Active carbon for adsorbing perfluorooctanoic acid

Abstract

To provide a high selective adsorptive active carbon for adsorbing perfluorooctanoic acid particularly excellent in absorptivity of PFOA in perfluoroalkyl compounds.SOLUTION: An active carbon adsorbent for adsorbing perfluorooctanoic acid (PFOA) has a BET specific surface area of 800 m2 / g or more, an average pore diameter of less than 4 nm, and a volume ratio (Vm) of a micropore volume sum (Vmic) of pores having a pore diameter of less than 2 nm in a measurement by a MP plot method and a mesopore volume (Vmet) of pores having a pore diameter of 2-50nm in a measurement by a DH plot method of 7-20.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to PFOA-adsorbing activated carbon that adsorbs PFOA and has excellent selective adsorption properties.

Background Art

[0002] Per- and polyfluoroalkyl compounds, which are one type of organic fluorine compounds, are fluorine-substituted aliphatic compounds having high thermal stability, high chemical stability, and high surface modification activity. Per- and polyfluoroalkyl compounds are widely used in industrial applications and chemical applications such as surface treatment agents, packaging materials, and liquid fire extinguishers, taking advantage of the above characteristics.

[0003] Some per- and polyfluoroalkyl compounds are very stable chemical substances, so they are difficult to decompose under natural conditions after being released into the environment. For this reason, in recent years, per- and polyfluoroalkyl compounds have been recognized as persistent organic pollutants (POPs), and perfluorooctane sulfonic 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 regulated in the Stockholm Convention on Persistent Organic Pollutants (POPs Convention) since 2010 in terms of production and use.

[0004] In particular, perfluorooctane sulfonic acid (PFOS), perfluorooctanoic acid (PFOA), and perfluorohexane sulfonic acid (PFHxS) are strongly suspected of being harmful, so their production and use are prohibited by the above-mentioned Stockholm Convention (POPs Convention) and they are subject to regulation.

[0005] Perfluoroalkyl compounds containing perfluorooctanesulfonic acid (PFOS), perfluorooctanoic acid (PFOA) (IUPAC name: 2,2,3,3,4,4,5,5,6,6,7,7,8,8,8-pentadecafluorooctanoic acid), etc. have a completely fluorinated straight-chain alkyl group and are substances represented by chemical formula (i). In addition, polyfluoroalkyl compounds refer to those in which part of the hydrogen in the alkyl group is replaced by fluorine and are substances represented by chemical formula (ii). For example, there are fluorotelomer alcohols, etc.

[0006]

Number

[0007]

Number

[0008] Thus, since per- and polyfluoroalkyl compounds continue to remain in nature (in water, soil, and the atmosphere), the establishment of a quantitative test method for per- and polyfluoroalkyl compounds is being studied. The challenge in the study of the quantitative test method is the development of a collecting material having high adsorption and desorption performance for per- and polyfluoroalkyl compounds. Water or air, which is a sample containing trace amounts of per- and polyfluoroalkyl compounds, is brought into contact with the collecting material to collect the per- and polyfluoroalkyl compounds, and the compounds adsorbed on the collecting material are desorbed into the extract by an extraction process and concentrated. After concentration, quantitative measurement can be performed with an apparatus such as LC-MS / MS or GC-MS / MS, and it becomes possible to measure the concentration of per- and polyfluoroalkyl compounds contained in the sample.

[0009] Therefore, the inventors have successfully developed activated carbon for adsorbing per- and polyfluoroalkyl compounds as a trapping material that enables accurate quantitative measurement of per- and polyfluoroalkyl compounds (see Patent Documents 1 and 2). By satisfying certain physical properties, this activated carbon enables good adsorption and desorption of per- and polyfluoroalkyl compounds, which are the measurement targets, and enables accurate quantitative measurement of these compounds.

[0010] Here, the adsorption mechanism of activated carbon is that the target substance is adsorbed by being taken into the pores formed by the activation treatment. For example, in recent years, activated carbon adsorbents have been preferably used for domestic wastewater treatment such as sewage treatment and industrial water drainage treatment. Due to its characteristics, the activated carbon adsorbent adsorbs various substances and the treated water is purified well. However, conventionally, organic substances and the like that are not harmful to the environment and remain in the treated water are also adsorbed and removed together. As a result, the treated water becomes too clean, and cases have been reported where the plankton in the coastal waters decreases and the catch decreases.

Prior Art Documents

Patent Documents

[0011]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0012] Therefore, the inventors have conducted intensive studies and derived the physical properties of an activated carbon adsorbent that can selectively adsorb specific adsorbed substances while suppressing the adsorption of active (useful) components into pores by limiting the substances to be adsorbed on the activated carbon adsorbent. As a result, it is possible to obtain treated water that removes pollutants leading to environmental pollution from domestic wastewater through wastewater treatment while leaving organic substances harmless to the ecosystem. Additionally, in the industrial field, by enabling selective adsorption of specific adsorbed substances as by-products without adsorbing chemical substances as active components in paints and chemicals, it becomes possible to comply with environmental regulations while maintaining manufacturing efficiency.

[0013] In view of the above points, the present invention particularly provides a perfluorooctanoic acid-adsorbing activated carbon with high selective adsorption performance and excellent adsorption performance for perfluorooctanoic acid (PFOA) among perfluoroalkyl compounds.

Means for Solving the Problems

[0014] That is, the first invention is an activated carbon adsorbent for adsorbing perfluorooctanoic acid (PFOA), having a BET specific surface area of 800 m 2 / g or more, an average pore diameter of less than 4 nm, and the volume ratio (V mic ) of the micropore volume sum (V met ) in pores with a pore diameter of less than 2 nm measured by the MP plot method and the mesopore volume sum (V m ) in pores with a pore diameter of 2 to 50 nm measured by the DH plot method being 7 to 20. This relates to perfluorooctanoic acid-adsorbing activated carbon.

[0015] The second invention is the perfluorooctanoic acid-adsorbing activated carbon according to the first invention, wherein the micropore volume sum (V mic ) is 0.5 cm 3 / g or more.

[0016] The third invention is the perfluorooctanoic acid-adsorbing activated carbon according to the first or second invention, which uses a synthetic resin raw material as a carbon source.

[0017] The fourth invention relates to the perfluorooctanoic acid-adsorbing activated carbon according to claim 2, wherein the synthetic resin raw material is a phenolic resin in the third invention.

Effects of the Invention

[0018] According to the perfluorooctanoic acid-adsorbing activated carbon according to the first invention, an activated carbon adsorbent for adsorbing perfluorooctanoic acid (PFOA), having a BET specific surface area of 800 m 2 / g or more, an average pore diameter of less than 4 nm, and a pore volume sum (V mic ) in pores with a pore diameter of less than 2 nm and a mesopore volume sum (V met ) in pores with a pore diameter of 2 to 50 nm measured by the DH plot method, the volume ratio (V m ) of which is 7 to 20, it is possible to selectively adsorb perfluorooctanoic acid.

[0019] According to the perfluorooctanoic acid-adsorbing activated carbon according to the second invention, in the first invention, since the micropore volume sum (V mic ) is 0.5 cm 3 / g or more, the adsorption performance of perfluorooctanoic acid is good.

[0020] According to the perfluorooctanoic acid-adsorbing activated carbon according to the third invention, in the first or second invention, since a synthetic resin raw material is used as a carbon source, it is easier to control the pore diameter distribution formed in the activated carbon than activated carbon derived from natural products.

[0021] According to the perfluorooctanoic acid-adsorbing activated carbon according to the fourth invention, in the third invention, since the synthetic resin raw material is a phenolic resin, it is easier to obtain activated carbon with developed pores that are more likely to adsorb perfluorooctanoic acid.

Embodiments for Carrying Out the Invention

[0022] The perfluorooctanoic acid-adsorbing activated carbon of the present invention is composed of fibrous activated carbon or granular activated carbon. The fibrous activated carbon is activated carbon obtained by carbonizing and activating an appropriate fiber, and examples thereof include phenolic resin-based, acrylic resin-based, cellulose-based, and coal pitch-based. The fiber length, cross-sectional diameter, etc. are appropriate.

[0023] As raw materials for granular activated carbon, in addition to natural material-derived raw materials such as wood (waste wood, thinned wood, sawdust), coffee grounds, rice husks, coconut husks, tree bark, fruit, and cellulose, there are synthetic resin raw materials such as phenolic resin-based, acrylic resin-based, and coal pitch-based. These natural material-derived raw materials are likely to develop pores by carbonization and activation. In addition, since they are secondary uses of waste, they can be procured at low cost. In addition, calcined products derived from synthetic resins such as tires, petroleum pitch, urethane resin, and phenolic resin, and even coal can be used as raw materials.

[0024] In particular, when a synthetic resin raw material is used as the raw material (carbon source) of fibrous or granular activated carbon, the synthetic resin raw material can be easily controlled in terms of the raw material, the composition of the catalyst, and the molecular structure by the polymerization reaction time, so the pore diameter formed in the activated carbon can be arbitrarily controlled, and thus it is preferably used. In addition, by adjusting the production conditions of the synthetic resin raw material in combination with the activation conditions of the activated carbon, it becomes easier to control the pore distribution formed in the activated carbon compared to natural material-derived raw materials.

[0025] The activated carbon raw material is heated and carbonized in a temperature range of 200°C to 600°C as necessary to form micropores. Subsequently, the activated carbon raw material is exposed to steam and carbon dioxide gas in a temperature range of 600°C to 1200°C for activation treatment. As a result, activated carbon with various developed pores is obtained. In addition, there is also zinc chloride activation, etc. during activation. Sequential washing is also performed.

[0026] The adsorption performance of the target adsorbed substance is defined by the physical properties of the activated carbon thus produced. In the case of an adsorbent such as activated carbon, among the pores with micro- to macro-pore diameters, there are a large number of pores of each type. Among them, depending on which range of pores is more developed, the adsorption target and performance of the activated carbon change. The basic adsorption performance of activated carbon is defined by the specific surface area, which is an index indicating the amount of pores formed in the activated carbon. In this specification, the specific surface area of each prototype example is measured by the BET method (Brunauer, Emmett, and Teller method).

[0027] In the activated carbon of the present invention, the required basic adsorption performance is exhibited by setting the specific surface area to 800 m 2 / g or more. Also, as a rough index of which of micropores, mesopores, and macropores are developed, it can also be defined by the average pore diameter. In the activated carbon of the present invention, the average pore diameter is defined as less than 4 nm.

[0028] Furthermore, the adsorption performance of the activated carbon that adsorbs perfluorooctanoic acid, which is the target adsorbed substance of the present invention, is defined by the pore diameter and its volume of the pores formed in the activated carbon. In particular, for the purpose of selectively adsorbing perfluorooctanoic acid among perfluoroalkyl compounds, the ratio of the mesopore volume of pores with a pore diameter of 2 to 50 nm (hereinafter, in this specification, pores having a pore diameter in this range are referred to as "mesopores") to the micropore volume of pores with a pore diameter of less than 2 nm (hereinafter, in this specification, pores having a pore diameter in this range are referred to as "micropores") is defined.

[0029] The activated carbon of the present invention selectively adsorbs perfluorooctanoic acid, and thus preferably adsorbs perfluorooctanoic acid while suppressing the adsorption of other components in a sample containing other components in addition to the target adsorbed substance. For example, in a water sample, such as so-called environmental water or industrial or domestic wastewater, it preferably adsorbs perfluorooctanoic acid and does not (or hardly) adsorb substances that are not harmful to the environment, such as organic substances. Further, it selectively adsorbs perfluorooctanoic acid from a sample containing a plurality of active ingredients, such as a drug, a paint, or a coating agent, and avoids the adsorption of the active ingredients.

[0030] That is, it is not the adsorption performance of perfluorooctanoic acid in purified water that does not contain impurities such as pure water, but rather it is excellent in the adsorption performance of perfluorooctanoic acid in, for example, a drug or the like containing other per- or polyfluoroalkyl compounds or the like, and does not remove other active ingredients, suppresses an increase in manufacturing cost without impairing the efficacy as a product, and can also contribute to a reduction in environmental load.

[0031] For example, other components contained in environmental water or wastewater include organic substances and metal ions. Examples of the organic substances include volatile organic substances, fulvic acid, and humic acid. In the present application, those dissolved in the water sample are referred to. In products such as drugs, examples of the active ingredients include chemical substances and the like, and per- or polyfluoroalkyl compounds other than perfluorooctanoic acid are also included. If such other components are adsorbed into the pores of the activated carbon, the active ingredients in the product will also be removed, resulting in a decrease in the manufacturing accuracy of the product or a concern about deterioration of the manufacturing efficiency.

[0032] Further, if the other component is a substance with a large molecular size, it will be adsorbed into the mesopores of the activated carbon and prevent the target adsorbed substance from reaching the micropores. Thus, there is a concern about blockage of the micropores due to the adsorption of other components into the mesopores before the target adsorbed substance reaches the micropores, which are considered effective for the adsorption of perfluorooctanoic acid. Therefore, it is considered better that the mesopores do not develop too much.

[0033] Furthermore, with respect to the micropores to which the target adsorbed substance is adsorbed, by developing them to a certain extent or more, the adsorption efficiency of perfluorooctanoic acid is improved. In particular, the sum of the micropore volumes (V mic ) is 0.5 cm 3 / g or more, preferably 0.6 cm 3 / g or more, and the adsorption performance of perfluorooctanoic acid becomes good.

[0034] Therefore, the perfluorooctanoic acid-adsorbing activated carbon of the present application defines the volume ratio (V mic ) of the sum of the micropore volumes (V met ) with a pore diameter of less than 2 nm and the sum of the mesopore volumes (V m ) with a pore diameter of 2 to 50 nm in the measurement by the DH plot method as shown in the following formula (iii). While preventing the adsorption of other components that are factors inhibiting the adsorption of the target adsorbed substance by blocking the pores of the activated carbon, good adsorption of the target adsorbed substance is made possible, and the activated carbon is provided with selective adsorption properties.

[0035]

Equation

[0036] In order to obtain the activated carbon having selective adsorption properties, the pores formed in the activated carbon are preferably controlled so that the pore diameters suitable for the target adsorbed substance are developed. Therefore, as the raw material which is the carbon source of the activated carbon, a synthetic resin raw material is preferably used. This is because since the synthetic resin has a uniform molecular structure, it is considered that the pores formed in the activated carbon are likely to be homogeneous by firing and activation. Among synthetic resins, phenolic resin is relatively inexpensive and has a high residual carbon rate as an activated carbon raw material, so it is easy to use and is preferably used.

[0037] Phenolic resin can easily control the development of pores having an arbitrary pore diameter depending on the resin composition. By using phenolic resin as the carbon source of the activated carbon of the present invention, the micropore volume (V mic ) and the mesopore volume (Vmet ) and the volume ratio (V m ) can be easily adjusted.

[0038] For the phenolic resin, formaldehyde, an emulsifier, and reaction medium water are added to and mixed with the raw material phenol, and a basic catalyst for the purpose of forming cross-links between both molecules is added. These are subjected to a dehydration condensation reaction by heating at 30 to 100 °C while being stirred, and spherical phenolic resin is synthesized. Note that the produced resin content is appropriately washed.

[0039] Instead of the phenol used in the above-described process, aromatic compounds having a hydroxyl group are also used. For example, cresol (o-, m-, p- positions), p-phenylphenol, xylenol (2,5-, 3,5-), resorcinol, various bisphenols, etc. can be mentioned. Further, instead of formaldehyde, the following aldehyde compounds are also used. Acetaldehyde, benzaldehyde, glyoxal, furfural, etc. can be mentioned.

[0040] An amine compound is used as the basic catalyst used for the synthesis of the resol resin. The amine compound is frequently used for the synthesis of the resol resin content and is suitable for obtaining a stable reaction. For example, hexamethylenetetramine (hexamine, 1,3,5,7-tetraazadamantane), triethylenetetramine (N,N'-di(2-aminoethyl)ethylenediamine) are used. In addition to these, sodium hydroxide, magnesium hydroxide, sodium carbonate, ammonia, etc. can also be mentioned as basic catalysts. The amount of the basic catalyst added in the resol resin preparation process is 1 to 10% by weight of the total charged amount during the process. The added amount depends on the type of the basic catalyst, etc.

[0041] When the activated carbon is made spherical or granular, an emulsifier is added. Due to the dispersion by the action of the emulsifier, the phenolic resin becomes granular or spherical. As the emulsifier, water-soluble polysaccharides such as hydroxyethyl cellulose and gum arabic are used. The added amount of the emulsifier is 0.1 to 5% by weight of the total charged amount. It is appropriately increased or decreased depending on the type of the emulsifier and the reaction conditions.

[0042] Since an emulsifier is added, emulsification proceeds through heating and stirring, and particulate or spherical phenol (resole) resin (phenol resin particles) is formed in the reaction solution. It is considered that the addition of the emulsifier increases the surface tension of the reaction solution containing phenol or the like, generates minute droplets, and promotes spheroidization. The desirable size of the phenol resin is particulate or spherical with an average particle diameter of 200 to 700 μm. The particle diameter within this range is sized in anticipation of the volume reduction accompanying the carbonization firing described below.

[0043] Since the above-described phenol resin is a resole resin, it is also conceivable to use a composite phenol resin with a novolak resin as a synthetic resin raw material. In that case, first, to granular phenol serving as a raw material for the phenol resin, formaldehyde and an acidic catalyst for producing a novolak resin, and an emulsifier for forming particulate or spherical shapes are added, and while stirring, it is heated to 30 to 100°C to prepare a novolak resin component. Note that reaction catalyst water is also appropriately added as needed. Thereafter, formaldehyde, an acid catalyst, and an emulsifier are added to a solution obtained by adding formaldehyde and a basic catalyst to phenol. The solution contains the novolak resin produced in the previous step and unreacted phenol. The unreacted phenol remaining in the solution, the added formaldehyde, and the added basic catalyst undergo a dehydration condensation reaction by heating at 30 to 100°C while stirring, and a resole resin component is synthesized from the unreacted phenol. Thus, a composite phenol resin containing the resole resin component synthesized in this step and the novolak resin component synthesized in the previous step is prepared. Note that the produced resin component is appropriately washed.

[0044] The phenol, alternative aromatic compounds, and alternative aldehyde compounds for formaldehyde used are the same as described above. And as the acidic catalyst, inorganic acids and organic acids are used. In addition to oxalic acid, carboxylic acids such as formic acid, dicarboxylic acids such as malonic acid, hydrochloric acid, sulfuric acid, phosphoric acid, etc. are cited as acidic catalysts.

[0045] The phenolic resin thus obtained is converted into a resin carbide after appropriate washing and drying. The phenolic resin is placed in a firing furnace such as a cylindrical retort electric furnace, and the inside of the furnace is set to an inert atmosphere such as nitrogen, argon, or helium. It is carbonized at 300 to 1000 °C, preferably 450 to 700 °C, over 1 to 20 hours to become a resin carbide.

[0046] After that, the resin carbide is placed in a heating furnace such as a rotary external heating furnace and steam-activated at 750 to 1000 °C, preferably 800 to 1000 °C, more preferably 850 to 950 °C. The activation time depends on the production scale, equipment, etc., but is 0.5 to 50 hours. Alternatively, gas activation with carbon dioxide or the like can also be used. The activated carbon after activation is washed with dilute hydrochloric acid. After washing with dilute hydrochloric acid, if necessary, the activated carbon is heat-treated and washed with water in a mixed gas of oxygen and nitrogen to remove impurities such as ash content. The residual hydrochloric acid content and the like are removed by the heat treatment.

[0047] Note that the method for producing the phenolic resin is not limited to the above method, and it may be produced using a known method. Also, in the case of producing fibrous activated carbon, the phenolic resin is formed into fibers, fired, and activated to obtain fibrous activated carbon.

[0048] In this way, by using a synthetic resin raw material whose composition of the raw material as the carbon source can be arbitrarily adjusted, the pore distribution of the activated carbon can be controlled, pores with a pore diameter suitable for the target adsorbed substance can be developed, and the development of other pores can be suppressed, thereby enabling the activated carbon to have selective adsorption properties.

Example

[0049] [Activated carbon adsorbent used] The inventors created the following prototype examples to evaluate the adsorption performance of perfluorooctanoic acid and other perfluoroalkyl compounds.

[0050] <Prototype Example 1> Spherical phenolic resin (manufactured by Lignite Co., Ltd., "LPS series") was activated at 900 °C in a steam atmosphere to obtain spherical activated carbon, which was designated as Prototype Example 1.

[0051] <Prototype Example 2> Phenol, formaldehyde (formalin), an acidic catalyst, and an emulsifier were heated and polymerized. Next, formaldehyde (formalin) and a basic catalyst were added to proceed with the reaction to obtain a composite spherical phenolic resin of novolak resin and resol resin. The obtained composite spherical phenolic resin was activated at 900 °C in a steam atmosphere to obtain spherical activated carbon, which was designated as Prototype Example 2.

[0052] <Prototype Example 3> Fibrous phenolic resin was activated at 900 °C in a steam atmosphere to obtain fibrous activated carbon, which was designated as Prototype Example 3.

[0053] <Prototype Example 4> Coconut shells were activated at 900 °C in a steam atmosphere to obtain coconut shell activated carbon, which was designated as Prototype Example 4.

[0054] <Prototype Example 5> Sawdust was impregnated with a zinc chloride solution and then activated at 600 °C to obtain woody activated carbon, which was designated as Prototype Example 5.

[0055] [Measurement of Activated Carbon] [Specific Surface Area] The specific surface area (m 2 / g) was determined by measuring the nitrogen adsorption isotherm at 77 K using an automatic specific surface area / pore size distribution measuring device "BELSORP-miniII" manufactured by MicrotracBEL Corp. and applying the BET method (BET specific surface area).

[0056] [Total Pore Volume] The pore volume (cm 3 / g) was measured by nitrogen adsorption using an automatic specific surface area / pore size distribution measuring device ("BELSORP-miniII", manufactured by MicrotracBEL Corp.).

[0057] [Average Pore Diameter] The average pore diameter (nm) was determined from Equation (iv) using the values of pore volume (cm 3 / g) and specific surface area (m 2 / g), assuming the pore shape to be cylindrical.

[0058]

Equation

[0059] 〔Sum of micropore volumes〕 The sum of micropore volumes (V mic ) was measured by nitrogen adsorption using an automatic specific surface area / pore size distribution measuring device (“BELSORP-miniII”, manufactured by MicrotracBEL Corp.) in the same manner as the total pore volume, as the sum of the pore volumes of micropores (cm 3 / g). The sum of the volumes of micropores with a pore diameter of less than 2 nm (cm 3 / g) was determined by analyzing the value of dV / dD in the range of a pore diameter of less than 2 nm from the t-plot of the nitrogen gas adsorption isotherm by the MP method.

[0060] 〔Sum of mesopore volumes〕 The sum of mesopore volumes (V met ) was measured by nitrogen adsorption in the same manner as the sum of the micropore volumes, as the sum of the pore volumes of mesopores (cm 3 / g). The sum of the volumes of mesopores with a pore diameter of 2 to 50 nm (cm 3 / g) was analyzed by the DH method from the nitrogen gas adsorption isotherm for the value of dV / dD in the range of a pore diameter of 2 to 50 nm. The diameter range of 2 to 50 nm in the analysis software is 2.43 to 51.624 nm. From this analysis result, the sum of the pore volumes of mesopores, which is the pore volume in the range of a pore diameter of 2 to 50 nm (cm 3 / g), was determined.

[0061] 〔Volume ratio〕 The volume ratio (V m ) was determined as shown in Equation (iii) by dividing the value of the above-mentioned sum of micropore volumes (V mic ) by the value of the sum of mesopore volumes (V met ).

[0062] The physical properties of the activated carbons in Prototype Examples 1 to 5 are as shown in Table 1. In order from the top of the table, specific surface area (m 2 / g), total pore volume (cm 3 / g), average pore diameter (nm), sum of micropore volumes (cm 3 / g), sum of mesopore volumes (cm 3 / g), and volume ratio.

[0063]

Table 1

[0064] [Adsorption Experiment of Perfluorooctanoic Acid in the Presence of Other Perfluoroalkyl Compounds] As perfluoroalkyl compounds, in the co - existence of perfluorooctanoic acid (PFOA), which is the target adsorbed substance, perfluorobutanoic acid (PFBA), and perfluorohexanoic acid (PFHxA), the adsorption performance of the activated carbons of each prototype example was evaluated.

[0065] Ultra - pure water was prepared, and standard reagents of PFOA, PFBA, and PFHxA were added to the ultra - pure water to prepare a test solution with the concentration of each perfluoroalkyl compound being 10 μg / L (total concentration 30 μg / L).

[0066] 0.04 mg of the activated carbon of each prototype example was added to a container containing 40 mL of the test solution, and it was shaken at 150 rpm for 24 hours at 23°C in a room using a shaker (manufactured by AS ONE Corporation). Then, the activated carbon was removed by solid - liquid separation, and a part of the solution was taken and diluted 10 - fold with methanol.

[0067] The diluted solution was quantitatively measured in MRM mode using LC - MS / MS (manufactured by Waters Japan K.K., "ACQUITY UPLC I - Class Plus Xevo TQ - S micro system") to measure the concentrations of PFOA, PFBA, and PFHxA.

[0068] Table 2 shows the removal rates (%) of target substances for Prototypes 1 to 5. Also, as an index indicating selective adsorption, the values obtained by dividing the removal rate of PFOA by the removal rate of PFBA (% / %) and the value obtained by dividing the removal rate of PFOA by the removal rate of PFHxA (% / %) are also shown together.

[0069]

Table 2

[0070] [Results and Discussion] Prototypes 1 to 4 were shown to have a higher adsorption amount of PFOA compared to the adsorption amounts of PFBA and PFHxA and to have selective adsorption properties. The activated carbon of Prototype 5 using a wood-based raw material has a large specific surface area, which is an index of the basic adsorption performance of activated carbon, because micro pores to macro pores tend to develop evenly due to the raw material characteristics. However, it is hard to say that the micro pores are particularly developed compared to meso pores and macro pores. Therefore, it cannot be said that a pore distribution suitable for the adsorption of perfluoroalkyl compounds is formed, and it is considered that the adsorption amounts of all perfluoroalkyl compounds of PFOA, PFBA, and PFHxA were low.

[0071] Next, the activated carbon of Prototype 4 using coconut shell as a raw material has a tendency for micro pores to easily develop as a characteristic of the activated carbon of coconut shell raw material. For this reason, it can be said that the pore distribution has a volume ratio (V m ) of 12.3 and more micro pores are developed compared to meso pores. Therefore, it is considered that more PFOA is adsorbed among PFOA, PFBA, and PFHxA and the result is that it has selective adsorption properties. However, since the specific surface area is relatively small, the adsorption performance as activated carbon is inferior to other prototypes, and it is considered that the removal rate of PFOA was not so high.

[0072] Prototype Examples 1 to 3 use a phenolic resin as a raw material and are examples in which micropores are more developed than mesopores. In all of them, more PFOA was adsorbed among PFOA, PFBA, and PFHxA, and as a result, the removal rate of PFOA was high. Compared with Prototype Example 5, Prototype Examples 1 to 3 showed high selective adsorption properties, and compared with Prototype Example 4, a high removal rate of PFOA was shown.

[0073] From these results, it was shown that activated carbon with more developed micropores than mesopores can have good selective adsorption properties for PFOA, and further, activated carbon with many micropores formed has high adsorption performance for PFOA. Therefore, in order to ensure good adsorption performance while having selective adsorption properties for PFOA, it was found that activated carbon with more developed micropores than mesopores and a large amount of micropores is good.

Industrial Applicability

[0074] The perfluorooctanoic acid-adsorbing activated carbon of the present invention can favorably adsorb only perfluorooctanoic acid even in the coexistence of other perfluoroalkyl compounds. Therefore, it can selectively adsorb and remove perfluorooctanoic acid, and can remove perfluorooctanoic acid, which is a regulated substance, without adsorbing other active ingredients, etc., and is expected to contribute to environmental problems.

Claims

Claim 1 An activated carbon adsorbent for adsorbing perfluorooctanoic acid (PFOA), The BET specific surface area is 800 m ２ / g or more, and having an average pore diameter of less than 4 nm, In the measurement by the MP plot method, the micropore pore volume sum (V ｍｉｃ ), and in the measurement by the DH plot method, the mesopore volume sum (V ｍｅｔ ) in pores with a pore diameter of 2 to 50 nm, and the volume ratio (V ｍ ) is 7 to 20 characterized in that it is an activated carbon for adsorbing perfluorooctanoic acid. Claim 2 The micropore volume sum (V ｍｉｃ ) is 0.5 cm ３ / g or more, and the perfluorooctanoic acid-adsorbing activated carbon according to claim 1. Claim 3 The activated carbon for adsorbing perfluorooctanoic acid according to claim 1 or 2, using a synthetic resin raw material as a carbon source. Claim 4 The activated carbon for adsorbing perfluorooctanoic acid according to claim 3, wherein the synthetic resin raw material is a phenolic resin.

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