Activated carbon adsorbent for adsorbing organic fluorine compounds

Abstract

This invention provides an activated carbon adsorbent for adsorbing organic fluorine compounds that reduces the impact on the measurement results of fluorine concentration in low-concentration analysis of organic fluorine compounds. [Solution] An activated carbon made by using phenolic resin as the activated carbon raw material, and after carbonizing the activated carbon raw material under nitrogen flow, the BET specific surface area is 1000 to 2000 m². 2 The fluorine content is less than 1000 ng / g, as determined by combustion ion chromatography. Furthermore, it is preferable that the phenolic resin is a composite phenolic resin composed of a novolac resin and a resol resin.

Description

[Technical Field]

[0001] This invention relates to an activated carbon adsorbent for adsorbing organofluorine compounds. [Background technology]

[0002] Perfluoroalkyl compounds, which are organofluorine compounds (PFCs), are fluorine-substituted aliphatic compounds that possess high thermal stability, high chemical stability, and high surface modification activity. Taking advantage of these properties, perfluoroalkyl compounds are widely used in industrial and chemical applications such as surface treatment agents, packaging materials, and liquid fire extinguishing agents.

[0003] Some perfluoroalkyl compounds are highly stable chemicals and, once released into the environment, are difficult to decompose under natural conditions. For this reason, in recent years, perfluoroalkyl compounds have been recognized as persistent organic pollutants (POPs), and perfluorooctanesulfonic acid (PFOS) (IUPAC name: 1,1,2,2,3,3,4,4,5,5,6,6,7,7,8,8,8-heptadecafluorooctane-1-sulfonic acid) has been subject to regulations on the manufacture and use of under the Stockholm Convention on Persistent Organic Pollutants (POPs Convention) since 2010.

[0004] In particular, perfluorooctanesulfonic acid (PFOS) and perfluorooctanoic acid (PFOA) (IUPAC name: 2,2,3,3,4,4,5,5,6,6,7,7,8,8,8-pentadecafluorooctanoic acid) are regulated worldwide, and in Japan, from April 1, 2020, a standard value of 50 ng / L or less for the combined value of perfluorooctanesulfonic acid (PFOS) and perfluorooctanoic acid (PFOA) was added to the water quality management target setting items.

[0005] Perfluoroalkyl compounds, including perfluorooctanesulfonic acid (PFOS) and perfluorooctanoic acid (PFOA), have a completely fluorinated linear alkyl group and are represented by chemical formula (i). Polyfluoroalkyl compounds, on the other hand, have some of the hydrogen atoms in the alkyl group replaced by fluorine and are represented by chemical formula (ii). Examples include fluorotelomer alcohols.

[0006]

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[0007]

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[0008] Thus, per- and polyfluoroalkyl compounds such as PFOS and PFOA remain in nature (in water, soil, and air), and have attracted attention as harmful substances known as PFAS. Activated carbon is suitably used as a collection material that can efficiently capture PFAS (see, for example, Patent Document 1).

[0009] Furthermore, as this PFAS problem has become apparent, various methods for extracting and measuring PFAS, focusing on specific PFAS, have been proposed. However, existing target measurements can only measure a very small fraction of PFAS, and it is practically impossible to individually measure the more than 7 million types of PFAS that are theoretically available.

[0010] Therefore, combustion ion chromatography (CIC) is attracting attention as one of the comprehensive PFAS management and measurement methods. In CIC, a sample containing PFAS is passed through activated carbon to adsorb the PFAS, and this activated carbon is then combusted at high temperature, after which the PFAS adsorbed on the activated carbon is ion-filtered. -The PFAS can be absorbed into an absorption solution, and the total fluorine concentration in the sample can be measured by ion chromatography. However, trace amounts of fluorine may be present in the activated carbon itself used to adsorb PFAS. Therefore, in the analysis of PFAS by CIC, for example, when analyzing samples with low fluorine concentrations (low-concentration analysis), trace amounts of fluorine from the activated carbon tend to affect the measurement results, making it difficult to perform accurate low-concentration analysis. [Prior art documents] [Patent Documents]

[0011] [Patent Document 1] Japanese Patent Publication No. 2021-35671 [Overview of the Initiative] [Problems that the invention aims to solve]

[0012] The present invention has been made in view of the above points, and provides an activated carbon adsorbent for adsorbing organic fluorine compounds that reduces the influence on the measurement results of fluorine concentration in low-concentration analysis of organic fluorine compounds, etc. [Means for solving the problem]

[0013] In other words, the first invention is an activated carbon made by using phenolic resin as the activated carbon raw material, and after the activated carbon raw material is carbonized under nitrogen flow, it is activated, and the BET specific surface area is 1000 to 2000 m². 2 The present invention relates to an activated carbon adsorbent for adsorbing organofluorine compounds, characterized in that the fluorine content is less than 1000 ng / g, as determined by combustion ion chromatography.

[0014] The second invention relates to an activated carbon adsorbent for adsorbing organic fluorine compounds, wherein the activated carbon has a total pore volume of 0.4 to 1.0 ml / g and a packing density of 0.3 to 0.6 g / ml, as described in the first invention.

[0015] The third invention relates to an activated carbon adsorbent for adsorbing organic fluorine compounds, wherein in the first or second invention, the average particle diameter of the activated carbon is 50 to 200 μm.

[0016] The fourth invention relates to an activated carbon adsorbent for adsorbing organic fluorine compounds, wherein in the first or second invention, the phenolic resin is a composite phenolic resin in which a novolak resin and a resol resin are combined.

[0017] The fifth invention relates to an activated carbon adsorbent for adsorbing organic fluorine compounds, wherein in the third invention, the phenolic resin is a composite phenolic resin in which a novolak resin and a resol resin are combined.

[0018] The sixth invention relates to an activated carbon adsorbent for adsorbing organic fluorine compounds, wherein in the first or second invention, the activated carbon adsorbent for adsorbing organic fluorine compounds is activated carbon for organic fluorine compound analysis for adsorbing and quantitatively measuring an organic fluorine compound from a sample.

[0019] The seventh invention relates to an activated carbon adsorbent for adsorbing organic fluorine compounds, wherein in the third invention, the activated carbon adsorbent for adsorbing organic fluorine compounds is activated carbon for organic fluorine compound analysis for adsorbing and quantitatively measuring an organic fluorine compound from a sample.

[0020] The eighth invention relates to an activated carbon adsorbent for adsorbing organic fluorine compounds, wherein in the fourth invention, the activated carbon adsorbent for adsorbing organic fluorine compounds is activated carbon for organic fluorine compound analysis for adsorbing and quantitatively measuring an organic fluorine compound from a sample.

[0021] The ninth invention relates to an activated carbon adsorbent for adsorbing organic fluorine compounds, wherein in the fifth invention, the activated carbon adsorbent for adsorbing organic fluorine compounds is activated carbon for organic fluorine compound analysis for adsorbing and quantitatively measuring an organic fluorine compound from a sample.

[0022] The tenth invention relates to an activated carbon adsorbent for adsorbing organic fluorine compounds, wherein in the first or second invention, the activated carbon is spherical activated carbon.

Advantages of the Invention

[0023] According to the first invention, the activated carbon adsorbent for adsorbing organic fluorine compounds uses a phenol resin as the activated carbon raw material, and the activated carbon is obtained by carbonizing the activated carbon raw material under nitrogen flow and then activating it, and has a BET specific surface area of ​​1000 to 2000 m². 2 Since the fluorine content is less than 1000 ng / g as determined by combustion ion chromatography, the amount of fluorine components derived from activated carbon is relatively small. This effectively suppresses the influence on the measurement results of fluorine concentration in low-concentration analysis of organofluorine compounds, making it possible to appropriately perform the analysis of trace amounts of organofluorine.

[0024] According to the activated carbon adsorbent for adsorbing organic fluorine compounds of the second invention, in the first invention, the total pore volume of the activated carbon is 0.4 to 1.0 ml / g and the packing density is 0.3 to 0.6 g / ml, thus providing an activated carbon adsorbent with excellent strength and adsorption performance.

[0025] According to the activated carbon adsorbent for adsorbing organic fluorine compounds of the third invention, in the first or second invention, since the average particle size of the activated carbon is 50 to 200 μm, the contact efficiency with the sample is good, and pressure loss and clogging are less likely to occur when the adsorbent is packed into a column or the like and passed through.

[0026] According to the activated carbon adsorbent for adsorbing organic fluorine compounds of the fourth invention, in the first or second invention, since the phenol resin is a composite phenol resin obtained by compounding a novolac resin and a resol resin, it is suitable as a raw material for activated carbon that is suitable for adsorbing organic fluorine compounds in the presence of impurities, and it is also easier to reduce the total amount of fluorine contained in the activated carbon.

[0027] According to the activated carbon adsorbent for adsorbing organic fluorine compounds of the fifth invention, in the third invention, since the phenol resin is a composite phenol resin obtained by compounding a novolac resin and a resol resin, it is suitable as a raw material for activated carbon that is suitable for adsorbing organic fluorine compounds in the presence of impurities, and it is also easier to reduce the total amount of fluorine contained in the activated carbon.

[0028] According to the activated carbon adsorbent for adsorbing organic fluorine compounds of the sixth invention, in the first or second invention, since the activated carbon adsorbent for adsorbing organic fluorine compounds is activated carbon for organic fluorine compound analysis for adsorbing organic fluorine compounds from a sample and quantitatively measuring them, it becomes possible to quantify low concentrations of organic fluorine compounds present in the sample.

[0029] According to the seventh invention, the activated carbon adsorbent for adsorbing organic fluorine compounds, in the third invention, since the activated carbon adsorbent for adsorbing organic fluorine compounds is activated carbon for organic fluorine compound analysis for adsorbing organic fluorine compounds from a sample and quantitatively measuring them, it becomes possible to quantify low concentrations of organic fluorine compounds present in the sample.

[0030] According to the activated carbon adsorbent for adsorbing organic fluorine compounds in the eighth invention, in the fourth invention, since the activated carbon adsorbent for adsorbing organic fluorine compounds is activated carbon for organic fluorine compound analysis for adsorbing organic fluorine compounds from a sample and quantitatively measuring them, it becomes possible to quantify low concentrations of organic fluorine compounds present in the sample.

[0031] According to the activated carbon adsorbent for adsorbing organic fluorine compounds in the ninth invention, in the fifth invention, since the activated carbon adsorbent for adsorbing organic fluorine compounds is activated carbon for organic fluorine compound analysis for adsorbing organic fluorine compounds from a sample and quantitatively measuring them, it becomes possible to quantify low concentrations of organic fluorine compounds present in the sample.

[0032] According to the activated carbon adsorbent for adsorbing organic fluorine compounds of the 10th invention, in the first or second invention, since the activated carbon is spherical activated carbon, the uniformity and fluidity of the particles are good, making it easy to pack into columns during analysis. [Brief explanation of the drawing]

[0033] [Figure 1] This is a schematic diagram of quantitative measurement using the activated carbon adsorbent for adsorption of organofluorine compounds of the present invention. [Modes for carrying out the invention]

[0034] The present invention relates to an activated carbon adsorbent for adsorbing organic fluorine compounds, and more particularly to an activated carbon adsorbent for adsorbing organic fluorine compounds from samples containing organic fluorine compounds at low concentrations. This activated carbon adsorbent for adsorbing organic fluorine compounds can be suitably used as an activated carbon for organic fluorine compound analysis, for example, to adsorb organic fluorine compounds from a sample and quantitatively measure them using a measurement method such as combustion ion chromatography (CIC) that can measure the total fluorine concentration in the sample. The main analytical samples in which this activated carbon adsorbent is used include samples containing impurities such as tap water and environmental water, from the viewpoint of enabling the analysis of organic fluorine compounds in natural environments.

[0035] Organic fluorine compounds (PFCs) are highly stable compounds containing carbon and fluorine, and because they do not easily decompose under natural conditions, they have recently attracted attention as hazardous substances. Examples of organic fluorine compounds include perfluorooctanesulfonic acid (PFOS) and perfluorooctanoic acid (PFOA), as well as perfluoroalkyl compounds (PFAS).

[0036] The activated carbon adsorbent for adsorbing organofluorine compounds of the present invention is activated carbon obtained by carbonizing an activated carbon raw material in a carbonization process and then activating it in an activation process. The activated carbon raw material is preferably a phenolic resin. Since phenolic resins have an aromatic ring structure in their molecules, the carbonization yield is increased, and activation produces activated carbon with a large surface area. Therefore, by using a phenolic resin as the activated carbon raw material, the activation can be enhanced, increasing the specific surface area and pore volume of the activated carbon, which makes it easier to improve the adsorption performance for organofluorine compounds to be adsorbed.

[0037] Furthermore, activated carbon derived from phenolic resin tends to have smaller pore sizes and higher packing density compared to other activated carbons such as wood, coconut shell, and petroleum pitch. In addition, it has lower ash content such as nitrogen, phosphorus, sodium, and magnesium, and a higher carbon-to-unit-mass ratio, making it possible to obtain activated carbon with fewer impurities. In particular, since phenolic resin is an artificially derived raw material, it tends to have a lower fluorine content compared to naturally derived raw materials such as wood, coconut shell, and coal, which tend to absorb and accumulate fluorine components from the environment such as soil, water, and air. This makes it easier to reduce the total amount of fluorine contained in the activated carbon, which is preferable.

[0038] Preferably, the phenolic resin is a composite phenolic resin, for example, a composite phenolic resin composed of a novolac resin and a resol resin. The composite phenolic resin contains phenolic resins with different properties, such as a thermoplastic novolac resin and a thermosetting resol resin. Therefore, the heat resistance, melting temperature, and volatilization rate differ between the novolac resin and resol resin components in the composite phenolic resin particles, and it is thought that the carbonization associated with firing, as described later, proceeds heterogeneously. Furthermore, it is thought that cracks and fissures occur in the resin char due to the volatilization of the resin components in the composite phenolic resin particles during heating and firing, making it easier for macropores with a pore diameter of approximately 50 nm or more to develop. For this reason, the composite phenolic resin is suitable as a raw material for activated carbon that is suitable for the adsorption of organofluorine compounds.

[0039] The manufacturing process for the composite phenolic resin can be as appropriate as long as it is a composite of a novolac resin and a resol resin, but it is preferable to manufacture it by a composite phenolic resin preparation process that includes a novolac resin synthesis process and a resol resin synthesis process.

[0040] In the novolac resin synthesis process, phenol is mixed with formaldehyde, an acidic catalyst for crosslinking of the two molecules is added, and a dehydration condensation reaction is promoted by stirring at a heating temperature of 80-100°C to synthesize the novolac resin. In the resol resin synthesis process, phenol and formaldehyde are added and mixed to the synthesized novolac resin, a basic catalyst for crosslinking of the newly added phenol and formaldehyde is added, and a dehydration condensation reaction is promoted by stirring at a heating temperature of 80-100°C to synthesize the resol resin component from the newly added phenol. This prepares a composite phenolic resin containing the synthesized novolac resin and resol resin, respectively. The obtained composite phenolic resin is washed as appropriate.

[0041] Furthermore, in each step of the manufacturing process for composite phenolic resins, a solvent (raw material dilution water) is used to dilute the raw materials during synthesis. For example, ion-exchanged water is preferably used as the raw material dilution water. Because ion-exchanged water contains significantly less fluorine than other dilution waters such as tap water, it can suppress the transfer of fluorine components from the dilution water to the synthesized composite phenolic resin, making it easier to reduce the total amount of fluorine contained in activated carbon.

[0042] In the carbonization process, the activated carbon raw material is carbonized under nitrogen flow, yielding a resin carbide in which micropores are formed on the activated carbon raw material. For example, the activated carbon raw material is placed in a firing furnace such as a cylindrical retort electric furnace, and carbonized at 300 to 1000°C, preferably 450 to 700°C, for 1 to 20 hours while nitrogen is flowing through the furnace, thereby obtaining a resin carbide. By carrying out the carbonization process under nitrogen flow, the incorporation of fluorine components contained in the atmosphere is suppressed, and the total amount of fluorine contained in the activated carbon can be reduced. Furthermore, when carbonizing under nitrogen flow, it is preferable to flow high-concentration nitrogen to carbonize under an inert atmosphere. By carbonizing the activated carbon raw material under an inert atmosphere with high-concentration nitrogen, the development of functional groups can be suppressed, thereby improving the affinity of the final activated carbon with PFAS and obtaining good adsorption performance.

[0043] In the activation process, the resin carbide obtained by carbonization in the carbonization process is activated to obtain activated carbon with various pores. For example, the resin carbide is placed in a heating furnace such as a rotary external heating furnace and activated with steam at 750 to 1000°C, preferably 800 to 1000°C, and more preferably 850 to 950°C to become activated carbon. The activation time is 0.5 to 50 hours, although this depends on the production scale and equipment. In steam activation, any water suitable for the purpose, such as tap water or ion-exchanged water, can be used as the raw water (introduced water for activation) used during activation. In particular, using ion-exchanged water as the introduced water for activation is preferable because it can suppress the inclusion of fluorine components originating from the introduced water. The activation method may also be gas activation such as carbon dioxide activation. After activation, the activated carbon adsorbent is washed with dilute hydrochloric acid. After washing with dilute hydrochloric acid, the activated carbon adsorbent is washed with water until the pH reaches 5-7, for example, by measuring the pH in accordance with JIS K 1474 (2014).

[0044] In the activation process, it is preferable to apply high-temperature heat treatment after activating the resin carbide. The temperature of the high-temperature heat treatment is preferably 850°C or higher, more preferably 1000°C or higher, and even more preferably 1100°C or higher. By applying high-temperature heat treatment after activation, the organofluorine compounds in the activated carbon can be thermally decomposed, thereby reducing the fluorine content. The treatment time for the high-temperature heat treatment is preferably about 1 to 120 minutes. If the treatment time is too short, the thermal decomposition of the organofluorine compounds may be insufficient, and if the treatment time is too long, it will be economically disadvantageous.

[0045] Furthermore, in activated carbon activated by the activation process, the degree of activation can be determined, for example, by the degree of activation. The degree of activation can be expressed using, for example, the total pore volume of the activated carbon, and a larger total pore volume indicates a higher degree of activation. In this invention, a total pore volume of 0.6 ml / g or more is considered to be a high degree of activation, and a total pore volume of less than 0.6 ml / g is considered to be a low degree of activation.

[0046] The obtained activated carbon is, if necessary, washed with dilute hydrochloric acid, then heat-treated in a mixture of oxygen and nitrogen gas, and washed with water to remove impurities such as ash. The heat treatment removes any remaining hydrochloric acid. Through each treatment, the amount of surface oxides on the activated carbon is adjusted. After acid washing, the amount of surface oxides on the activated carbon increases through heat treatment of the activated resin carbide. The oxygen concentration during this treatment is 0.1 to 21% by volume. The heating temperature is 150 to 1000°C, preferably 400 to 800°C, and the heating time is 15 minutes to 2 hours.

[0047] The shape of the activated carbon obtained is not particularly limited, but spherical activated carbon is preferred. Spherical activated carbon can be obtained, for example, by molding a composite phenolic resin, which is an activated carbon raw material, into a spherical shape. The spherical shape of the activated carbon results in good particle uniformity and fluidity. Therefore, it is easier to pack, for example, into a column during analysis.

[0048] Therefore, composite phenolic resin can be molded into spherical (granular) objects by adding an emulsifier during the composite phenolic resin preparation process and dispersing it through the action of the emulsifier. When an emulsifier is added during the composite phenolic resin preparation process, emulsification progresses through heating and stirring, and granular or spherical composite phenolic resin (composite phenolic resin particles) are produced in the reaction solution. It is thought that the addition of an emulsifier increases the surface tension of the reaction solution containing phenol, etc., which causes minute droplets to form and promotes spheroidization. The spherical composite phenolic resin preferably has an average particle size of about 50 to 300 μm, taking into account the volume reduction that occurs during carbonization.

[0049] Water-soluble polysaccharides such as hydroxyethylcellulose and gum arabic are preferably used as emulsifiers. Since emulsifiers are hydrocarbon compounds, they do not easily produce excess residue during carbonization. The amount of emulsifier added is 0.1 to 1% by weight of the total amount of material added in the composite phenol resin preparation process. This amount may be increased or decreased as appropriate depending on the type of emulsifier and reaction conditions.

[0050] The physical properties of the activated carbon produced in this way determine its adsorption and desorption performance for the target adsorbent, and it is used as an activated carbon adsorbent. The activated carbon of the present invention is an activated carbon adsorbent for adsorbing organic fluorine compounds such as per- and polyfluoroalkyl compounds (PFAS), and possesses physical properties suitable for adsorbing organic fluorine compounds. Furthermore, since this activated carbon adsorbent is made from composite phenolic resin, it is suitable for use in the presence of impurities such as tap water and environmental water.

[0051] The activated carbon adsorbent for adsorbing organic fluorine compounds of the present invention has a BET specific surface area of ​​1000 to 2000 m². 2 The BET specific surface area is calculated by measuring the nitrogen adsorption isotherm at 77K and performing a multi-point analysis based on the BET formula, and then extracting the value from the straight line in the relative pressure region of 0.05 to 0.3 of the resulting curve. It is used as an indicator of the amount of pores formed in activated carbon. A larger amount of pores in activated carbon (larger BET specific surface area) means a higher degree of activation, and since it can adsorb more of the target adsorbent, the adsorption performance of activated carbon can be defined by the BET specific surface area. If the BET specific surface area is too small, the adsorption performance will be insufficient, and if the BET specific surface area is too large, the packing density will deteriorate and the pore volume will increase, which may reduce the strength. By having an appropriate BET specific surface area, activated carbon adsorbents with excellent strength and adsorption performance can be obtained.

[0052] In the activated carbon adsorbent for adsorbing organic fluorine compounds of the present invention, it is preferable that the total pore volume is 0.4 to 1.0 ml / g and the packing density is 0.3 to 0.6 g / ml. The total pore volume can be used as an indicator of the adsorption and desorption performance of activated carbon from a different viewpoint than the BET specific surface area, and the total pore volume (cm³) can be determined by the BET method from the nitrogen gas adsorption isotherm of the activated carbon. 3The packing density ( / g) was calculated. The packing density was measured in accordance with JIS K 1474 (2014). Packing density can be used as an indicator of the adsorption and desorption performance of activated carbon from a different perspective than BET specific surface area and total pore volume. If the total pore volume is too small or the packing density is too large, the adsorption performance will be insufficient, and if the total pore volume is too large or the packing density is too small, the strength may decrease. By having an appropriate total pore volume and packing density, an activated carbon adsorbent with excellent strength and adsorption performance can be obtained.

[0053] In the activated carbon adsorbent for adsorbing organic fluorine compounds of the present invention, the average particle size is preferably 50 to 200 μm. This average particle size is the particle size at 50% of the integrated value of the particle size distribution determined by the laser diffraction-scattering method using a laser light scattering particle size distribution analyzer. If the average particle size is too small, it will increase the flow resistance when the material is packed into a column or the like and the sample is passed through, making clogging more likely. If it is too large, the contact efficiency with the sample will decrease, which may reduce the adsorption of the target substance to the activated carbon adsorbent. By adjusting the activated carbon to an appropriate average particle size, the contact efficiency with the sample will be improved, and pressure loss and clogging will be less likely to occur when the material is packed into a column or the like and the sample is passed through.

[0054] In the activated carbon adsorbent for adsorbing organic fluorine compounds of the present invention, the average pore diameter is preferably 1.60 to 2.00 nm. The average pore diameter is used as one of the indicators of the size of the substance that the activated carbon can adsorb and is measured by the BET method. Specifically, assuming the shape of the pores is cylindrical, the nitrogen adsorption isotherm at 77 K is measured, and the total specific surface area (m²) obtained from the above measurement is calculated. 2 It is calculated using the following formula (iii) with the values ​​of ( / g) and total pore volume (mL / g).

[0055]

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[0056] If the average pore diameter is too small, the adsorption performance of organofluorine compounds may decrease. If the average pore diameter is too large, unintended substances may be adsorbed unnecessarily, potentially blocking the pores for adsorbing organofluorine compounds and reducing adsorption performance. Activated carbon with an average pore diameter suitable for the size of the target adsorbent, the organofluorine compound, can smoothly adsorb organofluorine compounds.

[0057] Furthermore, for activated carbon adsorbents used for adsorbing organic fluorine compounds, it is preferable that the sum of the mesopore volumes is 0.030 to 0.300 ml / g. The sum of the mesopore volumes is the volume of pores (mesopores) with a pore diameter of 2 to 50 nm, and is calculated by measuring the nitrogen adsorption isotherm at 77 K and performing analysis by the DH method. The mesopore volume is related to the organic fluorine adsorption capacity in the presence of impurities. If the sum of the mesopore volumes is too small, the development of the mesopores may be insufficient, making it impossible to properly adsorb organic fluorine compounds, and the adsorption performance may decrease. If the sum of the mesopore volumes is too large, there is a risk of unintended adsorption of substances other than the target substance. By having an appropriate sum of mesopore volumes, organic fluorine compounds can be adsorbed more efficiently even in the presence of impurities.

[0058] Furthermore, for activated carbon adsorbents used for adsorbing organic fluorine compounds, a crushing strength of 0.20 to 2.00 N / particle is preferable. Crushing strength is the maximum force required to break a single activated carbon particle. Crushing strength can be used as an indicator of the hardness of the activated carbon adsorbent. If the crushing strength is too low, the activated carbon adsorbent may become brittle and easily crushed. If it is too high, it generally means that the activation has not progressed sufficiently and that there are insufficient pores necessary for adsorbing organic fluorine compounds. By having an appropriate crushing strength, an activated carbon adsorbent with superior strength can be obtained.

[0059] For activated carbon adsorbents used for adsorbing organofluorine compounds, the surface oxide content is preferably 0.80 meq / g or less, more preferably 0.50 meq / g or less, and even more preferably 0.20 meq / g or less. The surface oxide content is used as an indicator of the amount of acidic functional groups on the activated carbon surface. The surface oxide content of activated carbon affects the adsorption performance and can be determined by applying Boehm's method. For example, it can be determined by shaking activated carbon in a 0.05N sodium hydroxide aqueous solution, filtering the filtrate, and then titrating the filtrate with 0.05N hydrochloric acid to obtain the amount of sodium hydroxide.

[0060] When the amount of surface oxides in activated carbon increases, the affinity between activated carbon and water increases, relatively weakening the hydrophobic interaction with organofluorine compounds, which tends to reduce the adsorption performance of organofluorine compounds. For example, if the amount of surface oxides is low, even activated carbon with a small specific surface area and few pores can adsorb a certain amount of organofluorine compounds. Conversely, even if the amount of surface oxides is high, activated carbon with a large specific surface area and many pores can adsorb a certain amount of organofluorine compounds. Therefore, if the amount of surface oxides is within the above range, organofluorine compounds can be adsorbed more effectively.

[0061] The activated carbon adsorbent for adsorbing organofluorine compounds of the present invention suppresses the influence of activated carbon-derived fluorine components on the measurement results when performing low-concentration analysis of fluorine components, such as measuring the total fluorine concentration in a sample with a low fluorine concentration as a quantitative measurement of organofluorine compounds, and in particular, the fluorine content in the activated carbon is less than 1000 ng / g.

[0062] The fluorine content in activated carbon is a value determined by combustion ion chromatography (CIC), and corresponds to the total amount of fluorine contained in the activated carbon itself (activated carbon F blank). Combustion ion chromatography is a method in which the gas generated by burning the object to be measured is absorbed into an absorption solution, and the target component is measured by ion chromatography. Therefore, the fluorine content in activated carbon is determined by combustion ion chromatography, and the fluorine component (F blank) contained in the gas generated by burning the activated carbon is determined.- This is obtained by measuring the fluorine content in activated carbon. If the fluorine content in activated carbon is too high, the fluorine component in the activated carbon may also be reflected in the measurement results when analyzing low concentrations of organofluorine compounds adsorbed by the activated carbon, potentially hindering accurate measurement. If the fluorine content in the activated carbon is less than 1000 ng / g, the influence of fluorine components derived from the activated carbon on the measurement results can be suppressed, allowing for highly accurate analysis of low concentrations of organofluorine compounds adsorbed by the activated carbon.

[0063] In the activated carbon adsorbent for adsorbing organic fluorine compounds of the present invention, the total amount of fluorine contained in the activated carbon raw material (raw material F blank) is preferably 1000 ng / g or less, and more preferably 500 ng / g or less. If the fluorine content in the activated carbon raw material is too high, the fluorine content in the produced activated carbon may become too high. If the fluorine content in the activated carbon raw material is low, it becomes easier to reduce the total amount of fluorine contained in the produced activated carbon. In activated carbon raw materials, naturally derived raw materials such as coconut shells and charcoal generally tend to absorb and accumulate fluorine components from the environment, resulting in a high fluorine content. Therefore, by using artificially derived raw materials such as phenolic resin, it becomes easier to obtain a total fluorine content within the above range.

[0064] In the activated carbon adsorbent for adsorbing organofluorine compounds of the present invention, it is preferable that the thermogravimetric reduction rate of the activated carbon raw material (raw material TG reduction rate) is 50% or less. The raw material TG reduction rate can be used as an indicator of the carbonization yield of the activated carbon raw material, and a lower raw material TG reduction rate indicates a higher carbonization yield. A low raw material TG reduction rate makes it difficult for the fluorine component in the activated carbon raw material to be concentrated, so it is thought that the fluorine content in the activated carbon (activated carbon F blank) tends to be low. The raw material TG reduction rate is calculated from the following formula (iv) using the weight loss amount when heated from 100°C to 900°C measured under predetermined conditions. If the raw material TG reduction rate is too high, the carbonization yield may worsen and the fluorine content in the activated carbon may increase.

[0065]

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[0066] In the activated carbon adsorbent for adsorbing organic fluorine compounds of the present invention, the theoretical total fluorine content (carbide-equivalent F blank), obtained by converting the carbonized activated carbon raw material to carbide, is preferably 1200 ng / g or less, and more preferably 500 ng / g or less. The carbide-equivalent F blank is calculated from the following formula (v) using the raw material F blank and the raw material TG reduction rate, which is an indicator of the sensitization yield of the activated carbon raw material. If the carbide-equivalent F blank is too high, there is a risk that the fluorine content in the produced activated carbon will be too high. If the carbide-equivalent F blank is low, it becomes easier to reduce the total fluorine content contained in the produced activated carbon.

[0067]

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[0068] In the activated carbon adsorbent for adsorbing organic fluorine compounds of the present invention, when the fluorine content in the activated carbon (activated carbon F blank) is at a low level, the effective total amount of fluorine contained in the activated carbon (corrected F blank) is preferably 200 ng / g or less, and more preferably 100 ng / g or less. The corrected F blank is the value obtained by subtracting the amount of fluorine components present in the measurement environment such as the equipment and piping (equipment-derived F blank) from the activated carbon F blank to obtain the effective fluorine content in the activated carbon. When measuring this corrected F blank, the lower the value of the activated carbon F blank, the greater the influence of fluorine components originating from the equipment, etc., so it is preferable to target activated carbon with an activated carbon F blank of less than 500 ng / g. If the corrected F blank is too high, the effective fluorine content will be high, and it may not be possible to obtain activated carbon with a low level of fluorine. If the corrected F blank is low, the effective fluorine content in the activated carbon will be extremely low, so activated carbon suitable for low-concentration analysis of organic fluorine compounds can be obtained.

[0069] As described above, the activated carbon adsorbent for adsorbing organic fluorine compounds of the present invention is an activated carbon obtained by carbonizing a phenol resin as an activated carbon raw material under nitrogen flow and then activating it, and having a BET specific surface area of ​​1000 to 2000 m². 2The fluorine content is less than 1000 ng / g, as determined by combustion ion chromatography, indicating a relatively small amount of fluorine components derived from activated carbon. Therefore, for example, when performing low-concentration analysis of fluorine components in samples with low fluorine concentrations, the influence of fluorine components derived from activated carbon on the measurement results is effectively suppressed, making it possible to appropriately analyze trace amounts of organic fluorine, such as PFAS, contained in samples containing impurities such as tap water and environmental water.

[0070] Furthermore, by using a composite phenolic resin derived from artificial raw materials as the phenolic resin raw material for activated carbon, it becomes easier to reduce the total amount of fluorine contained in the activated carbon. For example, by using ion-exchanged water as the water used to dilute the raw materials in the manufacturing process of the composite phenolic resin, it becomes even easier to reduce the total amount of fluorine in the activated carbon. In addition, by performing high-temperature heat treatment after the activation of the activated carbon raw material to thermally decompose the organic fluorine compounds in the activated carbon, it becomes possible to further reduce the total amount of fluorine in the activated carbon.

[0071] This activated carbon adsorbent for adsorbing organic fluorine compounds can be used as activated carbon for organic fluorine compound analysis to adsorb organic fluorine compounds from a sample and quantify them, thereby enabling the quantitative determination of low concentrations of organic fluorine compounds present in the sample.

[0072] Figure 1 is a schematic diagram showing one embodiment of quantitative measurement using the activated carbon adsorbent for adsorption of organofluorine compounds of the present invention. In the figure, reference numeral 11 denotes a front column packed with the activated carbon adsorbent, 12 denotes a rear column connected to the front column 11 and also packed with the activated carbon adsorbent, 20 denotes a combustion device, 25 denotes an absorption tank packed with an absorption liquid such as ultrapure water, and 30 denotes an ion chromatograph analyzer.

[0073] As shown in Fig. 1, activated carbon adsorbents for adsorbing organic fluorine compounds are filled in a predetermined amount in a front-stage column 11 and a rear-stage column 12 connected in series, and a sample containing an organic fluorine compound is passed through from the front-stage column 11 side, and the organic fluorine compound in the sample is adsorbed by the activated carbon adsorbent in each column 11, 12. After the adsorption of the organic fluorine compound, a cleaning liquid such as an aqueous NaNO3 solution is passed through from the front-stage column 11 side to clean the activated carbon adsorbent in each column 11, 12.

[0074] Next, the activated carbon adsorbent after adsorbing the organic fluorine compound is put into the combustion device 20 from each column, preheated at a predetermined temperature and time under the flow of argon (Ar), and then combusted and decomposed at a predetermined combustion temperature and time under the flow of oxygen (O2), and the generated gas containing fluorine components (F - ) is introduced from the combustion device 20 into the absorption tank 25, and the fluorine component in the gas is absorbed by the absorption liquid 26 in the absorption tank 25. Then, the fluorine content in the absorption liquid 26 is measured by an ion chromatograph analyzer 30, and the total amount of fluorine adsorbed by the activated carbon adsorbent is calculated.

[0075] In this quantitative measurement, when adsorbing the organic fluorine compound in the sample with an activated carbon adsorbent, it is preferable that the recovery rate of the organic fluorine compound in the front-stage column is high. The recovery rate of the organic fluorine compound can be expressed, for example, by the column breakthrough rate (%) of the front-stage column. The column breakthrough rate is the ratio of the adsorbed substance that passed through to the rear-stage column side without being adsorbed in the front-stage column, and is calculated by dividing the fluorine adsorption amount of the rear-stage column by the total amount of fluorine adsorbed in the front-stage column and the rear-stage column. The lower the column breakthrough rate, the higher the recovery rate of the organic fluorine compound tends to be, and when the column breakthrough rate increases, there is a concern about the decrease in the recovery rate of the organic fluorine compound. Therefore, the column breakthrough rate of the front-stage column is preferably 10% or less.

[0076] The column breakthrough rate of the preceding column tends to improve as the activation level of the activated carbon adsorbent increases, such as by increasing the BET specific surface area, average pore diameter, and the sum of the mesopore volume, or by reducing the amount of surface oxides. Therefore, it is preferable to adjust the above-mentioned properties of the activated carbon adsorbent within a range that does not impair the effects of each property. [Examples]

[0077] [Production of activated carbon] In preparing the activated carbon for prototypes 1-11, coal was used for prototype 1, coconut shell for prototype 2, sawdust for prototype 3, and spherical phenolic resin for prototypes 4-11, each as the activated carbon raw material. The activated carbon for prototypes 1-11 was obtained by carbonizing and activating the raw materials according to the procedure described later. The raw materials and production conditions for the activated carbon for prototypes 1-11 are shown in Tables 1-3 below. In the tables, the degree of activation is defined as "high" when the total pore volume is 0.6 ml / g or more, and "low" when it is less than 0.6 ml / g.

[0078] [Prototype Example 1] Prototype Example 1 is a powdered activated carbon made from coal (manufactured by Futamura Chemical Co., Ltd.; "GB").

[0079] [Prototype Example 2] Prototype example 2 is a powdered activated carbon made from coconut shells (manufactured by Futamura Chemical Co., Ltd.; "CB").

[0080] [Prototype Example 3] Prototype example 3 is a powdered activated carbon made from sawdust (manufactured by Futamura Chemical Co., Ltd.; "P").

[0081] [Prototype Example 4] Prototype Example 4 is an activated carbon obtained by using tap water as the raw material dilution water, a phenol resin made by compounding novolac resin and resol resin as the activated carbon raw material, heating this activated carbon raw material to 500-700°C with air flowing through it to form a carbonized substance, and then heating and holding the carbonized substance to around 850-950°C to activate it to a high degree of activation.

[0082] [Prototype Example 5] Prototype Example 5 uses tap water as the raw material dilution water, and a phenol resin made by compounding novolac resin and resol resin is used as the raw material for activated carbon. This activated carbon raw material is heated to 500-700°C in an inert atmosphere of high-concentration nitrogen (oxygen concentration less than 10%) to form a carbide, and the carbide is heated and held at around 850-950°C. Tap water is used as the activation introduction water, and steam is introduced to activate the activated carbon at a low degree.

[0083] [Prototype Example 6] Prototype Example 6 is activated carbon obtained by modifying Prototype Example 5 to carbonize under a slightly activated atmosphere of low nitrogen concentration (oxygen concentration of approximately 10-18%) to achieve a higher degree of activation, while keeping all other aspects the same.

[0084] [Prototype Example 7] Prototype Example 7 is activated carbon obtained by modifying the process from Prototype Example 6, by performing high-temperature heat treatment at a processing temperature of 1000°C for a processing time of 2 hours after activation, while keeping all other conditions the same.

[0085] [Prototype Example 8] Prototype Example 8 is an activated carbon obtained by modifying Prototype Example 7 by activating it at a lower degree under a slightly activated atmosphere of low-concentration nitrogen without using activated water, while keeping everything else the same.

[0086] [Prototype Example 9] Prototype Example 9 is an activated carbon obtained by modifying Prototype Example 8 by using ion-exchanged water as the raw material dilution water and a phenol resin, which is a composite of novolac resin and resol resin, as the activated carbon raw material, while keeping everything else the same.

[0087] [Prototype Example 10] Prototype Example 10 is activated carbon obtained by modifying Prototype Example 9, except that it is carbonized under an inert atmosphere of high-concentration nitrogen, ion-exchanged water is used as the activation water, and steam is introduced to activate it, while all other aspects remain the same.

[0088] [Prototype Example 11] Prototype Example 11 is activated carbon obtained by modifying Prototype Example 10 to activate it to a higher degree, while keeping all other aspects the same.

[0089] [Table 1]

[0090] [Table 2]

[0091] [Table 3]

[0092] [Measurement of activated carbon] For the activated carbon prototypes 1-11, the following parameters were measured: average particle size, packing density, crushing strength, surface oxide content, BET specific surface area, total pore volume, average pore diameter, sum of mesopore volume, raw material F blank, raw material TG reduction rate, carbide-equivalent F blank, activated carbon F blank, corrected F blank, PFOA recovery rate, and pre-column breakthrough rate. The results for each measurement are shown in Tables 4-6 below.

[0093] [Average particle size] The average particle diameter (μm) was measured using a laser light scattering particle size distribution analyzer (Shimadzu Corporation; "SALD3000S"), and the particle size at 50% of the cumulative value in the particle size distribution determined by the laser diffraction-scattering method was used.

[0094] [Filling density] The packing density (g / ml) was measured in accordance with JIS K 1474 (2014).

[0095] [Crushing strength] The crushing strength (N / particle) was determined by measuring the maximum crushing strength at 10 or more points during the time it took for the activated carbon particles to break, using a digital force gauge (manufactured by IMADA Corporation; "ZTA-50N"). The average of these 10 points, excluding the maximum, minimum, and outlier values, was used as the crushing strength (N / particle).

[0096] [Surface oxide amount] The surface oxide content (meq / g) corresponds to the total amount of acidic groups on the activated carbon surface. The surface oxide content for each of the prototype examples 1 to 11 was measured using Boehm's method, by shaking the activated carbon in a 0.05 N sodium hydroxide aqueous solution, filtering the solution, and titrating the filtrate with a 0.05 N hydrochloric acid aqueous solution.

[0097] [BET specific surface area] BET specific surface area (m 2 The total specific surface area (m²) was determined by measuring the nitrogen adsorption isotherm at 77K using an automatic specific surface area / pore distribution analyzer (Microtrac-Bell Co., Ltd.; "BELSORP-miniII") and then using the BET method. 2 We calculated / g) for each.

[0098] [Total pore volume] Total pore volume (cm³) 3 The total pore volume (cm³ / g) was calculated using the BET method against the nitrogen adsorption isotherm obtained in the above measurement. 3 We calculated / g) for each.

[0099] [Average pore diameter] The average pore diameter (nm) is calculated by the BET method from the nitrogen adsorption isotherm obtained by the BET specific surface area measurement described above, and the pore volume (cm³) is calculated from that isotherm. 3 The specific surface area (m²) obtained from the BET specific surface area measurement above is calculated for each of them. 2 The value of ( / g) and pore volume (cm³) 3 The value of / g) was used to obtain the result from equation (iii) above.

[0100] [Sum of mesopore volume] Sum of mesopore volume (cm 3 The dV / dD value in the pore diameter range of 2 to 50 nm was determined by analyzing the nitrogen gas adsorption isotherm using the DH method. Note that the diameter range of 2 to 50 nm in the analysis software is 2.43 to 51.38 nm.

[0101] [Raw material F blank] The raw material F blank (ng / g) represents the total amount of fluorine contained in the activated carbon raw material. Approximately 50 mg each of the activated carbon raw materials (coal, coconut shell, sawdust, phenolic resin fiber) used in prototype examples 1-11 were packed into two columns. The columns were then burned at over 950°C for 10 minutes using a combustion device (manufactured by Nitto Seikou Analytech Co., Ltd.; "AQF-5000H"). Ultrapure water was then used as the absorption liquid to absorb the gas generated by the combustion, thereby removing the fluorine component (F). - The sample was recovered and the total fluorine content was measured by ion chromatography.

[0102] [Raw material TG reduction rate] The raw material TG reduction rate (%) is the rate of reduction of the activated carbon raw material by thermogravimetric analysis. Using a differential thermal-thermogravimetric analyzer (manufactured by Rigaku Corporation; "Thermo plus EVO2"), approximately 10 mg of the activated carbon raw materials (coal, coconut shell, sawdust, phenolic resin fiber) used in prototype examples 1 to 11 were heated to 100°C under a nitrogen flow and held for 10 minutes, then heated to 900°C and held for 10 minutes. The amount of weight loss when heating and holding from 100°C to 900°C under the above conditions was measured, and the raw material TG reduction rate was calculated using the above formula (iv).

[0103] [Carbide equivalent F blank] The carbide-equivalent F blank (ng / g) is the theoretical total fluorine content in carbide terms. Using the raw material F blanks and raw material TG reduction rates for prototype examples 1 to 11 calculated above, the carbide-equivalent F blank was calculated using the above formula (v).

[0104] [Activated Carbon F Blank] The activated carbon F blank (ng / g) represents the total amount of fluorine contained in the activated carbon. Approximately 50-80 mg of the activated carbons from prototype examples 1-11 were weighed and packed into two columns. The columns were then burned at over 950°C for 10 minutes using a combustion device (manufactured by Nitto Seikou Analytech Co., Ltd.; "AQF-5000H"). Ultrapure water was then used as the absorption liquid to absorb the gas generated by the combustion, thereby removing the fluorine component (F). - The sample was recovered and the total fluorine content was measured by ion chromatography.

[0105] [Correction F Blank] The corrected F blank (ng / g) represents the actual total amount of fluorine contained in the activated carbon. Two empty columns (without sample) are used and burned at over 950°C for 10 minutes in a combustion device (manufactured by Nitto Seikou Analytech Co., Ltd.; "AQF-5000H"). Ultrapure water is then used as the absorption liquid to absorb the gas generated by the combustion and extract the fluorine component (F - The activated carbon samples were collected and the total fluorine content was measured by ion chromatography, and this was defined as the total fluorine content originating from the equipment and piping (equipment-derived F blank). For the activated carbon samples from prototype examples 1 to 11 in which the activated carbon F blank was less than 500 ng / g, the actual total fluorine content contained in the activated carbon was calculated by subtracting the measured equipment-derived F blank value from the activated carbon F blank value.

[0106] [PFOA recovery rate] For the activated carbons from prototype examples 1 to 11, PFOA addition and recovery tests were conducted using real-world water for activated carbons with an activated carbon F blank value of less than 1000 ng / g. River water was used as the real-world water, and a water sample prepared by dissolving PFOA to a concentration of 100 μg / L in fluorine equivalent was used as the standard solution. Next, 30-50 mg of activated carbon was packed into each of two columns, and both ends were blocked with ceramic wool to create activated carbon columns. Two of these columns were connected in series, and 100 ml of standard solution was passed through them at a flow rate of 3 ml / min using an adsorption device (Nitto Seikou Analytech Co., Ltd.; "TXA-04"). Then, 25 ml of 0.01 M NaNO3 aqueous solution was passed through at a flow rate of 3 ml / min to wash away inorganic fluorine. After that, 2.5 ml of ultrapure water was passed through with a syringe to wash away the Na, and 5 ml of air was passed through with a syringe to push out the water. Next, the total amount of fluorine adsorbed on the activated carbon of the upstream and downstream columns was calculated by measuring one column each in the upper and lower stages using a combustion device (Nitto Seikou Analytech Co., Ltd.; "AQF-5000H") with an electrical temperature set to 950°C for a combustion time of 15 minutes. The PFOA recovery rate (%) was calculated by dividing the total amount of fluorine after adsorption by the total amount of fluorine before adsorption.

[0107] [Preceding column breakthrough rate] For the activated carbons from prototype examples 1 to 11, the percentage of PFOA that passed from the upstream column to the downstream column (column breakthrough rate) was calculated for activated carbons with an activated carbon F blank value of less than 1000 ng / g. The column breakthrough rate was calculated by dividing the amount of fluorine adsorbed in the downstream column by the total amount of fluorine adsorbed in the upstream and downstream columns for the two columns used to measure the PFOA recovery rate.

[0108] [Table 4]

[0109] [Table 5]

[0110] [Table 6]

[0111] [Results and Discussion] In prototypes 1-3, the activated carbon raw material was derived from natural sources (coal, coconut shell, sawdust), while in prototypes 4-11, the activated carbon raw material was derived from artificial sources (phenolic resin). As shown in Tables 4-6, when comparing the activated carbon blank (total fluorine content in activated carbon) in prototypes 1-3 with those in prototypes 4-11, the activated carbon blank in prototypes 1-3 had an extremely high value. Similarly, when comparing the raw material blank (total fluorine content in activated carbon raw materials), the value was also extremely high in prototypes 1-3.

[0112] Since naturally derived raw materials tend to contain more impurities compared to artificially derived raw materials, it is thought that the total amount of fluorine contained in the raw materials themselves is higher, and therefore the total amount of fluorine in the resulting activated carbon is also relatively higher. Furthermore, the quality of naturally derived raw materials varies greatly depending on the origin and time of year, making purity control difficult. For this reason, artificially derived raw materials are more suitable as activated carbon raw materials because it is easier to produce activated carbon with less fluorine content derived from the activated carbon than from naturally derived raw materials. However, in the case of naturally derived raw materials, as seen in prototype examples 2 and 3, the rate of reduction of raw material TG is high, meaning the carbonization yield is low, so it is thought that the total amount of fluorine derived from the activated carbon is largely due to the total amount of fluorine in the activated carbon raw material (raw material F blank).

[0113] Next, we compare prototypes 4-11, where the activated carbon raw material is of artificial origin. In prototypes 4-11, the activated carbon F blank exceeded 1000 ng / g in prototype 4, while it was less than 1000 ng / g (less than 700 ng / g) in prototypes 5-11. Comparing prototype 4 with prototypes 5-11, it was found that in prototype 4, the activated carbon raw material was carbonized under atmospheric flow, whereas in prototypes 5-11, the activated carbon raw material was carbonized under nitrogen flow. In prototype 4, it is thought that atmospheric fluorine components were mixed in during carbonization, resulting in a high activated carbon F blank. Therefore, it is thought that by carbonizing the activated carbon raw material under nitrogen inflow, as in prototypes 5-11, the mixing of atmospheric fluorine components can be suppressed, and activated carbon with a low activated carbon F blank can be obtained.

[0114] Comparing prototype example 6, which had not undergone high-temperature heat treatment at a similar activation level, with prototype example 7, which had undergone high-temperature heat treatment, prototype example 7 had a lower activated carbon F blank value than prototype example 6. From this, it can be concluded that the decomposition of organofluorine compounds in the activated carbon was promoted by the application of high-temperature heat treatment, thereby reducing the activated carbon F blank.

[0115] Examples 8 and 9 are examples of activated carbon with an extremely low total fluorine content (activated carbon F blank less than 500 ng / g). Comparing example 8, which used tap water as the raw material dilution water during the production of the activated carbon raw material, with example 9, which used ion-exchanged water, example 9 had a lower activated carbon F blank than example 8. In example 8, it is thought that the fluorine component in the tap water used as the raw material dilution water was mixed in, resulting in a higher activated carbon F blank. Therefore, it is thought that by using ion-exchanged water as the raw material dilution water, as in example 9, the mixing of fluorine components originating from the raw material dilution water can be suppressed, and activated carbon with a low activated carbon F blank can be obtained.

[0116] Furthermore, in prototypes 9-11, the corrected F blank, which represents the actual total amount of fluorine in the activated carbon, was extremely low. This indicates that in the activated carbon of prototypes 9-11, there was a greater amount of fluorine contamination from the equipment than from the activated carbon itself. Since the amount of fluorine contamination from the equipment is usually very small, this shows that the total amount of fluorine in the activated carbon of prototypes 9-11 is at a considerably low level.

[0117] When comparing Prototype Example 5, which used tap water as the raw material dilution water and activation introduction water at a similar activation level, with Prototype Example 10, which used ion-exchanged water as the raw material dilution water and activation introduction water and underwent high-temperature heat treatment, the activated carbon F blank in Prototype Example 10 was lower than that in Prototype Example 5. It is thought that in Prototype Example 5, fluorine components from the tap water used as the raw material dilution water and activation introduction water were mixed in, resulting in a higher activated carbon F blank than in Prototype Example 10. Therefore, it is thought that by using ion-exchanged water as the raw material dilution water and activation introduction water, as in Prototype Example 10, the mixing of fluorine components originating from water (dilution water and activation introduction water) is suppressed, and activated carbon with a low activated carbon F blank can be obtained. Furthermore, the reduction in activated carbon F blank was greater when comparing Prototype Example 7 and Prototype Example 10 (water quality of raw material dilution water and activation introduction water) compared to Prototype Example 6 and Prototype Example 7 (with or without heat treatment), indicating that using high-purity water has a greater contribution to the activated carbon F blank compared to the effect of high-temperature heat treatment.

[0118] Next, we will examine the adsorption performance of prototypes 5-11 for organofluorine compounds, where the activated carbon F blank was less than 1000 ng / g. All prototypes 5-11 showed high PFOA recovery rates of approximately 90% or more. The BET specific surface area, which is considered to contribute to the adsorption performance of organofluorine compounds, was 1000 m² for all prototypes 5-11. 2 It was above / g.

[0119] In prototype example 5, the activated carbon raw material was activated by water vapor, resulting in a small mesopore volume. This suggests that water vapor activation facilitates the development of smaller pore diameters suitable for PFOA adsorption, while hindering mesopore development. In this prototype example 5, the activated carbon showed a high PFOA recovery rate, but the column tended to have a relatively high breakthrough rate.

[0120] On the other hand, in prototype example 6, where the degree of steam activation was increased, the PFOA recovery rate was high and the column breakthrough rate was low. From this, it can be concluded that increasing the degree of steam activation can increase the PFOA recovery rate while lowering the column breakthrough rate.

[0121] In prototype example 9, the activated carbon raw material was gas-activated, resulting in a larger average pore size. This suggests that gas activation tends to result in larger pore sizes compared to steam activation. Therefore, although the PFOA recovery rate is slightly reduced, PFOA is more likely to penetrate the pores, leading to a lower column breakthrough rate even at low activation levels.

[0122] In prototype example 10, using a high-concentration nitrogen purge gas to create an inert atmosphere resulted in a lower surface oxide content compared to prototype example 9, and a significant improvement in PFOA adsorption rate. Furthermore, in prototype example 11, which involved further activation from prototype example 10, the column breakthrough rate was better compared to prototype example 10, resulting in an activated carbon adsorbent with a lower activated carbon F blank and superior PFAS adsorption capacity. [Industrial applicability]

[0123] The activated carbon adsorbent for adsorbing organic fluorine compounds of the present invention has a relatively low amount of fluorine components derived from activated carbon, and therefore can effectively suppress the influence of fluorine components derived from activated carbon on the measurement results, such as when performing low-concentration analysis. For this reason, it can be suitably used as an activated carbon adsorbent for analyzing trace amounts of organic fluorine, such as PFAS, contained in samples containing impurities such as tap water and environmental water. [Explanation of Symbols]

[0124] 11 Pre-column 12 Post-column 20 Combustion device 25 Absorption tanks 26 Absorbent solution 30 Ion Chromatography Analyzer

Claims

1. Using phenolic resin as the raw material for activated carbon, The activated carbon is obtained by carbonizing the activated carbon raw material under nitrogen flow and then activating it, BET specific surface area is 1000-2000 m² ２ / g, The fluorine content determined by combustion ion chromatography is less than 1000 ng / g. An activated carbon adsorbent for adsorbing organic fluorine compounds, characterized by the following features.

2. The activated carbon adsorbent for adsorbing organofluorine compounds according to claim 1, wherein the total pore volume of the activated carbon is 0.4 to 1.0 ml / g and the packing density is 0.3 to 0.6 g / ml.

3. The activated carbon adsorbent for adsorbing organic fluorine compounds according to claim 1 or 2, wherein the average particle size of the activated carbon is 50 to 200 μm.

4. The activated carbon adsorbent for adsorbing organofluorine compounds according to claim 1 or 2, wherein the phenol resin is a composite phenol resin obtained by combining a novolac resin and a resol resin.

5. The activated carbon adsorbent for adsorbing organofluorine compounds according to claim 3, wherein the phenol resin is a composite phenol resin obtained by combining a novolac resin and a resol resin.

6. The activated carbon adsorbent for adsorbing organic fluorine compounds according to claim 1 or 2, wherein the activated carbon adsorbent for adsorbing organic fluorine compounds is activated carbon for analyzing organic fluorine compounds for quantitative measurement after adsorbing organic fluorine compounds from a sample.

7. The activated carbon adsorbent for adsorbing organic fluorine compounds according to claim 3, wherein the activated carbon adsorbent for adsorbing organic fluorine compounds is activated carbon for analyzing organic fluorine compounds for adsorbing organic fluorine compounds from a sample and quantitatively measuring them.

8. The activated carbon adsorbent for adsorbing organic fluorine compounds according to claim 4, wherein the activated carbon adsorbent for adsorbing organic fluorine compounds is activated carbon for analyzing organic fluorine compounds for adsorbing organic fluorine compounds from a sample and quantitatively measuring them.

9. The activated carbon adsorbent for adsorbing organic fluorine compounds according to claim 5, wherein the activated carbon adsorbent for adsorbing organic fluorine compounds is activated carbon for analyzing organic fluorine compounds for adsorbing organic fluorine compounds from a sample and quantitatively measuring them.

10. The activated carbon adsorbent for adsorbing organic fluorine compounds according to claim 1 or 2, wherein the activated carbon is spherical activated carbon.

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