Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J20/00—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof
  • B01J20/02—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof comprising inorganic material
  • B01J20/20—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof comprising inorganic material comprising free carbon; comprising carbon obtained by carbonising processes
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J20/00—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof
  • B01J20/28—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof characterised by their form or physical properties
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B32/00—Carbon; Compounds thereof
  • C01B32/30—Active carbon
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F1/00—Treatment of water, waste water, or sewage
  • C02F1/28—Treatment of water, waste water, or sewage by sorption

Definitions

• the present invention relates to activated carbon for water treatment.
• PFAS Perfluoroalkyl and polyfluoroalkyl compounds
• PFOS perfluorooctane sulfonate
• PFOA perfluorooctanoic acid
• 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. For this reason, technology to remove PFAS, especially PFOS and PFOA, has been demanded.
• Patent Document 1 discloses an activated carbon adsorbent for adsorbing per- and polyfluoroalkyl compounds in a water sample, the activated carbon adsorbent having a BET specific surface area of 800 m2 /g or more or a surface oxide amount of 0.20 meq/g or less, for releasably adsorbing per- and polyfluoroalkyl compounds in the water sample.
• Patent Document 2 discloses activated carbon for adsorbing per- and polyfluoroalkyl compounds in a water sample, characterized in that 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) with pore diameters of 1 nm or less is 0.30 cm 3 /g or more.
• Patent Document 3 discloses an activated carbon adsorbent for adsorbing perfluoroalkyl compounds in water containing impurities, characterized in that the sum of the pore volumes of pores having a pore diameter of 2 to 50 nm in the activated carbon adsorbent is 0.025 cm 3 /g or less when measured by a DH plot method, and the sum of the pore volumes of pores having a pore diameter of 1.5 to 2 nm in the activated carbon adsorbent is 0.014 cm 3 /g or more when measured by an MP plot method.
• the object of the present invention is to provide activated carbon for treatment that has excellent adsorption performance for PFAS, especially PFOS and PFOA.
• the activated carbon of the present invention has the following composition.
• An activated carbon for water treatment having a specific surface area of 2020 to 4000 m 2 /g, a total amount of acidic functional groups per specific surface area of 0.20 ⁇ eq/m 2 or less, and a zeta potential of -40 mV or more.
• an activated carbon for treatment having 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.
• FIG. 1 is a graph showing the PFOS equilibrium adsorption amounts of the examples and the comparative examples.
• FIG. 2 is a graph showing the PFOA equilibrium adsorption amounts of the examples and the comparative examples.
• FIG. 3 is a graph showing the cumulative water flow rate of PFOA in the examples and the comparative examples.
• FIG. 4 is a graph showing the cumulative free residual chlorine water flow rate in the examples and the comparative examples.
• FIG. 5 is a graph showing the cumulative amount of chloramine passing through in the examples and the comparative examples.
• FIG. 6 is a graph showing the equilibrium adsorption amounts of chloroform in the examples and the comparative examples.
• the activated carbon of the present invention has a specific surface area of 2020 to 4000 m 2 /g, a total amount of acidic functional groups per specific surface area of 0.20 ⁇ eq/m 2 or less, and a zeta potential of ⁇ 40 mV or more.
• the specific surface area is a physical property defined in consideration of the adsorption performance for PFAS (particularly PFOA, PFOS, the same applies below).
• the specific surface area is 2020 m2 /g or more, the pore structure of the activated carbon has many pores suitable for adsorption of adsorbates such as PFAS, and the contact area with water, which is the medium to be treated, is large, so that the adsorption performance is significantly improved and the amount of PFAS adsorbed is also increased.
• the specific surface area exceeds 4000 m2 /g, the strength of the activated carbon decreases and the pore structure of the activated carbon changes, resulting in a decrease in the adsorption performance.
• the specific surface area of the activated carbon is 2020 m 2 /g to 4000 m 2 /g, preferably 2200 m 2 /g to 3800 m 2 /g, more preferably 2500 m 2 /g to 3500 m 2 /g, and further preferably 2800 m 2 /g to 3200 m 2 /g.
• the upper and lower limits of the numerical ranges can be arbitrarily combined.
• 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.
• 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). By reducing the total amount of acidic functional groups per specific surface area, the adsorption performance for PFAS can be significantly improved.
• the total amount of acidic functional groups per specific surface area of the activated carbon is 0.20 ⁇ eq/m 2 or less, preferably 0.18 ⁇ eq/m 2 or less, more preferably 0.15 ⁇ eq/m 2 or less, even more preferably 0.13 ⁇ eq/m 2 or less, and even more preferably 0.10 ⁇ eq/m 2 or less.
• the lower limit is not particularly limited because the total amount of acidic functional groups per specific surface area is preferably as small as possible, and may be 0 ⁇ eq/m 2 , but the lower limit may be, for example, more than 0 ⁇ eq/m 2 in consideration of production costs and technical difficulty.
• 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.
• the zeta potential is a physical property defined in consideration of the adsorption performance for PFAS (particularly PFOA and PFOS, the same applies below).
• the zeta potential is ⁇ 40 mV or more, 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 is too large, the repulsive force acting between the activated carbon surface and the PFAS molecules becomes large and they repel each other, which may result in a decrease in the adsorption force.
• 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.
• the activated carbon of the present invention is preferably alkali-activated activated carbon (hereinafter, sometimes referred to as alkali-activated carbon).
• Activated carbon that satisfies the above physical properties has excellent properties for adsorbing PFAS in water. Furthermore, the activated carbon of the present invention is effective not only in adsorbing PFAS, but also in removing total residual chlorine, including free residual chlorine such as hypochlorous acid and combined residual chlorine such as chloramine. On the other hand, as described below, the activated carbon of the present invention has the potential for competitive adsorption of adsorbates (compounds) that physically adsorb to the pores of the activated carbon, such as chloroform. Therefore, the activated carbon of the present invention exhibits excellent effects in adsorbing PFAS by reducing the amount of adsorption of compounds that competitively adsorb with PFAS.
• 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.
• Micropores with a pore size of 1 nm or less are smaller than the size of the optimal adsorption site for PFAS, particularly PFOS and PFOA, and therefore contribute little to improving the adsorption power of PFAS. Also, from the viewpoint of suppressing the adsorption of chloroform, as described later, the smaller the volume of micropores with a pore size of 1 nm or less, the more preferable it is. Hydrophobic compounds other than PFAS (hereinafter, sometimes referred to as other compounds) may be present in the water to be treated.
• PFAS when other compounds that have a higher adsorption power with activated carbon than PFAS are present, competitive adsorption between PFAS and the other compounds may occur, and one of the adsorbates may be desorbed.
• An example of the other compound that has 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 competitive adsorption.
• the micropore volume of the pore diameter of 1 nm or less is preferably smaller 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 of 1 nm or less may be 0 mL/g, but considering the difficulty of production, the lower limit may be, for example, more than 0 mL/g.
• the difference between the volume of micropores having a pore size of 2 nm or less and the volume of mesopores having a pore size of 2 to 30 nm is preferably as small as possible, taking into consideration the balance between an increase in the adsorption capacity for PFAS and an increase in the diffusion rate of water reaching the adsorption site.
• the difference between the volume of micropores having pore diameters of 2 nm or less and the volume of mesopores having 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 L/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.
• 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 mg/g or less, and most preferably 0 mg/g, but since it is difficult to completely eliminate the volume of micropores with a pore diameter of 1 nm or less, it may be more than 0 mg/g.
• Total Amount of Acidic Functional Groups 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 smaller the total amount of acidic functional groups in activated carbon and the lower the oxygen content, the more improved the adsorption performance for PFAS.
• 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 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 activated carbon of the present invention has a micropore volume proportion (micropore volume/(micropore volume+mesopore volume) ⁇ 100) of 80% or less and a mesopore volume proportion (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.
• the proportion of the micropore volume 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.
• 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 even more preferably 45% or more.
• the activated carbon of the present invention it is also a preferred embodiment to control the total pore volume.
• the pore volume In order to ensure the adsorption amount of PFAS, it is preferable that the pore volume is large. However, if the pore volume is too large, the packing density of the activated carbon during use decreases, and the adsorption performance per volume may decrease.
• 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.
• the average pore diameter is controlled. Increasing the average pore size improves the diffusibility of PFAS-containing water into the pores, improving the adsorption performance, whereas an excessively large average pore size increases the volume of the activated carbon, reducing the amount of PFAS adsorption sites and decreasing the 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.
• 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 cylinder, a sphere, a sheet, etc. together with a binder or other adsorbent as necessary.
• the particle size of the activated carbon can be appropriately adjusted according to the application.
• the activated carbon of the present invention is suitable for use in water treatment.
• water to be treated include various PFAS-containing waters, such as wastewater from factories and homes, river water, seawater, drinking water, and industrial water.
• PFAS particularly PFOS and PFOA
• 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.
• water treatment applications of the present invention include water purifiers, water treatment filters, and the like, so long as they remove PFAS, particularly PFOS and PFOA, by contacting the water to be treated with activated carbon.
• PFAS PFOS and PFOA
• 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, and therefore contamination by PFAS can be prevented when the activated carbon is disposed of.
• 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.
• plants such as wood, sawdust, charcoal, fruit shells such as coconut shells and walnut shells, fruit seeds,
• the carbonaceous raw materials can be used alone or in combination of two or more kinds.
• 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.
• Carbonization treatment Of the above-mentioned activation raw materials, it is preferable to carbonize the uncarbonized carbonaceous materials as necessary before the activation treatment.
• 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.
• 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.
• 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.
• alkali metal hydroxides are preferred, and potassium hydroxide is more preferred.
• the amount of activator used is such that the specific surface area of the activated carbon tends to increase as the mixing ratio of the activator to the activation raw material increases, so it is desirable to adjust the mixing ratio of the activator so that the specific surface area is as described above.
• the mass ratio of the activator to 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.
• the alkaline activation treatment is carried out under an atmosphere of any inert gas, such as argon, helium, or nitrogen.
• 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.
• the cleaning process is a process in which the activated carbon obtained from the alkali activation process is washed with water or with an inorganic acid to remove any alkali metals remaining in the alkali-activated carbon.
• the rate of alkali metal removal can be increased by repeating the cleaning process multiple times.
• the temperature of water used in the water washing treatment is preferably 20° C. to less than 100° C., more preferably 30° C. to 90° C., even more preferably 40° C. to 80° C., and still more preferably 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.
• an inorganic acid that can be used is a hydrogen acid such as hydrochloric acid or hydrofluoric acid, or an oxygen acid such as sulfuric acid, nitric acid, phosphoric acid or perchloric acid, and is preferably hydrochloric acid.
• 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 adjusted as necessary, and is preferably 0.1 wt % to 30 wt %, more preferably 0.5 wt % to 20 wt %, and even more 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 amount of potassium remaining in the alkali activated carbon is preferably 5000 mg/kg or less (more than 0 mg/kg) and the amount of alkali metal remaining 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 amount of alkali metal remaining in the alkali activated carbon can be measured using an ICP atomic emission spectrometer.
• 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.
• Drying treatment is a step for removing moisture from the alkali activated carbon after the washing treatment.
• the drying may be carried out under conditions that can remove the moisture remaining in the alkali activated carbon.
• 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 even more 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.
• 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.
• 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.
• it may be mixed with other materials, for example, any additive such as a binder.
• the alkaline activated carbon of the present invention obtained by appropriately adjusting the manufacturing conditions to obtain the above physical properties, exhibits excellent removal effects against PFAS, especially PFOS and PFOA, in liquids.
• 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.
• KOH/C ratio mass ratio
• the mixture was washed with 5.25 wt % hydrochloric acid for 1 hour, and then filtered by suction.
• the activated carbon after filtration was further repeatedly washed with hot water at 60° C. until the pH of the filtrate reached 6.5 or more, 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 1,150° 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.
• 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.
• 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.
• 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.
• the particle size was adjusted in advance to reduce the effect of particle size before the characteristics were examined. Specifically, the activated carbon was crushed using an agate mortar, and then classified using sieves with mesh sizes of 53 ⁇ m and 125 ⁇ m to adjust the particle size so that the average particle size (D50) was approximately 100 to 150 ⁇ m.
• Particle size of each sample was measured using a laser diffraction particle size distribution analyzer (Shimadzu Corporation, SALD (registered trademark)-2000). From the particle size distribution measurement results obtained, a volume-based cumulative frequency curve was determined, and the average particle size D50 at a cumulative frequency of 50% was calculated.
• the total pore volume (mL/g) was calculated from the nitrogen adsorption amount 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 total acidic functional group amount was determined according to the Boehm method (H.P.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 hydrochloric acid titration amount when the pH became 4.0 was measured.
• H.P.Boehm Adzan.Catal, 16,179(1966)
• Oxygen Content The oxygen content in the activated carbon of the sample dried at 120° C. for 2 hours was measured using a Vario EL cube manufactured by Elementar, with benzoic acid as the standard substance.
• Zeta potential 5 mg of a sample pulverized to an average particle size of about 5 to 10 ⁇ m using a disk mill was added to 25 mL of pure water and stirred to prepare a dispersion.
• 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 2 ⁇ zf(ka)/3 ⁇ z: Zeta potential
• Ue electrophoretic mobility f(ka): Henry function (1.5 for aqueous systems)
• ⁇ Dielectric constant
• PFOS, PFOA equilibrium adsorption test Preparation of PFOS, PFOA test solution 18.0 mg of PFOS (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., purity 100%) or PFOA (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., purity 100%) reagent was weighed into a 50 mL measuring flask, and methanol (manufactured by Kanto Chemical Co., Ltd., for high performance liquid chromatography) was added to dissolve. Next, 5.5 mL or 8.25 mL of this solution was dispensed into a 100 mL measuring flask, and methanol was added up to the mark to dilute. 1 mL or 30 mL of the diluted solution was placed in a 3 L measuring flask, and ultrapure water was added to the measuring flask to prepare PFOS or PFOA test water.
• PFOS, PFOA equilibrium adsorption test A predetermined 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 chamber set at 25°C. The mixture was then filtered through a 0.45 ⁇ m membrane filter and solid-phase extracted using a solid-phase column (PLS-3, manufactured by GL Sciences) to prepare a measurement sample.
• PLS-3 solid-phase column
• 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 analysis 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 ⁇ g/L was calculated using the Freundlich equation.
• PFOA Water Permeability Evaluation Preparation of PFOA Test Solution 301.8 mg of PFOA (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., purity 100%) was added to a 2 L measuring flask, and 1 mL of methanol was added to dissolve it, and then ultrapure water was added to the flask to prepare a PFOA solution with a concentration of 150 mg/L. This solution was transferred to a 2 L plastic bottle and mixed with pure water in the water permeability test device so that the initial concentration was 800 ⁇ g/L, and this was used as the test solution.
• PFOA manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., purity 100%
• Activated carbon dried at 105°C for 15 hours was packed in 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.
• test solution before passing through the column was sampled from the column inlet side before and after starting to pass water through the activated carbon 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.
• the cumulative amount of PFOA adsorbed per weight of activated carbon at a residual concentration of 0.07 ⁇ g/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 when the residual concentration reaches 0.07 ⁇ g/L (L/g-activated carbon) was calculated by dividing the obtained amount of PFOA adsorbed (mg/g-activated carbon) by the initial concentration ( ⁇ g/L) of the test solution.
• test solution 280 L of tap water filtered using a commercially available activated carbon cartridge filter (manufactured by AS ONE, Type-2) was poured into a tank with a capacity of 300 L, and 4.7 mL of sodium hypochlorite solution (manufactured by Kishida Chemical, effective chlorine concentration 12% by weight) was added using a pipetter so that the effective chlorine concentration was 2 mg/L. Then, the test solution was prepared by stirring with a chemical pump.
• the free residual chlorine concentration (mg / L) was measured by adding a 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 in the amount of water flowing per weight of activated carbon (L / g) was calculated, and the cumulative amount of water flowing at a removal rate of 80% was obtained.
• a DPD reagent Karlo Chemical Rapid DPD Reagent (packet)
• Type-2 activated carbon cartridge filter
• phosphate buffer 0.5 mL was added to the test water collected in the 10 mL colorimetric tube and mixed uniformly, and then DPD reagent (manufactured by Kanto Chemical Co., Ltd.) was added and shaken for about 20 seconds, and the residual free chlorine concentration was measured with a chlorine concentration meter (manufactured by HACH Co., Ltd.). Then, 0.1 g of potassium iodide (Kishida Chemical Co., Ltd.) 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 Co., Ltd.) 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%).
• Chloroform Adsorption Performance Evaluation 0.5 g of chloroform (CHCl 3 ) was diluted in 50 ml of methanol, and further diluted 10-fold with methanol to prepare a stock solution. 1 ml of the chloroform stock solution was diluted to 1 L 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.
• the activated carbon was filtered off using a syringe filter, and the filtrate was placed in a screw bottle filled with 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.) TurboMatrix HS, GC/MS: QP2010 manufactured by Shimadzu Corporation) was used.
• An adsorption isotherm was created by calculating the adsorption amount per weight of activated carbon (mg/g) from the concentration in the quantified filtrate, and the equilibrium adsorption amount when the residual chloroform concentration was 0.06 mg/L was determined.
• Example 1 is a preferred example of activated carbon of the present invention, which was subjected to a heat treatment 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.
• the activated carbon of Example 1 which satisfies the present invention, exhibited superior adsorption performance to the activated carbons of Comparative Examples 1 to 3 in tests of PFOS equilibrium adsorption amount, PFOA equilibrium adsorption amount, and PFOA cumulative water flow rate, and was able to increase the removal rate of PFOS and PFOA from water.
• the activated carbon of Example 1 was more effective at removing free residual chlorine (Figure 4) and chloramines ( Figure 5) than the activated carbon of Comparative Examples 2 and 3. Therefore, the activated carbon of the present invention is effective at removing not only PFAS such as PFOS and PFOA, but also total residual chlorine such as free residual chlorine and combined chlorine.
• the activated carbon of Example 1 had a lower effect of removing chloroform than the activated carbons of Comparative Examples 2 and 3.
• the activated carbon of the present invention had a low effect of adsorbing and removing chloroform, but was excellent in the effect of adsorbing and removing PFOS and PFOA.

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