Activated carbon for water treatment

Abstract

To provide activated carbon for treatment having excellent adsorption performance for PFAS, particularly PFOS and PFOA. Activated carbon for water treatment with a specific surface area of ​​2020-4000m2 / g, a total amount of acidic functional groups per specific surface area of ​​0.20μeq / m2 or less, and a zeta potential of -40mV or more.

Description

[Technical field]

[0001] The present invention relates to activated carbon for water treatment. [Background technology]

[0002] Perfluoroalkyl and polyfluoroalkyl compounds (hereinafter referred to as PFAS) are chemicals used in various industrial processes and consumer products, and currently, more than 4,700 different compounds are known as PFAS. In particular, PFOS (Perfluorooctane Sulfonate) and PFOA (Perfluorooctanoic Acid) are used in various products such as water repellents and fire extinguishing agents, but they have been pointed out to have problems with environmental persistence and bioaccumulation. PFOS and PFOA have also been detected in river water, seawater, and tap water, and contamination over a very wide area has become a problem. Therefore, technology to remove PFAS, especially PFOS and PFOA, has been required.

[0003] For example, in Patent Document 1, the BET specific surface area of ​​an activated carbon adsorbent is 800 m 2 20 meq / g or more or a surface oxide amount of 0.20 meq / g or less.

[0004] In Patent Document 2, the BET specific surface area of ​​the activated carbon adsorbent is 800 m 2 / g or more, the amount of surface oxide is 0.50 meq / g or less, and the sum of the micropore volumes (Vmic) of pores with diameters of 1 nm or less is 0.30 cm 3 / g or more of a per- and polyfluoroalkyl compound-adsorbing activated carbon in a water sample is disclosed.

[0005] Patent Document 3 describes an activated carbon adsorbent for adsorbing perfluoroalkyl compounds in water containing impurities, which has a pore volume sum of 0.025 cm3 in pores having a pore diameter of 2 to 50 nm as measured by a DH plot method. 3 / g or less, and the sum of the pore volumes of pores having a pore diameter of 1.5 to 2 nm is 0.014 cm when measured by the MP plot method. 3 / g or more. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] International Publication No. 2021 / 033596 [Patent Document 2] JP 2022-171711 A [Patent Document 3] International Publication No. 2022 / 255249 Summary of the Invention [Problem to be solved by the invention]

[0007] An object of the present invention is to provide an activated carbon for treatment having excellent adsorption performance for PFAS, particularly PFOS and PFOA. [Means for solving the problem]

[0008] The activated carbon of the present invention has the following composition. [1] Specific surface area is 2020~4000m 2 / g, total amount of acidic functional groups per specific surface area is 0.20 μeq / m 2 The following refers to activated carbon for water treatment with a zeta potential of -40mV or higher. [2] The activated carbon according to [1], wherein the volume of micropores having a pore diameter of 1 nm or less is less than 0.3 mL / g, and the difference between the volume of micropores having a pore diameter of 2 nm or less and the volume of mesopores having a pore diameter of 2 to 30 nm is 0.45 mL / g or less. [3] The activated carbon according to [1] or [2], having a total acidic functional group content of 0.5 meq / g or less and an oxygen content of 3.0 wt% or less. [4] The activated carbon according to any one of [1] to [3], having a micropore volume ratio calculated from the following formula (1) of 80% or less, and a mesopore volume ratio calculated from the following formula (2) of 20% or more: Micropore volume / (micropore volume + mesopore volume) × 100 (1) Mesopore volume / (micropore volume + mesopore volume) × 100 (2) [5] The activated carbon according to any one of [1] to [4], which has an adsorption ability for perfluoroalkyl compounds and polyfluoroalkyl compounds in water. [6] The activated carbon according to any one of [1] to [5], wherein the activated carbon is an alkali-activated carbon. [7] A water purifier using the activated carbon described in any one of [1] to [6]. Effect of the Invention

[0009] According to the present invention, it is possible to provide activated carbon for treatment that has excellent adsorption performance for PFAS, particularly PFOS and PFOA. Therefore, the activated carbon of the present invention is effective in removing PFAS, particularly PFOS and PFOA, present in water. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 is a graph showing the equilibrium adsorption amounts of PFOS in the examples and the comparative examples. [Diagram 2] FIG. 2 is a graph showing the PFOA equilibrium adsorption amounts in the examples and comparative examples. [Diagram 3] FIG. 3 is a graph showing the cumulative water flow rate of PFOA in the examples and the comparative examples. [Figure 4] FIG. 4 is a graph showing the cumulative free residual chlorine water flow rate in the examples and the comparative examples. [Diagram 5] FIG. 5 is a graph showing the cumulative amount of chloramine passing through in the examples and the comparative examples. [Figure 6] FIG. 6 is a graph showing the equilibrium adsorption amounts of chloroform in the examples and the comparative examples. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] As a result of extensive research, the inventors have discovered that by giving activated carbon a high specific surface area and appropriately controlling the total amount of acidic functional groups per specific surface area and the zeta potential, the adsorption performance due to the pores of the activated carbon and the adsorption performance due to the zeta potential have a synergistic effect, thereby improving the removal effect of PFAS present in water, and have arrived at the present invention. The activated carbon of the present invention has a specific surface area of ​​2020 to 4000 m 2 / g, total amount of acidic functional groups per specific surface area is 0.20 μeq / m 2 Hereinafter, the zeta potential is −40 mV or more.

[0012] specific surface area In the present invention, the specific surface area is a physical property defined in consideration of the adsorption performance for PFAS (particularly PFOA and PFOS, the same applies below). Specific surface area is 2020m 2 When the specific surface area is 4000 m / g or more, the pore structure of the activated carbon has many pores suitable for adsorption of adsorbed substances such as PFAS, and the contact area with the water, which is the medium to be treated, is large, so the adsorption performance is significantly improved and the amount of PFAS adsorbed is also increased. 2 If the amount exceeds 1 / g, the strength of the activated carbon decreases and the pore structure of the activated carbon changes, resulting in a decrease in adsorption performance. The specific surface area of ​​activated carbon is 2020m 2 / g~4000m 2 / g, preferably 2200m 2 / g~3800m 2 / g, more preferably 2500m 2 / g~3500m 2 / g, more preferably 2800m 2 / g~3200m 2 / g. In the present invention, the upper and lower limits of the numerical ranges can be arbitrarily combined. In addition, the preferred properties of the activated carbon of the present invention can be obtained by arbitrarily combining the numerical ranges of each physical property. The values ​​of each physical property of the activated carbon of the present invention are based on the conditions described in the Examples.

[0013] Total amount of acidic functional groups per specific surface area In the present invention, the total amount of acidic functional groups per specific surface area is a physical property defined in consideration of the adsorption performance for PFAS (particularly PFOA and PFOS, the same applies below). Reducing the total amount of acidic functional groups per specific surface area can significantly improve the adsorption performance for PFAS. The total amount of acidic functional groups per specific surface area of ​​activated carbon is 0.20 μeq / m 2 less than or equal to 0.18 μeq / m 2 Less than or equal to 0.15 μeq / m 2 Less than or equal to 0.13 μeq / m, more preferably 2 Less than or equal to 0.10 μeq / m, and even more preferably 0.10 μeq / m 2 The total amount of acidic functional groups per specific surface area is preferably as small as possible, so the lower limit is not particularly limited, and is 0 μeq / m 2 However, taking into consideration the manufacturing cost and technical difficulty, the lower limit is set to, for example, 0 μeq / m 2 Super is fine too. The acidic functional group is a group capable of reacting with a basic reagent shown in the Examples, and all acidic functional groups refer to (1) a hydroxy group (R-OH group), (2) a carboxy group (R-COOH group), (3) an ester group such as a lactone group (R-OCO group), and (4) a carbonyl group such as an α,β-unsaturated carbonyl group (such as a carbonyl group contained in a quinone structure: R=O group). The total amount of acidic functional groups refers to the total amount of the above acidic functional groups (1) to (4) contained in the activated carbon, determined by the measurement method described in the Examples.

[0014] Zeta potential In the present invention, the zeta potential is a physical property defined in consideration of the adsorption performance for PFAS (particularly PFOA and PFOS, the same applies below). When the zeta potential is -40 mV or higher, the adsorption performance for PFAS is significantly improved compared to when it is less than -40 mV. If the absolute value of the zeta potential becomes too large, the repulsive force acting between the activated carbon surface and the PFAS molecules becomes large, causing them to repel each other, which can reduce the adsorption power. The zeta potential of the activated carbon is −40 mV or more, preferably −38 mV to 38 mV, more preferably −35 mV to 35 mV, even more preferably −30 mV to 30 mV, and even more preferably −28 mV to 28 mV.

[0015] The activated carbon of the present invention is preferably alkali-activated activated carbon (hereinafter, sometimes referred to as alkali-activated carbon).

[0016] Activated carbon satisfying the above physical properties has excellent properties for adsorbing PFAS in water. In addition, the activated carbon of the present invention is effective not only in adsorbing PFAS, but also in removing total residual chlorine such as free residual chlorine such as hypochlorous acid and combined residual chlorine such as chloramine. On the other hand, as described later, the activated carbon of the present invention may have a competitive adsorption with PFAS for adsorbates (compounds) that physically adsorb to the activated carbon pores, such as chloroform. Therefore, the activated carbon of the present invention exhibits excellent effects in PFAS adsorption by reducing the adsorption amount of compounds that competitively adsorb with PFAS.

[0017] Appropriate control of the following physical properties of the activated carbon of the present invention is also effective in further improving the PFAS adsorption performance.

[0018] Micropore volume and mesopore volume In another preferred embodiment, the activated carbon of the present invention has a micropore volume having a pore size of 1 nm or less of less than 0.3 mL / g, and the difference between the micropore volume having a pore size of 2 nm or less and the mesopore volume having a pore size of 2 to 30 nm is 0.45 mL / g or less.

[0019] Micropores with a pore size of 1 nm or less are smaller than the optimal adsorption site size for PFAS, especially PFOS and PFOA, and therefore contribute little to improving the adsorption capacity of PFAS. Also, as described below, from the viewpoint of suppressing the adsorption of chloroform, the smaller the volume of micropores with a diameter of 1 nm or less, the better. Hydrophobic compounds other than PFAS (hereinafter sometimes referred to as other compounds) may be present in the treated water. In particular, if other compounds that have a higher adsorption power with activated carbon than PFAS are present, competitive adsorption between PFAS and other compounds may occur, and one of the adsorbates may be desorbed. An example of other compounds that have a high adsorption power with activated carbon is chloroform. Since the pore volume of 1 nm or less contributes to the adsorption of chloroform, the smaller the micropore volume of 1 nm or less, the more preferable it is from the viewpoint of suppressing the desorption of PFAS due to the above-mentioned competitive adsorption. The smaller the micropore volume with a pore diameter of 1 nm or less, the more preferable it is, in the order of less than 0.3 mL / g, 0.25 mL / g or less, 0.20 mL / g or less, 0.15 mL / g or less, 0.10 mL / g or less, and 0.05 mL / g or less. The lower limit of the micropore volume with a pore diameter of 1 nm or less may be 0 mL / g, but in consideration of the difficulty of production, the lower limit may be, for example, more than 0 mL / g.

[0020] The difference between the volume of micropores with pore diameters of 2 nm or less and the volume of mesopores with pore diameters of 2 to 30 nm (micropores - mesopores) is better when considering the balance between increasing the adsorption capacity for PFAS and improving the diffusion rate of water reaching the adsorption site. The difference between the volume of micropores with pore diameters of 2 nm or less and the volume of mesopores with pore diameters of 2 to 30 nm (micropores - mesopores) is preferably 0.45 mL / g or less, 0.40 mL / g or less, 0.35 mL / g or less, 0.30 mL / g or less, 0.25 mL / g or less, 0.20 mL / g or less, and 0.15 mL / g or less, in that order.

[0021] From the viewpoint of suppressing the desorption of PFAS, the smaller the chloroform adsorption amount of the activated carbon, the more preferable. The chloroform equilibrium adsorption amount of the activated carbon is preferably 2.5 mg / g or less, more preferably 2.0 mg / g or less, even more preferably 1.5 g / g or less, and most preferably 0 mg / g, but since it is difficult to completely eliminate the micropore volume with a pore diameter of 1 nm or less, it may be more than 0 mg / g.

[0022] Total acidic functional group amount and oxygen content It is also a preferred embodiment that the total amount of acidic functional groups is 0.5 meq / g or less and the oxygen content is 3.0 wt % or less. The lower the total amount of acidic functional groups in activated carbon and the lower the oxygen content, the better its adsorption performance for PFAS.

[0023] The total amount of acidic functional groups in the activated carbon is preferably 0.50 meq / g or less, more preferably 0.45 meq / g or less, even more preferably 0.40 meq / g or less, and even more preferably 0.35 meq / g or less. The smaller the total amount of acidic functional groups, the better, and it may be 0 meq / g, but considering the difficulty of production, the lower limit may be, for example, more than 0 meq / g.

[0024] The oxygen content of the activated carbon is preferably 3.0 wt% or less, more preferably 2.0 wt% or less, even more preferably 2.0 wt% or less, and even more preferably 1.5 wt% or less. The lower the oxygen content, the better, and it may be 0 wt%, but considering the difficulty of production, the lower limit may be, for example, more than 0 wt%.

[0025] Micropore volume fraction and mesopore volume fraction In another preferred embodiment, the activated carbon of the present invention has a micropore volume ratio (micropore volume / (micropore volume+mesopore volume)×100) of 80% or less and a mesopore volume ratio (mesopore volume / (micropore volume+mesopore volume)×100) of 20% or more. A high ratio of the micropore volume to the total of the micropore volume and mesopore volume is effective in increasing the amount of PFAS adsorbed, and a high ratio of the mesopore volume to the total is effective in improving the water diffusion rate, allowing for efficient treatment of PFAS-containing water.

[0026] The proportion of the micropore volume (micropore volume / (micropore volume+mesopore volume)×100) is preferably 80% or less, more preferably 70% or less, even more preferably 60% or less, and even more preferably 55% or less. The lower limit of the micropore volume ratio is a value corresponding to the mesopore volume ratio described below.

[0027] The mesopore volume ratio (mesopore volume / (micropore volume+mesopore volume)×100) is preferably 20% or more, more preferably 30% or more, even more preferably 40% or more, and still more preferably 45% or more.

[0028] In the activated carbon of the present invention, it is also a preferred embodiment to control the total pore volume. In order to ensure the amount of PFAS adsorption, a larger pore volume is preferable; however, if the pore volume is too large, the packing density of the activated carbon during use will decrease, which may result in a decrease in adsorption performance per volume. The total pore volume of the activated carbon of the present invention is preferably 0.5 mL / g to 4.0 mL / g, more preferably 0.7 mL / g to 3.0 mL / g, and even more preferably 1.0 mL / g to 2.0 mL / g.

[0029] In a preferred embodiment of the activated carbon of the present invention, the average pore diameter is controlled. Increasing the average pore size improves the diffusion of PFAS-containing water into the pores, improving adsorption performance. On the other hand, if the average pore size is too large, the activated carbon becomes bulky, reducing the amount of activated carbon packed in during use, and reducing the number of PFAS adsorption sites, which can reduce adsorption capacity. The average pore diameter of the porous carbon material of the present invention is preferably 1.5 nm to 5.0 nm, more preferably 1.75 nm to 4.0 nm, even more preferably 1.9 nm to 3.0 nm, and even more preferably 2.0 nm to 2.5 nm.

[0030] Activated carbon shape The activated carbon of the present invention may be formed into a shape according to the application, such as a powder, a granule, a crushed (granular) shape, a fiber shape, etc. The carbon-based metal adsorbent may be formed into any shape, such as a cylindrical shape, a spherical shape, a sheet shape, etc., together with a binder or other adsorbent as necessary. The particle size of the activated carbon may be appropriately adjusted according to the application.

[0031] The activated carbon of the present invention is suitable for water treatment applications. Specific examples of water to be treated include various PFAS-containing waters, such as wastewater from factories and homes, river water, seawater, drinking water, and industrial water. When PFAS-containing water is treated with the activated carbon of the present invention, PFAS, particularly PFOS and PFOA, can be removed from the treated water. The activated carbon of the present invention is also highly effective in removing compounds other than PFAS, such as free residual chlorine such as hypochlorous acid and combined residual chlorine such as chloramine, as well as total residual chlorine. The water treatment using the activated carbon of the present invention can be applied both in an equilibrium state and in a flow-through state. Specific examples of the water treatment application of the present invention include water purifiers, water treatment filters, and the like, which can remove PFAS, particularly PFOS and PFOA, by contacting the water to be treated with activated carbon. In addition, since the adsorbed PFAS does not desorb from the activated carbon of the present invention, PFAS does not flow out when the activated carbon is disposed of. Therefore, contamination by PFAS can be prevented when disposing of the activated carbon.

[0032] A method for producing alkali-activated carbon, which is a preferred embodiment of the activated carbon of the present invention, is described below, but the production method of the present invention is not limited to the following production method as long as the desired physical properties are obtained. Note that the following production conditions indicate preferred ranges, and each production condition must be appropriately adjusted to obtain the desired physical properties.

[0033] raw material The carbonaceous material to be the activation raw material of the activated carbon of the present invention is not particularly limited, but examples thereof include carbonaceous raw materials derived from plants such as wood, sawdust, charcoal, fruit shells such as coconut shells and walnut shells, fruit seeds, pulp manufacturing by-products, lignin, and blackstrap molasses; carbonaceous raw materials derived from minerals such as peat, lignite, brown coal, lignite, anthracite, coke, coal tar, coal pitch, petroleum distillation residue, and petroleum pitch; carbonaceous raw materials derived from synthetic resins such as phenolic resins, polyvinylidene chloride, and acrylic resins; carbonaceous raw materials derived from natural fibers such as natural fibers such as cellulose and regenerated fibers such as rayon; and carbonaceous materials derived from coal tar pitch and petroleum pitch such as pitch-based carbon fibers. The carbonaceous raw materials can be used alone or in combination of two or more kinds. Among these carbonaceous materials, carbonaceous raw materials derived from coal tar pitch and petroleum pitch, which are easy to control the specific surface area, the amount of acidic functional groups, and the zeta potential within the above ranges, are preferred, and pitch-based carbon fibers are more preferred.

[0034] Carbonization Of the above activation raw materials, it is preferable that uncarbonized carbonaceous materials are carbonized as necessary before activation. The carbonization treatment may be performed by heat treating the carbonaceous raw material in an inert gas such as nitrogen, for example, by holding the carbonaceous raw material at 400°C to 1000°C for 1 hour to 3 hours. Note that carbonaceous raw materials that have already been carbonized, such as pitch-based carbon fibers, do not need to be carbonized.

[0035] Alkaline activation treatment The alkali activation treatment of the present invention is a process in which an activator containing an alkali metal compound is mixed with an activation raw material and heated in an inert gas. The specific surface area can be controlled within the above range by adjusting the conditions of the alkali activation treatment. Examples of the alkali metal compound include alkali metal hydroxides such as potassium hydroxide and sodium hydroxide, alkali metal carbonates such as potassium carbonate and sodium carbonate, and alkali metal sulfates such as potassium sulfate and sodium sulfate. The alkali metal hydroxides are preferred, and potassium hydroxide is more preferred.

[0036] The amount of the activator used is preferably adjusted so that the specific surface area of ​​the activated carbon is as described above, since the higher the mixing ratio of the activator to the activation raw material, the larger the specific surface area of ​​the activated carbon tends to be. The mass ratio of the activator to the activation raw material (mass of the alkaline component of the activator / mass of the activation raw material) is preferably 0.5 or more, more preferably 1.0 or more, even more preferably 2.0 or more, and is preferably 10.0 or less, more preferably 5.0 or less, even more preferably 4.0 or less.

[0037] The alkali activation treatment is carried out in an atmosphere of any inert gas such as argon, helium, or nitrogen.

[0038] When the alkali activation treatment temperature is increased, activation proceeds, the specific surface area increases, and the total amount of acidic functional groups tends to decrease. Therefore, the heating temperature during the alkali activation treatment is preferably 350°C to 950°C, more preferably 400°C to 900°C, even more preferably 450°C to 850°C, and even more preferably 500°C to 800°C. The rate of temperature rise to the above heating temperature is preferably 1° C. / min or more, more preferably 5° C. / min or more, and is preferably 20° C. / min or less, more preferably 15° C. / min or less. The activation treatment time at the above heating temperature is preferably 1 hour to 10 hours, more preferably 2 hours to 8 hours, even more preferably 3 hours to 7 hours, and even more preferably 3.5 hours to 5 hours.

[0039] Washing treatment is a process in which the activated carbon obtained by the alkali activation treatment is washed with water or with an inorganic acid to remove the alkali metals remaining in the alkali activated carbon. The alkali metal removal rate can be increased by repeating the washing treatment multiple times.

[0040] Water washing treatment The temperature of the water used in the water washing treatment is preferably from 20° C. to less than 100° C., more preferably from 30° C. to 90° C., even more preferably from 40° C. to 80° C., and even more preferably from 50° C. to 70° C. The water washing treatment is desirably performed by repeating water washing and filtration multiple times until the pH of the filtrate becomes, for example, 7.0 or less.

[0041] Inorganic acid cleaning treatment In the inorganic acid washing, hydroacids such as hydrochloric acid and hydrofluoric acid, and oxygen acids such as sulfuric acid, nitric acid, phosphoric acid and perchloric acid can be used as the inorganic acid, and hydrochloric acid is preferred. The inorganic acid concentration is preferably adjusted from the viewpoint of increasing the alkali metal removal rate while maintaining the physical properties of the alkali activated carbon. The inorganic acid concentration in the aqueous inorganic acid solution may be appropriately adjusted as necessary, and is preferably 0.1 wt% to 30 wt%, more preferably 0.5 wt% to 20 wt%, and further preferably 1.0 wt% to 15 wt%. The temperature of the aqueous inorganic acid solution is desirably set within a temperature range that can enhance the efficiency of removing the alkali metal from the alkali activated carbon while suppressing the volatilization of the inorganic acid. The temperature of the aqueous inorganic acid solution is preferably from 20°C to less than 100°C, more preferably from 30°C to 90°C, even more preferably from 40°C to 80°C, and even more preferably from 50°C to 70°C. The inorganic acid washing treatment is preferably performed by repeating washing and filtration multiple times until the residual potassium content in the alkali activated carbon is preferably 5000 mg / kg or less (more than 0 mg / kg) and the residual alkali metal content in the alkali activated carbon is preferably 2500 mg / kg or less (more than 0 mg / kg), more preferably 1000 mg / kg or less (more than 0 mg / kg), and even more preferably 500 mg / kg or less (more than 0 mg / kg). The residual alkali metal content in the alkali activated carbon can be measured using an ICP atomic emission spectrometer.

[0042] Water washing treatment The water washing treatment is a step of removing inorganic acid remaining in the alkali activated carbon by washing with water after the inorganic acid washing treatment. The temperature of the water used in the water washing treatment is desirably set in consideration of the efficiency of removing inorganic acids. The temperature of the washing water is preferably from 20°C to less than 100°C, more preferably from 30°C to 90°C, even more preferably from 40°C to 80°C, and even more preferably from 50°C to 70°C. The water washing treatment is preferably carried out by repeating water washing and filtration several times until the pH of the filtrate becomes 6.5 or higher.

[0043] Drying process The drying treatment is a step of removing moisture from the alkali activated carbon after the washing treatment. The drying may be performed under conditions that can remove the moisture remaining in the alkali activated carbon. For example, it is preferable to heat the alkali activated carbon to about 100 to 120° C. in an air atmosphere and dry the carbon for 0.5 to 24 hours.

[0044] Heat treatment process The heat treatment step is a step in which the alkali activated carbon is heated to reduce the total amount of acidic functional groups and to control the zeta potential within the above range. Increasing the heating temperature can remove acidic functional groups from the alkali-activated carbon and can induce the zeta potential within the above range, but if the heating temperature is too high, the zeta potential will deviate from the above range or the pore structure will change. The temperature during the heat treatment is preferably 800°C to 1500°C, more preferably 900°C to 1400°C, and further preferably 1000°C to 1300°C. The rate of temperature rise to the above heating temperature is preferably 1° C. / min to 20° C. / min, more preferably 5° C. / min to 15° C. / min, and further preferably 10° C. / min to 15° C. / min. The heating time at the above heating temperature is preferably 30 minutes to 10 hours, more preferably 1 hour to 5 hours, and further preferably 2 hours to 4 hours.

[0045] Crushing process The alkali activated carbon of the present invention may be pulverized to a desired particle size using a pulverizer such as a mill, if necessary. The pulverization may be carried out at any stage of the production process, or a raw material that has been pulverized in advance may be used.

[0046] Molding process The alkali activated carbon of the present invention may be molded into a shape according to various applications as necessary. The molding method is not particularly limited, and it may be molded into a desired size and shape using various known molding methods. In addition, it may be mixed with other materials, for example, optional additives such as binders, during molding.

[0047] The alkali-activated carbon of the present invention, obtained by appropriately adjusting each production condition so as to obtain the above physical properties, exhibits excellent removal effects against PFAS, particularly PFOS and PFOA, in liquids. EXAMPLES

[0048] The present invention will be described in more detail below with reference to examples. However, the present invention is not limited to the following examples, and it is possible to carry out the present invention by making appropriate modifications within the scope of the above and below-mentioned aims, and all of these modifications are included in the technical scope of the present invention.

[0049] Example 1 A commercially available alkaline activator (aqueous potassium hydroxide solution with a concentration of 48.5%) was added and mixed with 1.0 part by weight of coal pitch-based carbon fiber as an activator so that the mass ratio ([mass of alkaline component of activator] / [mass of activation raw material]: hereinafter referred to as KOH / C ratio) was 3.0, and the mixture was heated to 800°C in a nitrogen atmosphere and maintained at that temperature for 3.75 hours to obtain alkaline activated carbon. The obtained alkali activated carbon was repeatedly washed with warm water at 60°C until the pH of the filtrate became 7.0 or less. Then, the mixture was washed with 5.25 wt % hydrochloric acid for 1 hour, and then filtered by suction. The activated carbon after filtration was repeatedly washed with hot water at 60° C. until the pH of the filtrate reached 6.5 or higher, to obtain a washed product. The resulting washed product was dried in a dryer set at 115° C. for 24 hours. The dried activated carbon was placed in an elevator (manufactured by Toyo Advantec Co., Ltd.) and heated to 1150° C. at a rate of 10 / min in a nitrogen atmosphere and held at that temperature for 2 hours to obtain the fibrous activated carbon of Example 1.

[0050] Comparative Example 1 A commercially available alkali-activated carbon fiber (MSF-A30M manufactured by MC Evatec Co., Ltd.) was used as the fibrous activated carbon of Comparative Example 1.

[0051] Comparative Example 2 A commercially available coconut shell steam activated carbon (W10-30 manufactured by MC Evatec Co., Ltd.) was used as the granular activated carbon of Comparative Example 2.

[0052] Comparative Example 3 A commercially available coal-based steam-activated activated carbon (C-6 manufactured by MC Evatec Co., Ltd.) was used as the granular activated carbon of Comparative Example 3.

[0053] In addition, in order to reduce the influence of particle size, the particle size of the granular carbon of Comparative Examples 2 and 3 was adjusted beforehand before examining the characteristics. Specifically, the activated carbon was crushed using an agate mortar, and then classified using sieves with sieve openings of 53 μm and 125 μm to adjust the particle size to an average particle size (D50) of about 100 to 150 μm.

[0054] Particle size The particle size of each sample was measured using a laser diffraction particle size distribution analyzer (Shimadzu Corporation, SALD (registered trademark)-2000). A volume-based cumulative frequency curve was obtained from the particle size distribution measurement results, and the average particle size D50 at a cumulative frequency of 50% was calculated.

[0055] specific surface area After drying the sample (0.2 g) in a vacuum at 250°C, the amount of nitrogen gas adsorbed in a liquid nitrogen atmosphere (-196°C) was measured using a nitrogen adsorption apparatus (Micromeritics ASAP-2420) to obtain a nitrogen adsorption isotherm, and the specific surface area (m 2 / g) was calculated.

[0056] Total Pore Volume The total pore volume (mL / g) was calculated from the amount of nitrogen adsorbed at a relative pressure (P / P0) of 0.93 from the nitrogen adsorption isotherm. Micropore volume and mesopore volume: The nitrogen adsorption isotherm was analyzed by the BJH method to determine the mesopore volume of 2 to 30 nm. The micropore volume was calculated by the following formula. Micropore volume (mL / g) = total pore volume (mL / g) - [mesopore volume of 2-30 nm analyzed by BJH method (mL / g)] Using the above values, the difference between the micropore volume and the mesopore volume was calculated according to the following formula. Micropore volume (mL / g) - Mesopore volume (mL / g) The ratio of the micropore volume and the ratio of the mesopore volume were calculated from the following formula. Micropore volume ratio = micropore volume / (micropore volume + mesopore volume) × 100 Mesopore volume ratio = mesopore volume / (micropore volume + mesopore volume) x 100 The pore volume of 1 nm or less was calculated by the following formula. Pore ​​volume of 1 nm or less (mL / g) = total pore volume (mL / g) - [pore volume of 1 to 30 nm analyzed by the BJH method (mL / g)]

[0057] Average pore diameter (4V / A) The pores of the activated carbon were assumed to be cylindrical, and the average pore diameter was calculated based on the following formula. Average pore diameter (nm) = 4 × total pore volume (mL / g) / specific surface area (m 2 / g) x 1000

[0058] Evaluation of total acidic functional groups The total amount of acidic functional groups was determined according to the Boehm method (reference "HP Boehm, Adzan. Catal, 16,179 (1966)"). Specifically, 50 mL of sodium ethoxide aqueous solution (0.1 mol / L) was added to 2 g of activated carbon, stirred at 500 rpm for 2 hours, and then left for 24 hours. After 24 hours, the mixture was stirred for another 30 minutes and separated by filtration. 0.1 mol / L hydrochloric acid was dropped into 25 mL of the obtained filtrate, and the amount of hydrochloric acid titrated when the pH became 4.0 was measured. In addition, as a blank test, 0.1 mol / L hydrochloric acid was dropped into 25 mL of the sodium ethoxide aqueous solution (0.1 mol / L) and the amount of hydrochloric acid titrated when the pH became 4.0 was measured. Then, the total amount of acidic functional groups (meq / g) was calculated by the following formula. Total acidic functional group amount (meq / g)=(ab)×0.1 / (S×25 / 50) a: Hydrochloric acid titration volume in blank test (mL) b: Amount of hydrochloric acid titrated when the sample was reacted (mL) S: sample weight (g)

[0059] Total amount of acidic functional groups per specific surface area The total amount of acidic functional groups per specific surface area was calculated by the following formula. Total amount of acidic functional groups per specific surface area (μeq / m 2 )=total acidic functional group amount (meq / g) / specific surface area (m 2 / g) x 1000 (unit adjustment)

[0060] oxygen content The sample was dried at 120°C for 2 hours and the oxygen content in the activated carbon was measured using an Elementar vario EL cube and benzoic acid as the standard substance.

[0061] Zeta potential A dispersion was prepared by adding 5 mg of a sample pulverized to an average particle size of about 5 to 10 μm using a disk mill to 25 mL of pure water and stirring. This dispersion was measured using a zeta potential measuring device, Zetasizer Nano Z (manufactured by Malvern Panalytical, model number ZEN2600). The zeta potential was calculated by measuring the electrophoretic mobility of particles in the dispersion placed in a specified capillary cell and using the following formula from the obtained electrophoretic mobility. Ue = 2εzf(ka) / 3η z: Zeta potential Ue: electrophoretic mobility f(ka): Henry function (1.5 for water systems) ε: Dielectric constant η: Viscosity

[0062] PFOS, PFOA equilibrium adsorption test Preparation of PFOS and PFOA test solutions 18.0 mg of PFOS (Fujifilm Wako Pure Chemical Industries, Ltd., 100% purity) or PFOA (Fujifilm Wako Pure Chemical Industries, Ltd., 100% purity) reagent was weighed into a 50 mL measuring flask and dissolved by adding methanol (Kanto Chemical Co., Ltd., for high performance liquid chromatography). Next, 5.5 mL or 8.25 mL of this solution was dispensed into a 100 mL measuring flask and diluted with methanol up to the mark. 1 mL or 30 mL of the diluted solution was placed in a 3 L measuring flask and made up to the mark with ultrapure water to prepare PFOS or PFOA test water.

[0063] PFOS, PFOA equilibrium adsorption test A specified amount of activated carbon dried at 105°C for 15 hours was placed in a 200mL glass Erlenmeyer flask, and 100mL of the PFOS or PFOA test solution prepared above was added, followed by shaking at a shaking speed of 200 rpm for 24 hours in a thermostatic bath set at 25°C. The sample was then filtered through a 0.45μm membrane filter and solid-phase extracted using a solid-phase column (PLS-3, manufactured by GL Sciences) to prepare a measurement sample. The measurement was performed according to the method described in "Waterworks Test Method III Organic Substances III-2 Organic Substances 31.3 Solid-phase Extraction - Liquid Chromatography Mass Spectroscopy 2", and a high-performance liquid chromatograph mass spectrometer (1260 Infinity LC / MS, manufactured by Agilent Technologies) was used as the analytical device. An adsorption isotherm was created from the relationship between the PFOS or PFOA residual concentration obtained from the LC / MS measurement results and the adsorption amount per weight of activated carbon (mg / g-activated carbon), and the adsorption amount at a residual concentration of 0.07 μg / L was calculated using the Freundlich equation.

[0064] PFOA water permeability evaluation Preparation of PFOA test solutions A PFOA solution with a concentration of 150 mg / L was prepared by adding 301.8 mg of PFOA reagent (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., purity 100%) to a 2 L measuring flask, dissolving it by adding 1 mL of methanol, and then filling it up with ultrapure water. This solution was transferred to a 2 L plastic bottle and mixed with pure water in the water flow test device so that the initial concentration was 800 μg / L, and this was used as the test solution.

[0065] PFOA water permeability evaluation test The activated carbon dried at 105°C for 15 hours was packed into a resin column with an inner diameter of 15.8 mm and a height of 100 mm so that the activated carbon layer thickness was 10 mm in Example 1 and 20 mm in Comparative Examples 2 and 3. The prepared activated carbon column was attached to a water flow test device and subjected to a test for SV=2500 h. -1The test solution was passed through the column at a flow rate of about 80 mL / min (Example 1, about 160 mL / min for Comparative Examples 2 and 3), and the test solution after adsorption to activated carbon was appropriately sampled from the outlet side of the column. In addition, before and after the start of passing water through the activated carbon column, the test solution before passing through the column was sampled from the inlet side of the column, and used to calculate the initial concentration of the test solution. The sampled test solution was analyzed using a high-performance liquid chromatograph mass spectrometer (1260 Infinity LC / MS manufactured by Agilent Technologies), and the removal rate was calculated from the initial concentration of the obtained test solution and the residual concentration in the solution sampled from the outlet side of the activated carbon, and a breakthrough curve was obtained from the obtained removal rate and the amount of water passing per weight of activated carbon. In addition, the cumulative amount of PFOA adsorbed per weight of activated carbon (mg / g-activated carbon) at a residual concentration of 0.07 μg / L was calculated from the relationship between the residual concentration after activated carbon adsorption sampled at each time point and the total amount of PFOA adsorbed to the activated carbon (mg / g-activated carbon), and the amount of PFOA that can pass through the water (L / g-activated carbon) when a residual concentration of 0.07 μg / L was reached was calculated by dividing the calculated amount of PFOA adsorbed (mg / g-activated carbon) by the initial concentration of the test solution (μg / L).

[0066] Free residual chlorine water flow performance evaluation Preparation of test solutions 280 L of tap water filtered using a commercially available activated carbon cartridge filter (As One, Type-2) was poured into a 300 L tank, and 4.7 mL of sodium hypochlorite solution (Kishida Chemical, effective chlorine concentration 12% by weight) was added using a pipetter so that the effective chlorine concentration was 2 mg / L. The test solution was then prepared by stirring with a chemical pump.

[0067] Free residual chlorine water flow performance evaluation test The evaluation test was conducted with reference to the household water purifier test method (JIS S 3201). Activated carbon dried at 115 ° C for 2 hours was packed into a resin column with an inner diameter of 19 mm and a height of 100 mm so that the activated carbon layer thickness was 10 mm. The prepared activated carbon column was attached to a water flow test device, and the test solution was passed through it so that SV = 6000 h-1 (flow rate about 280 mL / min), and 10 mL of the test solution before and after passing through the column was appropriately sampled in a vial. The free residual chlorine concentration (mg / L) was measured by adding DPD reagent (Kanto Chemical Rapid DPD Reagent (packet)) to the sampled test solution and shaking it for about 20 seconds, and the concentration was measured with a residual chlorine meter (HACH). From the measured concentration, the removal rate per water flow rate (L / g) per weight of activated carbon was calculated, and the cumulative water flow rate at a removal rate of 80% was calculated.

[0068] Chloramine water permeability evaluation Preparation of test solutions 280 L of tap water filtered using a commercially available activated carbon cartridge filter (As One, Type-2) was poured into a 300 L tank, and 3.3 ml of 28% ammonia water (Kishida Chemical) and 7.26 ml of 12% sodium hypochlorite solution (Kishida Chemical) were added so that the chloramine concentration was 3.0±0.3 mg / L, and the solution was then stirred with a hand pump for approximately 30 minutes.

[0069] Chloramine water permeability evaluation test The evaluation test was conducted with reference to the US water purifier standard (NSF / ANSI42). Activated carbon dried for 2 hours at 115°C was packed into a resin column with an inner diameter of 19 mm and a height of 100 mm so that the activated carbon layer was 15 mm thick. The activated carbon column was attached to a water flow test device and subjected to a test for SV=500h. -1The test solution was passed through the column at a flow rate of approximately 35 mL / min, and 10 mL of the test solution before and after passing through the column was appropriately sampled in a 10 mL colorimetric tube. 0.5 mL of phosphate buffer was added to the test water collected in the 10 mL colorimetric tube and mixed uniformly, then DPD reagent (Kanto Chemical) was added and shaken for approximately 20 seconds, and the residual free chlorine concentration was measured using a chlorine concentration meter (HACH). Then, 0.1 g of potassium iodide (Kishida Chemical) was added to the measured test water to develop color, and after leaving it to stand for 2 minutes, the residual chlorine concentration was measured using a chlorine concentration meter (HACH). The residual chloramine concentration was calculated from the measured residual free chlorine concentration and residual chlorine concentration using the following formula. Residual chloramine concentration (mg / L) = Residual chlorine concentration (mg / L) - Residual free chlorine concentration (mg / L) The removal rate per unit weight of activated carbon (L / g) was calculated from the measured concentration, and the cumulative amount of water passed was determined when the residual chloramine concentration in the test water after passing through the activated carbon reached 0.5 ppm (removal rate of approximately 83%).

[0070] Chloroform adsorption performance evaluation 0.5 g of chloroform (CHCl3) was diluted in 50 ml of methanol, and this was further diluted 10-fold with methanol to prepare a stock solution. 1 ml of the chloroform stock solution was then diluted to 1 liter with pure water to prepare a 1 mg / L chloroform solution. Five 100 mL Erlenmeyer flasks (Erlenmeyer flasks 1 to 5) were prepared, and a stirrer was placed in each Erlenmeyer flask. 0.013 g (Erlenmeyer flask 1), 0.026 g (Erlenmeyer flask 2), 0.064 g (Erlenmeyer flask 3), 0.13 g (Erlenmeyer flask 4), and 0.26 g (Erlenmeyer flask 5) of activated carbon were placed in each flask. The flasks were filled with 1 mg / L chloroform solution, sealed with glass stoppers coated with Teflon (registered trademark) grease, and secured in place with clips. The weight of the solution poured in was measured. The Erlenmeyer flasks were then stirred for 14 hours in a thermostatic chamber at 20°C using a magnetic stirrer. After stirring, the activated carbon was filtered off using a syringe filter, and the filtrate was placed in a screw bottle filled with the water and refrigerated in a thermostatic chamber at 10°C until immediately before measurement. The chloroform concentration was measured using HS-GC / MS (HS: PerkinElmer, Inc.) TurboMatrixHS, GC / MS: Shimadzu QP2010) was used. An adsorption isotherm was created by calculating the amount of adsorption (mg / g) per weight of activated carbon from the concentration in the quantified filtrate, and the equilibrium adsorption amount was determined when the residual chloroform concentration was 0.06 mg / L.

[0071] [Table 1]

[0072] Example 1 is a preferred activated carbon of the present invention, which is an example in which a heat treatment was carried out after alkali activation. Comparative Example 1 is an example in which the alkali activated carbon was not subjected to heat treatment, and the total amount of acidic functional groups per specific surface area was large, and the zeta potential was also unsatisfactory. Comparative Example 2 is an example in which the steam activated carbon was not subjected to heat treatment, and the specific surface area was small and the balance (difference, ratio) between the micropore volume and the mesopore volume was poor. Comparative Example 3 is an example in which the steam activated carbon was not subjected to heat treatment, and the specific surface area was small, and the balance (difference) between the total amount of acidic functional groups per specific surface area and the micropore volume and mesopore volume was poor.

[0073] As shown in Figures 1 to 3, the activated carbon of Example 1 satisfying the present invention exhibited superior adsorption performance to the activated carbons of Comparative Examples 1 to 3 in the tests of the PFOS equilibrium adsorption amount, the PFOA equilibrium adsorption amount, and the cumulative water flow amount of PFOA, and was able to increase the removal rate of PFOS and PFOA from water.

[0074] 4 and 5, the activated carbon of Example 1 also exhibited a better removal effect on free residual chlorine (FIG. 4) and chloramine (FIG. 5) than the activated carbon of Comparative Examples 2 and 3. Therefore, the activated carbon of the present invention has a removal effect not only on PFAS such as PFOS and PFOA, but also on total residual chlorine such as free residual chlorine and combined chlorine.

[0075] On the other hand, as shown in FIG. 6, the activated carbon of Example 1 had a lower effect of removing chloroform than the activated carbons of Comparative Examples 2 and 3. As shown in Figures 1 to 3 and Figure 6, the activated carbon of the present invention had a low adsorption and removal effect on chloroform, but was excellent in adsorption and removal effect on PFOS and PFOA.

Claims

1. Specific surface area is 2020 to 4000 m ２ / g, The total amount of acidic functional groups per specific surface area is 0.20 μeq / m ２ below, Zeta potential is -40mV or more, The present invention relates to a fibrous activated carbon for removing PFAS from water.

2. The volume of micropores having a pore diameter of 1 nm or less is less than 0.3 mL / g; and The difference between the volume of micropores having a pore diameter of 2 nm or less and the volume of mesopores having a pore diameter of 2 to 30 nm is 0.45 mL / g or less; 2. The fibrous activated carbon according to claim 1 ,

3. 2. The fibrous activated carbon according to claim 1, wherein the total amount of acidic functional groups is 0.5 meq / g or less and the oxygen content is 3.0 wt % or less.

4. The ratio of the micropore volume calculated by the following formula (1) is 80% or less, and The mesopore volume ratio calculated from the following formula (2) is 20% or more.

2. The fibrous activated carbon according to claim 1 , Micropore volume / (micropore volume+mesopore volume)×100 (1) Mesopore volume / (micropore volume+mesopore volume)×100 (2)

5. 2. The fibrous activated carbon according to claim 1, wherein the activated carbon has an adsorption ability for perfluoroalkyl compounds and polyfluoroalkyl compounds in water.

6. 2. The fibrous activated carbon according to claim 1, wherein the activated carbon is an alkali-activated carbon.

7. A water purifier using the fibrous activated carbon according to any one of claims 1 to 6.

Images