Method for separating water-absorbing resin

Abstract

To provide a technique for efficiently separating a water-absorbing resin from a waste containing an absorptive article.SOLUTION: A method for separating a water-absorbing resin separates a water-absorbing resin from an object to be treated containing an absorptive article that has the water-absorbing resin and a thermoplastic resin. The method for separating the water-absorbing resin includes: a drying step of stirring and drying the object to be treated; a heating step of heating the object to be treated at a temperature which is equal to or higher than a softening point of the thermoplastic resin and lower than a thermal decomposition temperature of the water-absorbing resin; a granulation step of stirring the object to be treated and cooling the object to be treated to be lower than the softening point of the thermoplastic resin, and thereby obtaining a granule, after the heating step; and a separation step of separating the water-absorbing resin on the basis of the grain size of the granule.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a recycling technology for absorbent articles. [Background technology]

[0002] From the viewpoint of effective utilization of resources, reduction of greenhouse gas emissions, etc., it is desirable to recycle used absorbent articles such as disposable diapers and sanitary napkins. Patent Document 1 discloses a method for producing a recycled superabsorbent polymer regenerated from a used superabsorbent polymer, in which the used superabsorbent polymer is dehydrated using an acid or a base, superabsorbent polymer particles are attached to the dehydrated polymer, and the polymer is then dried. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2021-166968 Summary of the Invention [Problem to be solved by the invention]

[0004] In addition to the water-absorbent polymer, the absorbent article also contains a thermoplastic resin, cellulose, etc., and these are integrated into a structure. However, Patent Document 1 does not disclose a means for extracting the superabsorbent polymer from a used absorbent article. Furthermore, the method described in Patent Document 1 may require a large amount of processing agent or large equipment, and more efficient recycling technology for absorbent articles is desired.

[0005] An object of the present invention is to provide a technique for efficiently separating a water-absorbent resin from waste containing absorbent articles. [Means for solving the problem]

[0006] A method for separating a water-absorbent resin according to one embodiment of the present invention is a method for separating the water-absorbent resin from a processing target including an absorbent article that has absorbed water and contains a water-absorbent resin and a thermoplastic resin. The method for separating the water-absorbent resin comprises: a drying step of stirring and drying the object to be treated; a heating step of heating the object to be treated at a temperature equal to or higher than the softening point of the thermoplastic resin and lower than the thermal decomposition temperature of the water-absorbing resin; a granulation step of stirring the material to be treated after the heating step and cooling it to a temperature lower than the softening point of the thermoplastic resin to obtain granules; and a separation step of separating the water-absorbent resin based on the particle size of the granular material. [Effects of the Invention]

[0007] According to the present invention, it is possible to efficiently separate the water-absorbent resin from waste containing absorbent articles. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a schematic diagram of a granulation device that can be used in one embodiment of the present invention. [Figure 2] FIG. 2 is a schematic diagram of the granulation device. [Figure 3] 4 is a flowchart showing a method for separating a water-absorbent resin according to the embodiment. [Figure 4] 10 is a flowchart showing a method for producing water-absorbent resin-containing granules according to a modified example of the embodiment. [Figure 5] 10 is a flowchart showing a method for producing granules (granules) with a low water-absorbent resin content according to a modified example of the embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0009] [Outline of an embodiment of the present invention] A method for separating a water-absorbent resin according to one embodiment of the present invention is configured to granulate a material to be treated, including absorbent articles that have absorbed water, to form granules of different particle sizes, and separate the water-absorbent resin from other materials, such as thermoplastic resin, based on particle size. This allows the water-absorbent resin to be efficiently separated from absorbent articles that are formed by integrating multiple components, thereby enabling the water-absorbent resin to be recycled. Furthermore, the present embodiment also allows the recovery of granules with a low content of water-absorbent resin, which can be effectively used as recycled material. Therefore, the separation method according to the present embodiment contributes to promoting the recycling of waste, including used absorbent articles, and ultimately contributes to the realization of a resource-circulating society.

[0010] In this embodiment, the absorbent article refers to an article that contains a water-absorbent resin and a thermoplastic resin and is capable of absorbing liquid. The absorbent article according to this embodiment includes, for example, one or more articles selected from disposable diapers, sanitary napkins, urine absorption pads, panty liners, pet toilet sheets, portable toilets, drip sheets, ice packs, and deodorizers. Note that a "drip sheet" refers to a water-absorbent sheet that absorbs excess water (such as body fluids) from food ingredients such as meat and fish. In this embodiment, the absorbent article that has absorbed water refers to an absorbent article that has absorbed water mainly by a water-absorbent resin. The water referred to here may be body fluids such as urine or menstrual blood. In other words, the absorbent article that has absorbed water may be a used absorbent article.

[0011] Absorbent articles used to absorb bodily fluids, such as disposable diapers and sanitary napkins, generally include an absorbent body containing a water-absorbent resin and sheet materials covering the front and back of the absorbent body, with these components joined together by adhesive or the like. The sheet materials include, for example, thermoplastic resin and / or cellulose. The absorbent body includes at least an absorbent core containing a water-absorbent resin and may further include a core wrap sheet covering the absorbent core. The core wrap sheet is made of a hydrophilic material, such as cellulose. The absorbent core may also include a hydrophilic material, such as cellulose pulp, in addition to the water-absorbent resin.

[0012] In this embodiment, the water-absorbent resin is a resin having water-absorbing properties, and includes, for example, one or more water-absorbent resins selected from polyacrylic acid, polyacrylic acid salts, partially crosslinked polymeric compounds having carboxyl groups or salts thereof, partially crosslinked polysaccharides, etc. Partially crosslinked polymeric compounds having carboxyl groups or salts thereof include crosslinked polyacrylates, poly(vinyl alcohol / acrylate) copolymers (crosslinked), starch-acrylate graft copolymers (crosslinked), and polyvinyl alcohol-polymaleic anhydride graft copolymers (crosslinked). Partially crosslinked polysaccharides include crosslinked carboxymethyl cellulose salts, etc. Furthermore, the "salt" constituting the water absorbent resin includes, for example, one or more salts selected from alkali metal salts (sodium salts, potassium salts, lithium salts, etc.), alkaline earth metal salts (calcium salts, magnesium salts, barium salts, etc.), ammonium salts (quaternary ammonium salts, quaternary alkylammonium salts, etc.), etc. The water-absorbing resin of the present invention preferably contains one or more water-absorbing resins selected from polyacrylic acid, sodium polyacrylate, or a crosslinked sodium polyacrylate.

[0013] In this embodiment, the thermoplastic resin is not limited to a specific type, and examples thereof include polyolefin, polyester, polystyrene, etc. Examples of polyolefin include polyethylene and polypropylene, etc. Examples of polyester include polyethylene terephthalate, etc. These thermoplastic resins are used, for example, as sheet materials or exterior materials in absorbent articles. Furthermore, thermoplastic resins may also be contained in objects to be treated other than absorbent articles.

[0014] The object to be treated according to this embodiment includes at least absorbent articles that have absorbed water, and may also include other waste, secondary materials, etc. The other waste is not particularly limited, and may include, for example, used packaging containers (food containers, bottles, etc.), marine debris, other waste generated from homes, businesses, etc.

[0015] In this embodiment, the material to be treated preferably contains cellulose. When the material to be treated contains cellulose, a portion of the material to be treated is easily carbonized in the heating step S2, as described below. The cellulose may be contained in an absorbent article, or may be contained in a material to be treated other than an absorbent article.

[0016] In this embodiment, "granular" refers to the shape of each fragment of the crushed material. Furthermore, "granular body" refers to an aggregate of multiple fragments that are separated from each other. Furthermore, "granulation" refers to converting the material to be crushed into granular bodies. In this embodiment, the maximum diameter of the granular body is preferably 5 cm or less, more preferably 1 cm or less, and even more preferably 0.5 cm or less, from the viewpoint of ease of handling.

[0017] In this embodiment, the particle size of a granular material refers to the size of the granular material. In other words, the particle size of a granular material serves as a standard for separating granular materials by size. The size of a granular material here may be defined as a range of particle diameters equivalent to the diameter of each granular material if it were assumed to be a sphere, but it does not have to be strictly defined by particle diameter as long as the size of the granular material can be classified. For example, the particle size of a granular material can be determined by the opening of a sieve or the classification point set in a classifier.

[0018] [Configuration of granulation equipment] First, a granulation apparatus 100 will be described as an example of a processing apparatus that can be used in the separation method according to this embodiment. FIG. 1 shows the granulation apparatus 100 from the front, and FIG. 2 shows the granulation apparatus 100 from the side. The granulation apparatus 100 has a processing tank 101. The processing tank 101 has a wall 101a and a storage section 101b. The storage section 101b can store materials to be granulated by the granulation apparatus 100, and is configured as an internal space of the processing tank 101 surrounded by the wall 101a. FIGS. 1 and 2 each show the interior of the storage section 101b by showing a vertical cross section of the wall 101a. In the processing tank 101, a portion of the wall 101a is configured to be openable and closable so that the storage section 101b can be accessed from the outside to load and unload the materials.

[0019] The granulation device 100 further includes an agitation shaft 102. The agitation shaft 102 includes a shaft portion 102a and multiple blade portions 102b. The shaft portion 102a is configured as a round bar-shaped member that can rotate around a rotation axis C extending horizontally laterally. Both ends of the shaft portion 102a are supported by the wall portion 101a on the sides of the storage portion 101b, and the portion between the both ends supported by the wall portion 101a is located within the storage portion 101b. The multiple blade portions 102b are provided at intervals along the longitudinal direction, substantially evenly distributed over the entire portion of the shaft portion 102a located within the storage portion 101b. Furthermore, each blade portion 102b protrudes in various radial directions from the outer circumferential surface of the shaft portion 102a.

[0020] The granulation apparatus 100 further includes a heater 103. The heater 103 is attached to the outside of the wall 101a of the treatment tank 101. The heater 103 is configured to be able to increase the temperature inside the storage section 101b through the wall 101a when current is applied to the heater 103. In other words, in the granulation apparatus 100, the heater 103 can heat the object to be treated stored in the storage section 101b. Note that the configuration of the heater 103, such as the heating method and installation position, can be determined in various ways depending on the configuration of the treatment tank 101 and the properties of the object to be treated.

[0021] In addition, the granulation apparatus 100 further includes a blower mechanism 104. The blower mechanism 104 includes an air intake section 104a and an exhaust section 104b. The air intake section 104a and the exhaust section 104b are respectively provided on the wall section 101a of the treatment tank 101 and laterally face each other across the storage section 101b. The blower mechanism 104 is configured to supply air into the storage section 101b through the air intake section 104a and exhaust air from the treatment tank 101 through the exhaust section 104b, thereby blowing air into the storage section 101b. Therefore, in the granulation apparatus 100, the blower mechanism 104 can promote a decrease in temperature during cooling of the workpiece. Note that the gas used to blow air by the blower mechanism 104 in the granulation apparatus 100 is not limited to air and may be, for example, an inert gas such as nitrogen.

[0022] With the above-described configuration, the granulating device 100 can effectively agitate the material to be processed within the storage section 101b by rotating the shaft section 102a around the rotation axis C through the interaction of gravity and the force applied from the multiple blade sections 102b. Therefore, the granulating device 100 can combine temperature control by the heater 103 and / or the air blowing mechanism 104 with agitation, and can perform the drying step S1, heating step S2, and granulating step S3 described below.

[0023] The configuration of the granulator 100 is not limited to the above and can be modified in various ways. For example, in the granulator 100, the rotation axis C of the shaft 102a does not necessarily have to extend horizontally, and may be tilted relative to the horizontal plane. However, to effectively obtain the stirring effect due to gravity in the granulator 100, it is necessary that at least the rotation axis C of the shaft 102a be tilted relative to the vertical direction, and it is preferable that the angle of the rotation axis C of the shaft 102a with respect to the horizontal plane is small. Specifically, in the granulator 100, it is preferable that the angle of the rotation axis C of the shaft 102a with respect to the horizontal plane is 30° or less.

[0024] [Method for separating water-absorbent resin] 3, the method for separating a water-absorbent resin according to this embodiment includes a drying step S1, a heating step S2, a granulation step S3, and a separation step S4. In this embodiment, an example will be described in which the granulation device 100 is used in the drying step S1, the heating step S2, and the granulation step S3. In this example, first, the object to be treated, including absorbent articles, is placed in the storage section 101b of the treatment tank 101, and the drying step S1 is performed.

[0025] (Drying step S1) In the drying step S1, the material to be treated is agitated and dried. As a result, the moisture contained in the material to be treated evaporates, making the material lighter, and the material to be treated is crushed by agitation. In this embodiment, the temperature inside the storage section 101b is adjusted by the heater 103 of the granulation device 100, and the agitation shaft 102 is rotated to agitate the material to be treated contained in the storage section 101b of the treatment tank 101.

[0026] The drying temperature in this step is not particularly limited, but can be 40°C or higher and lower than the softening point of the thermoplastic resin described below. The drying temperature may be maintained substantially constant, but is preferably set to increase continuously or stepwise from the viewpoint of smoothly transitioning to the heating step S2. When increasing the temperature, the rate of temperature increase is preferably 0.001°C / min or higher and 20°C / min or lower.

[0027] If drying is performed without stirring, when the moisture held in the water-absorbent resin seeps out, the water-absorbent resin and other highly hydrophilic materials such as pulp and core wrap sheets are likely to bond via the moisture. If drying is performed in this state, the water-absorbent resin and other materials will adhere to each other and form lumps, making it difficult to separate the water-absorbent resin. In contrast, in the present embodiment, drying is performed while stirring, so that the amount of moisture in the water-absorbent resin can be reduced while promoting separation of the water-absorbent resin and other materials.

[0028] Furthermore, as described above, in absorbent articles, the water-absorbent resin is often integrated with pulp or sheet material. Therefore, in this step, it is preferable to crush the absorbent article to expose the water-absorbent resin. This makes it possible to more efficiently reduce the moisture content of the water-absorbent resin and further promote separation of the water-absorbent resin from other materials.

[0029] (Heating step S2) Next, in heating step S2, the workpiece is heated to a temperature equal to or higher than the softening point of the thermoplastic resin and lower than the thermal decomposition temperature of the water-absorbent resin. This softens the thermoplastic resin and makes it more deformable, while the water-absorbent resin maintains its molecular structure without thermal decomposition. This allows the physical properties of the thermoplastic resin to be significantly changed relative to the water-absorbent resin. In this embodiment, the temperature of the workpiece is adjusted by, for example, heater 103. Also in this step, it is preferable to stir the workpiece by, for example, rotating stirring shaft 102. This allows the workpiece to be heated uniformly and makes it easier to crush.

[0030] In this embodiment, the term "softening point" refers to the temperature at which the thermoplastic resin contained in the workpiece begins to rapidly soften. When the workpiece contains multiple thermoplastic resins, the softening point of any of the thermoplastic resins can be selected as the "softening point of the thermoplastic resin." Preferably, the softening point of the thermoplastic resin with the highest softening point contained in the workpiece can be selected. When the thermoplastic resin contained in the workpiece can be identified, the softening point can be determined by measuring the Vicat softening temperature of the resin removed from the workpiece. When the thermoplastic resin contained in the workpiece cannot be identified, the softening point of the thermoplastic resin can be determined by measuring the Vicat softening temperature of the resin removed from the workpiece. For example, the softening point of polypropylene is 160 to 200°C, and the softening point of polyethylene terephthalate is 200 to 250°C.

[0031] In the present embodiment, the "thermal decomposition temperature" of a water-absorbent resin is a temperature at which molecular chains are cut by heat to lower the molecular weight. The thermal decomposition temperature is defined as a temperature at which the weight of a sample of the water-absorbent resin decreases by 5% when the sample is heated at a predetermined temperature increase rate (5 to 10°C / min) in an air atmosphere using a thermogravimetric differential thermal analyzer (TG-DTA). For example, in the present embodiment, the thermal decomposition temperature of the water-absorbent resin may be 450 to 500°C. A water-absorbent resin having a crosslinked structure and no softening point may undergo a large change in physical properties at the thermal decomposition temperature.

[0032] The heating temperature in this step may be maintained substantially constant or may vary within a range of not less than the softening point of the thermoplastic resin and not more than the thermal decomposition temperature of the water-absorbent resin. Specifically, the maximum temperature in this step is preferably not less than 150°C, more preferably not less than 200°C, and preferably not more than 450°C, more preferably not more than 350°C. The time period for maintaining the maximum temperature in this step is preferably not less than 60 minutes, more preferably not less than 120 minutes, and preferably not more than 480 minutes, more preferably not more than 300 minutes.

[0033] In this step, a portion of the material to be treated may be carbonized by performing the step under temperature conditions that promote carbonization of the material to be treated. In particular, if the material to be treated contains easily carbonized components such as cellulose, carbonized material is likely to be produced in this step. By carbonizing a portion of the material to be treated, highly brittle carbonized material is produced, which makes it easier to form fine granules in the subsequent granulation step S3.

[0034] (Granulation step S3) The heating step S2 is followed by the granulation step S3. In the granulation step S3, the material is agitated and cooled below the softening point of the thermoplastic resin to obtain granules. This step promotes homogenization, density, and weight reduction of the material, and also allows for the production of granules that are separated from one another. In the granulation step S3 of this embodiment, for example, heating of the material by the heater 103 is stopped, while the material is agitated by the agitation shaft 102. Furthermore, in the granulation step S3 of this embodiment, it is preferable to use the air blowing mechanism 104 to blow air. This allows the temperature of the heated material in the storage section 101b to be quickly lowered. However, the use of the air blowing mechanism 104 in this step is not essential.

[0035] During the cooling process of the thermoplastic resin softened by heat, hardening due to the drop in temperature and an increase in viscosity due to thixotropy proceed simultaneously. In the granulation step S3 of this embodiment, stirring is performed as the resin cools, thereby maintaining the viscosity of the thermoplastic resin at a low level due to its thixotropy while allowing the hardening of the thermoplastic resin to proceed. This allows the thermoplastic resin to be finely crushed to form small-sized granules without forming large, clumped granules. Furthermore, if highly brittle carbides are generated in the heating step S2, the stirring in this step can also finely crush the carbides to form small-sized granules.

[0036] On the other hand, a water-absorbent resin that has not been thermally decomposed is less likely to be crushed than a thermoplastic resin or a carbonized material. By being stirred while being cooled in this step, the water-absorbent resin is prevented from bonding with other granules to form a mass. Therefore, by this step, the water-absorbent resin can form granules that are larger in size than the other granules.

[0037] In this way, in this step, granules of different particle sizes are formed. The granules of larger particle sizes contain a large amount of water-absorbent resin, while the granules of smaller particle sizes are mainly composed of thermoplastic resin, carbide, etc. These granules are dry and have a form that makes them easy to separate from each other. Therefore, by separating these granules by particle size, it becomes possible to easily separate the granules containing a large amount of water-absorbent resin.

[0038] (Separation step S4) Subsequently, in a separation step S4, the water-absorbent resin is separated based on the particle size of the granules. The separation of the water-absorbent resin in this embodiment is not limited to a mode in which granules composed only of the water-absorbent resin are separated, but also includes a mode in which a part of the granules is separated so that the content of the water-absorbent resin in the first granules after separation is higher than that in the homogeneously mixed granules before separation.

[0039] In this embodiment, for example, the granular material is removed from the storage section 101b of the granulation device 100, and the granular material is separated by particle size using tools or devices such as a sieve or a classifier. The separation method may be either dry or wet, but a dry method is preferred because dry granular material is handled. In this step, it is preferable to use a vibrating sieve machine from the viewpoint of automatically separating the water-absorbent resin with a relatively simple device configuration. In addition, in this step, it is sufficient to separate the granular material into at least two particle sizes, but it may also be separated into three or more particle sizes.

[0040] In this embodiment, for example, it is possible to separate first granules having a first particle size from second granules having a second particle size smaller than the first particle size. The first granules are configured as water-absorbent-polymer-containing granules containing a water-absorbent polymer. The second granules are configured as low-absorbent-polymer granules having a lower water-absorbent polymer content than the first granules and mainly containing components other than the water-absorbent polymer. The water-absorbent polymer content in the first granules is preferably 31% by mass or more, more preferably 50% by mass or more. The second granules contain, for example, one or more components selected from thermoplastic resins, carbides, etc. The water-absorbent polymer content in the second granules is preferably 30% by mass or less, more preferably 25% by mass or less.

[0041] In this embodiment, for example, it is preferable that the particle size distribution of the granular material after the granulation step S3 has a first peak corresponding to the first particle size and a second peak corresponding to the second particle size. The peak in the particle size distribution refers to a peak that forms an upward convex mountain-like portion when a particle size distribution graph is created with particle size on the horizontal axis and frequency (%) on the vertical axis. Among the multiple particle size distributions, two particle sizes are selected in descending order of peak height, with the larger particle size designated as the first particle size and the other designated as the second particle size. Furthermore, "the first particle size corresponds to the first peak" means that the first particle size is set to include a particle size corresponding to the first peak. "The second particle size corresponds to the second peak" means that the second particle size is set to include a particle size corresponding to the second peak. Having a particle size distribution with two or more peaks in this manner allows the first granular material, which contains a large amount of water-absorbent resin, to be more reliably separated from the second granular material.

[0042] The lower limit of the particle size of the first particle size may be set based on a particle size distribution graph. Specifically, the lower limit of the particle size of the first particle size is preferably set between the particle size corresponding to the first peak and the particle size corresponding to the second peak, and more preferably set to a particle size corresponding to a downwardly convex portion of the particle size distribution graph located between the first peak and the second peak. The particle size distribution of the granular material can be confirmed by a known particle size distribution measurement method.

[0043] Specifically, the lower limit of the particle size of the first particle size is preferably 106 μm or more, more preferably 150 μm or more, and preferably 600 μm or less, more preferably 300 μm or less. For example, when a sieve is used in this step, the sieve opening is preferably 106 μm or more, more preferably 150 μm or more, and preferably 600 μm or less, more preferably 300 μm or less. When a sieve is used, the granules obtained in the granulation step S3 are passed through a sieve with the above openings, and the granules remaining on the sieve can be called the first granules, and the granules that passed through the sieve can be called the second granules.

[0044] [Method for manufacturing granular material] In this embodiment, the first granules and / or the second granules can be produced using the above-described method for separating a water-absorbent resin. 4, the method for producing the first granules (water-absorbent resin-containing granules) includes the drying step S1, heating step S2, and granulation step S3 described above, as well as a recovery step S41 of the first granules. In the recovery step S41, the first granules and the second granules are separated based on the particle size of the granules, and the first granules are recovered as water-absorbent resin-containing granules. In other words, the first granules can be obtained by recovering the first granules separated in the separation step S4 described above.

[0045] 5, the method for producing the second granules (granules) includes the drying step S1, heating step S2, and granulation step S3 described above, as well as a recovery step S42 of the second granules. In the recovery step S42, the first granules and the second granules are separated based on the particle size of the granules, and the second granules are recovered. That is, by recovering the second granules separated in the separation step S4 described above, the second granules can be obtained as granules with a low water-absorbent resin content.

[0046] [Effects of this embodiment] According to this embodiment, by subjecting the object to be treated, including the absorbent article, to the drying step S1, heating step S2, and granulation step S3 described above, the object to be treated can be treated as lightweight, finely separated granules. Furthermore, by setting the temperature in the heating step S2 to a value equal to or higher than the softening point of the thermoplastic resin and lower than the thermal decomposition temperature of the water-absorbent resin, the water-absorbent resin becomes less likely to be crushed into small pieces in the granulation step S3, and first granules with a large particle size can be formed. As a result, in the separation step S4, the water-absorbent resin can be efficiently separated based on the difference in particle size.

[0047] By recovering the first granules containing a large amount of water-absorbent resin from the material to be treated, the first granules can be used as a material containing water-absorbent resin. This allows the water-absorbent resin to be reused, resulting in effective use of resources. In addition, it is possible to reduce greenhouse gas emissions associated with the production of new water-absorbent resin.

[0048] On the other hand, the recovered second granules can be reused, for example, as fuel or fertilizer. Furthermore, when the second granules contain carbonized material, they can be effectively used, for example, as water purification treatment agents, building materials such as insulation, adsorbents, detoxifiers, deodorizers, raw materials for disposable hand warmers, activated carbon, etc. In addition to having high homogeneity, the second granules can suppress swelling and moisture absorption caused by water-absorbent resins, making them a recyclable material that is easy to handle.

[0049] Furthermore, in this embodiment, granules from which the water-absorbent resin can be separated are formed by a dry process. As a result, in this embodiment, the volume required to accommodate the material to be treated can be reduced compared to a wet process, and the size of the equipment can be suppressed. Furthermore, the dry process can prevent water pollution due to wastewater, etc. Furthermore, in this embodiment, since the material is densified by granulation, the volume required for storage after treatment is significantly reduced, and the mass is reduced by evaporation of water during the drying step S1 and heating step S2. As a result, the granules of the material to be treated obtained in this embodiment are easy to store and transport, making them a recycled material with excellent handleability.

[0050] [Additional Description of This Embodiment] When the granulation device 100 accommodates the workpiece in the drying step S1, it is preferable to accommodate a relatively large amount of workpiece in the storage section 101b. Specifically, the amount of workpiece accommodated in the storage section 101b at the start of the drying step S1 is preferably set so that the volume of the granular material in the storage section 101b at the end of the granulation step S3 exceeds the shaft portion 102a. The volume of the granular material in the storage section 101b is obtained, for example, as shown in FIGS. 1 and 2, as the vertical height L of the surface of the granular material smoothed along a horizontal plane in the storage section 101b. In this way, by determining the amount of workpiece accommodated in the storage section 101b at the start of the drying step S1 based on the state at the end of the granulation step S3, when the volume of the workpiece is at its lowest due to the progress of crushing, the shaft portion 102a is maintained submerged in the workpiece during agitation throughout the entire process of the drying step S1, the heating step S2, and the granulation step S3. This allows the workpiece to be efficiently agitated in the granulation step S3. From the perspective of efficiently agitating the workpiece, it is preferable that the volume of the granular material of the workpiece exceeds the entire shaft portion 102a in the storage unit 101b at the end of the granulation step S3, i.e., the shaft portion 102a is completely buried in the granular material of the workpiece. However, in cases such as those described above where the shaft portion 102a is tilted relative to the horizontal plane, the effect of efficiently agitating the workpiece can be achieved as long as the volume of the granular material of the workpiece exceeds at least a portion of the shaft portion 102a in the storage unit 101b at the end of the granulation step S3.

[0051] The object to be processed in this embodiment is not limited to waste including used absorbent articles, and may also include bulking materials. This ensures a sufficient amount of object to be processed in the storage section 101b. The bulking materials can be selected arbitrarily. For example, objects made of a hard, heat-resistant material such as ceramics that do not change during the drying, heating, and granulation processes (e.g., ceramic balls such as alumina balls, zirconia balls, silicon nitride balls, and silicon carbide balls) can be used as the bulking materials. By leaving such objects in the storage section 101b after the granulation step S3, they can be repeatedly used as bulking materials. In addition, any object other than absorbent articles (e.g., food waste, agricultural waste, etc.) can be used as the bulking materials. Furthermore, when carbonizing the object to be treated in the heating step S2, the carbonization of the object to be treated can be promoted by using, as a secondary material, an object whose main component is cellulose, which is easily carbonized (e.g., wood pellets, paper scraps, selected branches, etc.), or an already carbonized material (e.g., carbonized fuel pellets, activated carbon, etc.).

[0052] Furthermore, the granules of the material obtained in the granulation step S3 of the preceding granulation process can be used as a secondary material in the subsequent granulation process. In particular, when performing multiple granulation processes consecutively, by leaving at least a portion of the granules of the material in the storage section 101b after the previous granulation process in the granulation step S3 and adding new material in the drying step S1, the granules of the material obtained in the previous granulation process can be used as a secondary material. This allows for the amount of material to be kept constant in the storage section 101b, even if there is variation in the amount of material newly added in the drying step S1, by recovering the granules of the material from the storage section 101b in an amount calculated backward from the amount of waste to be newly added. This allows for stable repeated granulation processes.

[0053] Furthermore, when a portion of the workpiece is carbonized in the heating step S2, it is preferable to fix as much of the carbon constituting the carbon-resistant thermoplastic resin as part of the charcoal. This reduces the amount of carbon dioxide emitted from the carbon constituting the thermoplastic resin. From this perspective, it is preferable to add at least one of phosphoric acid and a phosphate as a catalyst to the workpiece in the storage section 101b. Phosphoric acid and a phosphate have the effect of promoting the desorption of hydrogen, water, and other elements from the thermoplastic resin. Therefore, using phosphoric acid or a phosphate as a catalyst promotes the desorption of hydrogen, water, and other elements from the thermoplastic resin contained in the waste during the heating step S2, making it easier for the thermoplastic resin to be fixed integrally as elemental carbon on the surface of the charcoal. The phosphate added to the workpiece as a catalyst can be, for example, at least one of ammonium phosphate, potassium phosphate, and sodium phosphate. Examples of ammonium phosphate include ammonium dihydrogen phosphate, diammonium hydrogen phosphate, and triammonium phosphate. Examples of potassium phosphate include potassium dihydrogen phosphate, dipotassium hydrogen phosphate, and tripotassium phosphate. Examples of sodium phosphate include sodium dihydrogen phosphate, disodium hydrogen phosphate, and trisodium phosphate. Phosphoric acid and phosphate salts condense upon heating to form polyphosphoric acid and polyphosphate salts, which soften in the heating step S2 and have the property of bonding fragments together during the cooling process, similar to thermoplastic resins. However, by stirring in the granulation step S3 according to this embodiment, the material to be treated remains in a granular state composed of separated fragments.

[0054] Furthermore, when the object to be treated contains two or more thermoplastic resins with different softening points, as described above, the heating temperature in the heating step S2 can be set based on the softening point of any of the thermoplastic resins. Therefore, the object to be treated may contain a thermoplastic resin (e.g., polyethylene terephthalate) with a softening point higher than the maximum temperature of the heating step S2. Such a thermoplastic resin that does not reach its softening point in the heating step S2 may not form granules but may form fibrous or string-like objects after the granulation step S3. This fibrous or string-like thermoplastic resin can be removed based on the difference in shape from the granules and can be easily separated from the granules. In other words, in this embodiment, even when the object to be treated contains a thermoplastic resin with a high softening point, separation of the water-absorbent resin based on particle size is possible in the separation step S4.

[0055] Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and it goes without saying that various modifications can be made within the scope of the gist of the present invention. [Example]

[0056] [Examples and Comparative Examples] Examples and comparative examples of the method for separating a water-absorbent resin according to this embodiment will be described. In each example and comparative example, a sample of the material to be treated was prepared, simulating an actual used absorbent article. Specifically, the sample of the material to be treated in each of Examples 1 to 4 and Comparative Examples 1 to 5 was prepared by allowing 15 kg of unused disposable diapers (Merrys Pants, size L, manufactured by Kao Corporation) to absorb 7.5 kg of tap water. In addition, 0.6 kg of ammonium dihydrogen phosphate was added to the sample to reproduce the nutritional components contained in urine and promote carbonization.

[0057] The treatment samples of Examples 1 to 4 were subjected to all of the above-mentioned steps including the drying step S1, the heating step S2, the granulation step S3, and the separation step S4. On the other hand, as shown in Table 1, at least one of the drying step S1, heating step S2, granulation step S3, and separation step S4 was not performed on the treatment samples of Comparative Examples 1 to 5. Specifically, none of the steps were performed in Comparative Example 1. In Comparative Example 2, the drying step S1 and heating step S2 were performed, but stirring was not performed in the granulation step S3, and the separation step S4, as described below, was also not performed. In Comparative Example 3, the drying step S1, heating step S2, and granulation step S3 were performed, but the separation step S4 was not performed. In Comparative Examples 4 and 5, none of the steps were performed, and instead a wet separation process, as described below, was performed.

[0058] In Examples 1 to 4 and Comparative Examples 2 and 3, the drying step S1 and the heating step S2 were carried out consecutively. In these steps, the temperature was raised from 20°C to 200°C at a rate of 0.5°C / min and maintained at 200°C for 180 minutes. The material to be treated was continuously stirred during these steps. In the granulation step S3 in Examples 1 to 4 and Comparative Examples 2 and 3, the temperature was lowered from 200°C to 30°C at a rate of 0.2°C / min while blowing air. Of these, in Examples 1 to 4 and Comparative Example 3, the material to be treated was stirred during cooling. On the other hand, in Comparative Example 2, the material to be treated was not stirred during cooling.

[0059] In Comparative Examples 4 and 5, one diaper was taken from the treated material sample and cut into 5 cm pieces. The cut diaper was placed in a 5% CaCl aqueous solution and stirred. After standing, the mixture was separated into floating matter and sediment. The floating matter and sediment were each placed in a 250-mesh nylon mesh bag and dehydrated in a stretch dehydrator to obtain samples. The floating matter sample was designated Comparative Example 4, and the sediment sample was designated Comparative Example 5.

[0060] [Table 1]

[0061] [Separation processing] The granular samples after the granulation step S3 in Examples 1 to 4 were subjected to a separation process (separation step S4) using a sieve. In Examples 1 and 3, the separation process was performed using a sieve with 150 μm openings. In Examples 2 and 4, the separation process was performed using a sieve with 300 μm openings. In Examples 1 and 2, the granular material (residue) remaining on the sieve was collected. In Examples 3 and 4, the granular material that passed through the sieve was collected.

[0062] On the other hand, the sample of Comparative Example 1 maintained the shape of the diaper itself, and the water-absorbent resin could not be separated. Furthermore, the sample of Comparative Example 2 was not stirred during cooling in the granulation step S3, so the treated material was in a lumpy state and separation by sieving was not possible. In Comparative Example 3, as described above, separation by sieving was not performed, and all the granules were collected.

[0063] [Measurement of calorific value] The calorific value of the recovered samples of each Example and Comparative Example was measured. The results are shown in Table 1. The calorific value is affected by the moisture content of the sample. In addition, the calorific value tends to decrease when the water-absorbent resin content is high, and increase when the water-absorbent resin content is low, so the calorific value is also affected by the content of the water-absorbent resin in the sample. The calorific value was measured as the total calorific value based on JIS Z 7302-2.

[0064] As shown in Table 1, the calorific values of the samples of Examples 1 and 2, which are granular materials with large particle sizes, were smaller than that of the sample of Comparative Example 3, which contained all granular materials. From this result, it is considered that the samples of Examples 1 and 2 contained more water-absorbent resin than the sample of Comparative Example 3. Note that the granulated sample of Comparative Example 3 and the dried sample of Comparative Example 2 had a lower moisture content than Comparative Example 1, which is the diaper itself containing absorbed water-absorbent resin, and therefore had a higher calorific value.

[0065] Furthermore, as shown in Table 1, the calorific values of the samples of Examples 3 and 4, which are granular bodies with small particle sizes, were higher than those of the samples of Comparative Example 3, Examples 1 and 2. This is thought to be because the samples of Examples 3 and 4 had a lower content of water-absorbent resin compared to the samples of Comparative Example 3, Examples 1 and 2. Furthermore, the results in Table 1 show that the samples of Examples 3 and 4 had a higher calorific value compared to the samples of Examples 1 and 2 and Comparative Examples 1 to 4, and were therefore suitable as fuel.

[0066] Furthermore, the calorific values of the wet-separated samples of Comparative Examples 4 and 5 were smaller than those of the samples of Comparative Examples 1 to 3 and Examples 1 to 4. This is thought to be because the samples of Comparative Examples 4 and 5 have a higher moisture content than those of Comparative Examples 1 to 3 and Examples 1 to 4. The calorific value of the sample of Comparative Example 4 was higher than that of the sample of Comparative Example 5. This is thought to be because the sample of Comparative Example 4 has a lower content of water-absorbent resin than the sample of Comparative Example 5.

[0067] [Calculation of water-absorbent resin content] Furthermore, the content of the water-absorbent resin in each of the collected samples of Examples and Comparative Examples was calculated. The results are shown in Table 1. The water-absorbent resin content was calculated as follows: First, all sodium in the sample was assumed to be derived from the water-absorbent resin, and the water-absorbent resin content was calculated from the sodium ratio. The sodium ratio was measured using IPC optical emission spectrometry based on "Refuse-derived fuel - Part 5: Test method for metal content (JIS Z 7302-5:2002)".

[0068] As shown in Table 1, the samples recovered in Examples 1 and 2 had a water-absorbent resin content of 50 mass% or more, which was higher than the content of the samples in Comparative Examples 2 and 3, which were not subjected to separation step S4. On the other hand, the samples recovered in Examples 3 and 4 had a water-absorbent resin content of less than 30%, which was lower than the content of the other samples. From these results, it was found that by performing separation step S4 using sieves with openings of 150 μm and 300 μm after performing drying step S1, heating step S2, and granulation step S3, granules with a high water-absorbent resin content and granules with a low water-absorbent resin content can be separated. [Explanation of symbols]

[0069] 100...granulation device 101... Treatment tank 101b...container 102...Agitator shaft 102a...Shaft part 102b...wing part 103...Heater 104...Ventilation mechanism C...Rotation axis

Claims

1. A method for separating a water-absorbent resin from a processing object including an absorbent article having a water-absorbent resin and a thermoplastic resin, comprising: A drying step of stirring and drying the object to be treated; A heating step of heating the object to be treated at a temperature equal to or higher than the softening point of the thermoplastic resin and lower than the thermal decomposition temperature of the water-absorbing resin; a granulation step of stirring the material to be treated after the heating step and cooling the material to a temperature lower than the softening point of the thermoplastic resin to obtain granules; and a separation step of separating the water absorbent resin based on the particle size of the granular material. A method for separating water-absorbent resin.

2. In the separation step, a first granular body containing the water absorbent resin and having a first particle size is separated from a second granular body having a second particle size smaller than the first particle size and a lower content of the water absorbent resin than the first granular body. A method for separating the water-absorbent resin according to claim 1.

3. The particle size distribution of the granular material has a first peak corresponding to the first particle size and a second peak corresponding to the second particle size. The method for separating the water-absorbent resin according to claim 2.

4. In the drying step, the absorbent article is crushed to expose the water-absorbent resin. A method for separating the water-absorbent resin according to claim 1 or 2.

5. In the heating step, a part of the object to be treated is carbonized. A method for separating the water-absorbent resin according to claim 1 or 2.

6. The material to be treated includes cellulose. A method for separating the water-absorbent resin according to claim 1 or 2.

7. The separation step uses a vibrating sieve. A method for separating the water-absorbent resin according to claim 1 or 2.

8. In the separation step, the water-absorbent resin is separated using a sieve having an opening of 106 μm or more. A method for separating the water-absorbent resin according to claim 1 or 2.

9. A method for producing a water-absorbent resin-containing granular material containing a water-absorbent resin from a processing object including an absorbent article having a water-absorbent resin and a thermoplastic resin, comprising: A drying step of stirring and drying the object to be treated; A heating step of heating the object to be treated at a temperature equal to or higher than the softening point of the thermoplastic resin and lower than the thermal decomposition temperature of the water-absorbing resin; a granulation step of stirring the material to be treated after the heating step and cooling the material to a temperature lower than the softening point of the thermoplastic resin to obtain granules; and a recovery step of separating a first granular body from a second granular body having a smaller particle size than the first granular body based on the particle size of the granular body, and recovering the first granular body as a water-absorbent resin-containing granular body. A method for producing water-absorbent resin-containing granules.

10. A method for producing a granular material from a processing target including an absorbent article having a water-absorbent resin and a thermoplastic resin and absorbing water, comprising: A drying step of stirring and drying the object to be treated; A heating step of maintaining the temperature of the object to be treated at a temperature equal to or higher than the softening point of the thermoplastic resin and lower than the thermal decomposition temperature of the water-absorbing resin; a granulation step of stirring the material to be treated after the heating step and cooling the material to a temperature lower than the softening point of the thermoplastic resin to obtain granules; and a recovery step of separating a first granular body from a second granular body having a lower particle size than the first granular body based on the particle size of the granular body, and recovering the second granular body. A method for producing granular material.

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