Method for producing activated carbon from superabsorbent polymer having acid group

Abstract

To provide a method for producing activated carbon from a highly water-absorbing polymer, capable of easily producing activated carbon.SOLUTION: A method for producing activated carbon from a superabsorbent polymer having an acid group, the method including a preparation step of preparing a crosslinked superabsorbent polymer in which the acid group of the superabsorbent polymer is crosslinked by a polyvalent metal, a carbonization step of carbonizing the crosslinked superabsorbent polymer to form a carbide, and an activation step of activating the carbide to form the activated carbon.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present disclosure relates to a method for producing activated carbon from a superabsorbent polymer having acid groups. [Background technology]

[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 material, which comprises contacting waste containing a superabsorbent resin that has absorbed moisture containing chlorides with an aqueous solution containing at least one of water-soluble phosphates or sulfates to remove chloride ions from the waste, and then heating the waste to carbonize it. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2022-21365 Summary of the Invention [Problem to be solved by the invention]

[0004] The inventors of the present invention have found that it is difficult to produce activated carbon from a highly water-absorbent polymer as it is. Therefore, an object of the present disclosure is to provide a method for producing activated carbon from a highly water-absorbent polymer, which allows for the easy production of activated carbon. [Means for solving the problem]

[0005] The present inventors have discovered a method for producing activated carbon from a superabsorbent polymer having acid groups, the method including 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 carbonized product; and an activation step of activating the carbonized product to form the activated carbon. [Effects of the Invention]

[0006] The method for producing activated carbon from a superabsorbent polymer according to the present disclosure allows for easy production of activated carbon. [Brief explanation of the drawings]

[0007] [Figure 1] Figure 1 is a photograph of superabsorbent polymer No. 1. [Figure 2] Figure 2 is a photograph of carbide No. 1. [Figure 3] Figure 3 is a photograph of activated carbon No. 1. [Figure 4] Figure 4 is a photograph of superabsorbent polymer No. 2. [Figure 5] Figure 5 is a photograph of carbide No. 2. [Figure 6] FIG. 6 is a photograph of activation-treated product No. 1. [Figure 7] Figure 7 is a photograph of superabsorbent polymer No. 3. [Figure 8] Figure 8 is a photograph of carbide No. 3. [Figure 9] FIG. 9 is a photograph of activation-treated product No. 2. DETAILED DESCRIPTION OF THE INVENTION

[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, comprising the steps of: 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 carbonized product; activating the carbonized material to form the activated carbon; A method comprising:

[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, it becomes easier to form a uniform carbonized product from the crosslinked superabsorbent polymer.

[0011] Furthermore, since the method for producing activated carbon includes a predetermined activation step, activated carbon can be easily produced from a uniform carbonized material. The inventors of the present invention have found that when a highly water-absorbent polymer is simply carbonized and activated, glass-like crystallization occurs during carbonization, and activated carbon is not formed.

[0012] [Aspect 2] The method according to aspect 1, wherein the activation step activates the carbonized material by a gas activation method. In the above-described method for producing activated carbon, the carbonized material is activated by a gas activation method in the activation step, and therefore 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, which is shorter than the time required for a typical deactivation step, making it possible to easily produce activated carbon from a superabsorbent polymer.

[0014] [Aspect 4] Aspect 4. The method according to any one of Aspects 1 to 3, wherein the crosslinked highly water-absorbent 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] 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 (individual particles are generally separated), which ultimately makes it possible to easily produce activated carbon from the superabsorbent polymer.

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

[0019] [Aspect 7] Aspect 7. The method of any one of aspects 1 to 6, wherein the polyvalent metal is calcium. In the above-described method for producing activated carbon, since the polyvalent metal is calcium, activated carbon can be easily produced from a highly water-absorbent polymer.

[0020] [Aspect 8] Aspect 8. The method of any one of aspects 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 collected sanitary goods, and therefore the superabsorbent polymer contained in the collected sanitary goods can be easily recycled into activated carbon, thereby reducing the environmental impact.

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

[0023] In the method for producing activated carbon, the cross-linked superabsorbent polymer is derived from used sanitary products, and therefore the superabsorbent polymer contained in the 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 absorbing body fluid, and then expelling 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 discharging 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] 12. The method of any one of Aspects 1-11, wherein the crosslinked superabsorbent polymer comprises a material derived from a hygiene product, and wherein the carbonization step involves agitating the crosslinked superabsorbent polymer.

[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 interior of the crosslinked superabsorbent polymer is difficult to carbonize during the carbonization step, and the carbonized material tends to be formed unevenly. In the above-mentioned method for producing activated carbon, the cross-linked 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] 13. The method of claim 12, further comprising, after the carbonizing step and before the activating step, grinding the carbonized material.

[0031] 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., stirring the crosslinked superabsorbent polymer makes it easier to form a uniform carbonized product, but the carbonized product may form large lumps. Since the above-mentioned method for producing activated carbon includes a predetermined pulverization step, even if the carbonized material forms large lumps in the carbonization step, activated carbon can be easily produced in the activation step.

[0032] The method for producing activated carbon from the highly absorbent polymer having acid groups of the present disclosure (hereinafter, sometimes simply referred to as "method for producing activated carbon") will be described in detail below. 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, sometimes referred to as the "preparation step"); - a carbonization step of carbonizing the crosslinked superabsorbent polymer to form a carbonized product (hereinafter, sometimes referred to as the "carbonization step"); - an activation step of activating the carbonized material to form the activated carbon (hereinafter sometimes referred to as the "activation step");

[0033] [Preparation Steps] 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, etc., with those containing a carboxyl group being preferred. Examples of superabsorbent polymers containing a carboxyl group include polyacrylates and polymaleic anhydrides, and examples of superabsorbent polymers containing a sulfo group, etc. include polysulfonates.

[0034] The polyvalent metal refers to a metal capable of forming an anion having a 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.

[0035] 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.

[0036] 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.

[0037] Examples of the polyvalent metal ion source include transition metal hydroxides (e.g., iron hydroxide, cobalt hydroxide, nickel hydroxide, copper hydroxide), salts of transition metal hydroxides and acids, and transition metal oxides (e.g., iron oxide, cobalt oxide, nickel oxide, copper oxide).

[0038] 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.

[0039] Examples of the organic acid include citric acid, tartaric acid, malic acid, succinic acid, oxalic acid (all of which are carboxylic acids having multiple carboxyl groups), gluconic acid (C6), pentanoic acid (C5), butanoic acid (C4), propionic acid (C3), glycolic acid (C2), acetic acid (C2), glacial acetic acid, formic acid (C1) (all of which are carboxylic acids having one carboxyl group), methanesulfonic acid, trifluoromethanesulfonic acid, benzenesulfonic acid, p-toluenesulfonic acid (all of which are sulfonic acids), and the like.

[0040] 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.

[0041] In addition, since the polyvalent metal ions crosslink the acid groups of the highly absorbent 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 highly absorbent polymer.

[0042] When the acid has a plurality of acid groups, for example, when the acid is a dibasic acid or a tribasic acid, it is preferable that the largest of the acid dissociation constants (pKa, in water) of the acid is smaller than the acid dissociation constant (pKa, in water) of the acid group of the superabsorbent polymer, and when the superabsorbent polymer has a plurality of types of acid groups, it is preferable that the largest of the acid dissociation constants (pKa, in water) of the acid is smaller than the smallest of the acid dissociation constants (pKa, in water) of the acid groups of the superabsorbent polymer. This is from the viewpoint that polyvalent metal ions crosslink the acid groups of the superabsorbent polymer.

[0043] In this specification, the acid dissociation constant (pKa, in water) may be the value described in the Electrochemical Handbook compiled by the Electrochemical Society.

[0044] 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, while 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.

[0045] 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.

[0046] 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). This ultimately facilitates 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.

[0047] 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 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.

[0048] 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.

[0049] 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.

[0050] An example of the crosslinked superabsorbent polymer containing a material derived from the above-mentioned sanitary goods is the superabsorbent polymer that has been subjected to the sieving step S41 in JP 2024-062047 A.

[0051] 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.

[0052] 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.

[0053] 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.

[0054] [Carbonization step] In the carbonization step, the crosslinked superabsorbent polymer is carbonized to form a carbonized product. The carbonization step can be carried out by 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.

[0055] 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 by blowing nitrogen, superheated steam, or the like into the carbonization furnace. The crosslinked superabsorbent polymer generates gas, which can also be used to achieve the oxygen-free state. The predetermined temperature is 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 hour 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.

[0056] 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 there for a certain period of time, and then heated to a relatively high temperature and maintained there 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.

[0057] 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.

[0058] 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.

[0059] Before the subsequent activation step, a grinding step may be performed to grind the carbonized material formed in the carbonization step. This facilitates the easy formation of activated carbon in the activation step, even if the carbonized material forms large lumps in 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 carried out using grinding equipment known in the art, for example, a jet mill.

[0060] [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.

[0061] 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.

[0062] 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 too short, activated carbon may not be formed, while if the predetermined time is too long, the activated carbon tends to have more pores. [Example]

[0063] 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 reverse-phase suspension polymerization method.

[0064] Several 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 broken down into the constituent materials of the used diapers, and the constituent materials were dispersed in the acidic aqueous solution. The acidic aqueous solution containing the dispersed constituent materials 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, thereby obtaining Superabsorbent Polymer No. 1. Superabsorbent Polymer No. 1 contained 43% by mass of calcium in the dry state.

[0065] The 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 at that temperature for one hour, and (iii) the contents inside the furnace were allowed to cool overnight, thereby carrying out 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.

[0066] [Activation step] Carbonized material No. 1 was placed in 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 of the furnace were cooled overnight, thereby forming activated carbon No. 1. Activated carbon No. 1 contained 38% by mass of calcium.

[0067] [Reference example 1] Commercially available activated carbon derived from palm stalks was designated as activated carbon No. 2. [Reference example 2] Commercially available activated carbon derived from PET was designated as activated carbon No. 3.

[0068] [Comparative Example 1] A commercially available superabsorbent polymer (unused) was designated as Superabsorbent Polymer No. 2. Superabsorbent Polymer No. 2 is a polyacrylic acid-based superabsorbent polymer formed by solution polymerization. Superabsorbent Polymer No. 2 did not contain calcium in the dry state and had a moisture content of 3% by mass. The superabsorbent polymer No. 2 was subjected to the carbonization step and activation step in Example 1 to form a carbonized product No. 2 and an activation-treated product No. 1 corresponding to the activated carbon No. 1.

[0069] Comparative Example 2 A commercially available superabsorbent polymer (unused) was designated as Superabsorbent Polymer No. 3. Superabsorbent Polymer No. 3 is a polyacrylic acid-based superabsorbent polymer formed by reverse-phase suspension polymerization. Superabsorbent Polymer No. 3 did not contain calcium in the dry state and had a moisture content of 3% by mass. The carbonization step and activation step in Example 1 were carried out on superabsorbent polymer No. 3 to form carbonized product No. 3 and activated product No. 2, which corresponds to activated carbon No. 1.

[0070] BET specific surface area (m 2 / g), micropore volume (mL / g), mesopore volume (mL / g), and iodine adsorption capacity (mg / g) are shown in Table 1.

[0071] The BET specific surface area was measured according to "6.3.1 Static volume method" in "Method for measuring the specific surface area of ​​powders (solids) by gas adsorption" of JIS Z8830:2013. The micropore volume (mL / g) was calculated based on the t-method using the volume of pores with diameters between 0.34 nm and 2.0 nm on the Harkins-Jura-BEL.t standard curve recommended by Microtrac-BEL, Inc.

[0072] The mesopore volume (mL / g) was calculated based on the BJH method, using the volume of pores with diameters of 3.4 nm to 200 nm on the BJH-Plot: FHH-BEL.t standard curve recommended by Microtrac-BEL Co., Ltd. The iodine adsorption performance was measured in accordance with "7.1.2.2 Iodine adsorption performance" of JIS K1474:2014.

[0073] [Table 1]

[0074] 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. For ease of 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). For ease of 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). For ease of comparison, the brightness of Figures 3, 6, and 9 (activated carbon No. 1, activated product No. 1, and activated product No. 2) was adjusted to the same degree.

[0075] Table 1 and Figure 3 show that activated carbon No. 1 has the required performance as activated carbon. On the other hand, Table 1 shows that activation-treated products No. 1 and No. 2 do not have the performance required for 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-treated products No. 1 and No. 2 contained whitish aggregates, as shown in Figures 6 and 9. When examined with an electron microscope, no glass-like crystals were observed on the surface of carbonized product No. 1, but glass-like crystals were confirmed on the surfaces of carbonized products No. 2 and No. 3. Therefore, it is presumed that the whitish aggregates in activation-treated products No. 1 and No. 2 are due to glass-like crystals.

[0076] [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 area (m 2 / g), micropore volume (mL / g), mesopore volume (mL / g), and iodine adsorption capacity (mg / g) are shown in Table 2.

[0077] [Table 2]

[0078] Table 2 shows that activated carbon No. 4, which had an inactivation time of 1 hour, had the same performance as activated carbon No. 1. In the activated products No. 3 and No. 4, which were inactivated for 5 and 10 hours, 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.

[0079] [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 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, Granular Shirasagi GM, manufactured by Osaka Gas Chemicals Co., Ltd.) was also used. 2X The deodorizing properties of the above-mentioned products were evaluated in the same manner. The results are shown in Table 3.

[0080] [Table 3]

[0081] Table 3 shows that activated carbon No. 1 has the same deodorizing performance as commercially available activated carbon.

[0082] [Example 4] [Evaluation of water quality improvement effects] The water quality improvement effect of activated carbon No. 1 was evaluated in accordance with JIS K0102:2016 "Testing methods for industrial wastewater" "Oxygen consumption by potassium permanganate at 17.100°C (CODMn)." 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. The amount of activated carbon No. 1 (g / L) per liter of raw water that would reduce the COD to 16 mg / L (1 / 10) was then 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 also evaluated in the same manner. The results are shown in Table 4.

[0083] [Table 4]

[0084] Table 4 shows that activated carbon No. 1 has the same water quality improvement effect as commercially available activated carbon for water purification, but at about 1 / 7 the amount.

Claims

1. A method for producing activated carbon from a superabsorbent polymer having acid groups, comprising the steps of: 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 carbonized product; an activation step of activating the carbonized material to form the activated carbon; A method comprising:

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

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

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

5. 10. The method of claim 1, wherein the crosslinked superabsorbent polymer has a moisture regain of greater than 0% and less than or equal to 40% by weight.

6. The method according to claim 1 , wherein the highly absorbent polymer is a polyacrylic acid-based highly absorbent polymer containing a carboxyl group as the acid group.

7. The method of claim 1 , wherein the polyvalent metal is calcium.

8. 10. The method of claim 1, wherein the crosslinked superabsorbent polymer is derived from recycled sanitary products.

9. 10. The method of claim 1, wherein the crosslinked superabsorbent polymer is derived from a used sanitary article.

10. The method of claim 1, 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. 2. The method of claim 1, 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. 10. The method of claim 1, wherein the crosslinked superabsorbent polymer comprises a material derived from a hygiene product, and the carbonization step involves agitating the crosslinked superabsorbent polymer.

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.

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