size range of 0.1 to 2.0 mm and an average particle size of 0.95 mm.

[0073] Next, these granules were placed in an externally heated rotary kiln and heated to 280°C at a rate of 7°C / min under an oxidizing gas atmosphere, held at 280°C for 2 hours, and then heated to 600°C at a rate of 7°C / min under a reducing gas atmosphere to carbonize them. 75.0 g of this carbonized carbon, calculated on a basis of 0 g of volatile matter, was placed in a fluidized bed furnace with an inner diameter of 57 mm and a height of 600 mm, and treated at 1000°C for 20 minutes under a combustion gas flow of 18 L / min of air and 0.85 L / min of LPG. Combustion gas activation was performed to achieve an activation yield of 45%, thereby obtaining activated carbon.

[0074] The obtained activated carbon was washed with 1N hydrochloric acid, then boiled six times to adjust the pH to 6.5 ± 0.5, and then dried at 120°C for 2 to 3 hours.

[0075] [Example 2] Activated carbon was obtained in the same manner as in Example 1, except that the activation time was set to 3 hours and the activated carbon was prepared to achieve an activation yield of 38%.

[0076] [Comparative Example 1] Activated carbon was obtained in the same manner as in Example 1, except that Material 2 was not mixed with Material 1, and only Material 1 was used, and the material was sized into granules with a particle size range of 0.1 to 2.0 mm and an average particle size of 0.95 mm.

[0077] Next, we will explain the evaluation methods for the activated carbon prepared in each example and comparative example shown in Table 1.

[0078] [BET specific surface area] Below is equation (2), an approximation derived from BET's formula.

[0079]

[0080] Using the above formula (2), a predetermined relative pressure (p / p) is obtained by multipoint method by nitrogen adsorption at liquid nitrogen temperature. ０ Substitute the measured adsorption amount (v) into the given value and then enter v ｍ The specific surface area (SSA: unit is m) of the sample is calculated using the following formula (3). ２ The calculation (per g) was performed.

[0081]

[0082] In the above equations (2) and (3), v ｍ The amount of adsorption (cm³) required to form a monolayer on the sample surface is the amount of adsorption required to form a monolayer on the sample surface. ３ / g), v is the measured adsorption amount (cm ３ / g), p ０ is the saturated vapor pressure, p is the absolute pressure, c is a constant (reflecting the heat of adsorption), and N is Avogadro's number 6.022 × 10⁻¹⁰. ２３ a (nm) ２ ) is the area occupied by adsorbate molecules on the sample surface (molecular occupied cross-sectional area).

[0083] Specifically, the amount of nitrogen adsorbed onto a carbon material at liquid nitrogen temperature was measured using the Autosorb-iQ-MP manufactured by CANTAChrome, Inc. as follows: The carbon material sample was filled into a sample tube, and the sample tube was cooled to -196°C (77K). The pressure was then reduced, and nitrogen (99.999% purity) was adsorbed onto the sample at the desired relative pressure. The amount of nitrogen adsorbed onto the sample when equilibrium pressure was reached at each desired relative pressure was defined as the adsorbed gas amount v.

[0084] [Iodine Adsorption Amount] In accordance with JIS K 1474, activated carbon was added in varying amounts to a 0.05 mol / L iodine solution (potassium iodide also dissolved: 0.15 mol / L), shaken for 15 minutes, then centrifuged the activated carbon. The supernatant was titrated with a 0.1 mol / L sodium thiosulfate solution to determine the residual iodine concentration, and an adsorption isotherm was created. The amount of adsorption at a residual iodine concentration of 2.5 g / L was defined as the iodine adsorption performance.

[0085] [Average particle size of unactivated granules and activated carbon] For unactivated granules or activated carbon, a mass-based particle size cumulative diagram was prepared in accordance with JIS K 1474. The average particle size was determined by drawing a horizontal line on the horizontal axis from the intersection of the vertical line at the 50% point on the horizontal axis and the particle size cumulative line on the particle size cumulative diagram, and finding the sieve opening (mm) indicated by the intersection point.

[0086] [Carbon Content] The carbon content in activated carbon was determined by TG analysis using a TG-DTA analyzer (Rigaku Corporation "TG8120"). Approximately 10 mg of the sample was placed in an alumina sample pan and heated to 1000°C with an airflow of 200 mL / min and a heating rate of 10°C / min. The weight at 100°C was set as 100%, and the carbon content was determined by calculating the weight loss percentage at 1000°C.

[0087]

[0088] [solid １９ [F-NMR Measurement] Next, the activated carbon prepared in each example and comparative example was subjected to solid １９ This section describes the method used to determine relaxation times T1(α) and T1(β) by performing F-NMR measurements.

[0089] Disperse 1 g of activated carbon in 100 g of methanol, and add perfluorooctanoic acid (PFOA:C) to it. ７ F １５ 0.01 g of COOH was added, and the mixture was shaken in a shaker at room temperature for 1 hour. After filtration, it was dried in a hot air dryer at 80°C for 3 hours. The activated carbon on which PFOA had been adsorbed in this manner was analyzed under the following measurement conditions.

[0090] (Measurement conditions) ・Measurement items: １９F • Resonance frequency: 470 MHz • Probe: 3.2 mm diameter • Measurement mode: MAS (Relaxation Delay = 10 s) • Rotation speed: 14 kHz • Measurement temperature: 10.0°C, 42.0°C, 60.0°C, 80.0°C • Broadening Factor (BF): 20 Hz

[0091] Next, the relaxation time T1 was determined using the NMR measurement software Delta ver5 manufactured by JEOL Ltd. Specifically, the signal intensity was read out by applying a 180° pulse using the Saturation Recovery method. The longitudinal magnetization that then recovered (recovery time τ) was read out as the signal intensity by applying a subsequent 90° pulse (continuous measurement). Then, by performing fitting based on the following equation (1), the relaxation time T1(α) originating from the fluorine at the α position of the perfluorocarboxylic acid having 4 to 8 carbon atoms, and the relaxation time T1(β) originating from the fluorine at the β position of the perfluorocarboxylic acid having 4 to 8 carbon atoms were determined.

[0092]

[0093] Here, Mz(τ) is the signal intensity, and M ０ τ is the maximum signal intensity. τ is the recovery time, and T1 is the relaxation time for each peak.

[0094] The activated carbon obtained in Example 1 was solidified under the above conditions. １９ Table 2 shows the results of F-NMR measurements, and the activated carbon obtained in Example 2 was solidified under the above conditions. １９ Table 4 shows the results of F-NMR measurements, and the activated carbon obtained in Comparative Example 1 was solidified under the above conditions. １９ The results of the F-NMR measurements are shown in Table 5.

[0095] Furthermore, the activated carbon obtained in Example 1 is solid １９ Under the above conditions for F-NMR measurement, the PFAS to be impregnated is converted from PFOA to perfluorobutanoic acid (PFBA:C ３ F ７ The relaxation time T1(α) and relaxation time T1(β) were determined by replacing COOH. The results are shown in Table 3.

[0096] Tables 2-5 also show the absolute value of the difference between relaxation time T1(α) and relaxation time T1(β) under the same measurement conditions.

[0097]

[0098]

[0099]

[0100]

[0101] [Water Treatment Experiment: Breakthrough Time Measurement] 10 g of activated carbon obtained in Examples 1-2 and Comparative Example 1 was each filled into a 10 mmφ × 300 mm tube. PFOA (Aldrich, 96% purity) was dissolved in tap water to achieve a PFOA concentration of 10 ppb. This solution was poured into the activated carbon at a rate of 10 ml / min using an upflow method (at 20°C and 60°C) to continuously obtain treated water. The obtained liquid was continuously sampled, and the PFOA concentration in the treated water was detected under the above measurement conditions. The lowest detected PFOA concentration was defined as the minimum detection concentration. The time at which the detected PFOA concentration reached 0.15 ppb or higher was defined as the breakthrough time. The breakthrough time was measured for the activated carbon obtained in Examples 1-2 and Comparative Example 1. The results are shown in Table 6.

[0102] The concentrations of fluorine-containing organic compounds (PFOA, etc.) in the treated water and the treated water were measured using a liquid chromatograph-tandem mass spectrometer (LC / MS / MS) manufactured by Waters Corporation under the following measurement conditions.

[0103] (Measurement conditions) ・HPLC system main unit: 2695 separation module ・Mobile phase solvent: acetonitrile 45 vol% / 0.15% acetic acid aqueous solution 55 vol% ・HPLC column: Atlantis dC18 3 μm 2.1 × 30 mm ・Tandem quadrupole mass spectrometer: Quattro micro API

[0104] In Table 6, "PFOA detection limit below the detection limit" indicates that the PFOA detection limit was 0.01 ppb or less.

[0105]

[0106] [Discussion] From the results in Tables 2-4 and 6, when water treatment was performed using the activated carbon of Examples 1 and 2, which have a relaxation time T1(α) of 1.1 seconds or less, the PFOA in the treated water was below the detection limit (0.01 ppb), indicating that fluorine-containing organic compounds can be efficiently removed from the water to be treated using the activated carbon of Examples 1 and 2. From the results in Tables 5-6, when water treatment was performed using the activated carbon of Comparative Example 1, which has a relaxation time T1(α) exceeding 1.1 seconds, the minimum detectable concentration of PFOA in the treated water was 0.13 ppb, indicating that fluorine-containing organic compounds could not be efficiently removed from the water to be treated.

[0107] This application is based on Japanese Patent Application No. 2025-50496, filed on March 25, 2025, the contents of which are included in this application.

[0108] In order to express the present invention, the invention has been adequately and sufficiently described above through embodiments with reference to specific examples, 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.

[0109] The present invention has broad industrial applicability in the technical fields of activated carbon, and water treatment methods and water treatment equipment using activated carbon.

Claims

1. At least one of a perfluoroalkyl compound and a polyfluoroalkyl compound is adsorbed onto activated carbon, and the solid is measured at 80.0°C or below. １９ Activated carbon in which the relaxation time T1(α) derived from the fluorine at the α-position of perfluorocarboxylic acids having 4 to 8 carbon atoms, as determined by F-NMR, is 1.1 seconds or less.

2. The activated carbon according to claim 1, wherein the absolute value of the difference between the relaxation time T1(α) measured at 10.0°C and the relaxation time T1(α) measured at 80.0°C is 0.8 seconds or less.

3. At least one of a perfluoroalkyl compound and a polyfluoroalkyl compound is adsorbed onto activated carbon, and the solid is measured under the same temperature conditions between 10.0°C and 80.0°C. １９ The activated carbon according to claim 1 or 2, wherein the absolute value of the difference between the relaxation time T1(β) derived from the fluorine at the β-position of the perfluorocarboxylic acid having 4 to 8 carbon atoms, as determined by F-NMR, and the relaxation time T1(α) is 0.8 seconds or less in both cases.

4. The activated carbon according to claim 1 or 2, which removes fluorine-containing organic compounds from a liquid or gas.

5. The average particle size is 0.001 to 10 mm, and the specific surface area is 500 m². ２ The activated carbon according to claim 1 or 2, wherein the amount is 1 / g or more and the carbon content is 95% or more.

6. The activated carbon according to claim 4, wherein the fluorine-containing organic compound is a polyfluoroalkyl compound having 2 to 12 carbon atoms.

7. A water treatment apparatus comprising the activated carbon described in claim 1 or 2.

8. A water treatment method comprising contacting activated carbon according to claim 1 or 2 with water to be treated containing a fluorine-containing organic compound to obtain treated water having a fluorine-containing organic compound content of 0.1 ppb or less.

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