Activated carbon derived from superabsorbent polymers, use of polyvalent metals for recycling superabsorbent polymers comprising acid groups into activated carbon, and use of superabsorbent polymers comprising acid groups for recycling superabsorbent polymers comprising acid groups into activated carbon

Abstract

To provide activated carbon derived from a highly water-absorbing polymer and excellent in adsorption performance.SOLUTION: Active carbon derived from a super absorbent polymer containing an acid group, wherein the active carbon has an iodine adsorption performance of 2000 to 4.0 000mg / g.SELECTED DRAWING: Figure 11

Description

[Technical Field]

[0001] The present disclosure relates to activated carbon derived from superabsorbent polymers, the use of polyvalent metals to recycle superabsorbent polymers containing acid groups into activated carbon, and the use of superabsorbent polymers containing acid groups to recycle superabsorbent polymers containing acid groups into activated carbon. [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 recycle a superabsorbent polymer into activated carbon. Therefore, an object of the present disclosure is to provide activated carbon that is derived from a highly water-absorbent polymer and has excellent adsorption performance. [Means for solving the problem]

[0005] The present inventors have discovered an activated carbon derived from a highly water-absorbent polymer containing an acid group, characterized in that the activated carbon has an iodine adsorption capacity of 2,000 to 4,000 mg / g. [Effects of the Invention]

[0006] The activated carbon according to the present disclosure is derived from a highly water-absorbent polymer and has excellent adsorption performance. [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. [Figure 10] FIG. 10 is an electron microscope photograph of carbide No. 1. [Figure 11] FIG. 11 is an electron microscope photograph of activated carbon No. 1. [Figure 12] FIG. 12 is an electron microscope photograph of activation-treated product No. 1. [Figure 13] FIG. 13 is an electron microscope photograph of activation-treated product No. 2. DETAILED DESCRIPTION OF THE INVENTION

[0008] Specifically, the present disclosure relates to the following aspects: [Aspect 1A] Activated carbon derived from a highly absorbent polymer containing acid groups, The activated carbon has an iodine adsorption capacity of 2,000 to 4,000 mg / g. Activated carbon characterized by:

[0009] 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.

[0010] [Aspect 1B] It has an iodine adsorption capacity of 2,000 to 4,000 mg / g. Activated carbon characterized by: The activated carbon has a predetermined iodine adsorption capacity and is excellent in adsorption capacity.

[0011] [Aspect 1C] Contains 10 to 50 mass% of polyvalent metals, Activated carbon characterized by: The activated carbon contains a predetermined amount of polyvalent metal, which makes it easier for the activated carbon to have a predetermined strength, and the activated carbon has excellent crushability and easy particle size adjustment.

[0012] [Aspect 2] The activated carbon according to any one of Aspects 1A and 1B, wherein the activated carbon contains 10 to 50% by mass of a polyvalent metal. The activated carbon contains a predetermined amount of polyvalent metal, which makes it easier for the activated carbon to have a predetermined strength, and the activated carbon has excellent crushability and easy particle size adjustment.

[0013] [Aspect 3] 3. The activated carbon of any one of Aspects 1A, 1B, 1C, and 2, wherein the activated carbon comprises micropores and mesopores, and the volume of the mesopores is greater than the volume of the micropores.

[0014] 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 volume of the mesopores in the activated carbon is larger than the volume of the micropores. This allows for efficient adsorption of adsorbates (molecules, ions, etc.) that are larger than the micropores. Furthermore, as is evident from the excellent iodine adsorption performance of the activated carbon, it can efficiently absorb iodine with a diameter of approximately 0.5 nm, and this adsorption performance is presumably due to the large volume of the mesopores. From the above, the activated carbon has excellent adsorption performance.

[0015] [Aspect 4] The activated carbon according to any one of Aspects 1A, 1B, 1C, 2, and 3, wherein the mesopore volume is 0.200 mL / g to 0.600 mL / g.

[0016] Since the mesopore volume of the activated carbon is within a predetermined range, the density of the activated carbon is reduced, in other words, the bulk density of the activated carbon is reduced, and when the activated carbon is used in a filter (for example, for gases, liquids, etc.), the weight of the filter can be reduced. Furthermore, because the bulk density of the activated carbon is 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.

[0017] [Aspect 5] The activated carbon according to any one of Aspects 1A, 1B, 1C, 2, 3, and 4, wherein the volume of the micropores is 0.005 to 0.100 mL / g. Since the activated carbon has a micropore volume within a predetermined low range, the activated carbon is likely to have excellent iodine adsorption performance, and therefore has excellent adsorption performance.

[0018] [Aspect 6] The activated carbon is 50 to 250 m 2 / g. The activated carbon has a predetermined BET specific surface area, which makes it less brittle and easier to handle.

[0019] [Aspect 7] The activated carbon according to any one of Aspects 1A, 1B, 1C, 2, 3, 4, 5, and 6, wherein the activated carbon has a bulk specific gravity of 0.100 to 0.500 g / mL.

[0020] 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.

[0021] [Aspect 8] The activated carbon according to any one of Aspects 1A, 1B, 1C, 2, 3, 4, 5, 6, and 7, wherein the activated carbon has a crushing strength of 200 to 7,000 kPa. The activated carbon has a predetermined crushing strength, and therefore has excellent crushability and the particle size can be easily adjusted.

[0022] [Aspect 9A] Use of a polyvalent metal for recycling a highly absorbent polymer containing acid groups into activated carbon, comprising: The superabsorbent polymer containing an acid group is a crosslinked superabsorbent polymer in which the acid group is crosslinked with the polyvalent metal. 10. The use characterized by:

[0023] The inventors of the present application have found that if a superabsorbent polymer is simply carbonized and activated in order to recycle the superabsorbent polymer into activated carbon, glass-like crystallization occurs during the carbonization, and activated carbon is not formed even after the activation step. In the above-mentioned use, since the superabsorbent polymer containing acid groups is a crosslinked superabsorbent polymer in which the acid groups are crosslinked with a polyvalent metal, the superabsorbent polymer can be easily recycled into activated carbon.

[0024] [Aspect 9B] Use of a polyvalent metal for producing activated carbon from a superabsorbent polymer containing acid groups, comprising: The superabsorbent polymer containing an acid group is a crosslinked superabsorbent polymer in which the acid group is crosslinked with the polyvalent metal. 10. The use characterized by:

[0025] The inventors of the present application have found that if a superabsorbent polymer is simply carbonized and activated in order to produce activated carbon from the superabsorbent polymer, glass-like crystallization occurs during the carbonization, and activated carbon is not formed even after the activation step. In the above-mentioned use, since the superabsorbent polymer containing acid groups is a crosslinked superabsorbent polymer in which the acid groups are crosslinked with a polyvalent metal, activated carbon can be easily produced from the superabsorbent polymer.

[0026] [Aspect 10A] 1. Use of a superabsorbent polymer containing acid groups for recycling the superabsorbent polymer containing acid groups into activated carbon, comprising: The superabsorbent polymer containing an acid group is a crosslinked superabsorbent polymer in which the acid group is crosslinked with a polyvalent metal. 10. The use characterized by:

[0027] The inventors of the present application have found that if a superabsorbent polymer is simply carbonized and activated in order to recycle the superabsorbent polymer into activated carbon, glass-like crystallization occurs during the carbonization, and activated carbon is not formed even after the activation step. In the above-mentioned use, since the high-grade aqueous polymer containing acid groups is a crosslinked highly absorbent polymer in which the acid groups are crosslinked with a polyvalent metal, the highly absorbent polymer can be easily recycled into activated carbon.

[0028] [Aspect 10B] 1. Use of a superabsorbent polymer containing acid groups for producing activated carbon, comprising: The superabsorbent polymer containing an acid group is a crosslinked superabsorbent polymer in which the acid group is crosslinked with a polyvalent metal. 10. The use characterized by:

[0029] The inventors of the present application have found that if a superabsorbent polymer is simply carbonized and activated in order to produce activated carbon from the superabsorbent polymer, glass-like crystallization occurs during the carbonization, and activated carbon is not formed even after the activation step. In the above-mentioned use, since the high-grade aqueous polymer containing acid groups is a crosslinked highly water-absorbent polymer in which the acid groups are crosslinked with a polyvalent metal, activated carbon can be easily produced from the highly water-absorbent polymer.

[0030] [Aspect 11] The use according to any one of Aspects 9A, 9B, 10A and 10B, wherein the activated carbon has an iodine adsorption capacity of 2,000 to 4,000 mg / g. In the above-mentioned use, the activated carbon has a predetermined iodine adsorption performance, and therefore, the superabsorbent polymer can be recycled into activated carbon with excellent adsorption performance.

[0031] [Aspect 12] The use according to any one of Aspects 9A, 9B, 10A, 10B, and 11, wherein the crosslinked superabsorbent polymer contains 10 to 50% by mass of the polyvalent metal in a dry state.

[0032] 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.

[0033] [Aspect 13] The use of any one of Aspects 9A, 9B, 10A, 10B, 11 and 12, wherein the crosslinked superabsorbent polymer has a moisture regain of greater than 0% and less than or equal to 40% by weight.

[0034] 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 where 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.

[0035] [Aspect 14] The use according to any one of aspects 9A, 9B, 10A, 10B, 11, 12 and 13, wherein the high-grade water-soluble polymer containing acid groups is absorbing body fluids. In the above-mentioned use, since the highly water-absorbent polymer containing acid groups absorbs body fluids, the used highly water-absorbent polymer can be reused.

[0036] [Aspect 15] The activated carbon of embodiment 1C, 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.

[0037] The activated carbon derived from a superabsorbent polymer according to the present disclosure (hereinafter, may be referred to as "activated carbon according to the present disclosure" or simply as "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, may be referred to as "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, may be referred to as "use of a superabsorbent polymer according to the present disclosure") will be described in detail below.

[0038] The activated carbon according to the present disclosure is derived from a superabsorbent polymer containing acid groups. 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.

[0039] 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 allows the activated carbon to have excellent adsorption capacity. In this specification, the iodine adsorption performance is measured in accordance with "7.1.2.2 Iodine adsorption performance" of "Test methods for activated carbon" in JIS K1474:2014.

[0040] 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. The polyvalent metal helps the activated carbon to have a predetermined strength, improves crushability, and facilitates particle size adjustment.

[0041] The concentration can be measured using an analytical scanning electron microscope, such as the FlexSEM1000II scanning electron microscope manufactured by Hitachi High-Tech Corporation.

[0042] The activated carbon may have pores, which may be divided into micropores, mesopores, and macropores, with the micropores having a size of 0.34 to 2.0 nm, the mesopores having a size of 3.4 to 200 nm, and the macropores having a size greater than 200 nm.

[0043] 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.

[0044] 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. When the activated carbon is used in a liquid filter, the liquid flow resistance can be reduced.

[0045] 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.

[0046] The mesopore volume (mL / g) was calculated using the nitrogen adsorption method based on the BJH method, using the FHH-BEL.t standard curve recommended by Microtrac-BEL Co., Ltd., for pore 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: Using the constant volume method, measure the adsorption / desorption isotherm with nitrogen. -Adsorption temperature: 77.35K -Saturated vapor pressure: Actual measurement -Adsorbate: Nitrogen -Adsorbate cross section: 0.162nm 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)

[0047] The micropore volume (mL / g) was calculated using the nitrogen adsorption method based on the t-plot: Harkins-Jura-BEL.t standard curve recommended by Microtrac-BEL, Inc., for pore diameters of 0.34 nm to 2.0 nm. The measurement conditions for the nitrogen adsorption method are the same as those for measuring the mesopore volume.

[0048] The activated carbon is preferably 50 ml 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, which gives the activated carbon excellent adsorption performance. In this specification, the BET specific surface area is measured in accordance with "6.3.1 Static volume method" of "Method for measuring specific surface area of ​​powder (solid) by gas adsorption" of JIS Z8830:2013.

[0049] 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 for a reduction in the weight of the filter (e.g., for gases, liquids, etc.) when the activated carbon is used in a filter. Furthermore, the reduced bulk density of the activated carbon allows for a reduction in the airflow resistance when the activated carbon is used in a gas filter, and a reduction in the liquid flow resistance when the activated carbon is used in a liquid filter.

[0050] In this specification, bulk specific gravity is measured in accordance with "7.8.2 Manual filling method" in "7.8 Filling density" of "Testing methods for activated carbon" in JIS K1474:2014.

[0051] 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.

[0052] 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: 500gf -Temperature: 25℃ -Humidity: 55%RH -Number of pieces: 10 The activated carbon sample used to measure the crushing strength is one that passes through a sieve with a mesh size of 500 μm and remains on a sieve with a mesh size of 300 μm.

[0053] The use of a polyvalent metal according to the present disclosure involves recycling a superabsorbent polymer containing acid groups into activated carbon, and the use of a superabsorbent polymer according to the present disclosure involves recycling a superabsorbent polymer containing acid groups into activated carbon.

[0054] In the use of the polyvalent metal according to the present disclosure, the superabsorbent polymer containing the acid groups is a crosslinked superabsorbent polymer in which the acid groups are crosslinked by the polyvalent metal, which allows the superabsorbent polymer to be easily recycled into activated carbon. Furthermore, in the use of the superabsorbent polymer according to the present disclosure, the superabsorbent polymer containing the acid groups is a crosslinked superabsorbent polymer in which the acid groups are crosslinked with a polyvalent metal, which allows the superabsorbent polymer to be easily recycled into activated carbon.

[0055] The polyvalent metal refers to a metal capable of forming an anion having a valence of 2 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 makes it easier to recycle the superabsorbent polymer into activated carbon.

[0056] 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.

[0057] 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.

[0058] 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).

[0059] 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.

[0060] 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.

[0061] 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.

[0062] 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.

[0063] 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.

[0064] In this specification, the acid dissociation constant (pKa, in water) may be the value described in the Electrochemical Handbook compiled by the Electrochemical Society.

[0065] 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 can prevent the crosslinked superabsorbent polymer from crystallizing into a glass-like state during the carbonization step described below, allowing for easy recycling of the superabsorbent polymer into activated carbon. 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 can result in a decrease in the activated carbon ratio, resulting in a decrease in activated carbon performance.

[0066] 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.

[0067] 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 allows the superabsorbent polymer to be easily recycled into activated carbon. 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.

[0068] 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.

[0069] 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.

[0070] 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.

[0071] 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.

[0072] 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.

[0073] 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.

[0074] The crosslinked superabsorbent polymer may include 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. This reduces the energy required for the carbonization step and allows the superabsorbent polymer contained in used sanitary products to be easily recycled into activated carbon, thereby reducing the environmental impact.

[0075] The use of polyvalent metals according to the present disclosure and the use of superabsorbent polymers according to the present disclosure can include the following steps for the recycling. - 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");

[0076] 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.

[0077] 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.

[0078] 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.

[0079] 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, which in turn allows the superabsorbent polymer to be easily recycled into activated carbon.

[0080] 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.

[0081] 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.

[0082] 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.

[0083] 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.

[0084] 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]

[0085] 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.

[0086] 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.

[0087] 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.

[0088] [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.

[0089] [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.

[0090] [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.

[0091] 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.

[0092] BET specific surface area (m 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.

[0093] [Table 1]

[0094] 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.

[0095] Electron microscope photographs of carbonized material No. 1 and activated carbon No. 1 are shown in Figures 10 and 11, respectively. Electron microscope photographs of activated material No. 1 and activated material No. 2 are shown in Figures 12 and 13, respectively.

[0096] Table 1, Figures 3, and 11 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. 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 confirmed on the surfaces of carbonized products No. 2 and No. 3. Therefore, the whitish aggregates in activation-treated products No. 1 and No. 2 are presumed to be due to glass-like crystals.

[0097] [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.

[0098] [Table 2]

[0099] 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.

[0100] [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.

[0101] [Table 3]

[0102] Table 3 shows that activated carbon No. 1 has the same deodorizing performance as commercially available activated carbon.

[0103] [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 (CODMn) by potassium permanganate at 17.100°C." 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.

[0104] [Table 4]

[0105] 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.

[0106] [Example 5] The bulk density and crushing strength of activated carbon No. 1 and a commercially available activated carbon for water purification (LO Corporation, water purification activated carbon, coal-based granular activated carbon) were measured according to the method described in this specification. The bulk density, crushing strength, and standard deviation of the crushing strength are shown in Table 5.

[0107] [Table 5]

[0108] 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 easier to grind uniformly. Commercially available activated carbon has a large standard deviation in crushing strength, suggesting that it is difficult to crush uniformly.

Claims

1. Activated carbon derived from a highly absorbent polymer containing acid groups, The activated carbon has an iodine adsorption capacity of 2,000 to 4,000 mg / g. Activated carbon characterized by:

2. The activated carbon according to claim 1, wherein the activated carbon contains 10 to 50 mass% of a polyvalent metal.

3. 2. The activated carbon of claim 1, wherein the activated carbon comprises micropores and mesopores, and the volume of the mesopores is greater than the volume of the micropores.

4. 4. The activated carbon according to claim 3, wherein the mesopore volume is from 0.200 mL / g to 0.600 mL / g.

5. 5. The activated carbon according to claim 3, wherein the volume of the micropores is 0.005 to 0.100 mL / g.

6. The activated carbon has a thickness of 50 to 250 m 2 5. The activated carbon according to claim 3 or 4, having a BET specific surface area of ​​1 / g.

7. 2. The activated carbon of claim 1, wherein the activated carbon has a bulk density of 0.100 to 0.500 g / mL.

8. The activated carbon of claim 1, wherein the activated carbon has a crushing strength of 200 to 7,000 kPa.

9. 1. Use of a polyvalent metal for recycling a highly absorbent polymer containing acid groups into activated carbon, comprising: The superabsorbent polymer containing an acid group is a crosslinked superabsorbent polymer in which the acid group is crosslinked with the polyvalent metal.

10. The use characterized by:

10. 1. Use of a superabsorbent polymer containing acid groups for recycling the superabsorbent polymer containing acid groups into activated carbon, comprising: The superabsorbent polymer containing an acid group is a crosslinked superabsorbent polymer in which the acid group is crosslinked with a polyvalent metal.

10. The use characterized by:

11. The use according to claim 9 or 10, wherein the activated carbon has an iodine adsorption capacity of 2,000 to 4,000 mg / g.

12. The use according to claim 9 or 10, wherein the crosslinked highly water-absorbent polymer contains 10 to 50% by mass of the polyvalent metal in a dry state.

13. 11. The use according to claim 9 or 10, wherein the crosslinked superabsorbent polymer has a moisture content of more than 0% and not more than 40% by weight.

14. 11. The use according to claim 9 or 10, wherein the highly water-soluble polymer containing acid groups is absorbing body fluids.

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