Method for recovering constituent member of used absorbent article

Abstract

Provided is a method for recovering a constituent member of a used absorbent article, the method being capable of reducing contaminants in the constituent member while suppressing an increase in cost. The present invention is a method for recovering a constituent member of a used absorbent article. This invention comprises: a dehydration and washing step (S3) for dehydrating and washing a mixture containing a highly-water-absorbent polymer having an acid group and a pulp fiber, which are constituent members, with a solution containing an oxidizing agent and a dehydrating agent capable of dehydrating the highly-water-absorbent polymer and the pulp fiber; and a separation step (S4) for separating at least the highly-water-absorbent polymer and the pulp fiber from the solution containing the mixture.

Description

Method for recovering components of used absorbent articles

[0001] The present invention relates to a method for recovering components of used absorbent articles.

[0002] Methods for recovering components of used absorbent articles are known. For example, Patent Document 1 discloses a method for recycling a water-absorbent resin derived from a used absorbent article, characterized by draining the absorbed liquid from the absorbent resin and restoring the absorbency of the absorbent resin. This method includes (i) an immersion step in which a used absorbent article containing a water-absorbent resin that has absorbed the absorbed liquid is immersed in an immersion liquid containing a hydrophilic organic solvent; (ii) a crushing step in which the used absorbent article is crushed into crushed material during or before the immersion step; and (iii) a separation step in which the water-absorbent resin is separated from a mixture of the immersion liquid and the crushed material. Patent Document 1 also discloses that in step (iii), one or more components selected from pulp, nonwoven fabric, and adhesive may be further separated and recovered, and that a sterilization / disinfection step in which the water-absorbent resin is sterilized and / or disinfected may be performed in parallel with or after the immersion step. Used absorbent articles from which components are to be collected include used sanitary materials that have absorbed liquids such as urine and blood (liquids to be absorbed).

[0003] International Publication No. 2021 / 162082

[0004] From the perspective of reducing environmental impact and ensuring sustainable consumption and production patterns, it is desirable to treat not only absorbent articles containing excrement but also absorbent articles not containing excrement as used absorbent articles, which are the targets for the recovery of constituent parts. Examples of absorbent articles not containing excrement include absorbent articles that have been used but do not contain excrement, absorbent articles that have been transferred or otherwise not used, and absorbent articles that have been manufactured or stored but then disposed of. In such cases, used absorbent articles may be contaminated with various contaminants, such as excrement, sebum, bacteria, odorous substances, and coloring substances derived from these substances, machine oil from manufacturing equipment, and various organic substances.

[0005] However, in Patent Document 1, the used absorbent articles from which the components are to be collected are used sanitary materials that have absorbed liquids such as urine and blood. Therefore, even if the sterilization / disinfection process can sterilize / disinfect the components of the used absorbent articles, there is a risk that it will not be possible to completely reduce various contaminants. This may make it difficult to safely and securely reuse the collected components for various purposes.

[0006] However, if it is not possible to completely reduce such various contaminants, adding a new process to reduce these contaminants may result in an increase in the cost of recovering the components.

[0007] Therefore, an object of the present invention is to provide a method for recovering components of used absorbent articles, which can reduce contaminants in the components while suppressing increases in costs.

[0008] The present invention is a method for recovering components of used absorbent articles, comprising a dehydration and washing step in which a mixture containing the components, a superabsorbent polymer having acid groups and pulp fibers, is dehydrated and washed with a solution containing a dehydrating agent and an oxidizing agent capable of dehydrating the superabsorbent polymer and the pulp fibers, and a separation step in which at least the superabsorbent polymer and the pulp fibers are separated from the solution containing the mixture.

[0009] According to the present invention, it is possible to provide a method for recovering components of used absorbent articles, which can reduce contaminants in the components while suppressing increases in costs.

[0010] FIG. 2 is a flow chart showing an example of a method for recovering components of used absorbent articles according to an embodiment.

[0011] The present embodiment relates to the following aspects.

[0012] [Mode 1] A method for recovering components of used absorbent articles, comprising: a dehydration and washing process in which a mixture containing the components, a superabsorbent polymer having acid groups and pulp fibers, is dehydrated and washed with a solution containing a dehydrating agent and an oxidizing agent capable of dehydrating the superabsorbent polymer and the pulp fibers; and a separation process in which at least the superabsorbent polymer and the pulp fibers are separated from the solution containing the mixture.

[0013] In this method, a dehydrating agent and an oxidizing agent are simultaneously used to simultaneously dehydrate and wash at least the superabsorbent polymer having acid groups and the pulp fibers. That is, the dehydrating agent can dehydrate the water absorbed by the superabsorbent polymer and the pulp fibers, which may contain contaminants. At the same time, the oxidizing agent can reduce contaminants contained in the superabsorbent polymer and the pulp fibers (e.g., feces, sebum, bacteria, odorous substances, and coloring substances derived therefrom, machine oils used in manufacturing facilities, and various organic substances). This reduces contaminants in at least the superabsorbent polymer and the pulp fibers. Furthermore, by simultaneously performing dehydration and washing, the number of processes is minimized, thereby minimizing increases in costs associated with these processes. Therefore, in a method for recovering components of used absorbent articles, contaminants in the components can be reduced while minimizing increases in costs.

[0014] [Aspect 2] The method of aspect 1, wherein the oxidizing agent includes at least one of ozone, hydrogen peroxide, and a chlorine-based substance.

[0015] In this method, the oxidizing agent contains at least one of ozone, hydrogen peroxide, and a chlorine-based substance, which have strong oxidizing power, so that the contaminants contained in the superabsorbent polymer and the pulp fibers can be more reliably reduced.

[0016] [Aspect 3] The method according to Aspect 1 or 2, wherein the dehydrating agent comprises a ketone-based organic solvent.

[0017] This method uses a ketone-based organic solvent as a dehydrating agent, which is resistant to oxidation even by highly oxidizing agents. This allows for more reliable dehydration of the water absorbed by the superabsorbent polymer and pulp fibers, which may contain contaminants, without being affected by the oxidizing power of the oxidizing agent.

[0018] [Aspect 4] The method according to any one of Aspects 1 to 3, wherein the oxidizing agent includes either an active species generated by irradiating another oxidizing agent contained in the solution with ultraviolet light, or, when the solution contains water, an active species generated by irradiating the water and / or another oxidizing agent contained in the solution with ultraviolet light.

[0019] In this method, the oxidizing agent contains an active species with strong oxidizing power, i.e., an active species generated by irradiating other oxidizing agents with ultraviolet light, and an active species generated by irradiating water and / or other oxidizing agents contained in the solution with ultraviolet light when the solution contains water. Therefore, the contaminants contained in both the superabsorbent polymer and the pulp fibers can be more reliably reduced.

[0020] [Aspect 5] A method described in any one of aspects 1 to 4, wherein the separation step includes a step of separating the superabsorbent polymer and the pulp fibers together from the solution containing the mixture, and a step of further separating the superabsorbent polymer and the pulp fibers that have been separated together from each other.

[0021] In this method, the superabsorbent polymer and pulp fibers that have been separated together have already been dehydrated and washed. Therefore, by separating the superabsorbent polymer and pulp fibers from each other, reusable superabsorbent polymer and pulp fibers can be obtained without further washing. In other words, it is possible to obtain superabsorbent polymer and pulp fibers with reduced contaminants while suppressing an increase in washing steps and thus costs.

[0022] [Aspect 6] A method described in any one of aspects 1 to 5, wherein the dehydration and washing process includes a process of dehydrating and washing the mixture further containing the plastic material that is the constituent component with the solution, and the separation process includes a process of separating the plastic material from the solution containing the mixture separately from the superabsorbent polymer and the pulp fibers.

[0023] In this method, the superabsorbent polymer, pulp fibers, and plastic material that are separated together have already been dehydrated and washed. Therefore, by separating at least the plastic material from the superabsorbent polymer, pulp fibers, and plastic material, a reusable plastic material can be obtained without further washing. In other words, a plastic material with reduced contaminants can be obtained while suppressing increases in costs.

[0024] [Aspect 7] The method according to any one of aspects 1 to 6, further comprising a pretreatment step of reducing the moisture absorbed by the used absorbent article prior to the dehydration and cleaning step.

[0025] This method includes a pretreatment step of reducing the moisture absorbed by the used absorbent article before the dehydration and washing step. Therefore, the amount of moisture in the used absorbent article that needs to be treated in the dehydration and washing step can be reduced in advance in the pretreatment step. This allows for more reliable reduction of contaminants contained in the superabsorbent polymer and pulp fibers in the dehydration and washing step.

[0026] [Aspect 8] The method described in Aspect 7, wherein the pretreatment step involves subjecting the used absorbent article to at least one of an acidic aqueous solution treatment, a polyvalent metal salt treatment, a high-pressure steam treatment, a freeze-drying treatment, and an organic solvent treatment.

[0027] In this method, as a pretreatment step prior to the dehydration and washing step, the used absorbent article is subjected to at least one of an acidic aqueous solution treatment, a polyvalent metal salt treatment, high-pressure steam treatment, freeze-drying, and an organic solvent treatment, thereby more reliably reducing the moisture in the used absorbent article in advance, which is to be treated in the dehydration and washing step.

[0028] [Aspect 9] The method described in Aspect 8, wherein the pretreatment step includes a step of subjecting the used absorbent article to an acidic aqueous solution treatment to inactivate the superabsorbent polymer with an acidic aqueous solution, and the dehydration and washing step includes a step of activating the inactivated superabsorbent polymer using alkali metal ions supplied from an alkali metal ion source.

[0029] In this method, by performing an acidic aqueous solution treatment as a pretreatment step, the superabsorbent polymer is inactivated with the acidic aqueous solution, allowing for more appropriate reduction (dehydration) of the moisture absorbed by the superabsorbent polymer. In other words, the amount of moisture to be treated in the dehydration and washing step in used absorbent articles can be more appropriately reduced in advance. In addition, by using an alkali metal ion source in the dehydration and washing step, the superabsorbent polymer can be reactivated with alkali metal ions while remaining in a dehydrated state. Since the reactivated superabsorbent polymer does not absorb moisture, subsequent handling is easier, and for example, it can be easily dried. This allows for a reactivated superabsorbent polymer with reduced contaminants to be obtained while suppressing cost increases.

[0030] [Aspect 10] The method according to Aspect 8, wherein the pretreatment step includes a step of performing a polyvalent metal salt treatment on the used absorbent article to inactivate the superabsorbent polymer with polyvalent metal ions supplied from a polyvalent metal salt, and the method further includes a step of substituting the polyvalent metal ions of the inactivated superabsorbent polymer with an acidic substance before the dehydration and washing step or during the dehydration and washing step, and a step of neutralizing the superabsorbent polymer whose polyvalent metal ions have been substituted with the acidic substance using an alkaline substance containing sodium during the dehydration and washing step.

[0031] In this method, by performing a polyvalent metal salt treatment as a pretreatment step, the superabsorbent polymer is inactivated with polyvalent metal ions, allowing for more appropriate reduction (dehydration) of the moisture absorbed by the superabsorbent polymer. That is, the amount of moisture to be treated in the dehydration and washing step in used absorbent articles can be more appropriately reduced. In addition, the polyvalent metal ions in the superabsorbent polymer are replaced with an acidic substance (acidic aqueous solution) before or during the dehydration and washing step. Then, during the dehydration and washing step, the superabsorbent polymer with the polyvalent metal ions replaced with the acidic substance is neutralized with an alkaline substance (alkaline aqueous solution) containing sodium. This reactivates the inactivated superabsorbent polymer in addition to the dehydration and washing step. This reduces contaminants and produces a reactivated superabsorbent polymer while minimizing cost increases.

[0032] [Aspect 11] A method according to any one of aspects 1 to 10, further comprising a crushing step of crushing the used absorbent articles, the crushing step being carried out before the separation step and either before, during, or after the dehydration and washing step.

[0033] In this method, the crushing step of crushing used absorbent articles is carried out before the separation step and either before, during, or after the dehydration and washing step, thereby more reliably separating at least the superabsorbent polymer and pulp fibers from the solution containing the mixture in the separation step.

[0034] [Aspect 12] A method described in any one of claims 1 to 11, further comprising a drying step of drying at least the superabsorbent polymer and the pulp fibers, the drying step being carried out at least one of after the dehydration and washing step and after the separation step.

[0035] In this method, the drying step for drying the superabsorbent polymer and pulp fibers is carried out at least one of after the dehydration-washing step and after the separation step. Therefore, since the superabsorbent polymer and pulp fibers are dehydrated in advance in the dehydration-washing step and are easily dried, the energy required for drying can be reduced, and the superabsorbent polymer and pulp fibers can be easily processed in the next step or reused. Therefore, the processing burden in the next step is reduced, and processing costs can be reduced.

[0036] [Aspect 13] The method according to any one of aspects 1 to 12, further comprising a re-supply step of recovering the dehydrating agent from the solution after the separation step and supplying the recovered dehydrating agent to the dehydration washing step.

[0037] This method further includes a step of recovering the dehydrating agent from the solution after the separation step and supplying it to the dehydration and washing step, thereby making it possible to reduce contaminants while suppressing increases in costs in the method for recovering components of used absorbent articles.

[0038] Hereinafter, a method for recovering components of used absorbent articles according to an embodiment will be described. This recovery method can also be considered as a method for producing reusable components, or in other words, a method for producing recycled components (e.g., recycled superabsorbent polymers, recycled pulp fibers).

[0039] However, used absorbent articles include absorbent articles that have been used, such as those containing excrement and those not containing excrement, as well as unused but discarded absorbent articles, such as those that were transferred but not used, and those that were manufactured or stored but discarded (factory loss, storage loss, etc.). Absorbent articles include those containing superabsorbent polymers and pulp fibers as absorbent materials, such as disposable diapers, urine pads, sanitary napkins, bed sheets, and pet sheets. Recycled superabsorbent polymers are superabsorbent polymers derived from used absorbent articles that have been recovered and regenerated from used absorbent articles. Recycled pulp fibers are pulp fibers derived from used absorbent articles that have been recovered and regenerated from used absorbent articles. Used absorbent articles contain contaminants. These contaminants include, for example, excrement, sebum, bacteria, odorous substances, and coloring substances derived from these substances, machine oil from manufacturing equipment, and various organic substances.

[0040] First, an example of the configuration of an absorbent article will be described. The absorbent article comprises a top sheet, a back sheet, and an absorbent body disposed between the top sheet and the back sheet. An example of the size of the absorbent article is a length of approximately 15 to 100 cm and a width of 5 to 100 cm. The absorbent article may further comprise other components that are typically included in absorbent articles, such as a diffusion sheet, a leak-proof wall, a side sheet, and an exterior sheet.

[0041] The material for the top sheet is not particularly limited as long as it can be used in absorbent articles, and examples thereof include liquid-permeable nonwoven fabrics, synthetic resin films with liquid-permeable holes, and composite sheets thereof. The material for the back sheet is not particularly limited as long as it can be used in absorbent articles, and examples thereof include liquid-impermeable nonwoven fabrics, liquid-impermeable synthetic resin films, and composite sheets thereof. The material for the diffusion sheet is not particularly limited as long as it can be used in absorbent articles, and examples thereof include liquid-permeable nonwoven fabrics. The materials for the leak barrier, side sheets, and exterior sheets are not particularly limited as long as they can be used in absorbent articles, and examples thereof include liquid-impermeable nonwoven fabrics. The materials for the nonwoven fabrics and synthetic resin films are not particularly limited as long as they can be used in absorbent articles, and examples thereof include synthetic resins. Examples of synthetic resins include olefin-based resins such as polyethylene and polypropylene, polyamide-based resins such as 6-nylon and 6,6-nylon, and polyester-based resins such as polyethylene terephthalate (PET) and polybutylene terephthalate (PBT). The nonwoven fabric may be made of natural fibers such as cotton, rayon, etc. In this embodiment, at least the nonwoven fabric and the synthetic resin film are referred to as plastic materials.

[0042] Examples of absorbent materials include absorbent materials, namely, pulp fibers and superabsorbent polymers. Pulp fibers are not particularly limited as long as they can be used in absorbent articles, and examples include cellulosic fibers. Cellulosic fibers include, for example, wood pulp, crosslinked pulp, non-wood pulp, regenerated cellulose, and semi-synthetic cellulose. Pulp fiber size includes an average fiber length of, for example, several tens of microns, preferably 20 to 40 microns, and an average fiber length of, for example, several millimeters, preferably 2 to 5 mm. Superabsorbent polymers (SAPs) are not particularly limited as long as they are usable in absorbent articles and contain acid groups, and examples include those containing carboxyl groups, sulfo groups, etc., with those containing carboxyl groups being preferred. Examples include absorbent polymers based on polyacrylates (containing carboxyl groups), polysulfonates (containing sulfo groups, etc.), and polymaleic anhydrides (containing carboxyl groups). The size of the superabsorbent polymer (when dry) can be, for example, an average particle size of several hundred μm, preferably 200 to 500 μm. The absorbent body may include a core wrap sheet formed of a liquid-permeable sheet such as tissue, which encloses the absorbent material.

[0043] One side and the other side of the absorbent body are bonded to the top sheet and the back sheet, respectively, via an adhesive. In a plan view, the portion (peripheral portion) of the top sheet that extends outward from the absorbent body so as to surround the absorbent body is bonded via an adhesive to the portion (peripheral portion) of the back sheet that extends outward from the absorbent body so as to surround the absorbent body. Therefore, the absorbent body is enclosed within the bonded body of the top sheet and the back sheet. If the absorbent body has a core wrap sheet, the absorbent material is bonded to the core wrap sheet via an adhesive. The diffusion sheet, leak-proof wall, side sheet, and exterior sheet are also each bonded to other components with an adhesive. The adhesive is not particularly limited as long as it can be used in absorbent articles, and examples thereof include hot-melt adhesives. Examples of hot-melt adhesives include pressure-sensitive adhesives or heat-sensitive adhesives that are primarily rubber-based, such as styrene-ethylene-butadiene-styrene, styrene-butadiene-styrene, and styrene-isoprene-styrene, or olefin-based, such as polyethylene.

[0044] As described above, an absorbent article having the above-mentioned configuration contains some or all of the above-mentioned contaminants at the stage of a used absorbent article.

[0045] Next, a method for collecting components of used absorbent articles according to an embodiment will be described. Some or all of the components of used absorbent articles collected by this method are recycled (reused) as materials for various products.

[0046] FIG. 1 is a flow chart showing an example of a method for recovering components of used absorbent articles according to an embodiment.

[0047] The method for recovering components of used absorbent articles includes a dehydration and washing step S3 and a separation step S4, and may further include at least one of a crushing step S1, a pre-treatment step S2, and a drying step S5. Each step will be described in detail below.

[0048] The shredding step S1 is a step of shredding used absorbent articles. The shredding device is not particularly limited as long as it can expose the internal superabsorbent polymer and pulp fibers, and examples thereof include a biaxial shredder (e.g., a biaxial rotary shredder, a biaxial differential shredder, or a biaxial shear shredder). As a result, part or all of the used absorbent article is shredded to generate multiple small pieces containing one or more component parts. The size of the small pieces is not particularly limited as long as they can be handled in each subsequent step, and examples include squares with sides of 1 to 10 cm in plan view or equivalent sizes (approximately the same area). Here, shredding also refers to the case where the sheets (e.g., top sheet, back sheet, and exterior sheet) constituting the outer surface of the used absorbent article are torn, thereby releasing the internal superabsorbent polymer and pulp fibers to the outside. In this case, the plurality of small pieces may include one or more pieces of a torn sheet, or one or more lumps containing discharged superabsorbent polymer or pulp fibers.

[0049] The crushing step S1 may be carried out in air or in a liquid. When the crushing step S1 is carried out in a liquid, examples of the liquid include water and the aqueous solutions used in the pretreatment step S2, i.e., an acidic aqueous solution (described below) and a polyvalent metal salt aqueous solution (described below). Therefore, when an acidic aqueous solution or a polyvalent metal salt aqueous solution is used as the liquid, the crushing step S1 and the pretreatment step S2 can be said to be carried out simultaneously.

[0050] The crushing step S1 is mainly performed to facilitate separation of one or more components of the used absorbent article from the other components in the separation step S4, and therefore may be performed before the separation step S4. Therefore, the crushing step S1 may be performed before the separation step S4, and either before the dehydration washing step S3, during the dehydration washing step S3, or after the dehydration washing step S3. However, "before the dehydration washing step S3" means either before the pretreatment step S2, during the pretreatment step S2, or after the pretreatment step S2.

[0051] In addition, if the crushing step S1 is not performed and uncrushed used absorbent articles are used as they are in the dehydration and cleaning step S3 (whether or not they have undergone the pre-treatment step S2), for example, by using an organic solvent (described below) as a dehydrating agent, the adhesive of the used absorbent articles can be dissolved in the organic solvent, allowing the used absorbent articles to be disassembled into individual component parts.

[0052] The pretreatment step S2 is a step of reducing the moisture absorbed by used absorbent articles (particularly superabsorbent polymers) that have been crushed through the crushing step S1 or have not been crushed, i.e., a step of dehydrating the used absorbent articles. However, since the pretreatment step S2 is a step carried out before the dehydration and washing step S3, it is sufficient that the used absorbent articles or their crushed counterparts can be dehydrated to a certain extent, and complete dehydration is not necessarily required. The proportion of moisture to be dehydrated can be, for example, 10 to 90% by mass of the moisture absorbed in the used absorbent articles.

[0053] Specifically, the pretreatment step S2 is a step in which the used absorbent article is subjected to at least one of an acidic aqueous solution treatment, a polyvalent metal salt treatment, a high-pressure steam treatment, a freeze-drying treatment, and an organic solvent treatment. These treatments are treatments for dehydrating the superabsorbent polymer. The acidic aqueous solution treatment is a treatment in which the superabsorbent polymer is brought into contact with an acidic aqueous solution. The polyvalent metal salt treatment is a treatment in which the superabsorbent polymer is brought into contact with an aqueous solution containing a polyvalent metal salt. The high-pressure steam treatment is a treatment in which the superabsorbent polymer is brought into contact with high-pressure steam. The freeze-drying treatment is a treatment in which the superabsorbent polymer is exposed to a low-temperature dry atmosphere. The organic solvent treatment is a treatment in which the high molecular weight water-absorbent polymer is brought into contact with a hydrophilic organic solvent. Although known methods can be used for each of these treatments, the acidic aqueous solution treatment and the polyvalent metal salt treatment in particular are as follows.

[0054] The acidic aqueous solution treatment as the pretreatment step S2 is a step of inactivating the superabsorbent polymer of a used absorbent article with an acidic aqueous solution. For example, the used absorbent article (which may or may not have been crushed in the crushing step S1) is immersed in an acidic aqueous solution to bring the superabsorbent polymer into contact with the acid and inactivate it. The acidic aqueous solution treatment is preferable to the polyvalent metal salt treatment in that it is less likely to leave ash residue.

[0055] The acid (inactivator) in the acidic aqueous solution is not particularly limited, and examples thereof include acidic substances such as inorganic acids and organic acids. Examples of inorganic acids include sulfuric acid, hydrochloric acid, and nitric acid, with sulfuric acid being preferred from the viewpoints of not containing chlorine and cost. Examples of organic acids include carboxylic acids having multiple carboxyl groups (e.g., citric acid), carboxylic acids having one carboxyl group (e.g., acetic acid), and sulfonic acids (e.g., methanesulfonic acid). Organic acids are preferably those having multiple carboxyl groups, and more preferably citric acid, because they readily form chelate complexes with divalent or higher metals (e.g., calcium) contained in excrement and are less likely to leave ash residue in the superabsorbent polymer and pulp fibers. The acid concentration of the acidic aqueous solution is not particularly limited as long as it can perform the dehydration function, and examples thereof include 0.1 to 30% by mass. Furthermore, the acid (inactivator) is preferably an acid dissociation constant (pK ａ , in water) ａ , in water).

[0056] The acidic aqueous solution preferably has a pH within a predetermined range. The upper limit of the pH is preferably 6.0, more preferably 5.0. A pH of 6.0 or less makes it easier to dehydrate the superabsorbent polymer. The lower limit of the pH is preferably 0.5, more preferably 1.0. A pH of 0.5 or more makes it less likely to damage the pulp fibers, which are another target for recovery. However, the pH is measured at 25°C using, for example, a twin pH meter AS-711 manufactured by Horiba, Ltd.

[0057] The specific configuration of the apparatus for performing the acidic aqueous solution treatment is not particularly limited as long as it can immerse a superabsorbent polymer in the acidic aqueous solution. The apparatus may, for example, have a tank in which used absorbent articles (or crushed products thereof) containing a superabsorbent polymer can be placed and in which the acidic aqueous solution can be stored, a supply means for supplying the acidic aqueous solution into the tank, and a stirring means for stirring the acidic aqueous solution in the tank.

[0058] In the acidic aqueous solution treatment, the temperature of the acidic aqueous solution is not particularly limited and may be, for example, room temperature (25° C.). To accelerate the reaction rate, the acidic aqueous solution may be heated to a temperature range lower than 100° C. The treatment time is not particularly limited and may be, for example, about 5 to 60 minutes.

[0059] When an acidic aqueous solution treatment step is performed as the pretreatment step S2, a reactivation treatment step is then performed, in which the superabsorbent polymer inactivated by the acidic aqueous solution treatment is activated using alkali metal ions supplied from an alkali metal ion source. The reactivation treatment step may be performed before the dehydration and cleaning step S3. Alternatively, the reactivation treatment step may be included in the dehydration and cleaning step S3 and therefore may be performed during the dehydration and cleaning step S3. In this case, an aqueous solution containing an alkali metal ion source is added to the solution used in the dehydration and cleaning step S3. Alternatively, the reactivation treatment step may be performed after the dehydration and cleaning step S3.

[0060] Specifically, the reactivation treatment involves reactivating the inactivated superabsorbent polymer with alkali metal ions in an alkaline aqueous solution, which is an aqueous solution containing an alkali metal ion source. At this time, the H ions in the inactivated superabsorbent polymer are replaced with alkali metal ions, neutralizing the polymer and turning it into a reactivated superabsorbent polymer. In other words, the water absorption capacity of the superabsorbent polymer is restored. Note that if the reactivation treatment is performed during the dehydration and washing step S3, the reactivated superabsorbent polymer will not absorb water because a dehydrating agent is present around it.

[0061] Examples of alkali metal ions include lithium ions, sodium ions, and potassium ions, as well as any combination thereof. The alkali metal ion source is not particularly limited as long as it can supply these alkali metal ions, and examples include alkali metal hydroxides and salts of alkali metal hydroxides with acids having a larger acid dissociation constant than the acid groups of the superabsorbent polymer. Examples of alkali metal hydroxides include lithium hydroxide, sodium hydroxide, and potassium hydroxide, as well as any combination thereof. Examples of salts include lithium carbonate, sodium carbonate, potassium carbonate, lithium bicarbonate, sodium bicarbonate, potassium bicarbonate, lithium chloride, sodium chloride, and potassium chloride. The aqueous solution containing the alkali metal ion source is preferably neutral or alkaline, and more preferably alkaline. The concentration of the alkali metal ion source in the alkaline aqueous solution is not particularly limited as long as it reactivates the superabsorbent polymer. When an alkali metal hydroxide is used as the alkali metal ion source, the concentration may be, for example, 0.5 to 50% by mass.

[0062] The specific configuration of the device for performing the reactivation treatment is not particularly limited as long as it can immerse the inactivated superabsorbent polymer in the alkaline aqueous solution. The device may, for example, have a tank in which used absorbent articles containing a superabsorbent polymer (or crushed products thereof) can be placed and in which the alkaline aqueous solution can be stored, a supply means for supplying the alkaline aqueous solution into the tank, and a stirring means for stirring the alkaline aqueous solution in the tank.

[0063] In the reactivation treatment, the temperature of the alkaline aqueous solution is not particularly limited and may be, for example, room temperature (25° C.). To accelerate the reaction rate, the alkaline aqueous solution may be heated to a temperature lower than 100° C. The treatment time is not particularly limited and may be, for example, about 5 to 60 minutes.

[0064] The polyvalent metal salt treatment as the pretreatment step S2 is a step of inactivating the superabsorbent polymer of a used absorbent article with polyvalent metal ions supplied from the polyvalent metal salt. For example, the used absorbent article (which may or may not have been crushed in the crushing step S1) is immersed in an aqueous solution of the polyvalent metal salt to bring the superabsorbent polymer into contact with the polyvalent metal ions and inactivate it. The polyvalent metal salt treatment is preferable to the acidic aqueous solution treatment in that dehydration is more easily promoted.

[0065] The polyvalent metal salt in the polyvalent metal salt aqueous solution is not particularly limited, and examples thereof include alkaline earth metal salts and transition metal salts. Examples of alkaline earth metal salts include salts of beryllium, magnesium, calcium, strontium, and barium, with calcium chloride, calcium nitrate, magnesium chloride, and magnesium nitrate being preferred, and calcium chloride being more preferred. Examples of transition metal salts include salts of iron, cobalt, nickel, copper, and aluminum, with their inorganic or organic acid salts being preferred. Examples of inorganic acid salts include iron chloride, iron sulfate, iron phosphate, iron nitrate, cobalt chloride, cobalt sulfate, cobalt phosphate, cobalt nitrate, nickel chloride, nickel sulfate, copper chloride, copper sulfate, and aluminum sulfate. Examples of organic acid salts include iron lactate, cobalt acetate, cobalt stearate, nickel acetate, and copper acetate. The concentration of the polyvalent metal salt in the aqueous polyvalent metal salt solution is not particularly limited as long as it can perform the dehydrating function, and when an alkaline earth metal salt is used as the polyvalent metal, the concentration is, for example, 0.1 to 10 mass %.

[0066] The specific configuration of the apparatus for performing the polyvalent metal salt treatment is not particularly limited as long as it can immerse a superabsorbent polymer in an aqueous solution of the polyvalent metal salt. The apparatus may, for example, have a tank in which a used absorbent article (or a disassembled product thereof) containing a superabsorbent polymer can be placed and in which the aqueous solution of the polyvalent metal salt can be stored, a supply means for supplying the aqueous solution of the polyvalent metal salt into the tank, and a stirring means for stirring the aqueous solution of the polyvalent metal salt in the tank.

[0067] In the polyvalent metal salt treatment, the temperature of the polyvalent metal salt aqueous solution is not particularly limited and may be, for example, room temperature (25°C). To increase the reaction rate, the polyvalent metal salt aqueous solution may be heated to a temperature range lower than 100°C. The treatment time is not particularly limited and may be, for example, about 10 to 120 minutes. The pH of the polyvalent metal salt aqueous solution is not particularly limited and may be, for example, 11 or less. When an alkaline compound is used, the pH of the aqueous solution is preferably greater than 7 and less than or equal to 11.

[0068] When polyvalent metal salt treatment is performed as the pretreatment step S2, a step of substituting polyvalent metal ions with an acidic substance (acidic aqueous solution) for the superabsorbent polymer inactivated by the polyvalent metal salt treatment (acidic substance substitution treatment) is then performed, followed by a step of neutralizing the superabsorbent polymer in which the polyvalent metal ions have been substituted with the acidic substance using an alkaline substance (alkaline aqueous solution) containing sodium (alkaline substance neutralization treatment). The step of substituting polyvalent metal ions with an acidic substance is performed before the dehydration and cleaning step S3 or during the dehydration and cleaning step S3. If performed during the dehydration and cleaning step S3, an aqueous solution containing an acidic substance is added to the solution used in the dehydration and cleaning step S3. On the other hand, the step of neutralizing the superabsorbent polymer with an alkaline substance is performed after the step of substituting polyvalent metal ions with an acidic substance, during the dehydration and cleaning step or after the dehydration and cleaning step S3. If performed during the dehydration and cleaning step S3, an aqueous solution containing an alkaline substance containing sodium is added to the solution used in the dehydration and cleaning step S3.

[0069] The step of substituting the polyvalent metal ions of the superabsorbent polymer inactivated by the polyvalent metal salt treatment with an acidic substance (acidic substance substitution treatment) is substantially the same as the acidic aqueous solution treatment described above. However, the acid in the acidic aqueous solution is preferably a strongly acidic inorganic acid. Examples of such inorganic acids include sulfuric acid, hydrochloric acid, and nitric acid, but sulfuric acid is preferred from the viewpoints of not containing chlorine and cost.

[0070] The above-mentioned step of neutralizing the superabsorbent polymer in which polyvalent metal ions have been substituted with an acidic substance using an alkaline substance (alkaline substance neutralization treatment) is substantially the same as the above-mentioned reactivation treatment, except that the alkali metal ion source is an alkaline substance containing sodium, such as sodium hydroxide, and the alkali metal ions in the alkaline aqueous solution, which is an aqueous solution containing the alkali metal ion source, are sodium ions.

[0071] In the pretreatment step S2, the proportion of used absorbent articles (or a plurality of small pieces) in the aqueous solution used in the various treatments is not particularly limited, as long as the various treatments can be carried out. Examples of the proportion include 0.1 to 50% by mass, and preferably 1 to 40% by mass. A proportion of 0.1% by mass or more allows the treatments to proceed efficiently. A proportion of 50% by mass or less allows the various treatments to proceed more easily.

[0072] Preferably, the pretreatment step S2 includes a step of separating and removing the water generated in the pretreatment step S2 before the dehydration and washing step S3. For example, the water solution containing the used absorbent articles (or a plurality of small pieces) in the pretreatment step S2 is filtered through a screen or the like to separate and remove the water generated in the pretreatment step S2. By removing the water once before the dehydration and washing step S3 in this way, the solution containing the dehydrating agent and the oxidizing agent (described below) in the dehydration and washing step S3 can be treated at the desired concentration without being diluted.

[0073] The dehydration and cleaning process S3 is a process in which a mixture containing a superabsorbent polymer having acid groups and pulp fibers, which are components of used absorbent articles, is dehydrated and cleaned with a solution containing a dehydrating agent and an oxidizing agent that can dehydrate the superabsorbent polymer and pulp fibers.

[0074] The mixture containing the superabsorbent polymer and pulp fibers, which are components of the absorbent article, is not particularly limited as long as it contains the superabsorbent polymer and pulp fibers of a used absorbent article. For example, the mixture may be a used absorbent article that has not undergone either the shredding step S1 or the pretreatment step S2. If the used absorbent article has undergone the shredding step S1, the mixture is a plurality of small pieces formed by shredding the used absorbent article, and contains the superabsorbent polymer and pulp fibers, but the superabsorbent polymer and pulp fibers have not been individually separated. If the used absorbent article has undergone the pretreatment step S2, the mixture is a pretreated used absorbent article, and contains the superabsorbent polymer and pulp fibers that have been dehydrated to a certain extent, but the superabsorbent polymer and pulp fibers have not been individually separated. When used absorbent articles have undergone both the shredding step S1 and the pretreatment step S2, the mixture is a plurality of small pieces that have been pretreated and contain superabsorbent polymer and pulp fibers that have been dehydrated to a certain extent, but the superabsorbent polymer and pulp fibers are not individually separated. Alternatively, the mixture may be a mixture containing superabsorbent polymer and pulp fibers that has been prepared separately in advance, regardless of the shredding step S1 or the pretreatment step S2.

[0075] The mixture may further contain a plastic material that is a component of used absorbent articles. In this case, the dehydration and washing step S3 is a step of dehydrating and washing the mixture containing the superabsorbent polymer, pulp fiber, and plastic material that are components of used absorbent articles with a solution containing a dehydrating agent and an oxidizing agent. The mixture containing the superabsorbent polymer, pulp fiber, and plastic material that are components of used absorbent articles is not particularly limited as long as it contains the superabsorbent polymer, pulp fiber, and plastic material of the used absorbent article, and may or may not have been subjected to the crushing step S1 and / or the pretreatment step S2, as in the case of the mixture containing the superabsorbent polymer and pulp fiber described above.

[0076] The solution containing a dehydrating agent and an oxidizing agent may be a solution composed only of a dehydrating agent and an oxidizing agent, or may contain other solvents, such as organic solvents or water, as long as they do not affect dehydration and oxidation. The total proportion of the dehydrating agent and oxidizing agent in the solution is, for example, 50% by mass or more, and preferably higher from the viewpoint of the dehydration and oxidation effects. Therefore, it is preferably 70% by mass or less, more preferably 80% by mass or less, and even more preferably 90% by mass or less. However, when water is contained as another solvent, the proportion of water is preferably 10% by mass or less, more preferably 5% by mass or less, and even more preferably 1% by mass or less.

[0077] The dehydrating agent is not particularly limited as long as it is not easily oxidized by an oxidizing agent and is capable of dehydrating the superabsorbent polymer and pulp fibers contained in the used absorbent article. The dehydrating agent is, for example, a liquid, and is thought to be able to dissolve and dehydrate the moisture contained in the components and also dissolve and remove contaminants, but is not limited to this mechanism.

[0078] Examples of dehydrating agents include organic solvents. Examples of organic solvents include hydrophilic organic solvents and polar organic solvents. Examples of organic solvents that belong to at least one of these groups include ketone-based organic solvents and alcohol-based organic solvents. Other organic solvents include fluorine-based organic solvents. Examples of ketone-based organic solvents include acetone. Acetone dissolves water well, is resistant to oxidation by oxidizing agents, and has the property of protecting functional groups. Therefore, acetone can dehydrate superabsorbent polymers and pulp fibers while suppressing the decomposition (dissolution) of components, particularly highly decomposable superabsorbent polymers, and can remove some or all of the contaminants contained in these components. Furthermore, when the dehydrating agent is an organic solvent, it can dissolve the adhesive that bonds the components of used absorbent articles, making it easier to separate the components from each other. Examples of alcohol-based organic solvents include ethanol and methanol. Examples of the fluorine-based organic solvent include 1-chloro-2,3,3-trifluoropropene and 1,1,1,3,3-pentafluorobutane.

[0079] The proportion of the dehydrating agent in the solution is, for example, 50% by mass or more. From the viewpoint of the effects of dehydration and removal of contaminants, the proportion of the dehydrating agent in the solution is preferably higher, and when the oxidizing agent is a gas, the proportion is preferably 70% by mass or more, and more preferably 90% by mass or more.

[0080] There are no particular limitations on the oxidizing agent, as long as it can remove contaminants contained in used absorbent articles while suppressing their impact on the constituent components (e.g., oxidative decomposition of superabsorbent polymers, damage to pulp fibers). The oxidizing agent is, for example, a liquid or a gas mixed with a liquid, and is thought to reduce contaminants by oxidatively decomposing the contaminants, reducing their molecular weight and making them more soluble in the solution, but is not limited to this mechanism.

[0081] Examples of oxidizing agents include ozone, hydrogen peroxide, and chlorine-based substances (e.g., chlorine), or a combination of two or more of these. These oxidizing agents have relatively high oxidizing power and are therefore likely to reduce contaminants contained in components of used absorbent articles, such as superabsorbent polymers, pulp fibers, and plastic materials. This makes it possible to remove bacteria and reduce odorous and discoloring substances, thereby sterilizing, deodorizing, and decolorizing (bleaching) the components. Note that when acetone is used as a dehydrating agent, hydrogen peroxide is not used as an oxidizing agent.

[0082] The oxidizing agent may be mixed into the liquid dehydrating agent, or may be mixed into another solvent (e.g., organic solvent, water) and then mixed into the dehydrating agent.

[0083] When gaseous ozone is used as an oxidizing agent and gaseous ozone is supplied to a dehydrating agent to form a solution containing a dehydrating agent and an oxidizing agent, the ozone concentration in the solution is not particularly limited as long as it can reduce contaminants contained in the components. The ozone concentration is, for example, 0.2 to 2 ppm by mass, preferably 0.4 to 1.5 ppm by mass. A concentration of 0.2 ppm by mass or more facilitates the reduction of contaminants, while a concentration of 2 ppm by mass or less can suppress oxidative decomposition of superabsorbent polymers and damage to pulp fibers. The contact time between the ozone-containing solution and the components is not particularly limited as long as it can reduce contaminants contained in the components. Generally, the contact time is shorter when the ozone concentration is high and longer when the ozone concentration is low. The contact time is, for example, 1 to 200 minutes, preferably 2 to 60 minutes. The product of ozone concentration (ppm by mass) and contact time (minutes) (hereinafter also referred to as the "CT value") is preferably 0.2 to 40 ppm by mass min, more preferably 0.5 to 20 ppm by mass min. A CT value of 0.2 ppm by mass min or more facilitates the reduction of contaminants, while a CT value of 40 ppm by mass min or less inhibits the oxidative decomposition of components, particularly easily decomposed superabsorbent polymers. Treatment with ozone can reduce contaminants contained in components, for example, remove bacteria and reduce odorous and coloring substances, and can sterilize, deodorize, and decolorize (bleach) the components. Examples of ozone generators that supply gaseous ozone to a dehydrating agent include the ED-OWX-2 Ozone Water Exposure Tester manufactured by Ecodesign Inc., the OS-25V Ozone Generator manufactured by Mitsubishi Electric Corporation, and the REX MC Ozonizer MC-985S manufactured by a subsidiary of Rex Industrial Co., Ltd.

[0084] When a gas (e.g., ozone) is used as the oxidizing agent, the oxidizing agent may be supplied to the dehydrating agent by, for example, the following method. This method involves generating a predetermined amount of oxidizing agent in an oxidizing agent generator, continuously supplying the oxidizing agent to the dehydrating agent in the treatment tank at a predetermined airflow rate, while continuously discharging (discharging) the same amount of waste oxidizing agent (used oxidizing agent) outside the treatment tank. In this case, a flow of oxidizing agent is easily generated, making it easier for new oxidizing agent to be continuously supplied to the surface of the component, and making it easier for reactants to be continuously discharged from the surface. This allows the oxidation reaction on the surface of the component to proceed more reliably.

[0085] Alternatively, the oxidizing agent may include either an activated species generated by irradiating another oxidizing agent contained in the solution with ultraviolet light, or an activated species generated by irradiating water and / or another oxidizing agent contained in the solution with ultraviolet light when the solution contains water. For example, when the wavelength of ultraviolet light is 253.7 nm, the activated species generated by the reaction of ultraviolet light with an oxidizing agent (ozone + water, hydrogen peroxide), i.e., hydroxyl radicals, can decompose at least a portion of the pollutants (organic matter). Furthermore, when the wavelength of ultraviolet light is 184.9 nm, the activated species generated by the reaction of ultraviolet light with water, i.e., hydroxyl radicals, can decompose at least a portion of the pollutants (organic matter).

[0086] The proportion of used absorbent articles (or a plurality of small pieces) in the solution is not particularly limited as long as the dehydration and washing step S3 can be carried out. Examples of the proportion include 0.1 to 20% by mass, and preferably 1 to 10% by mass. A proportion of 0.1% by mass or more allows for efficient processing. A proportion of 20% by mass or less allows for easier dehydration and washing.

[0087] Contaminants such as excrement, sebum, bacteria, odorous substances, and coloring substances derived from them, machine oils in manufacturing equipment, and various organic substances are believed to be reduced as follows: By dehydration, primarily contaminants absorbed inside the components are expelled to the outside along with the moisture. Contaminants attached to the components are also expelled along with the released moisture. At the same time, by oxidation, primarily contaminants attached to the components (including those expelled from the inside and attached) are oxidatively decomposed, reduced in molecular weight, solubilized, and removed. This also makes it possible to sterilize, deodorize, and bleach the components. However, the reduction of contaminants in the above-mentioned components is not limited to this mechanism.

[0088] In the dehydration and washing step S3, the temperature for the dehydration and washing is not particularly limited as long as the dehydration and washing treatment can be performed, but is at least performed at a temperature lower than the boiling point of the dehydrating agent. Examples of the temperature for the dehydration and washing include room temperature (e.g., 25°C) to 50°C, with 30 to 40°C being preferred. A temperature above room temperature makes it easy to shorten the time required for dehydration and washing. A temperature of 50°C or less makes it easy to suppress evaporation (boiling) of the organic solvent, suppress dehydration condensation of the acid groups of the superabsorbent polymer, and easily suppress a decrease in its water absorbency. The time for the dehydration and washing is not particularly limited as long as the dehydration and washing treatment can be performed, but may be, for example, 1 to 200 minutes.

[0089] The specific configuration of the device that performs the dehydration and washing step S3 is not particularly limited as long as it can bring into contact (or immerse) a mixture containing components of used absorbent articles (e.g., superabsorbent polymer, pulp fiber, plastic material) with a solution containing a dehydrating agent and an oxidizing agent. The device may, for example, have a tank in which used absorbent articles (or crushed articles) can be placed and in which a solution containing a dehydrating agent and an oxidizing agent can be stored, a supply means that can supply the dehydrating agent and the oxidizing agent into the tank, and a stirring means that can stir the solution in the tank.

[0090] However, in this method, when an acidic aqueous solution treatment is performed as the pretreatment step S2 and the reactivation treatment is performed during the dehydration washing step S3, it is preferable that the solution containing an oxidizing agent and a dehydrating agent in the dehydration washing step S3 contains as little unnecessary moisture as possible (except for the moisture discharged from used absorbent articles). An aqueous solution containing an alkali metal ion source is supplied to the solution separately from the oxidizing agent and the dehydrating agent. This allows the reactivation treatment to be performed while the dehydration washing step S3 is being performed. In this case, the aqueous solution containing the alkali metal ion source may be supplied to the solution containing the oxidizing agent and the dehydrating agent, and then used absorbent articles (or crushed articles thereof) may be supplied. Alternatively, used absorbent articles may be supplied to the solution containing the oxidizing agent and the dehydrating agent, and after a predetermined time has elapsed, the aqueous solution containing the alkali metal ion source may be supplied.

[0091] However, in this method, when polyvalent metal salt treatment is performed as the pretreatment step S2 and the acidic substance substitution treatment is performed during the dehydration and washing step S3, it is preferable that the solution containing an oxidizing agent and a dehydrating agent in the dehydration and washing step S3 contains as little moisture as possible (except for the moisture discharged from used absorbent articles). An aqueous solution containing an acidic substance is supplied to the solution separately from the oxidizing agent and the dehydrating agent. Thus, the acidic substance substitution treatment is performed while the dehydration and washing step S3 is being performed. In this case, the aqueous solution containing the acidic substance may be supplied to the solution containing the oxidizing agent and the dehydrating agent, and then used absorbent articles (or crushed articles thereof) may be supplied. Alternatively, used absorbent articles may be supplied to the solution containing the oxidizing agent and the dehydrating agent, and then, after a predetermined time, the aqueous solution containing the acidic substance may be supplied.

[0092] Furthermore, when polyvalent metal salt treatment is performed as the pretreatment step S2, and an alkaline substance neutralization treatment is performed during the dehydration and washing step S3 after the acidic substance substitution treatment, it is preferable that the solution containing an oxidizing agent and a dehydrating agent in the dehydration and washing step S3 contains as little unnecessary moisture as possible (except for the moisture discharged from used absorbent articles). An aqueous solution containing an alkaline substance containing sodium is supplied to the solution separately from the oxidizing agent and the dehydrating agent. This allows the alkaline substance neutralization treatment to be performed while the dehydration and washing step S3 is being performed. In this case, the aqueous solution containing an alkaline substance containing sodium may be supplied to the solution containing the oxidizing agent and the dehydrating agent, and then used absorbent articles (or crushed articles thereof) may be supplied. Alternatively, used absorbent articles may be supplied to the solution containing the oxidizing agent and the dehydrating agent, and after a predetermined time has elapsed, the aqueous solution containing an alkaline substance containing sodium may be supplied.

[0093] When both the acidic substance replacement treatment and the alkaline substance neutralization treatment are performed in the dehydration and washing step S3, first, used absorbent articles (or crushed absorbent articles) are supplied to a solution containing an oxidizing agent and a dehydrating agent, and a dehydration and washing treatment is performed for a predetermined time (e.g., 1 to 30 minutes). Next, an aqueous solution containing an acidic substance is supplied to the solution, and an acidic substance replacement treatment is performed for a predetermined time (e.g., 1 to 30 minutes). Next, an aqueous solution containing an alkaline substance including sodium is supplied to the solution, and an alkaline substance neutralization treatment is performed for a predetermined time (e.g., 1 to 30 minutes).

[0094] The separation step S4 is a step of separating at least the superabsorbent polymer and the pulp fibers from the solution containing the mixture of the superabsorbent polymer and the pulp fibers. In this separation step S4, the solution containing the mixture of the superabsorbent polymer and the pulp fibers is separated into the pulp fibers and the superabsorbent polymer and a solution containing contaminants and other materials. As a result, the pulp fibers and the superabsorbent polymer that have been dehydrated and washed and have had the contaminants and other materials reduced are separated and recovered, for example, together.

[0095] The specific configuration of the device for performing the separation step S4 is not particularly limited as long as it can separate a solution containing a mixture of superabsorbent polymer and pulp fiber into a solution containing pulp fiber and superabsorbent polymer and contaminants and other materials. Examples of the device include a device having a screen that does not allow the superabsorbent polymer and pulp fiber to pass through, but allows the solution (including contaminants and other materials (small foreign matter)) to pass through. If the mixture contains other materials (large foreign matter) larger than the superabsorbent polymer and pulp fiber, the device may further have a screen that allows the superabsorbent polymer and pulp fiber to pass through but does not allow the other materials (large foreign matter) to pass through.

[0096] When the pulp fibers and the superabsorbent polymer are separated and recovered together, they can be easily reused together as materials for a single product. Such products include absorbent sheets, absorbents, cat litter, sandbag modifiers, and solid fuels. The superabsorbent polymer and pulp fibers that have been separated together may be further separated from each other using a screen or the like.

[0097] However, the absorbent sheet is an absorbent article, for example, formed by placing pulp fibers and superabsorbent polymers, which have been separated and recovered together, either as they are or mixed with unused absorbent material, between a top sheet and a back sheet as an absorbent material. The absorbent body is formed, for example, by wrapping pulp fibers and superabsorbent polymers, which have been separated and recovered together, either as they are or mixed with unused absorbent material, in a core wrap sheet as an absorbent material. Cat litter is a water-absorbent granular material, for example, formed by molding pulp fibers and superabsorbent polymers, which have been separated and recovered together, into granules with molten resin. Sandbag modifiers impart water retention to soil, for example, by scattering pulp fibers and superabsorbent polymers, which have been separated and recovered together, on the soil as they are, or by forming them into an absorbent sheet and placing them on the soil. Solid fuel is solid fuel itself, formed by melting and molding pulp fibers and superabsorbent polymers, which have been separated and recovered together, with flammable resin.

[0098] The solution may further contain plastic materials that are components of used absorbent articles. In this case, the separation step S4 is a step of separating the superabsorbent polymer, pulp fibers, and plastic materials from the solution containing a mixture of the superabsorbent polymer, pulp fibers, and plastic materials that are components of used absorbent articles. As a result, the pulp fibers, superabsorbent polymer, and plastic materials that have been dehydrated and washed and have reduced contaminants and other materials are separated and recovered, for example, together. An example of an apparatus that can achieve this is an apparatus having one or more screens as described above.

[0099] When the pulp fibers, superabsorbent polymers, and plastic materials are separated and collected together, they can easily be reused together as materials for a single product. Examples of such products include cat litter, building materials (including sound-absorbing materials and cement), injection-molded products, and solid fuels. The plastic materials may be further separated from the separated pulp fibers, superabsorbent polymers, and plastic materials using a screen or other device. This allows the plastic materials to be used in individual applications (e.g., bags made by the inflation method).

[0100] However, cat litter is formed, for example, by melting the plastic material from pulp fibers, superabsorbent polymers, and plastic materials that are separated and recovered together and molding them into granules. Sound-absorbing materials are bags or plates of sound-absorbing granules (such as plastic materials) packed to a certain thickness. For example, pulp fibers, superabsorbent polymers, and plastic materials (with or without resin) that are separated and recovered together are melted and molded into granules or plates. Cement materials are materials for concrete and mortar, and are made by, for example, mixing all or part of the pulp fibers, superabsorbent polymers, and plastic materials that are separated and recovered together with cement. Injection-molded products are injection-molded products, for example, by melting and injection-molding pulp fibers, superabsorbent polymers, and plastic materials (with or without resin) that are separated and recovered together. The solid fuel is formed, for example, by melting and molding pulp fibers, a highly absorbent polymer, and a plastic material (to which a flammable resin may be added) that have been separated and recovered together.

[0101] The drying step S5 is a step of drying at least the superabsorbent polymer and pulp fibers separated in the separation step S5.

[0102] The drying step S5 is carried out by placing the components in a dry atmosphere at a temperature higher than room temperature, or by blowing dry air at a temperature higher than room temperature onto the components. The drying temperature can be, for example, 40 to 110°C, with 50 to 100°C being preferred. A drying temperature of 40°C or higher can shorten the drying time. A drying temperature of 110°C or lower can prevent the components from sticking to each other and from deteriorating due to heat. The drying time can be, for example, 30 to 300 minutes. The drying step S5 may be carried out under reduced pressure, for example, at 0.1 to 100 kPa, in order to accelerate drying.

[0103] The drying step S5 is performed after the dehydration and cleaning step S3 and before the separation step S4, or after the separation step S4. However, the drying step S5 can be omitted in cases where the components are easily dried by using a dehydrating agent in the dehydration and cleaning step S3.

[0104] The method may include a re-supply step of recovering a dehydrating agent (e.g., an organic solvent) from the solution after separation step S4 and supplying the recovered dehydrating agent to dehydration and washing step S3. In this re-supply step, the dehydrating agent is recovered from the solution from which at least the superabsorbent polymer and pulp fibers have been separated in separation step S4, and after reducing contaminants as necessary, the recovered dehydrating agent is supplied to dehydration and washing step S3.

[0105] For example, the solution from which at least the superabsorbent polymer and pulp fibers have been separated contains contaminants such as excrement in addition to the dehydrating agent. Therefore, the solution is heated and / or depressurized to boil and evaporate the dehydrating agent contained in the solution. The vapor is then cooled to recover the dehydrating agent. In other words, the dehydrating agent is distilled. As a result, the recovered dehydrating agent contains fewer contaminants. The recovered dehydrating agent is then resupplied to the dehydration and washing step S3.

[0106] Thus, in this method for recovering components of used absorbent articles, the dehydration and washing step S3 simultaneously uses a dehydrating agent and an oxidizing agent to simultaneously dehydrate and wash at least the superabsorbent polymer having acid groups and the pulp fibers. Therefore, the dehydrating agent can first dehydrate the water absorbed by the superabsorbent polymer and the pulp fibers, which may contain contaminants. At the same time, the oxidizing agent can reduce contaminants contained in the superabsorbent polymer and the pulp fibers (e.g., excrement, sebum, bacteria derived from them, odorous substances, coloring substances, machine oil from manufacturing equipment, various organic substances, etc.). This reduces contaminants in at least the superabsorbent polymer and the pulp fibers. Furthermore, by simultaneously performing dehydration and washing, the number of processes is reduced, thereby minimizing increases in costs associated with these processes. Therefore, the method for recovering components of used absorbent articles can reduce contaminants in the components while minimizing increases in costs.

[0107] In a preferred embodiment of the present method, the oxidizing agent in the dehydration and washing step S3 contains at least one of ozone, hydrogen peroxide, and a chlorine-based substance, which have strong oxidizing power, thereby more reliably reducing contaminants contained in the superabsorbent polymer and pulp fibers.

[0108] In a preferred embodiment of this method, the dehydrating agent used in the dehydration and washing step S3 contains a ketone-based organic solvent that is difficult to oxidize even with a strong oxidizing agent, so that the moisture absorbed by the superabsorbent polymer and the pulp fibers, which may contain contaminants, can be more reliably dehydrated without being affected by the oxidizing power of the oxidizing agent.

[0109] In another preferred embodiment of this method, the oxidizing agent used in the dehydration and washing step S3 contains an active species with strong oxidizing power, i.e., an active species (e.g., hydroxyl radicals) generated by irradiating other oxidizing agents contained in the solution with ultraviolet light, and an active species (e.g., hydroxyl radicals) generated by irradiating water and / or other oxidizing agents contained in the solution with ultraviolet light when the solution contains water. This allows for more reliable reduction of contaminants contained in both the superabsorbent polymer and the pulp fibers.

[0110] In a preferred embodiment of this method, the superabsorbent polymer and pulp fibers that are separated together in the separation step S4 have already been dehydrated and washed together in the dehydration and washing step S3. Therefore, by separating the superabsorbent polymer and pulp fibers from each other, reusable superabsorbent polymer and pulp fibers can be obtained without further washing. In other words, it is possible to obtain superabsorbent polymer and pulp fibers with reduced contaminants while suppressing an increase in the number of washing steps and thus preventing increases in costs.

[0111] In another preferred embodiment of this method, the superabsorbent polymer, pulp fibers, and plastic material, which are separated together in the separation step S4, have already been dehydrated and washed in the dehydration and washing step S3. Therefore, by separating at least the plastic material from the superabsorbent polymer, pulp fibers, and plastic material, a reusable plastic material can be obtained without further washing. In other words, a plastic material with reduced contaminants can be obtained while suppressing increases in costs.

[0112] In a preferred embodiment, the method includes a pretreatment step S2 for reducing the amount of moisture absorbed by the used absorbent article prior to the dehydration-washing step S3. Therefore, the amount of moisture in the used absorbent article that is to be treated in the dehydration-washing step S3 can be reduced in advance in the pretreatment step S2. This makes it possible to more reliably reduce the contaminants contained in the superabsorbent polymer and the pulp fibers in the dehydration-washing step S3.

[0113] In a preferred embodiment of the present method, the used absorbent article is subjected to at least one of an acidic aqueous solution treatment, a polyvalent metal salt treatment, high-pressure steam treatment, freeze-drying, and an organic solvent treatment as a pretreatment step S2 prior to the dehydration-washing step S3, thereby more reliably reducing the moisture in the used absorbent article in advance, which is to be treated in the dehydration-washing step S3, in the pretreatment step S2.

[0114] In a preferred embodiment of this method, the pretreatment step S2 involves an acidic aqueous solution treatment, which inactivates the superabsorbent polymer with the acidic aqueous solution, thereby more appropriately reducing (dehydrating) the amount of water absorbed by the superabsorbent polymer. In other words, the amount of water to be treated in the dehydration and washing step S3 in the used absorbent article can be more appropriately reduced in advance. In addition, by using an alkali metal ion source in the dehydration and washing step S3, the superabsorbent polymer can be reactivated with alkali metal ions while remaining in a dehydrated state. Because the reactivated superabsorbent polymer does not absorb water, subsequent handling is easier, and for example, it can be easily dried. This allows for a reactivated superabsorbent polymer with reduced contaminants to be obtained while suppressing cost increases.

[0115] In another preferred embodiment of this method, a polyvalent metal salt treatment is performed in the pretreatment step S2 to inactivate the superabsorbent polymer with polyvalent metal ions, thereby more appropriately reducing (dehydrating) the moisture absorbed by the superabsorbent polymer. That is, the amount of moisture to be treated in the dehydration-washing step S3 in used absorbent articles can be more appropriately reduced. In addition, the polyvalent metal ions in the superabsorbent polymer are replaced with an acidic substance (acidic aqueous solution) before or during the dehydration-washing step S3. Then, during the dehydration-washing step S3, the superabsorbent polymer with the polyvalent metal ions replaced with the acidic substance is neutralized with an alkaline substance (alkaline aqueous solution) containing sodium. This reactivates the inactivated superabsorbent polymer in addition to the dehydration-washing step. This reduces contaminants and produces a reactivated superabsorbent polymer while minimizing cost increases.

[0116] In a preferred embodiment of this method, a crushing step for crushing used absorbent articles is carried out before the separation step S4 and either before, during, or after the dehydration and washing step S3, thereby more reliably separating at least the superabsorbent polymer and pulp fibers from the solution containing the mixture in the separation step S4.

[0117] In a preferred embodiment of this method, the drying step S5 for drying the superabsorbent polymer and pulp fibers is carried out at least one of after the dehydration-washing step S3 and after the separation step S4. Therefore, since the superabsorbent polymer and pulp fibers are dehydrated in advance in the dehydration-washing step S3 and are easily dried, the energy required for drying can be reduced, and the superabsorbent polymer and pulp fibers can be easily treated in the next step or reused. This reduces the processing burden in the next step and reduces processing costs.

[0118] In a preferred embodiment, the method further comprises a step of recovering the dehydrating agent from the solution after the separation step S4 and supplying the recovered dehydrating agent to the dehydration and washing step S3. This makes it possible to reduce contaminants while suppressing increases in costs in the method for recovering components of used absorbent articles.

[0119] EXAMPLES The present invention will be described below based on examples, but the present invention is not limited to these examples. In the following examples, the dehydration and washing step S3 was investigated.

[0120] (1) Sample 1 (a) For testing the stability of a dehydrating agent 0.1 g of a commercially available superabsorbent polymer (polyacrylate-based) was prepared, and 50 ml of distilled water was absorbed into the superabsorbent polymer to form Sample A. Multiple similar Samples A were prepared. (b) For testing the ability to remove contaminants 10 g of a superabsorbent polymer (having an odor and coloration) extracted from a used absorbent article containing excrement was prepared, and this was used as Sample B. Multiple similar Samples B were prepared.

[0121] (2) Evaluation Methods (a) Stability Test of Dehydrating Agents (a-1) Dehydration Test Acetone was prepared as a dehydrating agent. Example 1: One of Samples A was immersed in 200 ml of acetone in a container (a 500 ml three-neck flat-bottom flask reactor manufactured by Deschem; the same applies hereinafter) for 3 hours, and then its wet weight and dry weight were measured. Comparative Example 1: One of Samples A was immersed in 200 ml of distilled water in a container for 3 hours, and then its wet weight and dry weight were measured. (a-2) Oxidation Test Ozone was prepared as an oxidizing agent. Example 2: One of Samples A was immersed in 200 ml of acetone in a container, and ozone was supplied to the container at a generation rate of 60 mg / h and an airflow rate of 13 L / min. The same amount of waste ozone was continuously discharged outside the container. One hour after the start of ozone supply, the wet weight and dry weight of Sample A were measured. Example 3: One of the samples A was immersed in 200 ml of acetone in a container, and ozone was supplied to the container at a generation rate of 60 mg / h and an airflow rate of 13 L / min. The same amount of waste ozone was continuously discharged outside the container. Three hours after the start of ozone supply, the wet and dry weights of the sample A were measured. Comparative Example 2: One of the samples A was immersed in 200 ml of distilled water in a container, and ozone was supplied to the container at a generation rate of 60 mg / h and an airflow rate of 13 L / min. The same amount of waste ozone was continuously discharged outside the container. The wet and dry weights of the sample A were measured three hours after the start of ozone supply. Note that ozone was supplied using an ozone generator: a REX MC Ozonizer MC-985S manufactured by Rex Industrial Co., Ltd. (the same applies below). The dissolved ozone concentration in acetone could not be measured, but was believed to be in the range of approximately 0.2 to 2 ppm by mass.

[0122] (b) Pollutant Removal Test Acetone was used as a dehydrating agent, and ozone was used as an oxidizing agent. Example 4: One of the samples B was immersed in 250 ml of acetone in a container. Ozone was supplied at a rate of 60 mg / h and an airflow rate of 13 L / min. The same amount of waste ozone was continuously discharged from the container. After one hour of ozone supply, the sample B was measured for odorous substances (presence or absence of odor) and colored substances (presence or absence of decolorization). Comparative Example 3: One of the samples B was immersed in 250 ml of acetone in a container. After one hour of ozone supply, the sample B was measured for odorous substances (presence or absence of odor) and colored substances (presence or absence of decolorization). Comparative Example 4: One of the samples B was immersed in 250 ml of distilled water in a container, and ozone was not supplied. After one hour, the sample B was measured for whether odorous substances (presence or absence of odor), colored substances (presence or absence of odor), and colored substances (presence or absence of decolorization). Comparative Example 5: One of the samples B was immersed in 250 ml of distilled water in a container, and ozone was supplied to give a generation rate of 60 mg / h and an airflow rate of 13 L / min. The same amount of waste ozone was continuously discharged outside the container. After one hour from the start of ozone supply, the sample B was measured for whether odorous substances (presence or absence of odor) and colored substances (presence or absence of decolorization) were removed.

[0123] However, in the sample (superabsorbent polymer), whether or not odorous substances in the sample had been removed (presence or absence of odor) was confirmed by the examiner smelling and comparing the odor of sample B before and after the pollutant removal test. Also, whether or not colored substances in the sample had been removed (presence or absence of decolorization) was confirmed by the examiner visually comparing the color of sample B before and after the pollutant removal test.

[0124] (3) Evaluation Results (a) Stability Test of Dehydrating Agent The evaluation results are summarized in Table 1 below. (a-1) Dehydration Test The wet weight of the superabsorbent polymer was initially 50.1 g, and in Comparative Example 1 it was 48 g, showing almost no change. However, in Example 1 it was 0.47 g, a significant decrease. From this comparison of the wet weights of Example 1 and Comparative Example 1, it was confirmed that the superabsorbent polymer was dehydrated by using acetone as a dehydrating agent. (a-2) Oxidation Test The dry weight of the superabsorbent polymer was initially 0.10 g, and in Comparative Example 1 it was 0.073 g, showing almost no change. In Examples 1 to 3, it was 0.070 g, 0.070 g, and 0.067 g, showing almost no change. From this comparison of the dry weights of Examples 1 to 3 and Comparative Example 1, it was confirmed that when acetone was used as a dehydrating agent, the superabsorbent polymer was not oxidatively decomposed, even when ozone was used as an oxidizing agent. On the other hand, the wet weight and dry weight of Comparative Example 2 were 11 g and 0.034 g, respectively, significantly reduced compared to the wet weight and dry weight of Comparative Example 1, which were 48 g and 0.073 g. From this comparison of the wet weights and dry weights of Comparative Examples 1 and 2, it was confirmed that the superabsorbent polymer was oxidatively decomposed in distilled water at the ozone concentration of this example. Therefore, it was confirmed that when ozone was used in distilled water, a portion of the superabsorbent polymer was oxidatively decomposed, but when the same concentration of ozone was used in acetone, the superabsorbent polymer was not oxidatively decomposed. Furthermore, the wet weight of the superabsorbent polymer was initially 50.1 g and decreased to 48 g in Comparative Example 1, showing little change, whereas in Examples 1 to 3 it decreased significantly to 0.47 g, 0.58 g, and 0.41 g. From this comparison of the wet weights of Examples 1 to 3 and Comparative Example 1, it was confirmed that when acetone was used as a dehydrating agent, dehydration was achieved to the same extent as when ozone was used as an oxidizing agent, even when ozone was used.

[0125]

[0126] (b) Contaminant Removal Test The evaluation results are summarized in Table 2 below. In Table 2, "◯" indicates that deodorization or decolorization was achieved, and "×" indicates that deodorization or decolorization was not achieved. Regarding the deodorization and decolorization of the superabsorbent polymer, in Example 4, both deodorization and decolorization were good (◯), while in Comparative Example 3, deodorization was achieved (◯) but decolorization was not achieved (×). In Comparative Example 4, neither deodorization nor decolorization was achieved (×). In Comparative Example 5, the superabsorbent polymer decomposed, making evaluation impossible. From a comparison of Example 4 and Comparative Examples 3 to 5, it was confirmed that using acetone as the dehydrating agent and ozone as the oxidizing agent eliminated the odor of the superabsorbent polymer (deodorized) and removed color (decolorized). However, when acetone was used as the dehydrating agent without an oxidizing agent, the superabsorbent polymer was deodorized but not decolorized.

[0127]

[0128] Good results were obtained in deodorization and decolorization, i.e., reduction of odorous and coloring substances among contaminants. Because these odorous and coloring substances are difficult to remove, it is believed that other contaminants, such as excrement, sebum, bacteria derived from these substances, machine oils used in manufacturing facilities, and various organic substances, can also be similarly removed or reduced. While details are omitted here, dehydration results were obtained with pulp fibers similar to those with superabsorbent polymers. Furthermore, deodorization and decolorization results were obtained with pulp fibers and plastic materials similar to those with superabsorbent polymers.

[0129] <Method for measuring wet weight> The method for measuring wet weight is as follows. (1) A bag made of a PE mesh sheet (PE200, Sanplatec, opening 102 μm) is prepared, and the mass A of the bag is measured. (2) The water-absorbed superabsorbent polymer to be measured is placed in the PE mesh sheet bag, the bag is lifted out, and left to stand on a draining net for 15 minutes to drain the water. (3) The mass B of the PE mesh sheet bag (containing the superabsorbent polymer) after draining the water in (2) above is measured. (4) The wet weight of the water-absorbed superabsorbent polymer to be measured is calculated by (mass B - mass A).

[0130] <Method for Measuring Dry Weight> The method for measuring the dry weight is as follows. (1) The superabsorbent polymer in the PE mesh sheet bag obtained by the above-mentioned method for measuring the wet weight is transferred to a heat-resistant container. (2) The container (containing the superabsorbent polymer) is left in an atmosphere at 105°C for 3 hours to completely dry the superabsorbent polymer. (3) The mass of the dried superabsorbent polymer is measured and used as the dry weight.

[0131] The abduction method of the present invention is not limited to the above-described embodiments, and suitable combinations and modifications can be made without departing from the scope and spirit of the present invention.

[0132] S3 Dehydration cleaning process S4 Separation process

Claims

1. A method for recovering components of used absorbent articles, comprising: a dehydration and washing step of dehydrating and washing a mixture containing the components, a superabsorbent polymer having an acid group and pulp fibers, with a solution containing a dehydrating agent and an oxidizing agent capable of dehydrating the superabsorbent polymer and the pulp fibers; and a separation step of separating at least the superabsorbent polymer and the pulp fibers from the solution containing the mixture.

2. The method of claim 1, wherein the oxidizing agent comprises at least one of ozone, hydrogen peroxide, and a chlorine-based material.

3. The method according to claim 1 or 2, wherein the dehydrating agent includes a ketone-based organic solvent.

4. A method according to any one of claims 1 to 3, wherein the oxidizing agent includes either an active species generated by irradiating another oxidizing agent contained in the solution with ultraviolet light, or, when the solution contains water, an active species generated by irradiating the water and / or another oxidizing agent contained in the solution with ultraviolet light.

5. The method of any one of claims 1 to 4, wherein the separation step includes: separating the superabsorbent polymer and the pulp fibers together from the solution containing the mixture; and further separating the superabsorbent polymer and the pulp fibers that have been separated together from each other.

6. A method according to any one of claims 1 to 5, wherein the dehydrating and washing step includes a step of dehydrating and washing the mixture further containing a plastic material which is the constituent part with the solution, and the separating step includes a step of separating the plastic material from the solution containing the mixture separately from the superabsorbent polymer and the pulp fibers.

7. The method according to any one of claims 1 to 6, further comprising a pretreatment step of reducing moisture absorbed by the used absorbent article prior to the dehydration and washing step.

8. The method according to claim 7, wherein the pretreatment step comprises subjecting the used absorbent article to at least one of an acidic aqueous solution treatment, a polyvalent metal salt treatment, a high-pressure steam treatment, a freeze-drying treatment, and an organic solvent treatment.

9. The method according to claim 8, wherein the pretreatment step includes a step of subjecting the used absorbent article to an acidic aqueous solution treatment to inactivate the superabsorbent polymer with an acidic aqueous solution, and the dehydration and washing step includes a step of activating the inactivated superabsorbent polymer with alkali metal ions supplied from an alkali metal ion source.

10. The method according to claim 8, wherein the pretreatment step includes a step of performing the polyvalent metal salt treatment on the used absorbent article to inactivate the superabsorbent polymer with polyvalent metal ions supplied from a polyvalent metal salt, and the method further comprises a step of substituting the polyvalent metal ions of the inactivated superabsorbent polymer with an acidic substance before the dehydration and cleaning step or during the dehydration and cleaning step, and a step of neutralizing the superabsorbent polymer in which the polyvalent metal ions have been substituted with the acidic substance with an alkaline substance containing sodium during the dehydration and cleaning step.

11. The method according to any one of claims 1 to 10, further comprising a crushing step of crushing the used absorbent articles, the crushing step being carried out before the separating step and either before, during or after the dehydrating and washing step.

12. The method according to any one of claims 1 to 11, further comprising a drying step of drying at least the superabsorbent polymer and the pulp fibers, the drying step being carried out at least one of after the dewatering and washing step and after the separation step.

13. The method according to any one of claims 1 to 12, further comprising a re-supply step of recovering the dehydrating agent from the solution after the separation step and supplying it to the dehydration washing step.

Images