Method for producing activated carbon from superabsorbent polymer having acid groups, activated carbon derived from superabsorbent polymer, use of superabsorbent polymer having acid groups for recycling into activated carbon, and use of superabsorbent polymer having acid groups for recycling superabsorbent polymer having acid groups into activated carbon

Abstract

The purpose of the present disclosure is to provide a method for producing activated carbon from a superabsorbent polymer, the method making it possible to produce activated carbon easily.　The method for producing activated carbon from a superabsorbent polymer having acid groups includes: a preparation step for preparing a crosslinked superabsorbent polymer in which the acid groups of the superabsorbent polymer are crosslinked by a polyvalent metal; a carbonization step for carbonizing the crosslinked superabsorbent polymer and forming a carbide; and an activation step for activating the carbide to form the activated carbon.

Description

Method for producing activated carbon from superabsorbent polymer having acid groups, activated carbon derived from superabsorbent polymer, use of polyvalent metal for recycling superabsorbent polymer containing acid groups into activated carbon, and use of superabsorbent polymer containing acid groups for recycling superabsorbent polymer containing acid groups into activated carbon

[0001] The present disclosure relates to a method for producing activated carbon from a superabsorbent polymer having acid groups, activated carbon derived from the superabsorbent polymer, the use of a polyvalent metal to recycle the superabsorbent polymer containing acid groups into activated carbon, and the use of a superabsorbent polymer containing acid groups to recycle the superabsorbent polymer containing acid groups into activated carbon.

[0002] From the viewpoint of protecting the global environment, recycling of used superabsorbent polymers has been considered. For example, Patent Document 1 discloses a method for producing a carbonized product, which comprises contacting waste containing a superabsorbent polymer that has absorbed moisture containing chloride with an aqueous solution containing at least one of water-soluble phosphates and sulfates to remove chloride ions from the waste, and then heating the waste to carbonize it.

[0003] Japanese Patent Application Laid-Open No. 2022-21365

[0004] First, with regard to the manufacturing method, the present inventors have found that it is difficult to produce activated carbon from a superabsorbent polymer as is. Therefore, an object of the present disclosure is to provide a method for producing activated carbon from a superabsorbent polymer, which allows for the easy production of activated carbon. Second, with regard to the product, the present inventors have found that it is difficult to recycle a superabsorbent polymer into activated carbon. Therefore, an object of the present disclosure is to provide activated carbon derived from a superabsorbent polymer and having excellent adsorption performance.

[0005] First, with regard to the manufacturing method, the present inventors have discovered a method for producing activated carbon from a superabsorbent polymer having acid groups, the method comprising the steps of: preparing a crosslinked superabsorbent polymer in which the acid groups of the superabsorbent polymer are crosslinked with a polyvalent metal; carbonizing the crosslinked superabsorbent polymer to form a carbonized product; and activating the carbonized product to form the activated carbon. Second, with regard to the product, the present inventors have discovered an activated carbon derived from a superabsorbent polymer having acid groups, the activated carbon being characterized by having an iodine adsorption capacity of 2,000 to 4,000 mg / g.

[0006] First, regarding the manufacturing method, the method for manufacturing activated carbon from a superabsorbent polymer according to the present disclosure allows for easy production of activated carbon. Second, regarding the substance, the activated carbon according to the present disclosure is derived from a superabsorbent polymer and has excellent adsorption performance.

[0007] Figure 1 is a photograph of superabsorbent polymer No. 1. Figure 2 is a photograph of carbonized product No. 1. Figure 3 is a photograph of activated carbon No. 1. Figure 4 is a photograph of superabsorbent polymer No. 2. Figure 5 is a photograph of carbonized product No. 2. Figure 6 is a photograph of activated product No. 1. Figure 7 is a photograph of superabsorbent polymer No. 3. Figure 8 is a photograph of carbonized product No. 3. Figure 9 is a photograph of activated product No. 2. Figure 10 is an electron microscope photograph of carbonized product No. 1. Figure 11 is an electron microscope photograph of activated carbon No. 1. Figure 12 is an electron microscope photograph of activated product No. 1. Figure 13 is an electron microscope photograph of activated product No. 2.

[0008] Specifically, the present disclosure relates to the following aspects: [Aspect 1] A method for producing activated carbon from a superabsorbent polymer having acid groups, the method comprising: a preparation step of preparing a crosslinked superabsorbent polymer in which the acid groups of the superabsorbent polymer are crosslinked with a polyvalent metal; a carbonization step of carbonizing the crosslinked superabsorbent polymer to form a char; and an activation step of activating the char to form the activated carbon.

[0009] The method for producing activated carbon includes a predetermined preparation step. In the crosslinked superabsorbent polymer, a polyvalent metal crosslinks the acid groups of the superabsorbent polymer, making the crosslinked superabsorbent polymer less sticky. As a result, the polyvalent metal can maintain a state in which individual particles of the crosslinked superabsorbent polymer are less likely to combine with other particles.

[0010] The method for producing activated carbon also includes a predetermined carbonization step. In the carbonization step, the superabsorbent polymer is crosslinked with a polyvalent metal, which prevents the crosslinked superabsorbent polymer from crystallizing into a glassy state while maintaining a state in which the individual particles of the crosslinked superabsorbent polymer are less likely to integrate with other particles (i.e., the individual particles are generally separated). As a result, a uniform carbonized product can be easily formed from the crosslinked superabsorbent polymer.

[0011] Furthermore, since the above-mentioned method for producing activated carbon includes a predetermined activation step, activated carbon can be easily produced from a uniform carbonized material. Note that the inventors of the present application have found that if a superabsorbent polymer is simply carbonized and activated, glass-like crystallization occurs during the carbonization, and activated carbon is not formed.

[0012] [Aspect 2] The method according to Aspect 1, wherein the carbonized material is activated by a gas activation method in the activation step. In the method for producing activated carbon, the carbonized material is activated by a gas activation method in the activation step, so that activated carbon can be produced easily.

[0013] [Aspect 3] The method according to Aspect 1 or 2, wherein the activation step is carried out for 0.1 to 2.0 hours. In the method for producing activated carbon, the activation step is carried out for a predetermined time. Since the predetermined time is shorter than the time for a typical deactivation step, activated carbon can be easily produced from a superabsorbent polymer.

[0014] [Aspect 4] The method according to any one of Aspects 1 to 3, wherein the crosslinked superabsorbent polymer contains 20 to 50% by mass of the polyvalent metal in a dry state.

[0015] In the method for producing activated carbon, the superabsorbent polymer in which acid groups are crosslinked contains a predetermined amount of polyvalent metal, which prevents the crosslinked superabsorbent polymer from crystallizing into a glass-like state during the carbonization step, making it possible to easily produce activated carbon from the superabsorbent polymer.

[0016] [Aspect 5] The method of any one of aspects 1 to 4, wherein the crosslinked superabsorbent polymer has a moisture regain of greater than 0% and less than or equal to 40% by weight.

[0017] In the above-mentioned method for producing activated carbon, since the crosslinked superabsorbent polymer has a predetermined moisture content in the preparation step, it is possible to prevent the crosslinked superabsorbent polymer from burning during the carbonization step, and it is easier to maintain a state in which individual particles of the crosslinked superabsorbent polymer are less likely to combine with other particles (a state in which the individual particles are largely separated), which ultimately makes it possible to easily produce activated carbon from the superabsorbent polymer.

[0018] [Aspect 6] The method according to any one of Aspects 1 to 5, wherein the superabsorbent polymer is a polyacrylic acid-based superabsorbent polymer containing a carboxyl group as the acid group. In the method for producing activated carbon, since the superabsorbent polymer is an acrylic acid-based superabsorbent polymer containing a carboxyl group, activated carbon can be easily produced from the superabsorbent polymer.

[0019] [Aspect 7] The method according to any one of Aspects 1 to 6, wherein the polyvalent metal is calcium. In the method for producing activated carbon, since the polyvalent metal is calcium, activated carbon can be easily produced from a superabsorbent polymer.

[0020] [Embodiment 8] The method of any one of embodiments 1 to 7, wherein the crosslinked superabsorbent polymer is derived from recycled sanitary products.

[0021] In the above-described method for producing activated carbon, the cross-linked superabsorbent polymer is derived from the recovered sanitary goods, and therefore the superabsorbent polymer contained in the recovered sanitary goods can be easily recycled into activated carbon, thereby reducing the environmental impact.

[0022] Aspect 9: The method of any one of aspects 1 to 8, wherein the crosslinked superabsorbent polymer is derived from a used sanitary product.

[0023] In the method for producing activated carbon, the cross-linked superabsorbent polymer is derived from used sanitary products, so the superabsorbent polymer contained in used sanitary products can be easily recycled into activated carbon, thereby reducing the environmental impact.

[0024] [Aspect 10] The method according to any one of Aspects 1 to 9, wherein the crosslinked superabsorbent polymer is formed by adding a polyvalent metal ion source capable of supplying polyvalent metal ions to the superabsorbent polymer that has absorbed body fluid, and then draining the body fluid from the superabsorbent polymer.

[0025] In the method for producing activated carbon, the crosslinked superabsorbent polymer is a predetermined one, which reduces the energy required for the subsequent carbonization step and also makes it possible to easily recycle the superabsorbent polymer contained in used sanitary products into activated carbon, thereby reducing the environmental impact.

[0026] [Aspect 11] The method of any one of Aspects 1 to 10, further comprising a crosslinking step of adding a polyvalent metal ion source capable of supplying polyvalent metal ions to the superabsorbent polymer absorbing body fluid, thereby draining the body fluid from the superabsorbent polymer and forming the crosslinked superabsorbent polymer.

[0027] In the method for producing activated carbon, the preparation step includes a specific crosslinking step, which reduces the energy required for the subsequent carbonization step and allows the superabsorbent polymer contained in used sanitary products to be easily recycled into activated carbon, thereby reducing the environmental impact.

[0028] [Aspect 12] The method according to any one of aspects 1 to 11, wherein the crosslinked superabsorbent polymer comprises a material derived from a hygiene product, and the crosslinked superabsorbent polymer is agitated in the carbonization step.

[0029] When the crosslinked superabsorbent polymer contains materials derived from sanitary products, particularly fragments of materials such as pulp fibers, pieces of nonwoven fabric, pieces of film, etc., the inside of the crosslinked superabsorbent polymer is difficult to carbonize in the carbonization step, and the carbonized product tends to be formed nonuniformly. In the above-mentioned method for producing activated carbon, the crosslinked superabsorbent polymer is stirred in the carbonization step, which makes it easier to produce a uniform carbonized product, and ultimately makes it possible to easily produce activated carbon from the superabsorbent polymer.

[0030] [Aspect 13] The method according to aspect 12, further comprising a milling step of milling the carbonized material after the carbonizing step and before the activating step.

[0031] When the crosslinked superabsorbent polymer contains materials derived from sanitary goods, particularly fragments of materials such as pulp fibers, pieces of nonwoven fabric, or pieces of film, stirring the crosslinked superabsorbent polymer facilitates the uniform formation of a carbonized product, but the carbonized product may form large lumps. Because the method for producing activated carbon includes a predetermined pulverization step, activated carbon can be easily produced during the activation step, even if the carbonized product forms large lumps during the carbonization step.

[0032] [Aspect 14A] Activated carbon derived from a highly water-absorbent polymer containing acid groups, characterized in that the activated carbon has an iodine adsorption capacity of 2,000 to 4,000 mg / g.

[0033] The activated carbon is derived from a highly water-absorbent polymer. The activated carbon also has a predetermined iodine adsorption capacity. Iodine has a molecular weight of approximately 254, and high iodine adsorption capacity means high adsorption capacity for odorous components, which are said to have a molecular weight of approximately 30 to 300. Therefore, the activated carbon has excellent adsorption capacity.

[0034] [Aspect 14B] Activated carbon having an iodine adsorption capacity of 2,000 to 4,000 mg / g. The activated carbon has a predetermined iodine adsorption capacity and is excellent in adsorption capacity.

[0035] [Aspect 14C] Activated carbon containing 10 to 50% by mass of a polyvalent metal. The activated carbon contains a predetermined amount of the polyvalent metal. Therefore, the polyvalent metal helps the activated carbon to have a predetermined strength, and the activated carbon has excellent crushability and easy particle size adjustment.

[0036] [Aspect 15] The activated carbon according to any one of Aspects 14A and 14B, wherein the activated carbon contains 10 to 50 mass% of a polyvalent metal. The activated carbon contains a predetermined amount of the polyvalent metal. Therefore, the polyvalent metal makes the activated carbon more likely to have a predetermined strength, and the activated carbon has excellent crushability and easy adjustment of particle size.

[0037] [Aspect 16] The activated carbon of any one of Aspects 14A, 14B, 14C, and 15, wherein the activated carbon comprises micropores and mesopores, and the volume of the mesopores is greater than the volume of the micropores.

[0038] Activated carbon generally has a larger micropore volume than mesopore volume, and as a result, often has a large BET specific surface area. Unlike general activated carbon, the activated carbon has a larger mesopore volume than micropore volume. This allows it to efficiently adsorb adsorbates (molecules, ions, etc.) that are larger in size than the micropores. Furthermore, as is clear from the excellent iodine adsorption performance of the activated carbon, it can efficiently absorb iodine with a diameter of about 0.5 nm, and this adsorption performance is presumed to be due to the large mesopore volume. From the above, the activated carbon has excellent adsorption performance.

[0039] [Aspect 17] The activated carbon according to any one of Aspects 14A, 14B, 14C, 15, and 16, wherein the mesopore volume is 0.200 mL / g to 0.600 mL / g.

[0040] Since the activated carbon has a mesopore volume within a predetermined range, the activated carbon has a low density, in other words, a low bulk density, and when used in a filter (for example, for gases, liquids, etc.), the weight of the filter can be reduced. Furthermore, the reduced bulk density of the activated carbon can reduce the airflow resistance when used in a gas filter, and can reduce the liquid flow resistance when used in a liquid filter.

[0041] [Aspect 18] The activated carbon according to any one of Aspects 14A, 14B, 14C, and 15 to 17, wherein the micropore volume is 0.005 to 0.100 mL / g. Since the activated carbon has a micropore volume in the predetermined low range, the activated carbon is likely to have excellent iodine adsorption performance, and therefore has excellent adsorption performance.

[0042] [Aspect 19] The activated carbon has a viscosity of 50 to 250 m 2 The activated carbon according to any one of Aspects 14A, 14B, 14C, and 15 to 18, having a BET specific surface area of ​​1 / g. The activated carbon has a predetermined BET specific surface area. Therefore, the activated carbon is less likely to become brittle and is easy to handle.

[0043] [Aspect 20] The activated carbon according to any one of Aspects 14A, 14B, 14C, and 15 to 19, wherein the activated carbon has a bulk density of 0.100 to 0.500 g / mL.

[0044] The activated carbon has a predetermined bulk density. Therefore, when the activated carbon is used in a filter (for example, for gases, liquids, etc.), the weight of the filter can be reduced. Furthermore, by reducing the bulk density of the activated carbon, when the activated carbon is used in a gas filter, the airflow resistance can be reduced, and when the activated carbon is used in a liquid filter, the liquid flow resistance can be reduced.

[0045] [Aspect 21] The activated carbon according to any one of Aspects 14A, 14B, 14C, and 15 to 20, having a crushing strength of 200 to 7,000 kPa. The activated carbon has a predetermined crushing strength. Therefore, the activated carbon has excellent crushability and easy adjustment of particle size.

[0046] [Aspect 22A] Use of a polyvalent metal for recycling a superabsorbent polymer containing acid groups into activated carbon, wherein the superabsorbent polymer containing acid groups is a crosslinked superabsorbent polymer in which the acid groups are crosslinked by the polyvalent metal.

[0047] The inventors of the present invention have found that if a superabsorbent polymer is simply carbonized and activated in order to recycle it into activated carbon, glass-like crystallization occurs during carbonization, and activated carbon is not formed even after the activation step. In the above-mentioned use, the superabsorbent polymer containing acid groups is a crosslinked superabsorbent polymer in which the acid groups are crosslinked with a polyvalent metal, so that the superabsorbent polymer can be easily recycled into activated carbon.

[0048] [Aspect 22B] Use of a polyvalent metal for producing activated carbon from a superabsorbent polymer containing acid groups, wherein the superabsorbent polymer containing acid groups is a crosslinked superabsorbent polymer in which the acid groups are crosslinked by the polyvalent metal.

[0049] The inventors of the present invention have found that if a superabsorbent polymer is simply carbonized and activated to produce activated carbon from it, glass-like crystallization occurs during carbonization, and activated carbon is not formed even after the activation step. In the above-mentioned use, the superabsorbent polymer containing acid groups is a crosslinked superabsorbent polymer in which the acid groups are crosslinked with a polyvalent metal, so that activated carbon can be easily produced from the superabsorbent polymer.

[0050] [Aspect 23A] Use of a superabsorbent polymer containing acid groups for recycling the superabsorbent polymer containing acid groups into activated carbon, wherein the superabsorbent polymer containing acid groups is a crosslinked superabsorbent polymer in which the acid groups are crosslinked with a polyvalent metal.

[0051] The inventors of the present invention have found that if a superabsorbent polymer is simply carbonized and activated in order to recycle it into activated carbon, glass-like crystallization occurs during carbonization, and activated carbon is not formed even after the activation step. In the above-mentioned use, the high-grade aqueous polymer containing acid groups is a crosslinked superabsorbent polymer in which the acid groups are crosslinked with a polyvalent metal, so that the superabsorbent polymer can be easily recycled into activated carbon.

[0052] [Aspect 23B] Use of a superabsorbent polymer containing acid groups for producing activated carbon, wherein the superabsorbent polymer containing acid groups is a crosslinked superabsorbent polymer in which the acid groups are crosslinked with a polyvalent metal.

[0053] The inventors of the present invention have found that if a superabsorbent polymer is simply carbonized and activated to produce activated carbon from it, glass-like crystallization occurs during carbonization, and activated carbon is not formed even after the activation step. In the above-mentioned use, the high-grade aqueous polymer containing acid groups is a crosslinked superabsorbent polymer in which the acid groups are crosslinked with a polyvalent metal, so that activated carbon can be easily produced from the superabsorbent polymer.

[0054] [Aspect 24] The use according to any one of Aspects 22A, 22B, 23A, and 23B, wherein the activated carbon has an iodine adsorption capacity of 2,000 to 4,000 mg / g. In this use, the activated carbon has a predetermined iodine adsorption capacity. Therefore, this use allows the superabsorbent polymer to be recycled into activated carbon with excellent adsorption capacity.

[0055] [Aspect 25] The use according to any one of Aspects 22A, 22B, 23A, 23B, and 24, wherein the crosslinked highly absorbent polymer contains 10 to 50% by mass of the polyvalent metal in a dry state.

[0056] In the above-mentioned use, the crosslinked superabsorbent polymer contains a predetermined amount of polyvalent metal in a dry state. Therefore, when the superabsorbent polymer is carbonized, the superabsorbent polymer can be prevented from crystallizing into a glass-like state. As a result, the above-mentioned use allows the superabsorbent polymer to be easily recycled into activated carbon.

[0057] [Aspect 26] The use according to any one of Aspects 22A, 22B, 23A, 23B, 24, and 25, wherein the crosslinked superabsorbent polymer has a moisture regain of greater than 0% and less than or equal to 40% by weight.

[0058] In the above-mentioned use, since the crosslinked superabsorbent polymer has a predetermined moisture content, the crosslinked superabsorbent polymer becomes less flammable during the carbonization step, and the individual particles of the crosslinked superabsorbent polymer tend to remain in a state in which they are less likely to combine with other particles (the individual particles are generally separated), which ultimately allows the superabsorbent polymer to be easily recycled into activated carbon.

[0059] [Aspect 27] The use according to any one of Aspects 22A, 22B, 23A, 23B, and 24 to 26, wherein the high-quality aqueous polymer containing acid groups absorbs body fluids. In this use, since the high-quality aqueous polymer containing acid groups absorbs body fluids, the used superabsorbent polymer can be reused.

[0060] [Aspect 28] The activated carbon according to Aspect 14C, having an iodine adsorption capacity of 2,000 to 4,000 mg / g. The activated carbon has a predetermined iodine adsorption capacity and is excellent in adsorption capacity.

[0061] The method for producing activated carbon from a superabsorbent polymer having acid groups according to the present disclosure (hereinafter, sometimes simply referred to as the "method for producing activated carbon"), the use of a polyvalent metal according to the present disclosure for recycling a superabsorbent polymer containing acid groups into activated carbon (hereinafter, sometimes referred to as the "use of a polyvalent metal according to the present disclosure"), and the use of a superabsorbent polymer containing acid groups according to the present disclosure for recycling a superabsorbent polymer containing acid groups into activated carbon (hereinafter, sometimes referred to as the "use of a superabsorbent polymer according to the present disclosure") will be described in detail below. Note that the use of a polyvalent metal according to the present disclosure and the use of a superabsorbent polymer according to the present disclosure are the same as the method for producing activated carbon according to the present disclosure, so separate descriptions will be omitted.

[0062] The method for producing activated carbon according to the present disclosure includes the following steps: - a preparation step of preparing a crosslinked superabsorbent polymer in which the acid groups of the superabsorbent polymer are crosslinked with a polyvalent metal (hereinafter, this step may be referred to as the "preparation step"); - a carbonization step of carbonizing the crosslinked superabsorbent polymer to form a carbonized product (hereinafter, this step may be referred to as the "carbonization step"); - an activation step of activating the carbonized product to form the activated carbon (hereinafter, this step may be referred to as the "activation step").

[0063] [Preparation Step] In the preparation step, a crosslinked superabsorbent polymer is prepared in which the acid groups of the superabsorbent polymer are crosslinked with a polyvalent metal. The superabsorbent polymer is not particularly limited as long as it has an acid group, and examples thereof include those containing a carboxyl group, a sulfo group, or the like, with those containing a carboxyl group being preferred. Examples of superabsorbent polymers containing carboxyl groups include polyacrylates and polymaleic anhydrides, and examples of superabsorbent polymers containing sulfo groups or the like include polysulfonates.

[0064] The polyvalent metal refers to a metal capable of forming an anion having an ionic valence of two or more, and examples thereof include alkaline earth metals and transition metals. Examples of the alkaline earth metals include beryllium, magnesium, calcium, strontium, and barium. Examples of the transition metals include iron, cobalt, nickel, and copper. Calcium is preferred as the polyvalent metal. This facilitates the easy production of activated carbon from the highly water-absorbent polymer.

[0065] The crosslinked superabsorbent polymer can be formed, for example, by mixing a superabsorbent polymer having acid groups with a polyvalent metal ion source capable of supplying the polyvalent metal ions, which are ions of the polyvalent metal, in the presence of water. The water can be water added from the outside, such as an aqueous solution of the polyvalent metal ion source, or it can be water absorbed by the superabsorbent polymer, such as body fluid.

[0066] Examples of the polyvalent metal ion source include alkaline earth metal hydroxides (e.g., calcium hydroxide, magnesium hydroxide), salts of alkaline earth metal hydroxides and acids (e.g., calcium chloride, calcium nitrate, magnesium chloride, magnesium nitrate), and alkaline earth metal oxides (e.g., calcium oxide, magnesium oxide), with calcium chloride being preferred.

[0067] Examples of the polyvalent metal ion source include transition metal hydroxides (e.g., iron hydroxide, cobalt hydroxide, nickel hydroxide, copper hydroxide), transition metal hydroxides and acid salts, and transition metal oxides (e.g., iron oxide, cobalt oxide, nickel oxide, copper oxide).

[0068] The acid is not particularly limited, and examples thereof include inorganic acids and organic acids. Examples of the inorganic acid include sulfuric acid, hydrochloric acid, and nitric acid. Of the inorganic acids, sulfuric acid is preferred from the viewpoints of not containing chlorine and cost. Examples of the organic acid include those having an acid group, such as a carboxyl group or a sulfo group. An organic acid having a sulfo group is called a sulfonic acid, and an organic acid having a carboxyl group but not a sulfo group is called a carboxylic acid.

[0069] Examples of the organic acid include citric acid, tartaric acid, malic acid, succinic acid, and oxalic acid (all of which are carboxylic acids having a plurality of carboxyl groups), gluconic acid (C6), pentanoic acid (C5), butanoic acid (C4), propionic acid (C3), glycolic acid (C2), and acetic acid (C2); glacial acetic acid and formic acid (C1) (all of which are carboxylic acids having one carboxyl group); methanesulfonic acid, trifluoromethanesulfonic acid, benzenesulfonic acid, and p-toluenesulfonic acid (all of which are sulfonic acids).

[0070] Specific examples of the hydroxides and acid salts of the transition metals include inorganic acid salts and organic acid salts. Examples of the inorganic acid salts include iron salts such as iron chloride, iron sulfate, iron phosphate, and iron nitrate, cobalt salts such as cobalt chloride, cobalt sulfate, cobalt phosphate, and cobalt nitrate, nickel salts such as nickel chloride and nickel sulfate, and copper salts such as copper chloride and copper sulfate. Examples of the organic acid salts include iron lactate, cobalt acetate, cobalt stearate, nickel acetate, and copper acetate.

[0071] In addition, since the polyvalent metal ions crosslink the acid groups of the superabsorbent polymer, it is preferable that the acid has an acid dissociation constant (pKa, in water) smaller than the acid dissociation constant (pKa, in water) of the acid groups in the superabsorbent polymer.

[0072] When the acid has multiple acid groups, for example, when the acid is a dibasic or tribasic acid, the largest of the acid dissociation constants (pKa, in water) of the acid is preferably smaller than the acid dissociation constant (pKa, in water) of the acid group of the superabsorbent polymer, and when the superabsorbent polymer has multiple types of acid groups, the largest of the acid dissociation constants (pKa, in water) of the acid is preferably smaller than the smallest of the acid dissociation constants (pKa, in water) of the multiple types of acid groups of the superabsorbent polymer. This is from the viewpoint of crosslinking the acid groups of the superabsorbent polymer with polyvalent metal ions.

[0073] In this specification, the acid dissociation constant (pKa, in water) may be the value described in the Electrochemical Handbook compiled by the Electrochemical Society.

[0074] The crosslinked superabsorbent polymer contains the polyvalent metal in a dry state, preferably at least 20% by mass, more preferably at least 25% by mass, and even more preferably at least 30% by mass. The crosslinked superabsorbent polymer contains the polyvalent metal in a dry state, preferably at most 50% by mass, more preferably at most 48% by mass, and even more preferably at most 45% by mass. This prevents the crosslinked superabsorbent polymer from crystallizing into a glass-like state during the carbonization step, making it easy to produce activated carbon from the superabsorbent polymer. A small amount of the polyvalent metal tends to make it difficult to form activated carbon, and an increase in the amount of the polyvalent metal may result in a decrease in the activated carbon ratio, resulting in a decrease in activated carbon performance.

[0075] In this specification, the above-mentioned dry state means a state in which the crosslinked superabsorbent polymer is dried at 110° C. for 3 hours.

[0076] The crosslinked superabsorbent polymer preferably has a moisture content of more than 0% by mass, more preferably 1% by mass or more, and even more preferably 2% by mass or more. The crosslinked superabsorbent polymer preferably has a moisture content of 40% by mass or less, more preferably 30% by mass or less, and even more preferably 20% by mass or less. This prevents the crosslinked superabsorbent polymer from burning during the carbonization step, and also helps maintain a state in which individual particles of the crosslinked superabsorbent polymer are less likely to combine with other particles (i.e., the individual particles are generally separated), thereby facilitating the production of activated carbon from the superabsorbent polymer. Note that a higher moisture content increases the energy required for the carbonization step, and also makes the individual particles of the crosslinked superabsorbent polymer more sticky and more likely to combine with other particles.

[0077] In this specification, the moisture content can be measured using an infrared moisture meter FD-720 manufactured by Kett Corporation. Specifically, approximately 5 g of a sample is placed on the sample tray of the FD-720, the temperature is set to 150°C, the automatic stop mode is selected, and the moisture content (mass%) of the sample is measured.

[0078] The cross-linked superabsorbent polymer may be free of other materials, for example, the cross-linked superabsorbent polymer may be formed from virgin superabsorbent polymer.

[0079] The crosslinked superabsorbent polymer may also contain other materials. Examples of the other materials include materials derived from sanitary products. The sanitary products are not particularly limited as long as they contain a superabsorbent polymer, and examples include disposable diapers, urine absorption pads, incontinence pads, sanitary napkins, panty liners, sanitary shorts, absorbent shorts, pet sheets, cat litter, bed sheets, and bedsore pads. Examples of the materials derived from sanitary products include materials such as pulp fibers, nonwoven fabrics, and films, particularly fragments of materials such as pulp fiber pieces, nonwoven fabric pieces, and film pieces.

[0080] An example of the crosslinked superabsorbent polymer containing materials derived from sanitary products is the superabsorbent polymer that has been subjected to the sieving step S41 in JP 2024-062047 A.

[0081] The crosslinked superabsorbent polymer can be derived from a sanitary product, for example, from a recycled sanitary product, such as an unused sanitary product or a used sanitary product. Because the crosslinked superabsorbent polymer is derived from a recycled sanitary product, the superabsorbent polymer contained in the recycled sanitary product can be easily recycled into activated carbon, thereby reducing the environmental impact. Because the crosslinked superabsorbent polymer is derived from a used sanitary product, the superabsorbent polymer contained in the used sanitary product can be easily recycled into activated carbon, thereby reducing the environmental impact.

[0082] When the crosslinked superabsorbent polymer is derived from a used sanitary product, the crosslinked superabsorbent polymer is preferably formed by adding a polyvalent metal ion source capable of supplying polyvalent metal ions to the superabsorbent polymer that has absorbed body fluids, and then draining the body fluids from the superabsorbent polymer. This reduces the energy required for the subsequent carbonization step, and allows the superabsorbent polymer contained in the used sanitary product to be easily recycled into activated carbon, thereby reducing the environmental impact. Note that the polyvalent metal ions refer to ions formed from the above-mentioned polyvalent metals, and the polyvalent metal ion source is as described above.

[0083] The crosslinked superabsorbent polymer can include a crosslinking step in which a polyvalent metal ion source capable of supplying polyvalent metal ions to the superabsorbent polymer absorbing body fluid is added to the superabsorbent polymer, thereby discharging the body fluid from the superabsorbent polymer and forming the crosslinked superabsorbent polymer. This reduces the energy required for the subsequent carbonization step and allows the superabsorbent polymer contained in used sanitary products to be easily recycled into activated carbon, thereby reducing the environmental impact.

[0084] [Carbonization Step] In the carbonization step, the crosslinked superabsorbent polymer is carbonized to form a carbonized product. The carbonization step can be carried out using a method known in the art. For example, the carbonization step can be carried out by placing the crosslinked superabsorbent polymer in a carbonization furnace and maintaining the furnace in an oxygen-free environment at a predetermined temperature for a predetermined time.

[0085] Examples of the carbonization furnace include a hybrid carbonization furnace (a hybrid of heat and microwave), a rocking drum carbonization furnace, and a fluidized bed carbonization furnace. The oxygen-free state can be achieved, for example, by blowing nitrogen, superheated steam, or the like into the carbonization furnace. The oxygen-free state can also be achieved by gas generated from the crosslinked superabsorbent polymer. The predetermined temperature is, for example, preferably 200°C or higher, more preferably 300°C or higher, and even more preferably 350°C or higher, and preferably 800°C or lower, more preferably 700°C or lower, and even more preferably 600°C or lower. The predetermined time is preferably 0.5 hours or higher, more preferably 1.0 hours or higher, and even more preferably 1.5 hours or higher, and preferably 5.0 hours or lower, more preferably 4.0 hours or lower, and even more preferably 3.0 hours or lower.

[0086] The predetermined temperature can be a plurality of different temperatures. For example, the carbonization furnace can be heated to a relatively low temperature and maintained for a certain period of time, and then heated to a relatively high temperature and maintained for a certain period of time. The difference between the relatively low temperature and the relatively high temperature is preferably 40°C or more, more preferably 60°C or more, and even more preferably 70°C or more, and is preferably 160°C or less, more preferably 140°C or less, and even more preferably 130°C or less. This can suppress the amount of gas generated from the crosslinked superabsorbent polymer.

[0087] When the crosslinked superabsorbent polymer contains materials derived from sanitary products, particularly pulp fibers, the crosslinked superabsorbent polymer can be stirred during the carbonization step. The stirring can be carried out, for example, for preferably at least 1 second, more preferably at least 3 seconds, and even more preferably at least 5 seconds, and preferably at most 60 seconds, more preferably at most 40 seconds, and even more preferably at most 30 seconds per 10 minutes. This facilitates the production of a uniform carbonized product, thereby facilitating the production of activated carbon from the superabsorbent polymer.

[0088] In addition, when the crosslinked superabsorbent polymer contains pulp fibers, the crosslinked superabsorbent polymers tend to bond together and granulate as the carbonization progresses due to the pulp fibers, making it difficult for the carbonization to proceed uniformly, and therefore it is preferable to carry out the stirring.

[0089] Before the subsequent activation step, a grinding step may be performed to grind the carbonized material formed in the carbonization step. This facilitates the formation of activated carbon during the activation step, even if the carbonized material forms large lumps during the carbonization step. When the crosslinked superabsorbent polymer contains materials derived from sanitary products, particularly pulp fibers, the particle size of the carbonized material tends to be large. Therefore, the grinding step is preferably performed to ensure uniform activation. The grinding step can be performed using a grinding device known in the art, such as a jet mill.

[0090] [Activation Step] In the activation step, the carbonized material is activated to form the activated carbon. The activation step can be performed using an activation method known in the art, such as a gas activation method or a chemical activation method. Gases used in the gas activation method include steam, carbon dioxide, and air. Chemicals used in the chemical activation method include zinc chloride, magnesium chloride, tin chloride, aluminum chloride, calcium chloride, quicklime, slaked lime, calcium phosphate, calcium sulfate, potassium sulfide, potassium thiocyanate, sulfuric acid, phosphoric acid, and boric acid.

[0091] In the activation step, the carbonized material is preferably activated by a gas activation method, which allows for easy formation of activated carbon. Furthermore, the gas activation method is preferably a gas activation method using water vapor, which allows for easy formation of activated carbon.

[0092] The activation step can be carried out by placing the carbonized material in an activation furnace and maintaining the furnace at a predetermined temperature for a predetermined time. Examples of the activation furnace include steam activation furnaces, such as rotary kilns. The predetermined temperature is preferably 800°C or higher and preferably 900°C or lower. The predetermined time is preferably 0.1 hours or higher, more preferably 0.2 hours or higher, and even more preferably 0.3 hours or higher. The predetermined time is preferably 2.0 hours or lower, more preferably 1.5 hours or lower, and even more preferably 1.0 hour or lower. By setting the predetermined time within the above range, activated carbon can be easily formed from the superabsorbent polymer. Note that if the predetermined time is short, activated carbon may not be formed, while if the predetermined time is long, the activated carbon tends to have more pores.

[0093] The activated carbon derived from a superabsorbent polymer according to the present disclosure (hereinafter, sometimes referred to as "activated carbon according to the present disclosure" or simply "activated carbon") will be described in detail below.

[0094] The activated carbon according to the present disclosure is derived from a highly water-absorbent polymer containing an acid group. The highly water-absorbent polymer is not particularly limited as long as it has an acid group, and examples thereof include those described in the "Preparation Step" in the "Method for Producing Activated Carbon" above.

[0095] The activated carbon according to the present disclosure has an iodine adsorption capacity of 2,000 mg / g or more, preferably 2,200 mg / g or more, and more preferably 2,300 mg / g or more. The activated carbon also has an iodine adsorption capacity of 4,000 mg / g or less, preferably 3,700 mg / g or less, and more preferably 3,500 mg / g or less. This provides the activated carbon with excellent adsorption capacity. In this specification, the iodine adsorption capacity is measured in accordance with "7.1.2.2 Iodine Adsorption Capacity" in "Test Methods for Activated Carbon" of JIS K1474:2014.

[0096] The activated carbon contains a polyvalent metal at a concentration of preferably 10% by mass or more, more preferably 15% by mass or more, even more preferably 20% by mass or more, and even more preferably 25% by mass or more. The activated carbon also contains a polyvalent metal at a concentration of preferably 50% by mass or less, more preferably 45% by mass or less, and even more preferably 43% by mass or less. This makes it easier for the activated carbon to have a predetermined strength due to the polyvalent metal, and the activated carbon has excellent crushability and is easy to adjust the particle size.

[0097] The concentration can be measured using an analytical scanning electron microscope, such as the FlexSEM1000II scanning electron microscope manufactured by Hitachi High-Tech Corporation.

[0098] The activated carbon may comprise pores, which may be divided into micropores, mesopores, and macropores, with the micropores having pores between 0.34 and 2.0 nm, the mesopores having pores between 3.4 and 200 nm, and the macropores having pores greater than 200 nm.

[0099] In the activated carbon, the volume of the mesopores is preferably larger than the volume of the micropores. This allows the activated carbon to have excellent adsorption performance. For the same reasons, the volume of the mesopores is preferably 5 times or more, more preferably 10 times or more, and even more preferably 15 times or more larger than the volume of the micropores. For the same reasons, the volume of the mesopores is preferably 50 times or less, more preferably 40 times or less, and even more preferably 30 times or less larger than the volume of the micropores.

[0100] The volume of the mesopores is preferably 0.200 mL / g or more, more preferably 0.300 mL / g or more, and even more preferably 0.330 mL / g or more. The volume of the mesopores is preferably 0.600 mL / g or less, more preferably 0.500 mL / g or less, and even more preferably 0.450 mL / g or less. This reduces the density of the activated carbon, and when used in filters (for example, gases, liquids, etc.), the weight of the filter can be reduced. When the activated carbon is used in a gas filter, the airflow resistance can be reduced, and when the activated carbon is used in a liquid filter, the liquid flow resistance can be reduced.

[0101] The volume of the micropores is preferably 0.005 mL / g or more, more preferably 0.010 mL / g or more, and even more preferably 0.013 mL / g or more. The volume of the micropores is preferably 0.100 mL / g or less, more preferably 0.060 mL / g or less, and even more preferably 0.040 mL / g or less. This provides the activated carbon with excellent adsorption performance.

[0102] The mesopore volume (mL / g) is calculated using the nitrogen adsorption method based on the BJH method, using the FHH-BEL.t standard curve recommended by Microtrac-Bell Corporation, to calculate the volume of pores with diameters of 3.4 nm to 200 nm. The measurement conditions for the nitrogen adsorption method are as follows: - Pretreatment method: Vacuum degassing at 120°C for 8 hours. - Measurement method: Nitrogen adsorption / desorption isotherm is measured using the constant volume method. - Adsorption temperature: 77.35 K - Saturated vapor pressure: measured - Adsorbate: nitrogen - Adsorbate cross-sectional area: 0.162 nm 2 - Equilibrium waiting time 1) :500 seconds 1) Waiting time after reaching adsorption equilibrium (the state where the pressure change during adsorption / desorption is below a specified value)

[0103] The micropore volume (mL / g) was calculated using the nitrogen adsorption method based on the t-plot method, using the volume of pores with diameters of 0.34 nm to 2.0 nm on the Harkins-Jura-BEL.t standard curve recommended by Microtrac-Bell Co., Ltd. The measurement conditions for the nitrogen adsorption method were the same as those for measuring the mesopore volume.

[0104] The activated carbon is preferably 50 m 2 / g or more, more preferably 60m 2 / g or more, and more preferably 70m 2 The activated carbon preferably has a BET specific surface area of ​​250 m 2 / g or less, more preferably 220m 2 / g or less, and more preferably 200m 2 / g or less, thereby providing the activated carbon with excellent adsorption performance. In this specification, the BET specific surface area is measured in accordance with "6.3.1 Static volume method" of JIS Z8830:2013, "Method for measuring the specific surface area of ​​powders (solids) by gas adsorption."

[0105] The activated carbon preferably has a bulk density of 0.100 g / mL or more, more preferably 0.150 g / mL or more, and even more preferably 0.180 g / mL or more. The activated carbon also preferably has a bulk density of 0.500 g / mL or less, more preferably 0.400 g / mL or less, and even more preferably 0.350 g / mL or less. This allows the weight of the filter to be reduced when the activated carbon is used in a filter (e.g., for gases, liquids, etc.). Furthermore, the reduced bulk density of the activated carbon allows for reduced airflow resistance when the activated carbon is used in a gas filter, and reduced liquid flow resistance when the activated carbon is used in a liquid filter.

[0106] In this specification, bulk specific gravity is measured in accordance with "7.8.2 Manual filling method" of "7.8 Filling density" of "Testing methods for activated carbon" in JIS K1474:2014.

[0107] The activated carbon preferably has a crushing strength of 200 kPa or more, more preferably 300 kPa or more, and even more preferably 400 kPa or more. The activated carbon also preferably has a crushing strength of 7,000 kPa or less, more preferably 5,000 kPa or less, and even more preferably 4,000 kPa or less. This allows the activated carbon to have excellent crushability and facilitates adjustment of particle size.

[0108] In this specification, the crushing strength can be measured using a Better Hardness Tester, BHT-500, manufactured by Seishin Enterprise Co., Ltd. under the following conditions: Load cell: 500 gf Temperature: 25°C Humidity: 55% RH Number of samples taken: 10 Note that the activated carbon sample used to measure the crushing strength is assumed to pass through a sieve with a mesh size of 500 μm and remain on a sieve with a mesh size of 300 μm.

[0109] The present disclosure will be described below using examples, but the present disclosure is not limited to these examples. [Example 1] A plurality of used disposable diapers were prepared. The plurality of used disposable diapers contained a polyacrylic acid-based superabsorbent polymer containing a carboxyl group as an acid group. The polyacrylic acid-based superabsorbent polymers included those formed by a solution polymerization method and those formed by a reversed-phase suspension polymerization method.

[0110] A number of used disposable diapers were immersed in an acidic aqueous solution containing sulfuric acid, and the superabsorbent polymer contained in the used disposable diapers was subjected to primary dehydration while the used disposable diapers were crushed and decomposed into the constituent materials of the used diapers, and the constituent materials were dispersed in the acidic aqueous solution. The acidic aqueous solution in which the constituent materials were dispersed was passed through a screen to separate the primarily dehydrated superabsorbent polymer. 4% by mass of slaked lime was added to the separated primarily dehydrated superabsorbent polymer, and the primarily dehydrated superabsorbent polymer was subjected to secondary dehydration and sterilization. The secondary dehydrated superabsorbent polymer was washed with water, and then the secondary dehydrated superabsorbent polymer was subjected to solid-liquid separation to obtain a secondary dehydrated superabsorbent polymer. The secondary dehydrated superabsorbent polymer was pre-dried to a moisture content of 3% by mass to obtain superabsorbent polymer No. 1. Superabsorbent polymer No. 1 contained 43% by mass of calcium in the dry state.

[0111] Superabsorbent Polymer No. 1 was subjected to a carbonization step and an activation step under the following conditions. [Carbonization Step] Superabsorbent Polymer No. 1 was placed in a hybrid carbonization furnace, and while blowing nitrogen into the furnace, (i) the temperature inside the furnace was increased from room temperature to 450°C over two hours and then held at 450°C for one hour, (ii) the temperature inside the furnace was increased from 450°C to 550°C over one hour and then held for one hour, and (iii) the contents inside the furnace were allowed to cool overnight, thereby performing the carbonization step and forming Carbonized Product No. 1. The contents of the hybrid carbonization furnace were stirred for 10 seconds every 10 minutes during the heating and cooling periods.

[0112] [Activation Step] Carbonized material No. 1 was loaded into a steam activation furnace (rotary kiln). (i) While blowing nitrogen into the furnace, the temperature inside the furnace was increased from room temperature to 850°C over 1 hour and 50 minutes, and then maintained at 850°C for 1 hour. (ii) While blowing steam into the furnace instead of nitrogen, activation was performed for 0.5 hours. (iii) While blowing nitrogen into the furnace, the contents inside the furnace were cooled overnight to form activated carbon No. 1. Activated carbon No. 1 contained 38% by mass of calcium.

[0113] [Reference Example 1] Commercially available activated carbon derived from palm stalk was designated as activated carbon No. 2. [Reference Example 2] Commercially available activated carbon derived from PET was designated as activated carbon No. 3.

[0114] Comparative Example 1 A commercially available superabsorbent polymer (unused) was designated as Superabsorbent Polymer No. 2. Superabsorbent Polymer No. 2 was a polyacrylic acid-based superabsorbent polymer formed by solution polymerization. Superabsorbent Polymer No. 2 contained no calcium in its dry state and had a moisture content of 3% by mass. Superabsorbent Polymer No. 2 was subjected to the carbonization and activation steps of Example 1 to form Carbonized Product No. 2 and Activated Product No. 1, which corresponds to Activated Carbon No. 1.

[0115] Comparative Example 2 A commercially available superabsorbent polymer (unused) was designated as Superabsorbent Polymer No. 3. Superabsorbent Polymer No. 3 was a polyacrylic acid-based superabsorbent polymer formed by reverse-phase suspension polymerization. Superabsorbent Polymer No. 3 contained no calcium in its dry state and had a moisture content of 3% by mass. Superabsorbent Polymer No. 3 was subjected to the carbonization and activation steps of Example 1 to form Carbonized Product No. 3 and Activated Product No. 2, which corresponds to Activated Carbon No. 1.

[0116] The BET specific surface area (m) of activated carbon No. 1, activated carbon No. 2, activated carbon No. 3, activated product No. 1, and activated product No. 2 2 The iodine adsorption capacity (mg / g), micropore volume (mL / g), mesopore volume (mL / g), and iodine adsorption capacity (mg / g) were measured according to the methods described in the specification. The results are shown in Table 1.

[0117]

[0118] Photographs of superabsorbent polymer No. 1, carbonized product No. 1, and activated carbon No. 1 are shown in Figures 1 to 3. Photographs of superabsorbent polymer No. 2, carbonized product No. 2, and activated product No. 1 are shown in Figures 4 to 6. Photographs of superabsorbent polymer No. 3, carbonized product No. 3, and activated product No. 2 are shown in Figures 7 to 9. To facilitate comparison, the brightness of Figures 1, 4, and 7 (superabsorbent polymer No. 1 to superabsorbent polymer No. 3) was adjusted to the same degree (decreased to the same degree). To facilitate comparison, the brightness of Figures 2, 5, and 8 (carbonized product No. 1 to carbonized product No. 3) was adjusted to the same degree (increased to the same degree). Furthermore, from the viewpoint of ease of comparison, the brightness of Figures 3, 6 and 9 (activated carbon No. 1, activation-treated product No. 1 and activation-treated product No. 2) was adjusted to the same degree.

[0119] Electron microscope photographs of Carbonized Product No. 1 and Activated Carbon No. 1 are shown in Figures 10 and 11, respectively. Electron microscope photographs of Activated Product No. 1 and Activated Product No. 2 are shown in Figures 12 and 13, respectively.

[0120] Table 1, Figures 3, and 11 show that Activated Carbon No. 1 exhibits the required performance as activated carbon. On the other hand, Table 1 shows that Activation Treatment Products No. 1 and No. 2 do not exhibit the required performance as activated carbon. This is likely due to the fact that glass-like crystallization occurred during the carbonization step, preventing the formation of a uniform carbonized product. As a result, activated carbon was not formed after the activation step, and activation treatment products No. 1 and No. 2 contained whitish aggregates, as shown in Figures 6 and 9. As shown in Figures 10, 12, and 13, no needle-like crystals were observed on the surface of Carbonized Product No. 1, but needle-like crystals were observed on the surfaces of Carbonized Product No. 2 and Carbonized Product No. 3. Therefore, it is presumed that the whitish aggregates in Activation Treatment Products No. 1 and No. 2 are due to glass-like crystals.

[0121] [Example 2] In Example 1, the activation time while blowing water vapor instead of nitrogen into the furnace was changed from 0.5 hours to 1 hour, 5 hours, and 20 hours, respectively, to form activated carbon No. 4, activation-treated product No. 3, and activation-treated product No. 4. The BET specific surface areas (m 2 / g), micropore volume (mL / g), mesopore volume (mL / g), and iodine adsorption capacity (mg / g) are shown in Table 2.

[0122]

[0123] Table 2 shows that activated carbon No. 4, which had been deactivation timed for 1 hour, had performance equivalent to that of activated carbon No. 1. In activation-treated products No. 3 and No. 4, which had been deactivation timed for 5 and 10 hours, respectively, the BET specific surface area decreased and whitening (ashing) progressed, so the micropore volume (mL / g), mesopore volume (mL / g), and iodine adsorption capacity (mg / g) were not measured.

[0124] Example 3 Evaluation of Deodorizing Properties The deodorizing properties of activated carbon No. 1 were evaluated in accordance with the detector tube method in "21. Deodorizing Properties Test" in "Chapter 6 Functionality Test" of the SEK Mark Textile Product Certification Standard (JEC301). Specifically, a test vessel was filled with air containing 100 ppm ammonia, 30 ppm acetic acid, 4 ppm hydrogen sulfide, 8 ppm methyl mercaptan, 28 ppm trimethylamine, and approximately 33 ppm indole. 1.0 g of activated carbon No. 1 was then added to the test vessel. After two hours, the air in the test vessel was analyzed and the reduction rate of each component was measured. The results are shown in Table 3. For reference, a commercially available activated carbon (deodorizing activated carbon, manufactured by Osaka Gas Chemicals Co., Ltd., Granular Shirasagi GM) was also used. 2X The results are shown in Table 3.

[0125]

[0126] From Table 3, it can be seen that activated carbon No. 1 has deodorizing performance equivalent to that of commercially available activated carbon.

[0127] Example 4 Evaluation of Water Quality Improvement Effect The water quality improvement effect of Activated Carbon No. 1 was evaluated in accordance with "17. Oxygen consumption by potassium permanganate at 100°C (CODMn)" in JIS K0102:2016, "Testing Methods for Industrial Wastewater." Specifically, raw water with a COD of 160 mg / g was prepared, and the amount of COD adsorbed (mg / g) to the raw water was measured. Next, the amount (g / L) of Activated Carbon No. 1 per liter of raw water that could reduce the COD to 16 mg / L (1 / 10) was calculated. The results are shown in Table 4. For reference, the water quality improvement effect of a commercially available activated carbon for water purification (manufactured by LO Corporation, water purification activated carbon, coal-based granular activated carbon) was similarly evaluated. The results are shown in Table 4.

[0128]

[0129] Table 4 shows that activated carbon No. 1 has the same water quality improvement effect as commercially available activated carbon for water purification at about 1 / 7 the amount.

[0130] [Example 5] The bulk density and crushing strength of activated carbon No. 1 and a commercially available activated carbon for water purification (water purification activated carbon, coal-based granular activated carbon, manufactured by LO Corporation) were measured according to the method described herein. Table 5 shows the bulk density, crushing strength, and standard deviation of the crushing strength.

[0131]

[0132] It can be seen that Activated Carbon No. 1 has smaller bulk density, crushing strength, and standard deviation of crushing strength compared to commercially available activated carbon. The small bulk density of Activated Carbon No. 1 is thought to be due to the large number of mesopores. The small crushing strength and its standard deviation of Activated Carbon No. 1 are thought to be due to calcium entering the C-C bonds of the activated carbon and the large number of mesopores. The small standard deviation of Activated Carbon No. 1 suggests that it is easy to crush uniformly. The large standard deviation of crushing strength of commercially available activated carbon suggests that it is difficult to crush uniformly.

Claims

1. A method for producing activated carbon from a superabsorbent polymer having acid groups, the method comprising: a preparation step of preparing a crosslinked superabsorbent polymer in which the acid groups of the superabsorbent polymer are crosslinked with a polyvalent metal; a carbonization step of carbonizing the crosslinked superabsorbent polymer to form a char; and an activation step of activating the char to form the activated carbon.

2. The method according to claim 1, wherein in the activation step, the carbonized material is activated by a gas activation method.

3. The method of claim 1 or 2, wherein the activation step is carried out for 0.1 to 2.0 hours.

4. The method according to any one of claims 1 to 3, wherein the crosslinked highly absorbent polymer contains 20 to 50 mass % of the polyvalent metal in a dry state.

5. The method of any one of claims 1 to 4, wherein the crosslinked superabsorbent polymer has a moisture content of greater than 0% and less than or equal to 40% by weight.

6. The method according to any one of claims 1 to 5, wherein the highly absorbent polymer is a polyacrylic acid-based highly absorbent polymer containing a carboxyl group as the acid group.

7. The method according to any one of claims 1 to 6, wherein the polyvalent metal is calcium.

8. The method of any one of claims 1 to 7, wherein the crosslinked superabsorbent polymer is derived from recycled sanitary products.

9. The method of any one of claims 1 to 8, wherein the crosslinked superabsorbent polymer is derived from a used sanitary product.

10. The method according to any one of claims 1 to 9, wherein the crosslinked superabsorbent polymer is formed by adding a polyvalent metal ion source capable of supplying polyvalent metal ions to the superabsorbent polymer absorbing body fluid, and then expelling the body fluid from the superabsorbent polymer.

11. The method of any one of claims 1 to 10, further comprising a crosslinking step of adding a polyvalent metal ion source capable of supplying polyvalent metal ions to the superabsorbent polymer absorbing body fluid, thereby expelling the body fluid from the superabsorbent polymer and forming the crosslinked superabsorbent polymer.

12. The method of any one of claims 1 to 11, wherein the crosslinked superabsorbent polymer comprises a material derived from a hygiene product, and the crosslinked superabsorbent polymer is agitated during the carbonization step.

13. The method of claim 12, further comprising a milling step of milling the carbonized material after the carbonizing step and before the activating step.

14. Activated carbon derived from a highly water-absorbent polymer containing acid groups, characterized in that the activated carbon has an iodine adsorption capacity of 2,000 to 4,000 mg / g.

15. The activated carbon according to claim 14, wherein the activated carbon contains 10 to 50 mass % of a polyvalent metal.

16. The activated carbon according to claim 14 or 15, wherein the activated carbon comprises micropores and mesopores, and the volume of the mesopores is greater than the volume of the micropores.

17. The activated carbon of claim 16, wherein the mesopore volume is 0.200 mL / g to 0.600 mL / g.

18. The activated carbon according to claim 16 or 17, wherein the volume of the micropores is 0.005 to 0.100 mL / g.

19. The activated carbon is 50 to 250 m 2 The activated carbon according to any one of claims 14 to 18, having a BET specific surface area of ​​1 / g.

20. The activated carbon of any one of claims 14 to 19, wherein the activated carbon has a bulk specific gravity of 0.100 to 0.500 g / mL.

21. The activated carbon according to any one of claims 14 to 20, wherein the activated carbon has a crushing strength of 200 to 7,000 kPa.

22. Use of a polyvalent metal for recycling a superabsorbent polymer containing acid groups into activated carbon, wherein the superabsorbent polymer containing acid groups is a crosslinked superabsorbent polymer in which the acid groups are crosslinked by the polyvalent metal.

23. Use of a superabsorbent polymer containing acid groups for recycling the superabsorbent polymer containing acid groups into activated carbon, wherein the superabsorbent polymer containing acid groups is a crosslinked superabsorbent polymer in which the acid groups are crosslinked with a polyvalent metal.

24. The use according to claim 22 or 23, wherein the activated carbon has an iodine adsorption capacity of 2,000 to 4,000 mg / g.

25. The use according to any one of claims 22 to 24, wherein the crosslinked highly water-absorbent polymer contains 10 to 50% by mass of the polyvalent metal in a dry state.

26. The use according to any one of claims 22 to 25, wherein the crosslinked superabsorbent polymer has a moisture content of more than 0% and not more than 40% by weight.

27. The use according to any one of claims 22 to 26, wherein the high-grade water-soluble polymer containing acid groups is absorbing body fluids.

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