Method for producing recycled fibers from mixture of superabsorbent polymer and pulp fibers

Abstract

Provided is a method for producing recycled fibers from a mixture of a superabsorbent polymer and pulp fibers, the method making it possible to achieve both treatment speed and energy efficiency in ozone treatment. This method for producing recycled fibers from a mixture of a superabsorbent polymer and pulp fibers comprises a first treatment step (S6) and a second treatment step (S9). The first treatment step includes removing at least part of the superabsorbent polymer by treating the mixture of the superabsorbent polymer and the pulp fibers with ozone in a first treatment liquid (52-1) within a first treatment tank (31-1) while supplying ozone to the first treatment liquid. The second treatment step includes treating the pulp fibers with ozone in a second treatment liquid (52-2) within a second treatment tank (31-2) while supplying ozone released from the first treatment liquid within the first treatment tank to the second treatment liquid.

Description

Method for producing recycled fibers from a mixture of superabsorbent polymer and pulp fibers

[0001] The present invention relates to a method for producing recycled fibers from a mixture of superabsorbent polymers and pulp fibers.

[0002] Methods for producing a mixture of superabsorbent polymer and pulp fibers are known. For example, Patent Document 1 discloses a method for producing recycled fibers from a mixture of fibers and a superabsorbent polymer. This method includes a continuous treatment step of continuously supplying a mixture containing fibers containing a superabsorbent polymer and water at a first flow rate into a treatment tank containing a treatment liquid capable of dissolving the superabsorbent polymer, while continuously discharging the treatment liquid containing the fibers from which the superabsorbent polymer has been dissolved and removed out of the treatment tank at a second flow rate. The treatment liquid capable of dissolving the superabsorbent polymer may be an aqueous solution containing a gaseous substance that decomposes the superabsorbent polymer so that it can dissolve the superabsorbent polymer. The gaseous substance may include ozone.

[0003] Patent No. 6523376

[0004] In Patent Document 1, superabsorbent polymers are more easily decomposed when an aqueous solution containing a high concentration of dissolved ozone is used as the treatment liquid. However, when ozone is injected into an aqueous solution at a high concentration and a high flow rate in an attempt to dissolve ozone in the aqueous solution at a high concentration, not only is some of the ozone actually dissolved in the aqueous solution, but a large amount of ozone is likely to pass through without dissolving. If ozone passes through the aqueous solution and is released from the aqueous solution, much of the ozone will not contribute to the decomposition of the superabsorbent polymer, and the energy consumed to generate the ozone may be wasted. This may result in a decrease in the energy efficiency of the ozone treatment.

[0005] On the other hand, if the energy efficiency of the ozone treatment is prioritized and at least one of the concentration and flow rate of ozone injected into the aqueous solution is reduced, the proportion of ozone passing through the aqueous solution is reduced, and the energy efficiency of the ozone treatment improves. However, if one wants to shorten the treatment time of the ozone treatment, that is, to increase the treatment speed, one ultimately has no choice but to use the method of injecting ozone into the aqueous solution at a high concentration and a high flow rate, as described above.

[0006] An object of the present invention is to provide a method for producing recycled fibers from a mixture of a superabsorbent polymer and pulp fibers, which can achieve both high processing speed and energy efficiency in ozone treatment.

[0007] One aspect of the present invention is a method for producing recycled fibers from a mixture of superabsorbent polymer and pulp fibers, comprising: a first treatment step in which ozone is supplied to a first treatment liquid in a first treatment tank, and the mixture of superabsorbent polymer and pulp fibers is treated with the ozone in the first treatment liquid to remove at least a portion of the superabsorbent polymer; and a second treatment step in which ozone released from the first treatment liquid in the first treatment tank is supplied to a second treatment liquid in a second treatment tank, and the pulp fibers are treated with the ozone in the second treatment liquid.

[0008] According to the present invention, a method for producing recycled fibers from a mixture of a superabsorbent polymer and pulp fibers can be provided that can achieve both high processing speed and energy efficiency in ozone treatment.

[0009] 1 is a schematic diagram showing an example of a method for producing recycled fibers from a mixture of a superabsorbent polymer and pulp fibers according to an embodiment of the present invention;

[0010] This embodiment relates to the following aspects: [Aspect 1] A method for producing recycled fibers from a mixture of a superabsorbent polymer and pulp fibers, comprising: a first treatment step of treating the mixture of superabsorbent polymer and pulp fibers with ozone in a first treatment liquid in a first treatment tank while supplying ozone to the first treatment liquid, thereby removing at least a portion of the superabsorbent polymer; and a second treatment step of treating pulp fibers with ozone in a second treatment liquid in a second treatment tank while supplying the ozone released from the first treatment liquid in the first treatment tank to the second treatment liquid.

[0011] In this method, ozone is supplied to a first treatment liquid in a first treatment tank for ozone treatment of pulp fibers in the first treatment step, and then released from the first treatment liquid (passing through the first treatment liquid). This ozone is then supplied to a second treatment liquid in a second treatment tank and utilized for ozone treatment of pulp fibers in the second treatment step. That is, in this method, ozone is supplied to the first treatment liquid at a high concentration and a high flow rate to increase the treatment rate of ozone treatment. Even if a large amount of ozone is released (passes through) without being dissolved in the first treatment liquid, the released ozone can be utilized in the second treatment step. In this manner, ozone supplied for ozone treatment in the first treatment step is also utilized for ozone treatment in the second treatment step, thereby enabling effective utilization of ozone. This allows for an increase in the treatment rate of ozone treatment in the first treatment step and an increase in the energy efficiency of the ozone treatment. Therefore, in a method for producing recycled fibers from a mixture of a superabsorbent polymer and pulp fibers, both treatment rate and energy efficiency in ozone treatment can be achieved.

[0012] [Aspect 2] The method described in Aspect 1, wherein the first treatment step includes a continuous treatment step of continuously supplying the pulp fibers and the first treatment liquid into the first treatment tank, treating the pulp fibers with the ozone, and continuously sending the first treatment liquid containing the pulp fibers treated with the ozone out of the first treatment tank.

[0013] In this method, pulp fibers and a first treatment liquid are continuously supplied into a first treatment tank, and the pulp fibers are treated with ozone (while the superabsorbent polymer is oxidatively decomposed, dissolved, and removed), and the first treatment liquid containing the ozone-treated pulp fibers is continuously discharged from the first treatment tank. In other words, the pulp fibers are continuously treated. Therefore, a continuous and stable flow of the first treatment liquid can be generated in the first treatment tank from the supply port of the first treatment liquid toward the discharge port of the first treatment liquid. This allows ozone dissolved in the first treatment liquid and ozone passing through the first treatment liquid and the pulp fibers to be drawn into the flow, facilitating their contact with each other. In other words, the pulp fibers can be continuously contacted with ozone. Therefore, more ozone can contribute to the decomposition of the superabsorbent polymer, thereby improving the treatment speed and energy efficiency of the ozone treatment.

[0014] [Aspect 3] The method described in Aspect 1 or 2, wherein the first treatment process includes a preparation process of preparing the first treatment liquid containing the pulp fibers in the first treatment tank, a batch treatment process of treating the pulp fibers with ozone after the preparation process, and a delivery process of delivering the first treatment liquid containing the pulp fibers treated with ozone out of the first treatment tank after the batch treatment process.

[0015] In this method, a first treatment solution containing pulp fibers is first prepared in a first treatment tank. The pulp fibers are then treated with ozone (the superabsorbent polymer is oxidatively decomposed, dissolved, and removed). The first treatment solution containing the ozone-treated pulp fibers is then discharged from the first treatment tank. In other words, the pulp fibers are batch-treated. Therefore, the pulp fibers remaining in the first treatment solution in the first treatment tank can be easily and continuously exposed to ozone dissolved in the first treatment solution and ozone passing through the first treatment solution. This allows the pulp fibers to be continuously treated with ozone. This allows for more ozone to contribute to the decomposition of the superabsorbent polymer, thereby improving the treatment speed and energy efficiency of the ozone treatment.

[0016] [Aspect 4] The method according to any one of aspects 1 to 3, further comprising a separation step of separating the pulp fibers treated in the first treatment step from the first treatment liquid, and supplying the separated pulp fibers to the second treatment tank.

[0017] The first treatment liquid after the first treatment step contains not only pulp fibers from which at least a portion of the superabsorbent polymer has been removed, but also low-molecular-weight organic matter produced by oxidative decomposition of the superabsorbent polymer. Therefore, if the pulp fibers are supplied to the second treatment step together with the first treatment liquid, the second treatment liquid in the second treatment step will contain not only pulp fibers but also low-molecular-weight organic matter. In this case, the ozone in the second treatment liquid will be supplied not only to the pulp fibers but also to the low-molecular-weight organic matter, which may result in the ozone not being effectively used to treat the pulp fibers. Therefore, in this method, the pulp fibers treated in the first treatment step are separated from the first treatment liquid and the separated pulp fibers are supplied to the second treatment tank. That is, the pulp fibers are separated from the low-molecular-weight organic matter before being supplied to the second treatment tank, thereby preventing the second treatment liquid in the second treatment step from containing low-molecular-weight organic matter. As a result, the ozone in the second treatment liquid is supplied almost exclusively to the pulp fibers, allowing the ozone to be effectively used to treat the pulp fibers. Therefore, the treatment speed and energy efficiency of the ozone treatment in the second treatment step can be improved.

[0018] [Aspect 5] The method according to any one of aspects 1 to 4, further comprising a separation step of separating the pulp fibers treated in the first treatment step from the first treatment liquid, and an adjustment step of adjusting the solid content of the second treatment liquid with the separated pulp fibers, wherein the second treatment liquid containing the pulp fibers with the adjusted solid content is supplied to the second treatment tank.

[0019] In this method, the pulp fibers treated in the first treatment step are separated from the first treatment liquid, and the second treatment liquid, the solid content of which is adjusted to include the separated pulp fibers, is supplied to the second treatment tank. That is, the pulp fibers are separated from low-molecular-weight organic matter and mixed with new second treatment liquid to achieve an appropriate solid content, which is then supplied to the second treatment tank. This prevents low-molecular-weight organic matter from being contained in the second treatment liquid in the second treatment step, and also optimizes the ratio of ozone to pulp fiber during ozone treatment. This ensures that the ozone in the second treatment liquid is supplied almost exclusively to the pulp fibers, and the pulp concentration is appropriate, allowing the ozone to be more effectively used in treating the pulp fibers. This improves the processing speed and energy efficiency of the ozone treatment in the second treatment step.

[0020] [Aspect 6] The method according to any one of aspects 1 to 5, wherein the second treatment step includes treating the pulp fibers treated in the first treatment step with ozone in a treatment solution in the second treatment tank to perform at least one of deodorization, bleaching, and sterilization.

[0021] In this method, the second treatment step includes a step of treating the pulp fibers treated in the first treatment step with ozone in a treatment solution in a second treatment tank to perform at least one of deodorization, bleaching, and sterilization. By utilizing the ozone supplied for the ozone treatment in the first treatment step in the ozone treatment for performing at least one of deodorization, bleaching, and sterilization in the second treatment step, the ozone can be effectively utilized. Furthermore, this method can produce pulp fibers that have been further deodorized, bleached, and sterilized than in the first treatment step.

[0022] [Aspect 7] The method according to any one of aspects 1 to 6, wherein the second treatment step includes treating the pulp fibers treated in the first treatment step with ozone in a treatment solution in the second treatment tank to remove at least a portion of the superabsorbent polymer.

[0023] In this method, the second treatment step includes treating the pulp fibers treated in the first treatment step with ozone in a treatment solution in a second treatment tank to remove at least a portion of the superabsorbent polymer. In this way, the ozone supplied for the ozone treatment in the first treatment step is utilized in the ozone treatment in the second treatment step to remove at least a portion of the superabsorbent polymer, thereby enabling effective use of the ozone. This method also allows for the production of pulp fibers from which the superabsorbent polymer has been further removed than in the first treatment step.

[0024] [Aspect 8] The method according to any one of aspects 1 to 7, further comprising the step of preparing a mixture of the superabsorbent polymer and pulp fibers removed from a used absorbent article as the mixture of the superabsorbent polymer and pulp fibers used in the first treatment step.

[0025] In this method, a mixture of superabsorbent polymer and pulp fibers extracted from used absorbent articles is used in the first treatment step. Therefore, the constituent materials of used absorbent articles, which are often discarded, can be recycled, thereby reducing the environmental impact.

[0026] Hereinafter, a method for producing recycled fibers from a mixture of a superabsorbent polymer and pulp fibers according to this embodiment will be described.

[0027] Here, the mixture of superabsorbent polymer and pulp fiber that serves as the raw material for the recycled fiber to be produced is not particularly limited as long as it is a mixture of pulp fiber and superabsorbent polymer. The origin of the mixture can be, for example, a mixture of pulp fiber and superabsorbent polymer contained in an absorbent body that absorbs some kind of liquid. Examples of absorbent bodies include absorbents provided in sanitary products such as absorbent articles that can absorb body fluids (e.g., excrement, blood). The state of the mixture can be, for example, a simple mixture of pulp fiber and superabsorbent polymer, a pulp fiber aggregate containing superabsorbent polymer, or a pulp fiber aggregate with superabsorbent polymer attached to some or all of its surface (such an aggregate of pulp fibers).

[0028] In this embodiment, an example will be described in which the mixture of superabsorbent polymer and pulp fiber is pulp fiber containing superabsorbent polymer obtained from used absorbent articles. However, the present invention is not limited to this embodiment, and appropriate modifications and the like are possible within the scope of the present invention. Used absorbent articles include absorbent articles that have been transferred (e.g., sold) and have been used to absorb excrement (e.g., urine, feces, menstrual blood), those that have been used but have not absorbed excrement, unused absorbent articles, and absorbent articles that have not been transferred due to production losses, etc. Examples of absorbent articles include disposable diapers, urine absorption pads, incontinence pads, sanitary napkins, disposable shorts, bed sheets, and pet sheets.

[0029] First, an example of the configuration of an absorbent article will be described. The absorbent article comprises a topsheet, a backsheet, and an absorbent body disposed between the topsheet and the backsheet. The size of the absorbent article can be, for example, approximately 15 to 100 cm in length and 5 to 100 cm in width, but is not limited to this example. The absorbent article may further comprise other components typically found in absorbent articles, such as a diffusion sheet, a leak barrier, a side sheet, an exterior sheet, and thread-like or sheet-like elastic members disposed on the leak barrier or exterior sheet.

[0030] Examples of constituent materials for the top sheet include liquid-permeable nonwoven fabrics, synthetic resin films with liquid-permeable holes, and composite sheets thereof. Examples of constituent materials for the back sheet include liquid-impermeable nonwoven fabrics, liquid-impermeable synthetic resin films, and composite sheets thereof. Examples of constituent materials for the diffusion sheet include liquid-permeable nonwoven fabrics. Examples of constituent materials for the leak-proof walls and side sheets include water-repellent nonwoven fabrics. Examples of constituent materials for the exterior sheet include liquid-impermeable and breathable nonwoven fabrics, liquid-impermeable and breathable synthetic resin films, and composite sheets thereof. Examples of constituent materials for the elastic member include rubber-based synthetic resins. There are no particular limitations on the type of nonwoven fabric, and examples include meltblown nonwoven fabrics, spunbond nonwoven fabrics, air-laid nonwoven fabrics, and air-through nonwoven fabrics. There are no particular limitations on the type of synthetic resin film, and known film materials can be used. The materials for the nonwoven fabrics and synthetic resin films are not particularly limited as long as they can be used in absorbent articles, but examples 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 and polybutylene terephthalate. Further examples of nonwoven fabric materials include cellulose-based fibers. To provide breathability, synthetic resin films may contain inorganic particles such as calcium carbonate. The rubber-based synthetic resin materials are not particularly limited as long as they can be used in absorbent articles, but examples include styrene butadiene rubber and urethane rubber. These materials for nonwoven fabrics, synthetic resin films, elastic members, etc. are synthetic resins and can be considered plastic materials.

[0031] The constituent components of the absorbent body include absorbent materials such as pulp fibers, which are fibrous materials, and superabsorbent polymers, which are particulate materials. Examples of pulp fibers, which are fibrous materials, include cellulosic fibers. Examples of cellulosic fibers include wood pulp fibers, crosslinked pulp fibers, non-wood pulp fibers, regenerated cellulose fibers, and semi-synthetic cellulose fibers. The size of the pulp fibers 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. Examples of superabsorbent polymers (SAP), which are particulate materials, include polyacrylate-based, polysulfonate-based, and maleic anhydride-based water-absorbing polymers. The size (when dry) of the superabsorbent polymer includes an average particle size of, for example, several hundred microns, preferably 200 to 500 microns. The absorbent body may include a core wrap formed of a liquid-permeable sheet.

[0032] 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 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. There are no particular limitations on the adhesive, and examples 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, styrene-isoprene-styrene, polyurethane, or olefin-based, such as polyethylene.

[0033] Next, a method for producing recycled fibers from a mixture of a superabsorbent polymer and pulp fibers according to an embodiment will be described. In this embodiment, the mixture of a superabsorbent polymer and pulp fibers is derived from used absorbent articles, as described above.

[0034] 1 is a flow diagram showing an example of a method for producing recycled fibers from a mixture of a superabsorbent polymer and pulp fibers according to an embodiment.

[0035] As shown in FIG. 1 , this method includes a first processing step S6 and a second processing step S9. This method may further include a fourth separation step S7, a supplying step S8, and a fifth separation step S10. This method may further include a shredding step S1, a first separation step S2, a dust removal step S3, a second separation step S4, and a third separation step S5. Among these steps, the shredding step S1 to the third separation step S5 can also be considered as steps for preparing pulp fibers containing superabsorbent polymer (a mixture of superabsorbent polymer and pulp fiber), which are the raw material for the recycled fibers produced by this method. Furthermore, the shredding step S1 to the fifth separation step S10 can also be considered as methods for producing recycled plastic materials, superabsorbent polymer (SAP), and pulp fibers using used absorbent articles. A detailed description is provided below.

[0036] In this embodiment, used absorbent articles are collected from outside for reuse (recycling). At that time, multiple used absorbent articles are sealed in a collection bag to prevent excrement, bacteria, and odors from leaking to the outside. Each used absorbent article in the collection bag is collected, for example, in a rolled or folded state with the top sheet, on which excrement is excreted, facing inward so that excrement and bacteria are not exposed to the outside and odors are not diffused to the surrounding area. Note that the used absorbent articles do not have to be sealed in a collection bag or rolled up.

[0037] The crushing step S1 is a step of crushing used absorbent articles together with an inactivating aqueous solution containing an inactivating agent that inactivates the superabsorbent polymer. The crushing step S1 is carried out using a crushing device such as a biaxial crusher. Crushing together with an inactivating aqueous solution includes crushing used absorbent articles while supplying them to the crushing device together with the inactivating aqueous solution, crushing used absorbent articles in the inactivating aqueous solution stored in the crushing device, and combinations thereof. In this embodiment, used absorbent articles are crushed while being supplied to the crushing device together with the inactivating aqueous solution. In this method, when an inactivating aqueous solution is used in the first separation step S2 or later, the inactivating aqueous solution is replenished as needed when it runs short.

[0038] In this embodiment, collection bags containing used absorbent articles are supplied to a receiving device and then moved to a crushing device connected to the receiving device below. At the same time, an inactivating aqueous solution (e.g., an acidic aqueous solution) is supplied to the crushing device via the receiving device. The inactivating aqueous solution may be supplied so that it falls onto the used absorbent articles from above. This is to prevent the scattering of crushed material (including substances derived from excrement, such as bacteria and odorous substances) during crushing. The collection bag is crushed together with the inactivating aqueous solution by the crushing device. The used absorbent articles in the collection bag are crushed together with the collection bag in the inactivating aqueous solution, producing crushed material with a size of, for example, 1 to 150 mm. During this process, the superabsorbent polymer is inactivated and dehydrated by the inactivating aqueous solution, resulting in small particle sizes. The crushed material is sent to the first separation step S2 together with the inactivating aqueous solution.

[0039] As the inactivation aqueous solution, it is preferable to use an aqueous solution of an inorganic acid or an organic acid, i.e., an acidic aqueous solution. Compared to using an aqueous solution such as lime or calcium chloride, the use of an acidic aqueous solution makes it less likely that ash or chlorine will remain in plastic materials, superabsorbent polymers, pulp fibers, etc., and makes it easier to adjust the degree of inactivation (particle size and specific gravity) by pH. As the organic acid, citric acid, which has a chelating effect and a cleaning effect, is preferred, and as the inorganic acid, sulfuric acid, which is chlorine-free and low-cost, is preferred. Note that the inactivation aqueous solution may be an aqueous solution containing a known polyvalent metal ion source capable of supplying polyvalent metal ions.

[0040] The pH of the acidic aqueous solution is preferably 1.0 to 4.0. A pH of 1.0 or higher makes equipment less susceptible to corrosion and reduces the amount of alkaline chemicals required for neutralization during wastewater treatment, while a pH of 4.0 or lower allows the superabsorbent polymer to be sufficiently small and enhances sterilization ability. Since pH varies depending on water temperature, the pH in the present invention refers to the pH measured at an aqueous solution temperature of 20°C. The concentration of the acidic aqueous solution is not particularly limited, but is preferably 0.5 to 4 mass% in the case of citric acid and 0.1 to 2.0 mass% in the case of sulfuric acid.

[0041] During the shredding step S1, the heat generated during shredding and / or the heat of the acidic aqueous solution can reduce the adhesive strength of the adhesive (e.g., hot melt adhesive) between the components, allowing the components to be easily separated from each other. Alternatively, heating the acidic aqueous solution (temperature: 70 to 95°C) can soften the adhesive (e.g., hot melt adhesive) used to bond the components of the used absorbent article, thereby reducing the adhesive's adhesive strength. This allows the components to be easily separated from each other naturally or with a small impact. It also makes it possible to more effectively sterilize (disinfect) the used absorbent article.

[0042] Next, in the first separation step S2, the mixture of plastic material, inactivated superabsorbent polymer, pulp fiber, excrement, and inactivating aqueous solution supplied from the shredding step S1 is separated into a first fraction containing plastic material and a second fraction containing inactivated superabsorbent polymer, pulp fiber, excrement, and inactivating aqueous solution. The first separation step S2 is carried out by a separation device such as a screen separator, a pulper separator, or a combination thereof.

[0043] In this embodiment, the acidic aqueous solution containing the crushed material produced in the shredding process S1 is stored and stirred in the pulper separator, and the crushed material is disintegrated into constituent materials. The acidic aqueous solution containing the crushed material (disintegrated constituent materials) is then separated through a screen, and a second fraction containing inactivated superabsorbent polymer, pulp fibers, excrement, and the acidic aqueous solution is accepted and sent to the dust removal process S3. Meanwhile, the first fraction, including the collection bags, film, nonwoven fabric, etc., is rejected and removed. The removed collection bags, film, nonwoven fabric, etc. are sterilized, washed, dried, etc. as needed, and recovered as plastic materials. Note that a different acidic aqueous solution not used in the shredding process S1 may be supplied as the acidic aqueous solution to the first separation process S2. In this case, some of the pulp fibers, superabsorbent polymer, and excrement may not pass through the screen and may remain on the screen along with the first fraction. Meanwhile, some of the collection bags, film, and nonwoven fabric may pass through the screen along with the second fraction.

[0044] In this embodiment, if the superabsorbent polymer is inactivated and granulated to reduce its water absorption capacity before the first separation step S2 (such as in the crushing step S1), the inactivating aqueous solution (acidic aqueous solution) may not be used in the first separation step S2 and thereafter, and the inactivating aqueous solution may be largely removed before using water (aqueous solution) that does not contain an inactivating agent. In this case, water (aqueous solution) that does not contain an inactivating agent may be used from any step after the first separation step S2. This reduces the amount of inactivating aqueous solution (and inactivator) used and reduces the burden on wastewater treatment.

[0045] In this embodiment, in the first separation step S2, the pH of the acidic aqueous solution may be adjusted to be maintained within a predetermined range. The predetermined pH range refers to a pH fluctuation range of ±1.0 or less. This allows the difference between the specific gravity and size of the superabsorbent polymer and the specific gravity and size of the pulp fiber to be within a predetermined range. In this case, the difference within the predetermined range refers, for example, to a difference of 0.2 to 5 times that of the other. This allows the difference between the pulp fiber and the superabsorbent polymer to be within a predetermined range in specific gravity and a predetermined range in size. As a result, the pulp fiber and the superabsorbent polymer can be easily separated from other materials (mainly plastic materials) of the used absorbent article by utilizing the differences in size and specific gravity. The pH can be adjusted using an acidic or alkaline aqueous solution from a pH adjustment device installed in the separation device based on the pH value measured by a pH sensor installed in the separation device. The pH may also be adjusted in a similar manner in at least one of the dust removal step S3, the second separation step S4, and the third separation step S5, which will be described later.

[0046] Next, the dust removal step S3 is a step of removing foreign matter (dust removal) from the mixed liquid containing the pulp fibers, the superabsorbent polymer, the excrement, and the acidic aqueous solution separated in the first separation step S2. The dust removal step S3 is performed using a dust removal device (e.g., a screen separator, a cyclone separator, or a combination thereof).

[0047] In this embodiment, the dust removal device separates foreign matter, such as other materials (collection bags, films, nonwoven fabrics, elastic materials, etc.) that were not completely separated, from the mixed liquid supplied from the first separation step S2. The dust removal device may, for example, comprise a screen separator (with a relatively large mesh size), a screen separator (with a relatively small mesh size), and a cyclone separator, arranged in this order, to sequentially separate foreign matter from the mixed liquid. This results in a mixed liquid containing pulp fibers, superabsorbent polymers, excrement, and an acidic aqueous solution with little foreign matter. The mixed liquid is then supplied to the second separation step S4. Note that the dust removal step S3 can be omitted if there is no need to separate foreign matter from the mixed liquid (e.g., if the mixed liquid contains only a small amount of foreign matter and the foreign matter is separated in a later step).

[0048] Next, the second separation step S4 is a step of separating the superabsorbent polymer from the mixture containing pulp fibers with little foreign matter, the superabsorbent polymer, excrement, and the acidic aqueous solution supplied from the dust removal step S3 (or the first separation step S2). The second separation step S4 is performed using a separation device such as a screen separator, a drum screen separator, or a combination thereof.

[0049] In this embodiment, the superabsorbent polymer, excrement, and acidic aqueous solution, and the pulp fibers with the superabsorbent polymer remaining on their surfaces, excrement, and acidic aqueous solution are separated by a drum screen separator from the mixed solution supplied from the dust removal step S3 (or step S2). The pulp fibers with the superabsorbent polymer remaining on their surfaces can be referred to as pulp fibers containing the superabsorbent polymer (a mixture of the superabsorbent polymer and the pulp fibers). This results in a mixed solution containing the superabsorbent polymer, excrement, and acidic aqueous solution, and a mixed solution containing the pulp fibers with the superabsorbent polymer, excrement, and acidic aqueous solution. The mixed solution containing the superabsorbent polymer, excrement, and acidic aqueous solution is then removed from the mixed solution, and is subjected to sterilization, washing, drying, etc., as necessary, and recovered as a superabsorbent polymer. The superabsorbent polymer separated and recovered in this manner is reactivated as necessary to become a so-called recycled superabsorbent polymer (SAP in FIG. 1 ). On the other hand, the mixture containing the pulp fibers containing the superabsorbent polymer, the excrement, and the acidic aqueous solution is supplied to a third separation step S5.

[0050] Next, the third separation step S5 is a step of separating the pulp fibers containing the superabsorbent polymer from the mixed liquid containing the pulp fibers containing the superabsorbent polymer, excrement, and the acidic aqueous solution supplied from the second separation step S4. The third separation step S5 is performed by a separation device such as a screen separator, a drum screen separator, a screw press separator, or a combination thereof.

[0051] In this embodiment, the pulp fibers containing the superabsorbent polymer, the excrement, and the acidic aqueous solution are separated from the mixed liquid supplied from the second separation step S4 by a screen separator and / or a drum screen device. As a result, the pulp fibers containing the superabsorbent polymer, the excrement, and the acidic aqueous solution are each extracted. The pulp fibers containing the superabsorbent polymer are mixed with the first treatment liquid used in the first treatment step S6, for example, and then supplied to the first treatment step S6.

[0052] In this way, the crushing process S1 to the third separation process S5 can be said to be processes that use used absorbent articles to prepare pulp fibers containing superabsorbent polymers (a mixture of superabsorbent polymers and pulp fibers), which will be the raw material for the recycled fibers produced by this method.

[0053] Next, the first processing step S6 to the second processing step S9 according to the embodiment will be described. First, the apparatus that performs the first processing step S6 to the second processing step S9 will be described.

[0054] 2 is a schematic diagram showing an example of the configuration of the device 2 that performs the first treatment step S6 to the second treatment step S9. In the figure, the outline arrows indicate the movement of pulp fibers, the thick arrows indicate the movement of ozone, and the thin arrows indicate the movement of the treatment liquid.

[0055] The apparatus 2 includes a first treatment device 4-1 that ozone treats the pulp fibers separated in the third separation step S5 in a first treatment liquid 52-1, and a second treatment device 4-2 that ozone treats the pulp fibers ozone-treated in the first treatment device 4-1 in a second treatment liquid 52-2. The apparatus 2 may further include a storage section 3 that temporarily stores the pulp fibers separated in the third separation step S5, a separator 14 that separates the pulp fibers ozone-treated in the first treatment liquid 52-1 from the first treatment liquid 52-1, and an adjustment device 15 that adjusts the solids content of the second treatment liquid 52-2 with the separated pulp fibers.

[0056] The storage unit 3 includes a mixed liquid tank 12 and an agitator 13. The mixed liquid tank 12 stores a mixed liquid 51 containing a certain ratio of pulp fibers in a first treatment liquid, which is supplied via a pipe 61. The agitator 13 agitates the mixed liquid 51 in the mixed liquid tank 12 so that the pulp fibers in the mixed liquid 51 do not sink to the bottom of the mixed liquid 51.

[0057] The first treatment device 4-1 includes a supply pump P1, a first treatment tank 31-1, an ozone supply device 41 having an ozone generator 42 and a nozzle 43, and an ozone discharge device 44-1. The supply pump P1 is provided midway through a pipe 62 connecting the mixed liquid tank 12 and the first treatment tank 31-1, and supplies the mixed liquid 51 from the mixed liquid tank 12 into the first treatment tank 31-1. The first treatment tank 31-1 contains a first treatment liquid 52-1. There are no particular limitations on the first treatment liquid 52-1 as long as it does not affect the ozone treatment, and examples thereof include water, an acidic aqueous solution (e.g., an aqueous sulfuric acid solution, an aqueous citric acid solution), and an organic solvent (e.g., methanol, acetone).

[0058] The ozone supplying device 41 supplies an ozone-containing gas 53, which is a gaseous substance, to the first treatment tank 31-1. Examples of the ozone generator 42 of the ozone supplying device 41 include the ED-OWX-2 ozone water exposure tester manufactured by Ecodesign Inc. and the OS-25V ozone generator manufactured by Mitsubishi Electric Corporation. The ozone-containing gas 53 is another type of gas containing ozone, such as oxygen gas containing ozone. The ozone-containing gas 53 is supplied to the first treatment tank 31-1 via a pipe 71 connecting the ozone generator 42 and the first treatment tank 31-1. A nozzle 43 that delivers the ozone-containing gas 53 into the first treatment tank 31-1 is disposed at the lower part (preferably the bottom) of the first treatment tank 31-1. The nozzle 43 supplies the ozone-containing gas 53 as a plurality of fine bubbles into the first treatment liquid 52-1 from the lower part to the upper part of the first treatment tank 31-1.

[0059] The ozone delivery device 44-1 is provided midway through a pipe 72 connecting the upper part of the first treatment tank 31-1 and the second treatment device 4-2 (a nozzle 43: described later). The ozone delivery device 44-1 supplies the ozone-containing gas 53, which is supplied to the first treatment liquid 52-1, passes through the first treatment liquid 52-1, and is released from the first treatment liquid 52-1, to the second treatment device 4-2 via the pipe 72 while adjusting the flow rate as necessary (unnecessary portions are branched off for other uses, for example (not shown)).

[0060] Before the start of the first processing step S6, the first processing liquid 52-1 in the first processing tank 31-1 is the first processing liquid 52-1 alone, and after the start of the first processing step S6, the first processing liquid 52-1 becomes a mixture of the first processing liquid 52-1 and the mixed liquid 51. Usually, the same processing liquid is used as the first processing liquid 52-1 and the mixed liquid 51. In this embodiment, the liquid in the first processing tank 31-1 includes the mixture of the first processing liquid 52-1 and the mixed liquid 51, and is referred to as the first processing liquid 52-1.

[0061] The separator 14 is provided midway along a pipe 63 connecting the lower part of the first treatment tank 31-1 and the second treatment device 4-2 (the upper part of the second treatment tank 31-2 of the second treatment device 4-2; described below). The separator 14 separates the pulp fibers that have been ozone-treated with the first treatment liquid 52-1 in the first treatment tank 31-1 from the first treatment liquid 52-1. This is because the first treatment liquid 52-1 contains SAP decomposition products, which are unnecessary substances. The separated pulp fibers are supplied to the adjustment device 15 via a pipe 63. Alternatively, the separated pulp fibers are supplied directly to the second treatment device 4-2 via the pipe 63 (without passing through the adjustment device 15). The separated first treatment liquid 52-1 is discharged via a pipe 81 to the first treatment tank 31-1 or to the outside (e.g., a wastewater treatment device). Examples of the separator 14 include a screen separator, a drum screen separator, a screw press separator, and combinations thereof.

[0062] The adjusting device 15 is provided at a position along the pipe 63 closer to the second treatment device 4-2 (the second treatment tank 31-2 thereof) than the separating device 14. The adjusting device 15 uses the separated pulp fibers to adjust the solid content of the second treatment liquid supplied via the pipe 82. The second treatment liquid containing the pulp fibers and having its solid content adjusted is supplied to the second treatment device 4-2 (the second treatment tank 31-2 thereof) via the pipe 63 by a supply pump P2 (described below).

[0063] The pulp fibers separated in the third separation step S5 may be supplied directly to the first treatment device 4-1. In this case, the storage unit 3 can be omitted. Also, the pulp fibers treated with ozone in the first treatment device 4-1 may be supplied directly to the second treatment device 4-2 without being separated from the first treatment liquid 52-1. In this case, the separation device 14 and the adjustment device 15 can be omitted.

[0064] The second treatment device 4-2 includes a supply pump P2, a second treatment tank 31-2, an ozone supply nozzle 43, and an ozone delivery device 44-2. The supply pump P2 is provided midway through the piping 63 and supplies a first treatment liquid 52-1 containing pulp fibers or a second treatment liquid containing pulp fibers whose solid content has been adjusted by the adjustment device 15 into the second treatment tank 31-2. The second treatment tank 31-2 contains a second treatment liquid 52-2. There are no particular limitations on the second treatment liquid 52-2 as long as it does not affect the ozone treatment, and examples include water, an acidic aqueous solution, and an organic solvent. Furthermore, the second treatment liquid 52-2 is typically the same as the first treatment liquid 52-1, but it does not necessarily have to be the same as the first treatment liquid 52-1.

[0065] The ozone supply nozzle 43 is disposed in the lower portion (preferably the bottom portion) of the second treatment tank 31-2 and is connected to the ozone delivery device 44-1 via a pipe 72. Therefore, the nozzle 43 supplies the ozone-containing gas 53 supplied from the ozone delivery device 44-1 as a plurality of fine bubbles into the second treatment liquid 52-2 from the bottom to the top of the second treatment tank 31-2. The second treatment device 4-2 may further include an ozone supply device 41 to supplement the ozone-containing gas 53 supplied from the ozone delivery device 44-1.

[0066] The ozone delivery device 44-2 is provided in the middle of a pipe 73 connecting the upper part of the second treatment tank 31-2 and another device (not shown) to which an ozone-containing gas is to be supplied. The ozone delivery device 44-2 supplies the ozone-containing gas 53 that has passed through the second treatment liquid 52-2 and been released from the second treatment liquid 52-2 to the other device to which the ozone-containing gas is to be supplied via the pipe 73.

[0067] Note that the second treatment liquid 52-2 in the second treatment tank 31-2 contains only the second treatment liquid 52-2 before the start of the second treatment step S9, and after the start, it becomes a mixture of the first treatment liquid 52-1 from the first treatment tank 31-1 and the second treatment liquid 52-2, or a mixture of the second treatment liquid 52-2 in the adjustment device 15 and the second treatment liquid 52-2 in the second treatment tank 31-2. Typically, the same treatment liquid is used as the first treatment liquid 52-1 and the second treatment liquid 52-2. In this embodiment, the liquid in the second treatment tank 31-2, including both the first treatment liquid 52-1 and the second treatment liquid 52-2, is referred to as the second treatment liquid 52-2. Alternatively, the first treatment liquid 52-1 and the second treatment liquid 52-2 may be the same.

[0068] Next, the first processing step S6 to the second processing step S9 will be described.

[0069] The first treatment step S6 is a step in which ozone is supplied to the first treatment liquid 52-1 in the first treatment tank 31-1, and pulp fibers containing a superabsorbent polymer are treated with the ozone in the first treatment liquid 52-1 to remove at least a portion of the superabsorbent polymer. In this step, the ozone treatment involves oxidatively decomposing the superabsorbent polymer contained in the pulp with the ozone in the first treatment liquid 52-1, reducing its molecular weight and converting it into a decomposition product of the superabsorbent polymer. The decomposition product is a low-molecular-weight organic substance soluble in the first treatment liquid 52-1, and is removed from the pulp fibers by dissolving in the first treatment liquid 52-1. This removes impurities, such as the superabsorbent polymer, from the pulp fibers, resulting in high-purity pulp fibers. In the first treatment step S6, the ozone treatment can also sterilize, bleach, and deodorize the pulp fibers.

[0070] In this embodiment, first, the pulp fibers separated in the third separation step S5 (mainly with the superabsorbent polymer remaining on the surface) are mixed with an acidic aqueous solution to a predetermined concentration to form a mixed liquid 51. The concentration of the pulp fibers in the mixed liquid 51 is set so that the pulp fibers are added to the first treatment tank 31-1 and mixed with the first treatment liquid 52-1 to reach the predetermined concentration. The mixed liquid 51 is supplied to the mixed liquid tank 12 via piping 61 and stored therein. Because the specific gravity of the pulp fibers is greater than 1, the mixed liquid 51 is stirred by the agitator 13 in the mixed liquid tank 12 to prevent separation of the pulp fibers and water.

[0071] The mixed liquid 51 in the mixed liquid tank 12 is continuously or intermittently supplied to the first treatment tank 31-1 in accordance with the opening and closing control of the valve V1 of the pipe 62 and the flow rate control of the supply pump P1. As a result, the pulp fibers are supplied into the first treatment liquid 52-1 from the first supply port 32-1 provided in the upper part of the first treatment tank 31-1. The first treatment liquid 52-1 is an acidic aqueous solution, and has a specific gravity of approximately 1. Therefore, the pulp fibers settle from the top to the bottom of the first treatment liquid 52-1.

[0072] On the other hand, the ozone-containing gas 53 generated by the ozone generator 42 is supplied to the first treatment tank 31-1 via a pipe 71 and is released in the form of fine bubbles (e.g., microbubbles or nanobubbles) into the first treatment liquid 52-1 from a nozzle 43 of the first treatment tank 31-1. The ozone-containing gas 53 rises from the bottom to the top of the first treatment liquid 52-1.

[0073] Then, within the first treatment liquid 52-1, the pulp fibers sinking from top to bottom and the ozone-containing gas 53 rising from bottom to top collide with each other as they move in opposite directions. The ozone-containing gas 53 then adheres to the surface of the pulp fibers, enveloping the pulp fibers. At this time, the ozone in the ozone-containing gas 53 reacts with the superabsorbent polymer in the pulp fibers, oxidatively decomposing the superabsorbent polymer and reducing its molecular weight, which is then dissolved in the first treatment liquid 52-1. As a result, the superabsorbent polymer on the pulp fibers is removed from the pulp fibers. The pulp fibers then sink to the bottom of the first treatment tank 31-1, and the ozone-containing gas 53 escapes into the space above the first treatment tank 31-1.

[0074] Thereafter, the first treatment liquid 52-1 (containing pulp fibers) at the bottom of the first treatment tank 31-1 is supplied to the separation device 14 via the first outlet 33-1 of the first treatment tank 31-1, the open valve V2, and the pipe 63.

[0075] Next, the fourth separation step (separation step) S7 is a step of separating the pulp fibers treated in the first treatment step S6 from the first treatment liquid 52-1. The separated pulp fibers are supplied to the adjustment device 15 or to the second treatment device 4-2. The method for separating the pulp fibers from the first treatment liquid 52-1 is not particularly limited, but an example is a method of passing the first treatment liquid 52-1 containing the pulp fibers through a screen mesh with a mesh size of 0.15 to 2 mm. When the first treatment liquid 52-1 containing the pulp fibers is passed through a screen mesh with a mesh size of 0.15 to 2 mm, wastewater containing products of oxidative decomposition of the superabsorbent polymer passes through the screen, but the pulp fibers do not pass through and remain on the screen mesh.

[0076] In this embodiment, by controlling the opening and closing of valve V2 of pipe 63, first treatment liquid 52-1 containing ozone-treated pulp fibers is supplied to separator 14 (screen separator) from first outlet 33-1 of first treatment tank 31-1 via pipe 63. In separator 14, pulp fibers are separated from first treatment liquid 52-1 containing pulp fibers. The pulp fibers separated from first treatment liquid 52-1 are supplied to adjustment device 15 via pipe 63. The remaining first treatment liquid 52-1 from which pulp fibers have been separated is sent to first treatment tank 31-1 or the like via pipe 81 for reuse, or is discharged to the outside (e.g., wastewater treatment device).

[0077] Next, in an adjustment step S8, the solid content of the second treatment liquid is adjusted using the separated pulp fibers. The second treatment liquid containing the pulp fibers and having the adjusted solid content is supplied to the second treatment tank 31-2. However, the second treatment liquid used to adjust the solid content is a different treatment liquid from the second treatment liquid 52-2 stored in the second treatment tank 31-2.

[0078] In this embodiment, the separated pulp fibers are supplied to the adjusting device 15 from the separating device 14 via a pipe 63. The adjusting device 15 adjusts the solid content of the second treatment liquid supplied via a pipe 82 using the separated pulp fibers so that the solid content is at a desired value. The second treatment liquid containing the pulp fibers and having the adjusted solid content is supplied to the second treatment device 4-2 (the second treatment tank 31-2 of the second treatment device 4-2) via the pipe 63 by a supply pump P2 (described below).

[0079] The solid content of the second treatment liquid 52-2 is the content of pulp fibers in the second treatment liquid, and is, for example, 0.5 to 20% by mass, preferably 1 to 15% by mass. If the solid content is too low, the efficiency of supply and ozone treatment may be reduced too much, while if the solid content is too high, supply may be difficult, and the ozone treatment may not be thoroughly carried out.

[0080] The fourth separation step S7 (separation device 14) and the adjustment step S8 (adjustment device 15) may not be performed if the amount of decomposition products of the superabsorbent polymer in the first treatment liquid 52-1 after the first treatment step S6 is small, etc. In this case, the treatment efficiency can be improved and costs can be reduced.

[0081] Next, the second treatment step S9 is a step in which ozone released from the first treatment liquid 52-1 in the first treatment tank 31-1 is supplied to the second treatment liquid 52-2 in the second treatment tank 31-2, and the pulp fibers are treated with ozone in the second treatment liquid 52-2. However, it is sufficient to use at least a portion of the ozone released from the first treatment liquid 52-1 in the first treatment tank 31-1, and it is preferable to use as much of it as possible. Note that, if there is any remaining ozone released from the first treatment liquid 52-1 in the first treatment tank 31-1, that ozone may be used for another purpose. Furthermore, if necessary, additional ozone may be added in the second treatment step S9. The ozone treatment performed in the second treatment step S9 is not particularly limited, but may include, for example, at least one of the following treatment steps.

[0082] That is, the second treatment step S9 may involve treating the pulp fibers treated in the first treatment step S6 with ozone in the second treatment liquid 52-2 in the second treatment tank 31-2 to perform at least one of deodorization, bleaching, and sterilization. This may be performed, for example, when the superabsorbent polymer in the pulp fibers has been sufficiently removed in the first treatment step S6. In this case, the ozone concentration (ppm by mass), the treatment time (minutes) in the treatment tank, or the product of these (hereinafter also referred to as the "CT value (ppm·min)") may be significantly smaller than in the first treatment step S6. Therefore, the ozone released from the first treatment liquid 52-1 in the first treatment tank 31-1 may be sufficient, not only when ozone is injected into the first treatment liquid 52-1 at a high concentration and a high flow rate, but also when this is not the case.

[0083] Alternatively, the second treatment step S9 may involve treating the pulp fibers treated in the first treatment step S6 with ozone in the second treatment liquid 52-2 in the second treatment tank 31-2 to remove at least a portion of the superabsorbent polymer. This may be performed, for example, when the superabsorbent polymer in the pulp fibers is not sufficiently removed in the first treatment step S6. In this case, the ozone concentration (ppm by mass), treatment time (minutes) in the treatment tank, or CT value (ppm / minute) may be similar to or slightly smaller than those in the first treatment step S6. Therefore, when ozone is injected into the first treatment liquid 52-1 at a high concentration and a high flow rate, the ozone released from the first treatment liquid 52-1 in the first treatment tank 31-1 may be sufficient.

[0084] In this embodiment, first, a first treatment liquid 52-1 containing pulp fibers treated in the first treatment step S6, pulp fibers separated in the fourth separation step S7, or a second treatment liquid in which the solid content of pulp fibers has been adjusted in the adjustment step S8 is continuously or intermittently supplied to the second treatment tank 31-2 in accordance with the opening and closing control of the valves V2 and / or V3 of the pipe 63 and the flow rate control of the supply pump P2. As a result, the pulp fibers are supplied into the second treatment liquid 52-2 from a second supply port 32-2 provided in the upper part of the second treatment tank 31-2. The second treatment liquid 52-2 is an acidic aqueous solution and has a specific gravity of approximately 1. Therefore, the pulp fibers settle from the top to the bottom of the second treatment liquid 52-2.

[0085] Meanwhile, the ozone-containing gas 53 released from the first treatment liquid 52-1 in the first treatment tank 31-1 is supplied to the second treatment tank 31-2 via the pipe 72 and is released in the form of fine bubbles (e.g., microbubbles or nanobubbles) into the second treatment liquid 52-2 from the nozzle 43 of the second treatment tank 31-2. The ozone-containing gas 53 rises from the bottom to the top of the second treatment liquid 52-2.

[0086] Then, within the second treatment liquid 52-2, the pulp fibers sinking from top to bottom and the ozone-containing gas 53 rising from bottom to top collide with each other as they move in opposite directions. The ozone-containing gas 53 then adheres to the surface of the pulp fibers, enveloping the pulp fibers. At this time, the ozone in the ozone-containing gas 53 reacts with the superabsorbent polymer in the pulp fibers, oxidatively decomposing the superabsorbent polymer and reducing its molecular weight, which is then dissolved in the second treatment liquid 52-2. As a result, the superabsorbent polymer on the pulp fibers is removed from the pulp fibers. The pulp fibers then sink to the bottom of the second treatment tank 31-2, and the ozone-containing gas 53 escapes into the space above the second treatment tank 31-2.

[0087] Thereafter, the second treatment liquid 52-2 (containing pulp fibers) at the bottom of the second treatment tank 31-2 is supplied to the fifth separation step S10 via the second outlet 33-2 of the second treatment tank 31-2, through the open valve V4, and via the piping 64.

[0088] Next, the fifth separation step S10 is a step in which the pulp fibers treated in the second treatment step S9 are separated from the second treatment liquid 52-2. The separated pulp fibers are extracted as recycled pulp fibers. The method for separating the pulp fibers from the second treatment liquid 52-2 is not particularly limited, but an example is a method in which the second treatment liquid 52-2 containing the pulp fibers is passed through a screen mesh with a mesh size of, for example, 0.15 to 2 mm. As a result, the wastewater containing products of oxidative decomposition of the superabsorbent polymer passes through the screen. Meanwhile, the pulp fibers remain on the screen and are extracted as high-quality pulp fibers (recycled pulp fibers).

[0089] In this embodiment, the pulp fibers processed in the second treatment step S9 are supplied to a separation device (screen separator; not shown) from the second outlet 33-2 of the second treatment tank 31-2 in accordance with the opening and closing control of the valve V4 of the pipe 64 and the flow rate control of the supply pump P3. In the separation device, the pulp fibers are separated from the second treatment liquid 52-2 containing the pulp fibers and extracted. The remaining second treatment liquid 52-2 from which the pulp fibers have been separated is sent, for example, via a pipe to the second treatment tank 31-2 or the like and reused, or is discharged to the outside. The extracted pulp fibers are sterilized, washed, dried, etc., as necessary, and then recovered as pulp fibers. The pulp fibers separated and recovered in this manner become so-called recycled pulp fibers.

[0090] In the above embodiment, the pulp fibers treated with ozone in the first treatment step S6 are further treated with ozone in the second treatment step. However, the second treatment step is not limited to this example. For example, the second treatment step may involve ozone treatment of newly supplied pulp fibers containing a superabsorbent polymer, separate from the pulp fibers treated with ozone in the first treatment step S6, in the second treatment liquid 52-2 in the second treatment tank 31-2, to remove at least a portion of the superabsorbent polymer. This may be performed, for example, when it is desired to remove the superabsorbent polymer from pulp fibers separate from the pulp fibers treated in the first treatment step S6.

[0091] Alternatively, the second treatment step may include a step of ozone treating newly supplied pulp fibers, separate from the pulp fibers treated in the first treatment step S6, in the second treatment liquid 52-2 in the second treatment tank 31-2 to perform at least one of deodorization, bleaching, and sterilization. This may be performed, for example, when at least one of deodorization, bleaching, and sterilization is required for pulp fibers separate from the pulp fibers treated in the first treatment step S6.

[0092] Alternatively, in the above embodiment, the second treatment step is an ozone treatment step for pulp fibers using the second treatment device 4-2. However, the second treatment step is not limited to this example. The second treatment step may also include a step of ozone treatment of components other than the pulp fibers in the first treatment step S6, such as plastic materials or superabsorbent polymers, in another second treatment solution in another second treatment tank to perform at least one of deodorization, bleaching, and sterilization. This may be performed, for example, when at least one of deodorization, bleaching, and sterilization is required for components other than the pulp fibers treated in the first treatment step S6. For example, a process of performing at least one of deodorization, bleaching, and sterilization on the plastic materials recovered in the first separation step or the superabsorbent polymers recovered in the second separation step S4 may be performed. In this case, the present method may also be considered a method for treating plastic materials or superabsorbent polymers.

[0093] In the ozone treatment for oxidatively decomposing the superabsorbent polymer in the first treatment step S6 and the second treatment step S9, the ozone concentration in the treatment solution is not particularly limited, as long as it is a concentration that can decompose the superabsorbent polymer. Examples of ozone concentrations in the treatment solution include 10 to 50 ppm by mass. A concentration that is not too low can completely solubilize the superabsorbent polymer, while a concentration that is not too high will not damage the pulp fibers. The treatment time in the treatment solution is not particularly limited, as long as it is a time that can decompose the superabsorbent polymer; however, the higher the ozone concentration in the treatment solution, the shorter the treatment time, and the lower the ozone concentration, the longer the treatment time. The contact time is typically 5 to 300 minutes. The CT value (ppm·min), which is the product of the ozone concentration (ppm) in the treatment solution and the treatment time (min) of the treatment step, is, for example, 100 to 15,000 ppm·min. If the CT value is too small, the superabsorbent polymer may not be completely solubilized and may remain in the pulp fibers, whereas if the CT value is too large, the pulp fibers may be damaged.

[0094] In the ozone treatment in the second treatment step S9, which performs at least one of deodorizing, bleaching, and sterilizing of components (e.g., pulp fibers, superabsorbent polymers, plastic materials), the ozone concentration in the treatment solution is not particularly limited, as long as it is a concentration that can perform at least one of deodorizing, bleaching, and sterilizing of the components. Examples of ozone concentrations in the treatment solution include 0.3 to 2 ppm by mass. If the concentration is too low, it becomes difficult to remove bacteria, etc., while if the concentration is too high, it may begin to have adverse effects on the components. The contact time between the ozone water and the components is not particularly limited, as long as it is a time that can remove bacteria and other organic matter adhering to the surfaces of the components. However, the contact time is shorter when the ozone concentration in the treatment solution is high and longer when the ozone concentration is low. The contact time is typically 0.3 seconds to 15 minutes. The CT value (ppm·min), which is the product of the ozone concentration (ppm) in the treatment solution and the contact time (min), is, for example, 0.05 to 20 ppm·min. If the CT value is too small, sterilization becomes difficult, and if the CT value is too large, there is a risk that adverse effects will begin to appear on the components.

[0095] As described above, in this method, ozone is supplied to the first treatment liquid 52-1 in the first treatment tank 31-1 for the ozone treatment of pulp fibers in the first treatment step S6, and then released from the first treatment liquid 52-1 (passing through the first treatment liquid 52-1) is supplied to the second treatment liquid 52-2 in the second treatment tank 31-2 and used for the ozone treatment of pulp fibers in the second treatment step S9. That is, in this method, ozone is supplied to the first treatment liquid 52-1 at a high concentration and a high flow rate in order to increase the treatment speed of the ozone treatment. Even if a large amount of ozone is released (passes through) without being dissolved in the first treatment liquid 52-1, the released ozone can be used in the second treatment step S9. In this way, the ozone supplied for the ozone treatment in the first treatment step S6 is also used in the ozone treatment in the second treatment step S9, thereby enabling effective use of the ozone. Therefore, the treatment speed of the ozone treatment in the first treatment step S6 can be increased, and the energy efficiency of the ozone treatment can be improved. Therefore, in the method for producing recycled fibers from pulp fibers containing a superabsorbent polymer, both the treatment speed and energy efficiency of the ozone treatment can be achieved.

[0096] In a preferred embodiment of this method, the first treatment step S6 may include a continuous treatment step in which pulp fibers and the first treatment liquid 52-1 are continuously supplied into the first treatment tank 31-1, the pulp fibers are treated with ozone, and the first treatment liquid 52-1 containing the pulp fibers treated with ozone is continuously discharged out of the first treatment tank 31-1. In other words, this first treatment step S6 is a continuous treatment in which the first treatment step S6 is continuously performed without interruption. Accordingly, the second treatment step S9 may also include a similar continuous treatment.

[0097] For example, continuous processing can be achieved by opening valves V1 and V2 in the first processing apparatus 4-1, continuously supplying the first processing liquid (mixed liquid 51) to the first processing tank 31-1 using supply pumps P1 and P2, and controlling the flow rate of the first processing liquid 52-1 so that it is continuously discharged from the first processing tank 31-1. It is preferable that the flow rate of the first processing liquid supplied to the first processing tank 31-1 and the flow rate of the first processing liquid 52-1 discharged from the first processing tank 31-1 are equal. Accordingly, continuous processing can be similarly achieved by opening valves V3 and V4 in the second processing apparatus 4-2, and similarly controlling the flow rates of the first processing liquid 52-1 or the second processing liquid 52-2 supplied to the second processing tank 31-2 using supply pumps P2 and P3, and the second processing liquid 52-2 discharged from the second processing tank 31-2. However, in this case, the first processing liquid 52-1 remains the second processing liquid 52-2.

[0098] Thus, in a preferred embodiment of this method, pulp fibers and the first treatment liquid (mixed liquid 51) are continuously supplied into the first treatment tank 31-1, and the pulp fibers are treated with ozone (while the superabsorbent polymer is oxidatively decomposed, dissolved, and removed), and the first treatment liquid 52-1 containing the ozone-treated pulp fibers is continuously discharged from the first treatment tank 31-1. In other words, the pulp fibers are continuously treated. Therefore, in the first treatment tank 31-1, a continuous and stable flow of the first treatment liquid 52-1 can be generated from the first supply port 32-1 toward the first discharge port 33-1. This allows the ozone dissolved in the first treatment liquid 52-1 and the ozone passing through the first treatment liquid 52-1 to be drawn into the flow, facilitating contact between the pulp fibers and the ozone. In other words, the pulp fibers can be continuously contacted with the ozone. Therefore, the amount of ozone that contributes to the decomposition of the highly water-absorbent polymer can be increased, and the processing speed and energy efficiency of the ozone treatment can be improved.

[0099] In a preferred embodiment of this method, the first treatment step S6 may include a preparation step, a batch treatment step, and a delivery step. The preparation step is a step of preparing a first treatment liquid 52-1 containing pulp fibers in the first treatment tank 31-1. The batch treatment step is a step of treating the pulp fibers with ozone after the preparation step. The delivery step is a step of delivering the first treatment liquid 52-1 containing the pulp fibers treated with ozone to the outside of the first treatment tank 31-1 after the batch treatment step. In other words, the first treatment step S6 is a batch treatment in which the pulp fibers and the first treatment liquid 52-1 are introduced into the first treatment tank 31-1 and then the first treatment step S6 is performed in a closed state. Accordingly, the second treatment step S9 may also include a similar batch treatment.

[0100] For example, in the first processing apparatus 4-1, valve V1 is opened, valve V2 is closed, and the supply pump P1 controls the flow rate of the first processing liquid (mixed liquid 51) so that a predetermined amount is supplied to the first processing tank 31-1. Then, the supply pump P1 is stopped, valve V1 is closed, and ozone treatment of the pulp fibers is performed in the first processing tank 31-1 containing a predetermined amount of the first processing liquid 52-1 (containing the mixed liquid 51), thereby achieving batch treatment. Then, in the second processing apparatus 4-2, valves V2 and V3 are opened, valve V4 is closed, and the supply pump P2 controls the flow rate of the first processing liquid 52-1 so that a predetermined amount is supplied to the second processing tank 31-2. Then, the supply pump P2 is stopped, valves V2 and V3 are closed, and ozone treatment of the pulp fibers is performed in the second processing tank 31-2 containing a predetermined amount of the first processing liquid 52-1, thereby similarly achieving batch treatment. In this case, however, the first processing liquid 52-1 remains the second processing liquid 52-2.

[0101] Thus, in a preferred embodiment of this method, first, a first treatment liquid 52-1 containing pulp fibers is prepared in the first treatment tank 31-1. The pulp fibers are then treated with ozone (the superabsorbent polymer is oxidatively decomposed, dissolved, and removed). The ozone-treated first treatment liquid 52-1 containing the pulp fibers is then discharged from the first treatment tank 31-1. In other words, the pulp fibers are batch-treated. Therefore, the pulp fibers remaining in the first treatment liquid 52-1 in the first treatment tank 31-1 can be easily and continuously exposed to ozone dissolved in the first treatment liquid 52-1 and ozone passing through the first treatment liquid 52-1. This allows the pulp fibers to be continuously treated with ozone. This allows for more ozone to contribute to the decomposition of the superabsorbent polymer, thereby improving the treatment speed and energy efficiency of the ozone treatment.

[0102] In a preferred embodiment of this method, a separation step (fourth separation step S7) is further provided in which the pulp fibers treated in the first treatment step S1 are separated from the first treatment liquid 52-1. The separated pulp fibers are then supplied to the second treatment tank 31-2.

[0103] The first treatment liquid 52-1 after the first treatment step S6 contains not only pulp fibers from which at least a portion of the superabsorbent polymer has been removed, but also low-molecular-weight organic matter produced by oxidative decomposition of the superabsorbent polymer. Therefore, if the pulp fibers are supplied to the second treatment step S9 together with the first treatment liquid 52-1, the second treatment liquid 52-2 in the second treatment step S9 will contain not only pulp fibers but also low-molecular-weight organic matter. In this case, the ozone in the second treatment liquid 52-2 will be supplied not only to the pulp fibers but also to the low-molecular-weight organic matter, which may prevent the ozone from being effectively used to treat the pulp fibers.

[0104] Therefore, in this method, the pulp fibers treated in the first treatment step S6 are separated from the first treatment liquid 52-1 (fourth separation step S7), and the separated pulp fibers are supplied to the second treatment tank 31-2. That is, the pulp fibers are separated from the low-molecular-weight organic matter before being supplied to the second treatment tank 31-2, which prevents the low-molecular-weight organic matter from being contained in the second treatment liquid 52-2 in the second treatment step S9. As a result, the ozone in the second treatment liquid 52-2 is supplied almost exclusively to the pulp fibers, and the ozone can be effectively used to treat the pulp fibers. This increases the treatment speed and energy efficiency of the ozone treatment in the second treatment step S9.

[0105] In a preferred embodiment of the present method, the method further includes a separation step (fourth separation step S7) of separating the pulp fibers treated in the first treatment step S6 from the first treatment liquid 52-1, and an adjustment step S8 of adjusting the solid content of the second treatment liquid 52-2 using the separated pulp fibers. The second treatment liquid 52-2 containing the pulp fibers and having the adjusted solid content is supplied to the second treatment tank 31-2.

[0106] Thus, in a preferred embodiment of this method, the pulp fibers treated in the first treatment step S6 are separated from the first treatment liquid 52-1 (fourth separation step S7), and the second treatment liquid 52-2, whose solid content has been adjusted with the separated pulp fibers, is supplied to the second treatment tank 31-2 (adjustment step S8). That is, the pulp fibers are separated from low-molecular-weight organic matter and mixed with fresh second treatment liquid 52-2 to achieve an appropriate solid content, which is then supplied to the second treatment tank 31-2. This prevents low-molecular-weight organic matter from being contained in the second treatment liquid 52-2 in the second treatment step S9, and also optimizes the ratio of ozone to pulp fiber during ozone treatment. This ensures that the ozone in the second treatment liquid 52-2 is supplied almost exclusively to the pulp fibers, and the pulp concentration is appropriate, allowing the ozone to be more effectively utilized in the treatment of the pulp fibers. This improves the processing speed and energy efficiency of the ozone treatment in the second treatment step S9.

[0107] In a preferred embodiment of this method, the second treatment step S9 includes a step of treating the pulp fibers treated in the first treatment step S6 with ozone in the second treatment liquid 52-2 in the second treatment tank 31-2 to perform at least one of deodorization, bleaching, and sterilization. By utilizing the ozone supplied for the ozone treatment in the first treatment step S6 in the ozone treatment for performing at least one of deodorization, bleaching, and sterilization in the second treatment step S9, the ozone can be effectively utilized. This method allows for the production of pulp fibers that have been further deodorized, bleached, and sterilized in the first treatment step S6.

[0108] In a preferred embodiment of this method, the second treatment step S9 includes treating the pulp fibers treated in the first treatment step S6 with ozone in the second treatment liquid 52-2 in the second treatment tank 31-2 to remove at least a portion of the superabsorbent polymer. In this manner, the ozone supplied for the ozone treatment in the first treatment step S6 is utilized in the ozone treatment for removing at least a portion of the superabsorbent polymer in the second treatment step S9, thereby enabling effective use of the ozone. This method allows for the production of pulp fibers from which the superabsorbent polymer has been further removed since the first treatment step S6.

[0109] In this embodiment, pulp fibers containing a superabsorbent polymer (a mixture of a superabsorbent polymer and pulp fibers) are treated in two stages (first treatment stage S6 and second treatment stage S9) using ozone in the first treatment stage S6, but the ozone may also be treated in three or more stages.

[0110] In this embodiment, the ozone that is supplied to the first treatment liquid 52-1 for the ozone treatment of the pulp fibers in the first treatment step S6 and that has passed through (released from) the first treatment liquid 52-1 is reused in another step, such as the ozone treatment of the pulp fibers in the second treatment step S9. As described above, this method reuses ozone that is released (passed through) without being used and discarded, and therefore can also be referred to as a method for reusing waste ozone (a method for recycling ozone). Furthermore, the first treatment step S6 to the second treatment step S9 can also be referred to as a method for removing superabsorbent polymer from pulp fibers containing the superabsorbent polymer (a mixture of superabsorbent polymer and pulp fibers).

[0111] The absorbent article of the present invention is not limited to the above-described embodiments, and suitable combinations and modifications can be made without departing from the object and spirit of the present invention.

[0112] S6 First processing step S9 Second processing step 31-1 First processing tank 31-2 Second processing tank 52-1 First processing liquid 52-2 Second processing liquid

Claims

1. A method for producing recycled fibers from a mixture of a superabsorbent polymer and pulp fibers, comprising: a first treatment step of treating a mixture of the superabsorbent polymer and pulp fibers with ozone in a first treatment liquid in a first treatment tank while supplying ozone to the first treatment liquid in the first treatment tank to remove at least a part of the superabsorbent polymer; and a second treatment step of treating pulp fibers with ozone in a second treatment liquid in a second treatment tank while supplying the ozone discharged from the first treatment liquid in the first treatment tank to the second treatment liquid in the second treatment tank.

2. The method according to claim 1, wherein the first treatment step includes a continuous treatment step of continuously supplying the pulp fibers and the first treatment liquid into the first treatment tank, treating the pulp fibers with ozone, and continuously sending out the first treatment liquid containing the pulp fibers treated with ozone out of the first treatment tank.

3. The method according to claim 1 or 2, wherein the first treatment step includes: a preparation step of preparing the first treatment liquid containing the pulp fibers in the first treatment tank; a batch treatment step of treating the pulp fibers with ozone after the preparation step; and a sending-out step of sending out the first treatment liquid containing the pulp fibers treated with ozone out of the first treatment tank after the batch treatment step.

4. The method according to any one of claims 1 to 3, further comprising a separation step of separating the pulp fibers treated in the first treatment step from the first treatment liquid, and the separated pulp fibers are supplied to the second treatment tank.

5. The method according to any one of claims 1 to 4, further comprising: a separation step of separating the pulp fibers treated in the first treatment step from the first treatment liquid; and an adjustment step of adjusting the solid content ratio of the second treatment liquid with the separated pulp fibers, and the second treatment liquid containing the pulp fibers with the adjusted solid content ratio is supplied to the second treatment tank.

6. The method according to any one of claims 1 to 5, wherein the second treatment step includes a step of treating the pulp fibers treated in the first treatment step with ozone in the second treatment liquid in the second treatment tank to perform at least one of deodorization, bleaching, and sterilization.

7. The method according to any one of claims 1 to 6, wherein the second treatment step includes a step of treating the pulp fibers treated in the first treatment step with ozone in the second treatment liquid in the second treatment tank to remove at least a part of the superabsorbent polymer.

8. The method according to any one of claims 1 to 9, further comprising a step of preparing a mixture of the superabsorbent polymer and pulp fibers taken out from a used absorbent article as the mixture of the superabsorbent polymer and pulp fibers used in the first treatment step.

Images