JP7446369B2 - Method for regenerating superabsorbent polymer, method for producing superabsorbent recycled polymer, and use of alkali metal ion source - Google Patents

Description

The present disclosure provides a method for regenerating acid-inactivated superabsorbent polymers into superabsorbent recycled polymers having predetermined water absorption properties from used sanitary products, including pulp fibers and superabsorbent polymers. , a method for producing a super absorbent recycled polymer having a predetermined water absorbency, and a method for producing a super absorbent recycled polymer having a predetermined water absorbency; Relating to use for regeneration into recycled polymers.

A method for recovering superabsorbent polymers from used sanitary products is known.
For example, Patent Document 1 discloses a method for regenerating a water-absorbent resin, in which a water-absorbent resin that has absorbed a liquid to be absorbed is extracted from a used body fluid-absorbent article and subjected to cleaning and dehydration treatment. However, a method for regenerating a water-absorbing resin is described, which includes an operation of placing the water-absorbing resin in an environment where the absorbed liquid absorbed by the water-absorbing resin is discharged.

Further, in paragraph [0037] of Patent Document 1, it is stated that the water absorbent resin after undergoing the regeneration treatment as exemplified above is the regenerated water absorbent resin of the present invention (hereinafter referred to as the regenerated water absorbent resin of the present invention). Although it may be used as it is for applications such as absorbent articles, it is described that it is preferable to add a basic compound again to adjust the pH if necessary.

Japanese Patent Application Publication No. 2003-326161

When recycling used sanitary products, for example, when recycling disposable diapers, light incontinence pads, sanitary napkins, panty liners, etc., the superabsorbent polymer to be recycled must have relatively high water absorption. Super absorbent polymers (e.g. those found in disposable diapers) and super absorbent polymers with relatively low water absorption but excellent gel strength when wet (e.g. light incontinence pads, sanitary napkins, panty liners, etc.) Therefore, the recycled superabsorbent polymer contains superabsorbent polymers with relatively high water absorption and superabsorbent polymers with relatively low water absorption. tend to be included.

Furthermore, even if the sanitary products to be recycled are limited to, for example, disposable diapers, disposable diapers from different manufacturers generally contain superabsorbent polymers with different water absorption properties, so In principle, water-absorbing polymers and regenerated super-absorbent polymers tend to contain super-absorbent polymers with different water-absorbing properties.

Therefore, superabsorbent polymers recycled from used sanitary products are generally used for applications with a wide tolerance for water absorption (for example, soil conditioners).
When reusing superabsorbent polymers recycled from used sanitary products for purposes with narrow tolerances for water absorption, such as sanitary products, it is important to It is thought that it is necessary to mix the superabsorbent polymer in a virgin superabsorbent polymer at a low ratio (for example, 10 to 30% by mass of the superabsorbent polymer contained in sanitary products). Currently, there is generally no project to reuse superabsorbent polymers recycled from used sanitary products into sanitary products.

In the regeneration method described in Patent Document 1, the regeneration of the absorbent resin is completed by implementing the "regeneration method" including predetermined "washing" and "dehydration treatment", and the regeneration method described in Patent Document 1 is described in paragraph [0037 The basic compound described in ] is used to adjust the pH of the absorbent resin, which becomes acidic due to the acidic compound added in the "dehydration treatment" to shrink the gel, specifically to neutralize it. It is only added to the water, and is not used to adjust the water absorption of the recycled absorbent resin.
Therefore, since the absorbent resin regenerated by the regeneration method described in Patent Document 1 has not had its water absorbency adjusted, in order to reuse it for sanitary products, it is necessary to take care not to impede the water absorbency of the sanitary products. It is necessary to use it by mixing it in a low proportion, for example, 10 to 30% by mass.

As described above, an object of the present disclosure is to provide a method for regenerating a superabsorbent polymer inactivated by an acid, which can form a superabsorbent recycled polymer having a predetermined water absorption property.

The present disclosure discloses a method for regenerating a superabsorbent polymer inactivated by an acid into a superabsorbent recycled polymer having a predetermined water absorption property, the method comprising: A preparation step for preparing a superabsorbent polymer that has been inactivated by the acid, adding an alkali metal ion source capable of supplying alkali metal ions to the regeneration aqueous solution containing the superabsorbent polymer that has been inactivated by the acid; A super absorbent recycled polymer forming step of forming the super absorbent recycled polymer in a wet state from the super absorbent polymer obtained by drying the super absorbent recycled polymer in a wet state, and drying the super absorbent recycled polymer in a wet state to have the predetermined water absorbency. A method has been discovered that includes a drying step to form a superabsorbent recycled polymer.

The method of regenerating an acid-inactivated superabsorbent polymer of the present disclosure can form a superabsorbent recycled polymer having a predetermined water absorption property.

FIG. 1 is a block diagram of a system 1 for implementing the manufacturing method, reclamation method, and use according to one embodiment of the present disclosure. FIG. 2 is a schematic diagram showing a configuration example of the bag breaking device 11 and the crushing device 12 in FIG. 1. FIG. 3 is a flowchart illustrating a method for producing recycled pulp fibers and superabsorbent recycled polymers from used sanitary products using System 1. FIG. 4 is a diagram showing the results of the example. FIG. 5 is a diagram showing the results of the example. FIG. 6 is a diagram showing the results of the example.

<Definition>
・"Absorption rate"
In this specification, "absorption capacity" is measured as follows.
(1) Wet superabsorbent polymer or superabsorbent recycled polymer is placed in a mesh and hung for 5 minutes to remove moisture attached to its surface and measure its mass before drying: m ₁ (g) do.
(2) The superabsorbent polymer or superabsorbent recycled polymer from which water adhering to the surface has been removed is dried at 50° C. for 180 minutes, and the mass: m ₂ (g) after drying is measured.
(3) Absorption capacity (g/g) is calculated using the following formula:
Absorption capacity (g/g) = m ₁ /m ₂
Calculated by

・“Inactivation” regarding super absorbent polymers
In this specification, "inactivation" regarding super absorbent polymer (SAP) means that the super absorbent polymer holding excrement etc. is preferably 50 times or less, more preferably 30 times or less, More preferably, it means adjusting to have an absorption capacity of 25 times or less, for example, releasing retained excreta, suppressing absorption of acid-containing aqueous solutions, etc.

Specifically, the present disclosure relates to the following aspects.
[Aspect 1]
A method for regenerating a super absorbent polymer inactivated by acid into a super absorbent recycled polymer having a predetermined water absorbency, the method comprising:
a preparatory step of preparing a superabsorbent polymer having acid groups and inactivated by acid;
An alkali metal ion source capable of supplying alkali metal ions is added to the regeneration aqueous solution containing the superabsorbent polymer inactivated by the acid, and the superabsorbent polymer inactivated by the acid is used in a wet state. a super absorbent recycled polymer forming step for forming the super absorbent recycled polymer;
a drying step of drying the super absorbent recycled polymer in a wet state to form a super absorbent recycled polymer having the predetermined water absorbency;
The above methods, including:

Since the above recycling method includes a predetermined step of forming a superabsorbent recycled polymer and a drying step, the recycled superabsorbent recycled polymer can be used in various applications that require different water absorption properties and narrow water absorption tolerances. Can be used. Moreover, the regenerated super absorbent recycled polymer can be used in a high proportion for various purposes.

[Aspect 2]
The method according to aspect 1, wherein the predetermined water absorption is an arbitrary value of absorption capacity of 100 to 400 times (g/g) relative to deionized water.
In the above regeneration method, since the predetermined water absorbency is an arbitrary value of the predetermined absorption capacity, the superabsorbent recycled polymer is used for applications where superabsorbent polymers with low water absorption are preferred (for example, light incontinence pads, sanitary It can be used in any of the following applications (for example, disposable diapers, etc.) to applications in which superabsorbent polymers with high water absorption are preferred (for example, disposable diapers, etc.).

[Aspect 3]
Embodiment 1 or 2, wherein the alkali metal ion source is an alkali metal hydroxide or a salt of an alkali metal hydroxide and an acid having a larger acid dissociation constant than the acid group of the superabsorbent polymer. The method described in.
In the above-mentioned regeneration method, since the alkali metal ion supply source is a predetermined compound, the water absorbency of the super absorbent recycled polymer to be regenerated can be easily adjusted.

[Aspect 4]
The method according to any one of aspects 1 to 3, wherein the alkali metal ions are selected from the group consisting of lithium ions, sodium ions and potassium ions, and any combinations thereof.
In the above regeneration method, the super absorbent recycled polymer has excellent water absorbency because it is selected from a predetermined group.

[Aspect 5]
The method according to any one of aspects 1 to 4, wherein the predetermined water absorption is adjusted by controlling the pH of the regeneration aqueous solution.
In the above regeneration method, the predetermined water absorption is adjusted by controlling the pH of the regeneration aqueous solution, so even if the amount of superabsorbent polymer to be regenerated is unknown, the superabsorbent recycled polymer Water absorption can be easily adjusted.

[Aspect 6]
The method according to aspect 5, wherein the pH of the regeneration aqueous solution is adjusted to 5.0 to 9.0 (25° C.).

In the above regeneration method, in order to adjust the pH of the regeneration aqueous solution to a predetermined range, the super-absorbent recycled polymer is changed from an application in which a super-absorbent polymer with low water absorption is preferred to an application in which a super-absorbent polymer with high water absorption is preferred. The water absorbency of super absorbent recycled polymers can be easily adjusted up to

[Aspect 7]
A method for producing a superabsorbent recycled polymer having a predetermined water absorption property from used sanitary products comprising pulp fibers and a superabsorbent polymer, the method comprising:
The sanitary product component material that constitutes the sanitary product, which includes the pulp fiber and a superabsorbent polymer having an acid group, is immersed in an acid-containing aqueous solution containing an acid, and the superabsorbent polymer that has been inactivated by the acid is soaked. an inactivation step to form;
An alkali metal ion source capable of supplying alkali metal ions is added to the regeneration aqueous solution containing the superabsorbent polymer inactivated by the acid, and the superabsorbent polymer inactivated by the acid is used in a wet state. a super absorbent recycled polymer forming step for forming the super absorbent recycled polymer;
a drying step of drying the super absorbent recycled polymer in a wet state to form a super absorbent recycled polymer having the predetermined water absorbency;
The above method, characterized in that it comprises.

Since the above production method includes a predetermined step of forming a super absorbent recycled polymer and a drying step, the produced super absorbent recycled polymer can be used for various applications requiring different water absorbing properties and a narrow water absorbing tolerance. It can be used for. Furthermore, the produced superabsorbent recycled polymer can be used in a high proportion for various purposes.

[Aspect 8]
According to aspect 7, the alkali metal ion supply source is an alkali metal hydroxide or a salt of an alkali metal hydroxide and an acid having a larger acid dissociation constant than the acid group of the superabsorbent polymer. the method of.
In the above manufacturing method, since the alkali metal ion supply source is a predetermined compound, the water absorbency of the super absorbent recycled polymer to be regenerated can be easily adjusted.

[Aspect 9]
The method according to aspect 7 or 8, wherein the predetermined water absorbency is adjusted by controlling the pH of the regeneration aqueous solution.

In the above manufacturing method, the predetermined water absorption is adjusted by controlling the pH of the aqueous solution for regeneration, so even if the amount of superabsorbent polymer to be recycled is unknown, superabsorbent recycled polymer Water absorption can be easily adjusted.

[Aspect 10]
The method according to aspect 9, wherein the pH of the regeneration aqueous solution is adjusted to 5.0 to 9.0 (25° C.).

In the above manufacturing method, in order to adjust the pH of the regeneration aqueous solution to a predetermined range, the super absorbent recycled polymer is changed from an application in which a super absorbent polymer with low water absorption is preferred to an application in which a super absorbent polymer with high water absorption is preferred. The water absorbency of super absorbent recycled polymers can be easily adjusted up to

[Aspect 11]
Embodiment 9 or 10, in the super absorbent recycled polymer forming step, the acid-containing aqueous solution is used as the regeneration aqueous solution, and the pH of the regeneration aqueous solution is adjusted to 5.0 to 7.0 (25°C). The method described in.

In the above manufacturing method, in the step of forming a superabsorbent recycled polymer, an acid-containing aqueous solution is used as a regeneration aqueous solution and the pH of the regeneration aqueous solution is adjusted to a predetermined range, so a superabsorbent polymer with low water absorption is suitable for use. A suitable super absorbent recycled polymer can be easily produced.

[Aspect 12]
The regeneration aqueous solution is a neutral aqueous solution or an alkaline aqueous solution, and in the superabsorbent recycled polymer forming step, the superabsorbent polymer inactivated by the acid is immersed in the regeneration aqueous solution. The method according to aspect 9 or 10, wherein the pH is adjusted to more than 7.0 and less than or equal to 9.0.

In the above production method, the regeneration aqueous solution is a neutral aqueous solution or an alkaline aqueous solution, and in the superabsorbent recycled polymer forming step, the superabsorbent polymer inactivated by the acid is immersed in the regeneration aqueous solution, and the regenerated Since the pH of the aqueous solution is adjusted to a predetermined range, highly water-absorbent recycled polymers suitable for applications where highly water-absorbent polymers are preferred can be easily produced by reducing the amount of alkali metal ion supply source. can do.

[Aspect 13]
Use of an alkali metal ion source capable of supplying alkali metal ions to regenerate a superabsorbent polymer inactivated by acid into a superabsorbent recycled polymer having a predetermined water absorption property, the method comprising:
The alkali metal ion source is added to a regeneration aqueous solution containing a superabsorbent polymer having an acid group and inactivated by the acid, and the superabsorbent polymer inactivated by the acid is extracted from the superabsorbent polymer in a wet state. a super absorbent recycled polymer forming step for forming the super absorbent recycled polymer;
Including the above uses.

Since the use includes a predetermined step of forming a superabsorbent recycled polymer, the superabsorbent recycled polymer formed can be used in a variety of applications requiring different water absorption properties and narrow tolerances. Furthermore, the recycled highly water-absorbent recycled polymer can be used in a high proportion for various purposes.

[Aspect 14]
According to aspect 13, the alkali metal ion source is an alkali metal hydroxide or a salt of an alkali metal hydroxide and an acid having a larger acid dissociation constant than the acid group of the superabsorbent polymer. Use of.
In the above use, since the alkali metal ion supply source is a predetermined compound, the water absorbency of the super absorbent recycled polymer to be regenerated can be easily adjusted.

(1) A method of regenerating a superabsorbent polymer inactivated by acid into a superabsorbent recycled polymer having a predetermined water absorbency (hereinafter referred to as "superabsorbent polymer regeneration method", "this method") (2) A method for producing a super absorbent recycled polymer having a predetermined water absorbency from used sanitary products containing pulp fibers and a super absorbent polymer. (Hereinafter, this may be referred to as “the manufacturing method of a super absorbent recycled polymer”, “the manufacturing method of the present disclosure”, etc.), and (3) an alkali metal ion source capable of supplying alkali metal ions is Use for regenerating an activated superabsorbent polymer into a superabsorbent recycled polymer having a predetermined water absorption property (hereinafter referred to as "use of an alkali metal ion source", "use of the present disclosure") ) will be explained in detail below.
From the viewpoint of ease of explanation, we will first explain (2) the method for producing a superabsorbent recycled polymer, and then explain (1) the method for regenerating a superabsorbent polymer and (3) the use of an alkali metal ion supply source. Regarding this, the differences from (2) method for producing super absorbent recycled polymer will be explained.

<<Production method of super absorbent recycled polymer>>
The method for producing a super absorbent recycled polymer includes the following steps.
・Immerse sanitary product constituent materials that make up sanitary products, including pulp fibers and a superabsorbent polymer with acid groups, in an acid-containing aqueous solution to form a superabsorbent polymer that is inactivated by the acid. (hereinafter sometimes referred to as "inactivation step")
・A super absorbent recycled polymer in which an alkali metal ion source capable of supplying alkali metal ions is added to a regenerating aqueous solution containing a super absorbent polymer inactivated by acid to form a super absorbent recycled polymer in a wet state. Formation step (hereinafter sometimes referred to as "super absorbent recycled polymer formation step")
・Drying step of drying the super absorbent recycled polymer in a wet state to form a super absorbent recycled polymer having a predetermined water absorbency (hereinafter sometimes referred to as "drying step")

<Inactivation step>
In the inactivation step, sanitary product constituent materials containing pulp fibers and a superabsorbent polymer having acid groups are immersed in an acid-containing aqueous solution containing an acid, and the superabsorbent polymer (hereinafter referred to as acid) is inactivated by the acid. The superabsorbent polymer inactivated by the above method is sometimes referred to as "acid-inactivated superabsorbent polymer").

The above acid is not particularly limited, but includes, for example, inorganic acids and organic acids. When superabsorbent polymers are inactivated using acids, pulp fibers are inactivated compared to when superabsorbent polymers are inactivated using lime, calcium chloride, magnesium sulfate, magnesium chloride, aluminum sulfate, aluminum chloride, etc. Hard to leave ash behind.

Examples of the inorganic acid include sulfuric acid, hydrochloric acid, and nitric acid. As the inorganic acid, sulfuric acid is preferred from the viewpoint of not containing chlorine and cost. Examples of the organic acids include those having an acid group, such as a carboxyl group or a sulfo group. Note that an organic acid having a sulfo group is called a sulfonic acid, and an organic acid having a carboxyl group and no sulfo group is called a carboxylic acid. The organic acid is preferably an organic acid having a carboxyl group, particularly a carboxylic acid, from the viewpoint of protecting equipment.

When the organic acid has a carboxyl group, the organic acid can have one or more carboxyl groups per molecule, and preferably has a plurality of carboxyl groups. By doing so, organic acids can easily form chelate complexes with divalent or higher-valent metals, such as calcium, contained in excreta, making it easier to reduce the ash content of recycled pulp fibers produced from used sanitary products. Become.

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

The acid-containing aqueous solution preferably has a predetermined pH, and the predetermined pH is preferably 4.5 or less, more preferably 4.0 or less, still more preferably 3.5 or less, and even more preferably 3. .0 or less. If the above-mentioned predetermined pH is too high, the superabsorbent polymer will not be sufficiently inactivated, the excrement retained by the superabsorbent polymer will tend to be insufficiently discharged, and separation from pulp fibers, etc. will be difficult. It tends to be difficult to do.

Further, the predetermined pH is preferably 0.5 or more, and more preferably 1.0 or more. If the predetermined pH is too low, the superabsorbent polymer will be further inactivated, and it will take time for the inactivated superabsorbent polymer to react with the alkali metal ion source in the superabsorbent recycling polymer formation step. Tend. In addition to the recycling method of the present disclosure, when pulp fibers contained in used sanitary products are recycled to produce recycled pulp fibers, there is a risk that the recycled pulp fibers may be damaged.
In addition, in this specification, pH means the value at 25 degreeC. Further, the pH can be measured using, for example, a twin pH meter AS-711 manufactured by Horiba, Ltd.

In the manufacturing method of the present disclosure, it is preferable that the acid-containing aqueous solution at least satisfy the predetermined pH at the time of starting the inactivation step, for example, when the sanitary product constituent material is immersed in the acid-containing aqueous solution. This is to inactivate the super absorbent polymer, and if the inactivation of the super absorbent polymer is insufficient, the super absorbent polymer will not be inactivated sufficiently and the body fluids etc. retained by the super absorbent polymer will be Liquid discharge tends to be insufficient, and separation from pulp fibers and the like tends to be difficult.
In the manufacturing method of the present disclosure, it is preferable that the predetermined pH is satisfied at the end of the inactivation step. This is from the viewpoint of continuing to inactivate the super absorbent polymer.

The superabsorbent polymer is not particularly limited as long as it is used in the art as a superabsorbent polymer having an acid group, and examples thereof include those containing a carboxyl group, a sulfo group, etc. Those containing a carboxyl group are preferred.
Examples of superabsorbent polymers containing carboxyl groups include polyacrylate-based and polymaleic anhydride-based ones, and examples of superabsorbent polymers containing sulfo groups include polysulfonate-based ones. Can be mentioned.
The above-mentioned pulp fiber is not particularly limited as long as it can be included in sanitary products.

Note that the acid for inactivating the superabsorbent polymer is an acid that is smaller than the acid dissociation constant (pK _a , in water) of the acid group in the superabsorbent polymer in order to efficiently inactivate the superabsorbent polymer. It is preferable to have a dissociation constant (pK _a , in water).

When the acid has a plurality of acid groups, for example, when the acid is a dibasic acid or a tribasic acid, the acid dissociation constant (pK _a , in water) that is the largest among the acid dissociation constants (pK _a , in water) is preferably smaller than the acid dissociation constant (pK _a , in water) of the acid group of the superabsorbent polymer, and when the superabsorbent polymer has multiple types of acid groups, the The largest acid dissociation constant (pK _a , in water) among the acid dissociation constants (pK _a , in water) is smaller than the smallest acid dissociation constant (pK _a , in water) among the multiple types of acid groups in the superabsorbent polymer. It is preferable. This is from the viewpoint of the efficiency of inactivating the superabsorbent polymer.

In this specification, the value described in the Electrochemical Handbook edited by the Electrochemical Society can be adopted as the acid dissociation constant ( _pka , in water).
According to the Electrochemistry Handbook, the acid dissociation constants ( _pka , water, 25°C) of the main compounds are as follows.
[Organic acid]
・Tartaric acid: 2.99 (pK _a1 ), 4.44 (pK _a2 )
・Malic acid: 3.24 (pK _a1 ), 4.71 (pK _a2 )
・Citric acid: 2.87 (pK _a1 ), 4.35 (pK _a2 ), 5.69 (pK _a3 )
[Inorganic acid]
・Sulfuric acid: 1.99

The acid dissociation constant ( _pka , in water) of an acid that is not listed in the Electrochemistry Handbook can be determined by measurement. An example of an instrument capable of measuring the acid dissociation constant ( _pka , in water) of an acid is the compound physical property evaluation analysis system T3 manufactured by Sirius.

In the manufacturing method of the present disclosure, the specific method is not particularly limited as long as the sanitary product constituent materials can be immersed in an acid-containing aqueous solution; for example, the sanitary product constituent materials may be placed in a tank containing an acid-containing aqueous solution. Alternatively, the acid-containing aqueous solution may be poured into the tank in which the sanitary product components are placed.

The sanitary products mentioned above are not particularly limited as long as they contain super absorbent polymers, and include, for example, disposable diapers, disposable shorts, sanitary napkins, panty liners, urine absorbing pads, bed sheets, pet sheets, etc. It will be done. Preferably, the sanitary product contains pulp fiber and a superabsorbent polymer.
Examples of the sanitary products include those containing a liquid-permeable sheet, a liquid-impermeable sheet, and an absorbent body (absorbent core and core wrap) between them.

In the manufacturing method of the present disclosure, the sanitary product constituent material in the inactivation step can be a mixture of pulp fibers and a superabsorbent polymer, such as an absorbent core taken from a used sanitary product. Further, the sanitary product constituent material may be the sanitary product itself.

When the sanitary product constituent materials to be immersed in an acid-containing aqueous solution include pulp fibers and superabsorbent polymers (hereinafter sometimes referred to as "specified materials"), additional materials (hereinafter referred to as "non-specified materials") For example, when the sanitary product itself is immersed in an acid-containing aqueous solution as a sanitary product constituent material, after the inactivation step, The method may further include a removal step (hereinafter sometimes referred to as a "removal step") of removing non-specific materials. In addition, in the above-mentioned removal step, all of the non-specific materials may be removed, or a part of the non-specific materials may be removed.

A specific example of the above removal step will be described later in connection with the system 1 shown in FIG. 1 and the flowchart shown in FIG. 3.

In the inactivation step, for example, the superabsorbent polymer is inactivated by stirring the sanitary product components in an inactivation tank containing an acid-containing aqueous solution for about 5 to 60 minutes, depending on the temperature. A deactivated superabsorbent polymer can be formed.

In the inactivation step, the acid groups of the superabsorbent polymer having acid groups change from a salt (eg, sodium salt) state to a free acid state, so that the water absorbency of the superabsorbent polymer decreases.
The present inventor discovered that when a superabsorbent polymer that has absorbed water is placed in an acid-containing aqueous solution, negatively charged hydrophilic groups (for example, -COO ^- ) are neutralized by positively charged hydrogen ions (H ⁺ ). It has been found that the ionic repulsion of the hydrophilic group is weakened, the water absorption capacity is reduced, and the superabsorbent polymer is dehydrated.

The temperature of the acid-containing aqueous solution in the inactivation step is not particularly limited, and may be, for example, room temperature (25° C.) or higher than room temperature.
Specifically, the temperature of the acid-containing aqueous solution in the inactivation step is preferably higher than room temperature, more preferably 60-100°C, even more preferably 70-95°C, and even more preferably 80-90°C. . By doing so, the acid contained in the acid-containing aqueous solution can easily sterilize bacteria derived from excrement, etc. contained in the acid-containing aqueous solution.

<Super absorbent recycled polymer formation step>
In the step of forming a superabsorbent recycled polymer, an alkali metal ion source capable of supplying alkali metal ions is added to the regeneration aqueous solution containing the acid-inactivated superabsorbent polymer to form a superabsorbent recycled polymer in a wet state. .
Note that in this specification, a superabsorbent polymer obtained by recycling an inactivated superabsorbent polymer is referred to as a "superabsorbent recycled polymer."

The inventors of the present invention contact an acid-inactivated superabsorbent polymer with an alkali metal ion supply source in water or the like while adjusting the amount of the alkali metal ion source, thereby converting some of the acid groups of the superabsorbent polymer into alkali metal salts. It has been found that the water absorption of the super absorbent recycled polymer in a wet state (that is, the water absorbency of the super absorbent recycled polymer in a dry state) can be controlled by this method.

The alkali metal ion supply source is not particularly limited as long as it can supply alkali metal ions; for example, an alkali metal hydroxide, or a salt of an alkali metal hydroxide and an acid ( (Hereinafter, it may be simply referred to as "salt").

The alkali metal ions include lithium ions, sodium ions, potassium ions, and any combination thereof.
The alkali metal hydroxides include lithium hydroxide, sodium hydroxide, potassium hydroxide, and any combination thereof.

The above-mentioned salt may be an acid salt, a basic salt, or the like.
The alkali metal hydroxide in the above salt includes lithium hydroxide, sodium hydroxide, potassium hydroxide, and any combination thereof.
The acid in the above salt is not particularly limited, and includes, for example, the acids listed in the "inactivation step" (eg, hydrochloric acid, sulfuric acid), carbonic acid, and the like.

The acid preferably has an acid dissociation constant (pK _a , in water) larger than the acid dissociation constant (pK _a , in water) of the acid group in the superabsorbent polymer. By doing so, the acid groups of the superabsorbent polymer become more likely to form an alkali metal salt.

When the acid has a plurality of acid groups, for example, when the acid is a dibasic acid or a tribasic acid, the smallest acid dissociation constant (pK _a , in water) of the acid _a , in water) is preferably larger than the acid dissociation constant (pK _a , in water) of the acid group of the superabsorbent polymer, and when the superabsorbent polymer has multiple types of acid groups, the The smallest acid dissociation constant (pK _a , in water) among the acid dissociation constants (pK _a , in water) is larger than the largest acid dissociation constant (pK _a , in water) among the multiple types of acid groups in the superabsorbent polymer. It is preferable. This is from the viewpoint of making it easier to convert the acid groups of the super absorbent polymer into alkali metal salts.

Carbonic acid is preferable as the acid because carbonic acid hardly remains in the inactivating aqueous solution or can be easily removed by heating or the like.
In addition, the acids other than carbonic acid depend on the pH of the superabsorbent recycled polymer in a wet state, but for example, if the superabsorbent recycled polymer in a wet state is at an acidic pH, the superabsorbent recycled polymer in a wet state Antibacterial properties can be imparted to recycled polymers, superabsorbent recycled polymers in a dry state, and the like.

Examples of the above salts include lithium carbonate, sodium carbonate, potassium carbonate, lithium hydrogen carbonate, sodium hydrogen carbonate, potassium hydrogen carbonate, lithium chloride, sodium chloride, potassium chloride, and the like.

In the superabsorbent recycled polymer formation step, the regeneration aqueous solution can be acidic (pH < 7.0), neutral (pH = 7.0) or alkaline (7.0 < pH); It is preferably alkaline, and preferably alkaline. This is from the perspective of the effects of the present disclosure.

In order to make the regeneration aqueous solution acidic, neutral or alkaline, the regeneration aqueous solution may contain an acidic substance, an alkaline substance or a buffer substance (buffer solution), and the alkali metal ion source may contain an acidic substance, an alkaline substance or a buffer substance (buffer solution). , an alkaline substance or a buffer substance (buffer solution).
The above acidic substance, alkaline substance or buffer substance (buffer solution) should be used when the alkali metal ion source is difficult to change the pH of the regeneration aqueous solution (for example, the alkali metal ion source is lithium chloride, sodium chloride, potassium chloride). etc.) is preferable in cases where it is desired not to change the pH of the regeneration aqueous solution.

The above-mentioned acidic substance is not particularly limited as long as it can make the pH of deionized water alkaline (7.0<pH), and any substances known in the art can be adopted. Examples include acids, carbonic acid, etc. listed in "Step".
The above-mentioned alkaline substance is not particularly limited as long as it can make the pH of deionized water alkaline (7.0<pH), and any substance known in the art can be employed, such as alkali metals. Examples include hydroxides or salts thereof, hydroxides of alkaline earth metals or salts thereof, and from the viewpoint of making it difficult to inactivate the superabsorbent polymer, hydroxides of alkali metals or salts thereof are preferable. . The alkali metal hydroxide or its salt is as described above.
Examples of the buffer substance (buffer solution) include carbonate-bicarbonate buffer solution containing sodium carbonate, sodium hydrogen carbonate, and water.

The regeneration aqueous solution is not particularly limited as long as it contains water, and can be an approximately neutral aqueous solution (for example, tap water, deionized water, etc.), or an acidic aqueous solution (aqueous solution with a pH < 7.0). ), for example, the acid-containing aqueous solution used in the inactivation step, the aqueous solution containing an inorganic or organic acid described in the inactivation step, or an alkaline aqueous solution (aqueous solution with a pH <7.0), for example, the above-mentioned aqueous solution. It can be an aqueous solution containing a source of alkali metal ions.

The inventors also determined that by adjusting the pH of the system containing the acid-inactivated superabsorbent polymer, that is, the pH of the aqueous regeneration solution, the water absorption of the superabsorbent recycled polymer in the wet state (i.e., It has been found that the water absorbency of a water-absorbing recycled polymer can be adjusted within a predetermined range.

Note that the "superabsorbent recycled polymer in a wet state" formed in the superabsorbent recycled polymer formation step has the same water absorbency as the "superabsorbent recycled polymer" obtained in the drying step, but Depending on the specific method, the water absorption of the super absorbent recycled polymer may vary.For example, the reaction between the acid groups of the super absorbent recycled polymer and the alkali metal may further progress, causing the water absorbency of the super absorbent recycled polymer to change. It is the superabsorbent recycled polymer formation step that adjusts the absorbency of the superabsorbent recycled polymer in the dry state, although it may be slightly higher.

The above pH is not particularly limited as long as the super absorbent recycled polymer can achieve a predetermined water absorbency (absorption capacity) in a dry state, but may be in the acidic pH range (pH < 7.0), neutral It may be in the pH range (pH=7.0) or alkaline pH range (7.0<pH), and the above pH is preferably 5.0 to 9.0.

When adjusting the pH within an acidic pH range, the aqueous regeneration solution is preferably an acidic aqueous solution, and an alkali metal ion source is added to the acidic aqueous regeneration solution, either as is or as an aqueous solution. Preferably, the addition forms a superabsorbent recycled polymer in a wet state.

When the pH is adjusted within the range of neutral pH or alkaline pH, the regeneration aqueous solution can be an acidic aqueous solution, a generally neutral aqueous solution, or an alkaline aqueous solution, and a generally neutral aqueous solution, Alternatively, an alkaline aqueous solution is preferable. This is from the viewpoint of efficiently using an alkali metal ion supply source for forming a super absorbent recycled polymer.
Further, it is preferable to form a superabsorbent recycled polymer in a wet state by adding an alkali metal ion supply source as it is or as an aqueous solution to a regeneration aqueous solution that is a generally neutral aqueous solution or an alkaline aqueous solution.

As mentioned above, the alkali metal ion source may be present in the regeneration aqueous solution, and the alkali metal ion source can be added to the regeneration aqueous solution as is or as an aqueous solution.
When an alkali metal hydroxide is added to the regeneration aqueous solution as an alkali metal ion supply source, the alkali metal hydroxide is preferably an aqueous solution, and the aqueous solution has a concentration of hydroxide ions. , preferably 0.1 to 5.0 mol/L, more preferably 0.3 to 3.0 mol/L, and preferably 0.4 to 1.0 mol/L, added to the regeneration aqueous solution. be done. This is from the viewpoint of ease of adjusting the pH of the regenerating aqueous solution and, ultimately, the water absorbency of the super absorbent recycled polymer.

Note that the acid-inactivated superabsorbent polymer is separated from the acid-containing aqueous solution using a device capable of solid-liquid separation, and then the acid-inactivated superabsorbent polymer separated from the acid-containing aqueous solution is converted into an aqueous solution for regeneration. May be immersed. Examples of the device capable of solid-liquid separation include a rotary drum screen, an inclined screen, and a vibrating screen.

The step of forming a superabsorbent recycled polymer can be carried out by stirring the regeneration aqueous solution at a predetermined temperature, for example, 2 to 80° C., for a predetermined time, for example, 5 to 60 minutes.

<Drying step>
In the drying step, the superabsorbent recycled polymer in a wet state is dried to form a superabsorbent recycled polymer having a predetermined water absorbency.
The above predetermined water absorbency is not particularly limited, but considering the practicality of the super absorbent recycled polymer, the absorption capacity is preferably 100 times that of deionized water (g/g). above, more preferably 200 times (g/g) or more, and even more preferably 300 times (g/g) or more.

The predetermined water absorbency is not particularly limited, but considering the gel strength of the superabsorbent recycled polymer when it swells, the absorption capacity is preferably 500 times (g) that of deionized water. /g) or less, more preferably 450 times (g/g) or less, and even more preferably 400 times (g/g) or less.

In the drying step, the regeneration aqueous solution containing the superabsorbent recycled polymer in a wet state obtained in the superabsorbent recycled polymer forming step is directly dried to obtain a superabsorbent recycled polymer in a dry state.
Further, the super absorbent recycled polymer can also be separated from the recycled aqueous solution containing the super absorbent recycled polymer using an apparatus capable of solid-liquid separation. Examples of the device capable of solid-liquid separation include a rotary drum screen, an inclined screen, and a vibrating screen.

Before drying, the separated superabsorbent recycled polymer may be washed with tap water, deionized water, or the like to remove the regeneration aqueous solution adhering to the surface of the superabsorbent recycled polymer.
In addition, the separated super absorbent recycled polymer is brought into contact with a hydrophilic organic solvent (for example, immersed in a hydrophilic organic solvent) before drying to remove the water contained in the separated super absorbent recycled polymer. It is possible to dehydrate to an absorption capacity of preferably 100 times (g/g) or less, more preferably 70 times (g/g) or less, and even more preferably 50 times (g/g) or less. By doing so, the drying temperature can be lowered and/or the drying time can be reduced.

The hydrophilic organic solvent is preferably one that is miscible with water, such as alcohol solvents (e.g., methanol, ethanol, propyl alcohol and its isomers, butyl alcohol and its isomers), ketone solvents, etc. Examples include solvents (eg, acetone, methyl ethyl ketone), nitrile solvents (eg, acetonitrile), and the like.

In the drying step, the superabsorbent recycled polymer in the wet state is dried at a drying temperature, preferably from room temperature (eg 25°C) to 120°C, more preferably from 30 to 80°C, and preferably from 40 to 60°C. When the drying temperature is low, the drying time tends to be longer, and when the drying temperature is high, the acid groups of the superabsorbent recycled polymer may undergo dehydration condensation, resulting in a decrease in the water absorbency of the superabsorbent recycled polymer. There is.
When the separated superabsorbent recycled polymer is brought into contact with a hydrophilic organic solvent before drying, the drying temperature can be low, for example, room temperature to 60°C.

The drying step may be carried out under reduced pressure, for example at 0.1 kPa or more and less than 100 kPa.
The drying step can be carried out for, for example, 30 to 300 minutes.
The drying step is preferably carried out so that the weight loss on drying of the superabsorbent recycled polymer is preferably 15% or less (2.0 g, 105° C., 3 hours). This is from the perspective of using super absorbent recycled polymers.
The above loss on drying is based on the "Standards for materials for sanitary products" attached as an appendix to the "Standards for materials for sanitary products" notified by the Ministry of Health, Labor and Welfare on March 25, 2015 as Pharmaceutical and Food Safety Review No. 0325 No. 24. <2. Measured according to "7. Loss on Drying Test Method" in "General Test Methods".

After the drying step, if the dried super absorbent recycled polymer is fixed, integrated, etc., the dried super absorbent recycled polymer may be pulverized, classified, etc.

<<Method for regenerating superabsorbent polymer inactivated by acid>>
The method for regenerating a superabsorbent polymer includes the following steps.
・Preparation step of preparing a superabsorbent polymer having acid groups and inactivated by acid (hereinafter sometimes referred to as "preparation step")
・A super absorbent recycled polymer in which an alkali metal ion source capable of supplying alkali metal ions is added to a regenerating aqueous solution containing a super absorbent polymer inactivated by acid to form a super absorbent recycled polymer in a wet state. Formation step (hereinafter sometimes referred to as "super absorbent recycled polymer formation step")
・Drying step of drying the super absorbent recycled polymer in a wet state to form a super absorbent recycled polymer having a predetermined water absorbency (hereinafter sometimes referred to as "drying step")

<Preparation steps>
In the preparation step, an acid-inactivated superabsorbent polymer having acid groups is prepared.
The acid-inactivated superabsorbent polymer is not particularly limited as long as it has been inactivated with an acid, and for example, in the "inactivation step" section of the "method for producing superabsorbent recycled polymer" in this specification. It can be prepared as described in .
In addition to the above-mentioned acid-inactivated superabsorbent polymers, superabsorbent polymers contained in used sanitary products are inactivated using polyvalent metal salts, such as alkaline earth metal salts. , and then treated with an acid.

<Super absorbent recycled polymer formation step and drying step>
"Super absorbent recycled polymer forming step" and "drying step" in the regeneration method of the present disclosure are respectively the "super absorbent recycled polymer forming step" and "drying step" in the "method for producing super absorbent recycled polymer". Since they are similar, the explanation will be omitted.

<Use of alkali metal ion source>
Use of an alkali metal ion source includes the following steps.
・Adding an alkali metal ion source capable of supplying alkali metal ions to a regeneration aqueous solution containing a superabsorbent polymer that has acid groups and has been inactivated by acid to form a superabsorbent recycled polymer in a wet state A step of forming a super absorbent recycled polymer (hereinafter sometimes referred to as a "step of forming a super absorbent recycled polymer").

The "superabsorbent recycled polymer forming step" in the use of the present disclosure is the same as the "superabsorbent recycled polymer forming step" in the "method for producing a superabsorbent recycled polymer", so the explanation will be omitted.

FIG. 1 is a block diagram of a system 1 for implementing the manufacturing method, reclamation method, and use according to one embodiment of the present disclosure. FIG. 1 is a diagram for explaining the manufacturing method, recycling method, and use according to one embodiment of the present disclosure, and does not limit the present disclosure in any way.
The system 1 includes a bag breaking device 11, a crushing device 12, a first separating device 13, a first dust removing device 14, a second dust removing device 15, a third dust removing device 16, a second separating device 17, A third separation device 18, an oxidizing agent treatment device 19, and a fourth separation device 20 are provided.

The bag breaking device 11 is filled with an acid-containing aqueous solution in which an opening is formed in a collection bag containing used sanitary products. The crushing device 12 crushes the used sanitary products submerged below the surface of the acid-containing aqueous solution, including the collection bag. FIG. 2 is a schematic diagram showing a configuration example of the bag breaking device 11 and the crushing device 12 in FIG. 1.

The bag breaking device 11 is filled with an acid-containing aqueous solution B, and forms an opening in the collection bag A that has settled in the acid-containing aqueous solution B. A bag 91 is formed. The bag breaking device 11 includes a solution tank V and an aperture forming section 50. The solution tank V stores an acid-containing aqueous solution B. The opening forming part 50 is provided in the solution tank V, and forms an opening in the surface of the collection bag A that comes into contact with the acid-containing aqueous solution B when the collection bag A is placed in the solution tank V. .

The hole forming section 50 includes a feeding section 30 and a bag breaking section 40. The feeding unit 30 (physically and forcibly) feeds (draws) the collection bag A into the acid-containing aqueous solution B in the solution tank V. The feeding unit 30 is, for example, a stirrer, and includes a stirring blade 33, a support shaft (rotation shaft) 32 that supports the stirring blade 33, and a drive device 31 that rotates the support shaft 32 along the axis. The stirring blade 33 rotates around the rotation shaft (support shaft 32) by the drive device 31, thereby causing a swirling flow in the acid-containing aqueous solution B. The feeding unit 30 draws the collection bag A toward the bottom of the acid-containing aqueous solution B (solution tank V) by swirling flow.

The bag-breaking section 40 is arranged at the lower part (preferably at the bottom) of the solution tank V, and includes a bag-breaking blade 41, a support shaft (rotating shaft) 42 that supports the bag-breaking blade 41, and a support shaft 42 that supports the bag-breaking blade 41. and a drive device 43 that rotates along the axis. The bag tearing blade 41 is rotated around the rotation shaft (support shaft 42) by the drive device 43, thereby forming an opening in the collection bag A that has been moved to the lower part of the acid-containing aqueous solution B (solution tank V).

The crushing device 12 crushes the used sanitary products in the collection bag A submerged below the surface of the acid-containing aqueous solution B, together with the collection bag A. The crushing device 12 includes a crushing section 60 and a pump 63. The crushing unit 60 is connected to the solution tank V by a pipe 61, and collects a collection bag 91 containing used sanitary products discharged from the solution tank V and has an opening into an acid-containing aqueous solution together with the collection bag A. B to form an acid-containing aqueous solution 92 containing the crushed material.

The crushing section 60 includes a two-shaft crusher (for example, a two-shaft rotary crusher, a two-shaft differential crusher, a two-shaft shear crusher), and for example, a Sumicutter (Sumitomo Heavy Industries Environment Co., Ltd.). company). The pump 63 is connected to the crushing section 60 through a pipe 62, and draws out the acid-containing aqueous solution 92 containing the crushed material obtained in the crushing section 60 from the crushing section 60 and sends it to the next process. However, the crushed material includes materials including pulp fibers, acid-inactivated superabsorbent polymers, materials for collection bag A, films, nonwoven fabrics, elastic bodies, and the like.

The first separation device 13 stirs the acid-containing aqueous solution 92 containing the crushed materials obtained by the crushing device 12, performs washing to remove dirt (excretion, etc.) from the crushed materials, and cleans the acid containing the crushed materials. The acid-containing first aqueous solution 93 from which foreign substances have been removed is separated from the acid-containing aqueous solution 92 and sent to the first dust removal device 14 . Note that the acid-containing first aqueous solution 93 contains pulp fibers and an acid-inactivated superabsorbent polymer.

As the first separation device 13, for example, a washing machine including a washing tub/dehydrating tub and a water tub surrounding the washing tub and a dehydrating tub can be mentioned. However, the washing tank and dewatering tank (rotating drum) is used as the washing tank and sieving tank (separation tank). Examples of the washing machine include horizontal washing machine ECO-22B (manufactured by Inamoto Seisakusho Co., Ltd.).

The first dust removal device 14 further removes foreign substances present in the acid-containing first aqueous solution 93 using a screen having a plurality of openings, and the acid-containing second aqueous solution has more foreign substances removed than the acid-containing first aqueous solution 93. Form 94. Note that the acid-containing second aqueous solution 94 contains pulp fibers and an acid-inactivated superabsorbent polymer. Examples of the first dust removal device 14 include a screen separator (rough screen separator), specifically, for example, a pack pulper (manufactured by Satomi Seisakusho Co., Ltd.).

The second dust remover 15 uses a screen having a plurality of openings to remove finer foreign substances from the acid-containing second aqueous solution 94 sent from the first dust remover 14, and removes more foreign substances than the acid-containing second aqueous solution 94. A third acid-containing aqueous solution 95 is formed. Note that the acid-containing third aqueous solution 95 contains pulp fibers and an acid-inactivated superabsorbent polymer. As the second dust removal device 15, for example, a screen separator, specifically, for example, Ramo Screen (manufactured by Aikawa Iron Works Co., Ltd.) can be mentioned.

The third dust removing device 16 further removes foreign substances from the acid-containing third aqueous solution 95 sent out from the second dust removing device 15 by centrifugation, and the third dust removing device 16 removes even more foreign substances from the acid-containing third aqueous solution 95 than the acid-containing third aqueous solution 95. A fourth containing aqueous solution 96 is formed. Note that the acid-containing third aqueous solution 95 contains pulp fibers and an acid-inactivated superabsorbent polymer. Examples of the third dust removal device 16 include a cyclone separator, specifically, an ACT low concentration cleaner (manufactured by Aikawa Tekko Co., Ltd.).

The second separation device 17 separates the fourth acid-containing aqueous solution 96 sent from the third dust removal device 16 through a screen having a plurality of openings, separating the acid-containing aqueous solution containing the acid-inactivated superabsorbent polymer and the pulp fibers into the acid-containing aqueous solution containing mainly the pulp fibers. It is separated into an acid-containing aqueous solution 97 contained in Note that the acid-inactivated superabsorbent polymer also remains in the acid-containing aqueous solution 97 that mainly contains pulp fibers.
Examples of the second separation device 17 include a drum screen separator, specifically, a drum screen dehydrator manufactured by Toyo Screen Co., Ltd.

The third separation device 18 separates the acid-containing aqueous solution 97 mainly containing pulp fibers sent from the second separation device 17 into solids containing pulp fibers and acid-inactivated superabsorbent polymers through a screen having a plurality of openings. 98 and a liquid containing an acid-inactivated superabsorbent polymer and an acid-containing aqueous solution, the solid 98 containing pulp fibers and an acid-inactivated superabsorbent polymer is pressurized to form pulp fibers and an acid-inactivated superabsorbent polymer. The acid-inactivated superabsorbent polymer in the solid 98 containing the polymer is crushed.
Examples of the third separation device 18 include a screw press dehydrator, specifically, a screw press dehydrator manufactured by Kawaguchi Seiki Co., Ltd.

The oxidizing agent treatment device 19 treats the solid 98 containing pulp fibers and acid-inactivated superabsorbent polymer sent from the third separation device 18 with an aqueous solution (treatment liquid) containing an oxidizing agent. Thereby, the acid-inactivated superabsorbent polymer is oxidatively decomposed and removed from the pulp fibers, and a treatment liquid 99 containing recycled pulp fibers is delivered.

When using ozone as an oxidizing agent, the oxidizing agent treatment device includes, for example, a treatment tank and an ozone supply device. The processing tank stores an acidic aqueous solution as a processing liquid. The ozone supply device supplies ozone-containing gas, which is a gaseous substance, to the processing tank. Examples of the ozone generator of the ozone supply device include the ozone water exposure tester ED-OWX-2 manufactured by Eco Design Co., Ltd. and the ozone generator OS-25V manufactured by Mitsubishi Electric Corporation.
Note that the oxidizing agent treatment device decomposes the acid-inactivated superabsorbent polymer using other oxidizing agents, such as chlorine dioxide, peracid (e.g., peracetic acid), sodium hypochlorite, and hydrogen peroxide. be able to.

The fourth separation device 20 uses a screen having a plurality of openings to separate recycled pulp fibers and a treatment liquid from the treatment liquid 99 containing recycled pulp fibers treated in the oxidizing agent treatment device 19. An example of the fourth separation device 20 is a screen separator.

FIG. 3 is a flowchart illustrating a method for producing recycled pulp fibers and superabsorbent recycled polymers from used sanitary products using the system 1 shown in FIG. The flowchart shown in FIG. 3 is an example and does not limit the present disclosure in any way.

FIG. 3 shows an inactivation step S1 (preparation step S1), a removal step S2, a superabsorbent recycled polymer formation step S3, and a recycled pulp fiber recovery step S4. The inactivation step S1 (preparation step S1) includes an opening forming step P11 and a crushing step P12, and the removal step S2 includes a first separation step P13, a first dust removal step P14, and a second The dust removal step P15 and the third dust removal step P16 are included, the super absorbent recycled polymer forming step S3 includes a second separation step P17, and the recycled pulp fiber recovery step S3 includes a fourth separation step P20. is included. This will be explained in detail below.

The opening forming step P11 is performed using the bag tearing device 11. A collection bag A containing used sanitary products is put into a solution tank V storing an acid-containing aqueous solution B, and an opening is formed on the surface of the collection bag A that comes into contact with the acid-containing aqueous solution B. When the opening is formed in the collection bag A, the acid-containing aqueous solution B is applied around the collection bag A to prevent dirt, fungi, odors, etc. from the used sanitary products inside the collection bag A from being released to the outside. Surround and seal. When the acid-containing aqueous solution enters the collection bag A through the opening, the gas inside the collection bag A escapes to the outside of the collection bag A, and the specific gravity of the collection bag A becomes heavier than the acid-containing aqueous solution B. Precipitates into acid-containing aqueous solution B. Furthermore, the acid in the acid-containing aqueous solution B acts as an inactivating agent and inactivates the superabsorbent polymer in the used sanitary product in the collection bag A.

When superabsorbent polymers in used sanitary products are inactivated, their water absorption capacity decreases, and the superabsorbent polymers dehydrate and become smaller in particle size, making them easier to handle in subsequent steps. , improving processing efficiency. Compared to inactivating superabsorbent polymers using lime, calcium chloride, etc., using acid for inactivation has the advantage that no ash remains in the pulp fibers, and the degree of inactivation (particle size, specific gravity) It has the advantage that it is easy to adjust the size (e.g., size) by adjusting the pH.

If the sanitary product components to be immersed in an acid-containing aqueous solution include non-specific materials, such as liquid-permeable sheets, liquid-impermeable sheets, etc., for example, the sanitary product itself may be immersed in an acid-containing aqueous solution. In the case of immersion in water, it is preferable that the size, specific gravity, etc. of the pulp fibers constituting the specific material are relatively similar to the size, specific gravity, etc. of the superabsorbent polymer. Also from this point of view, it is preferable that the acid-containing aqueous solution has the above-mentioned predetermined pH in the inactivation step.

In the bag breaking device 11 shown in FIG. 2, rotation of the stirring blade 33 around the rotating shaft (support shaft 32) generates a swirling flow in the acid-containing aqueous solution B, and the collection bag A is physically forced into the acid-containing aqueous solution. It is drawn toward the bottom of B (solution tank V). Then, the collection bag A that has moved to the bottom comes into contact with the bag tearing blade 41 due to rotation around the rotation axis (support shaft 42) of the bag tearing blade 41, and an opening is formed in the collection bag A. .

The crushing process P12 is executed by the crushing device 12. A collection bag 91 containing used sanitary products and having an opening is moved from the solution tank V to the crushing device 12 together with the acid-containing aqueous solution B, and in the crushing device 12, the used sanitary products in the collection bag A are removed. The articles are crushed together with the collection bag A in an acid-containing aqueous solution B.

For example, in the crushing device 12 of FIG. 2, first, the crushing unit 60 converts the collection bag 91 containing the used sanitary products sent out from the solution tank V together with the acid-containing aqueous solution B and having an opening into the collection bag 91. A is crushed in an acid-containing aqueous solution B (submerged crushing step). In the crushing device 12 of FIG. 2, the acid-containing aqueous solution 92 containing crushed materials obtained in the crushing unit 60 (submerged crushing process) is drawn out from the crushing unit 60 (withdrawal process) by the pump 63, and sent to the next process. be done.

The first separation step P13 is performed by the first separation device 13. While stirring the acid-containing aqueous solution 92 containing the crushed materials obtained by the crushing device 12 and washing to remove dirt from the crushed materials, the acid-containing aqueous solution 92 containing the crushed materials is mixed with the specified materials and the acid-containing aqueous solution ( That is, it is separated into an acid-containing aqueous solution containing pulp fibers and an acid-inactivated superabsorbent polymer) and non-specific materials for sanitary products. At this time, an acid-containing aqueous solution may be added separately in order to enhance the cleaning effect and/or adjust the pH.

As a result, an acid-containing first aqueous solution 93 containing pulp fibers and an acid-inactivated superabsorbent polymer is separated from the acid-containing aqueous solution 92 containing the crushed material through the through-hole, and is sent out from the first separation device 13. be done. On the other hand, relatively large non-specific materials in the acid-containing aqueous solution 92 containing crushed materials cannot pass through the through-holes and remain within the first separation device 13 or are sent out through another route. Note that small pieces of the crushed non-specific materials cannot be completely separated by the first separation device 13 and are included in the acid-containing first aqueous solution 93.

Here, when a washing machine is used as the first separation device 13, the size of the through hole in the washing tub that functions as a sieve is 5 mm to 20 mmφ in the case of a round hole, and 5 mm to 20 mmφ in the case of a round hole. In some cases, the area may be approximately the same as that of the round hole.

The first dust removal process P14 is performed by the first dust removal device 14. The acid-containing first aqueous solution 93 sent from the first separation device 13 is passed through a screen to further separate the acid-containing aqueous solution containing pulp fibers and acid-inactivated superabsorbent polymers and crushed non-specific materials (foreign substances). To separate. As a result, the crushed non-specific material (foreign matter) cannot pass through the screen and is separated, and the acid-containing second aqueous solution 94 is sent out from the first dust removal device 14. On the other hand, crushed non-specific materials (foreign objects) cannot pass through the screen and remain within the first dust removal device 14, or are sent out through another route. Note that smaller pieces of the crushed non-specific materials are not completely separated by the first dust removal device 14 and are included in the acid-containing second aqueous solution 94.

The second dust removal step P15 is executed by the second dust removal device 15, in which the acid-containing second aqueous solution 94 sent from the first dust removal device 14 is passed through a screen, and an acid containing pulp fibers and an acid-inactivated superabsorbent polymer is removed. The containing aqueous solution and the crushed non-specific material (foreign matter) are further separated. As a result, the crushed non-specific material (foreign matter) is separated without being able to pass through the screen, and the acid-containing third aqueous solution 95 is sent out from the second dust removal device 15. On the other hand, crushed non-specific materials (foreign objects) cannot pass through the screen and remain in the second dust removal device 15, or are sent out through another route. Note that smaller pieces of the crushed non-specific materials are not completely separated by the second dust removal device 15 and are included in the acid-containing third aqueous solution 95.

The third dust removal step P16 is executed by the third dust removal device 16, and the acid-containing third aqueous solution 95 sent out from the second dust removal device 15 is centrifuged in an upside-down conical casing to remove the pulp fibers and the acid. The acid-containing aqueous solution containing the activated superabsorbent polymer and the crushed non-specific material (foreign matter) are further separated. As a result, the acid-containing fourth aqueous solution 96 is sent out from the upper part of the third dust removal device 16 (cyclone separator). On the other hand, crushed non-specific materials (foreign materials), especially heavy materials such as metals, are sent out from the lower part of the third dust removal device 16 (cyclone separator).
The pH of the acid-containing aqueous solution is adjusted so that the specific gravity and size of the acid-inactivated superabsorbent polymer and the specific gravity and size of the pulp fibers are within predetermined ranges.

The second separation step P17 is performed by the second separation device 17. The fourth acid-containing aqueous solution 96 sent from the third dust removal device 16 is separated by a drum screen into an acid-containing aqueous solution containing an acid-inactivated superabsorbent polymer and an acid-containing aqueous solution 97 mainly containing pulp fibers. . As a result, the acid-containing aqueous solution containing the acid-inactivated superabsorbent polymer is separated from the acid-containing fourth aqueous solution 96 through the drum screen and sent out from the second separation device 17 . On the other hand, of the fourth acid-containing aqueous solution 96, the acid-containing aqueous solution 97 that mainly contains pulp fibers cannot pass through the drum screen and is sent out from the second separation device 17 through a different route.

The acid-containing aqueous solution containing the acid-inactivated superabsorbent polymer is transferred to a stirring device together with the acid-containing aqueous solution, and while stirring the acid-containing aqueous solution containing the acid-inactivated superabsorbent polymer, a sodium hydroxide aqueous solution, etc. is added to the stirring device. can be added to adjust the pH and form a superabsorbent recycled polymer.

In addition, the acid-containing aqueous solution containing the acid-inactivated superabsorbent polymer is separated into the acid-inactivated superabsorbent polymer and the acid-containing aqueous solution using a solid-liquid separator, for example, a rotary drum screen. , the acid-inactivated superabsorbent polymer is transferred as an aqueous solution for regeneration to a stirring device filled with tap water, an alkaline aqueous solution, etc., and an alkali metal ion source is added to adjust the pH, and the superabsorbent polymer in a wet state is A recycled polymer can be formed.

The superabsorbent recycled polymer in the wet state is then dried using a vacuum dryer to form a superabsorbent recycled polymer in the dry state, and then the superabsorbent recycled polymer in the dry state is dried using a vacuum dryer, for example. It can be pulverized using a pulverizer to form particulate superabsorbent recycled polymers.

The third separation step P18 is performed by the third separation device 18. An acid-containing aqueous solution 97 mainly containing pulp fibers sent from the second separation device 17 is separated by a drum screen into a solid 98 containing pulp fibers and an acid-inactivated superabsorbent polymer, and a solid 98 containing an acid-inactivated superabsorbent polymer and an acid-inactivated superabsorbent polymer. It is separated into a liquid containing an acid-containing aqueous solution. At the same time as the separation, the acid-inactivated superabsorbent polymer in the solid 98 containing the pulp fibers and the acid-inactivated superabsorbent polymer is crushed under pressure. As a result, a liquid containing the acid-inactivated superabsorbent polymer and the acid-containing aqueous solution passes through the drum screen and is separated from the acid-containing aqueous solution 97 mainly containing pulp fibers, and sent out from the third separation device 18. On the other hand, out of the acid-containing aqueous solution 97 mainly containing pulp fibers, the solid 98 containing pulp fibers and acid-inactivated superabsorbent polymer could not be added to the drum screen, and a third It is sent out to the outside of the separation device 18.

The oxidizing agent treatment step P19 is executed by the oxidizing agent treatment device 19. The pulp fibers and the crushed acid-inactivated superabsorbent polymer in the solid 98 containing pulp fibers and acid-inactivated superabsorbent polymer delivered from the third separation device 18 are treated with an aqueous solution containing an oxidizing agent. Ru. Thereby, the acid-inactivated superabsorbent polymer is oxidatively decomposed and removed from the pulp fibers. As a result, the acid-inactivated super-absorbent polymer that was attached to the pulp fiber and the solid 98 pulp fiber containing the acid-inactivated super-absorbent polymer (example: remaining on the surface of the pulp fiber) was removed by the aqueous solution containing the oxidizing agent. It is oxidatively decomposed and changed into a low molecular weight organic substance soluble in an aqueous solution, thereby being removed from the pulp fibers, and a treatment liquid 99 containing recycled pulp fibers is formed.

For example, in the oxidizing agent treatment device 19, a solid 98 containing pulp fibers and an acid-inactivated superabsorbent polymer is introduced from the top of the treatment tank, and settles from the top to the bottom of the treatment liquid, that is, an aqueous solution containing the oxidizing agent. I'm going to go. On the other hand, ozone-containing gas is continuously released in the form of fine bubbles (for example, microbubbles or nanobubbles) into the processing liquid from a nozzle in the processing tank. That is, the ozone-containing gas rises from the bottom to the top of the processing liquid. Within the treatment liquid, the pulp fibers that settle and the ozone-containing gas that rises collide with each other while advancing in opposite directions. Then, the ozone-containing gas adheres to the surface of the pulp fibers so as to wrap around the pulp fibers. At this time, ozone in the ozone-containing gas reacts with the acid-inactivated superabsorbent polymer in the pulp fibers, oxidatively decomposes the acid-inactivated superabsorbent polymer, and dissolves it in the treatment liquid. Thereby, the acid-inactivated superabsorbent polymer contained in the pulp fiber and the solid 98 containing the acid-inactivated superabsorbent polymer is oxidatively decomposed and removed from the pulp fiber, and the treatment liquid 99 containing the recycled pulp fiber is produced. Form.

The fourth separation step P20 is executed by the fourth separation device 20, in which the treated liquid 99 containing recycled pulp fibers passes through a screen having a plurality of slits, and the recycled pulp fibers are separated from the treated liquid 99 containing recycled pulp fibers. and the processing liquid are separated. As a result, the treatment liquid passes through the screen and is separated from the treatment liquid 99 containing recycled pulp fibers, and is sent out from the fourth separation device 20. On the other hand, among the treated liquid 99 containing recycled pulp fibers, the recycled pulp fibers cannot pass through the screen and remain in the fourth separation device 20 or are sent out through another route.

The superabsorbent recycled polymer formed by the production method of the present disclosure, the recycling method of the present disclosure, and the use of the present disclosure can be used without particular limitation in applications in which the superabsorbent polymer is used, such as sanitary products ( For example, it can be used for disposable diapers, incontinence pads (eg, light incontinence pads), disposable shorts, sanitary napkins, panty liners, bed sheets), pet sheets, cat litter, soil conditioners, and the like.

Hereinafter, the present disclosure will be explained by giving examples, but the present disclosure is not limited to these examples.
[Example 1]
A polyacrylic acid-based super absorbent polymer (manufactured by Sumitomo Seika Co., Ltd., Aqua Keep, unused product) was heated to a mass ratio of 150 in a constant temperature and humidity room at a temperature of 25 ± 5°C and a humidity of 65 ± 5% RH. It was immersed in twice the amount of physiological saline for 10 minutes.
In addition, when the absorption capacity (physiological saline) of the soaked superabsorbent polymer was measured according to the method described in this specification, the absorption capacity (physiological saline) was 86.6 (g/g).
In addition, when the absorption capacity (deionized water) was measured by changing "150 times the amount of physiological saline by mass ratio" to "deionized water 1,000 times the amount by mass ratio", the absorption capacity (deionized water) was measured. water) was about 600 times (g/g).

450 g of the superabsorbent polymer taken out from the physiological saline was placed in a polytetrafluoroethylene bag and immersed in a citric acid aqueous solution (1,000 mL, pH=2.52) for 5 minutes to obtain an acid-inactivated superabsorbent polymer. The polymer was prepared.
Next, the acid-inactivated superabsorbent polymer was placed in a 1 L beaker filled with 500 mL of deionized water as a regeneration aqueous solution along with the bag, and while stirring, 0.1 mL of a 1.0 mol/L NaOH aqueous solution was added. Added. Ten minutes after the addition of NaOH, the bag was taken out from the beaker, the pH of the regeneration aqueous solution was measured, and the absorption capacity of the superabsorbent polymer (superabsorbent recycled polymer) in the bag was measured. The results are shown in Figure 4.

[Examples 2 to 6]
The regeneration aqueous solution was prepared in the same manner as in Example 1, except that the amount of the 1.0 mol/L NaOH aqueous solution added was changed to 0.2 mL, 0.3 mL, 0.4 mL, 0.5 mL, and 0.6 mL. The pH and the absorption capacity (g/g) of the super absorbent polymer (super absorbent recycled polymer) were measured. The relationship between the amount of NaOH aqueous solution added, pH and absorption capacity (g/g) is shown in FIG. 4, and the relationship between pH and absorption capacity (g/g) is shown in FIG.

[Reference example 1]
In Example 1, the pH of the regeneration aqueous solution before adding the NaOH aqueous solution was measured. The results are shown in FIG. 4 as pH values when the amount of NaOH added was 0 mL. In addition, in Example 1, the absorption capacity of the acid-inactivated superabsorbent polymer before being put into a 1L beaker filled with deionized water is shown in Figure 4 as the absorption capacity value when the amount of NaOH added is 0mL. show.

From FIG. 4, it can be seen that the absorption capacity of the super absorbent polymer (super absorbent recycled polymer) can be adjusted by adjusting the amount of the NaOH aqueous solution added. Moreover, from FIG. 5, it can be seen that there is a high correlation between the pH of the regeneration aqueous solution and the water absorbency of the super absorbent recycled polymer.

[Example 7]
An acid-inactivated superabsorbent polymer was prepared according to Example 1, and 450 g of the prepared acid-inactivated superabsorbent polymer was placed in a bag made of polytetrafluoroethylene. Place the bag in a 1L beaker filled with deionized water, add a predetermined amount of Na ₂ CO ₃ to the beaker while stirring the beaker, and 10 minutes after the addition of Na ₂ CO ₃ , remove the bag from the beaker and place inside the bag. The absorption capacity of the super absorbent polymer (super absorbent recycled polymer) was measured. The results are shown in FIG. In Example 7, the experiment was conducted multiple times by changing the predetermined amount of Na ₂ CO ₃ .
In FIG. 6, the horizontal axis is the molar concentration of Na ₂ CO ₃ (mmol/L), and the vertical axis is the absorption capacity (g/g) of the super absorbent recycled polymer.

[Example 8]
The absorption capacity of the super absorbent polymer (super absorbent recycled polymer) was measured according to Example 7 except that Na ₂ CO ₃ was changed to NaHCO ₃ . The results are shown in FIG. In addition, in FIG. 6, the horizontal axis is the molar concentration (mmol/L) of NaHCO ₃ .

[Examples 9 to 13]
A polyacrylic acid-based super absorbent polymer (manufactured by Sumitomo Seika Co., Ltd., Aqua Keep, unused product) was placed in a constant temperature and humidity room at a temperature of 25 ± 5°C and a humidity of 65 ± 5% RH. A container filled with urea (prepared by dissolving 200 g of urea, 80 g of sodium chloride, 8 g of magnesium sulfate, 3 g of calcium chloride, and approximately 1 g of dye Blue No. 1 in 10 L of exchange water) (the container contains unused The superabsorbent polymer was immersed for 30 minutes in a solution (filled with artificial urine in an amount approximately 1000 times the mass ratio of the superabsorbent polymer), and the superabsorbent polymer after immersion was allowed to stand on a net for 10 minutes.

After standing, the superabsorbent polymer is placed in a container filled with 1% by mass citric acid aqueous solution (the container is filled with citric acid aqueous solution in an amount approximately 1000 times the mass ratio of the unused superabsorbent polymer The superabsorbent polymer was immersed for 30 minutes in the immersed polymer, and the superabsorbent polymer was allowed to stand on a net for 10 minutes. The superabsorbent polymer after standing is placed in a container filled with a 20 mmol/L NaOH aqueous solution (the container is filled with an NaOH aqueous solution in an amount approximately 1000 times the mass ratio of the unused superabsorbent polymer). After immersion, the superabsorbent polymer (superabsorbent recycled polymer in a wet state) was allowed to stand on a net for 10 minutes to obtain a superabsorbent recycled polymer in a wet state. When a part of the super absorbent recycled polymer in a wet state was sampled and the absorption capacity (after regeneration) was measured, it was 201.0 times.

A portion of the super absorbent recycled polymer in a wet state is stored in each container filled with a hydrophilic organic solvent (each container contains a hydrophilic organic solvent in an amount approximately 600 times the mass ratio of the unused super absorbent polymer). The super absorbent recycled polymer is dehydrated by immersing it in a solvent (filled with a solvent) for 30 minutes, and the super absorbent recycled polymer is left to stand for 10 minutes on a net. ) was measured. The results are shown in Table 1.
Note that the hydrophilic organic solvent used was methanol, ethanol, acetone, or acetonitrile, and as a control, a sample that was not immersed in the hydrophilic organic solvent was prepared.

The super absorbent recycled polymer in a wet state after being left standing was dried at 60° C. for 24 hours to obtain a super absorbent recycled polymer in a dry state.
A container filled with deionized water containing the super absorbent recycled polymer in a dry state (the container is filled with deionized water in an amount approximately 1000 times the mass ratio of the unused super absorbent polymer) The super absorbent recycled polymer was immersed in water for 30 minutes, and the super absorbent recycled polymer was left standing on a net for 10 minutes, and the absorption capacity (after drying) was measured. The results are shown in Table 1.

From Table 1, it can be seen that the super absorbent recycled polymers (Examples 9 to 12) that were dehydrated using a hydrophilic solvent had the same absorption capacity ( After drying).

1 System 11 Bag breaking device 12 Crushing device 13 First separation device 14 First dust removal device 15 Second dust removal device 16 Third dust removal device 17 Second separation device 18 Third separation device 19 Oxidizing agent treatment device 20 Fourth separation device S1 Inactivation step S2 Removal step S3 Super absorbent recycled polymer formation step S4 Recycled pulp fiber recovery step P11 Opening part formation step P12 Crushing step P13 First separation step P14 First dust removal step P15 Second dust removal step P16 Third dust removal step P17 Second separation process P18 Third separation process P19 Oxidizing agent treatment process P20 Fourth separation process

Claims (10)

A method for regenerating a superabsorbent polymer inactivated by acid into a superabsorbent recycled polymer in a wet state, the method comprising:
a preparatory step of preparing a solution containing a superabsorbent polymer having acid groups and inactivated by acid and an acid-containing aqueous solution;
a separation step of separating the acid-inactivated superabsorbent polymer from the acid-containing aqueous solution from the solution using a device capable of solid-liquid separation;
An alkali metal ion supply source capable of supplying alkali metal ions is added to the regeneration aqueous solution containing the superabsorbent polymer inactivated by the acid, and the superabsorbent polymer inactivated by the acid is recovered in the wet state. a superabsorbent recycled polymer forming step of forming a superabsorbent recycled polymer in
including ;
the super absorbent recycled polymer has a predetermined water absorbency;
The method , wherein the predetermined water absorption is adjusted by controlling the pH of the regeneration aqueous solution . 2. The method of claim 1, wherein the device capable of solid-liquid separation is a rotary drum screen. 2. The method of claim 1, wherein the solid-liquid separable device is a tilted screen. 2. The method of claim 1, wherein the device capable of solid-liquid separation is a vibrating screen. Claims 1 to 3, wherein the alkali metal ion supply source is an alkali metal hydroxide or a salt of an alkali metal hydroxide and an acid having a larger acid dissociation constant than the acid group of the superabsorbent polymer. 4. The method according to any one of 4. A method according to any one of claims 1 to 5, wherein the alkali metal ions are selected from the group consisting of lithium ions, sodium ions and potassium ions, and any combinations thereof. The method according to any one of claims 1 to 6, further comprising a drying step of drying the superabsorbent recycled polymer in the wet state. The method according to any one of claims 1 to 7 , wherein the pH of the regeneration aqueous solution is adjusted to 5.0 to 9.0 (25°C). The superabsorbent polymer inactivated by the acid is derived from used sanitary products,
the solution in the preparation step further comprises pulp fibers derived from used sanitary products;
After the preparation step and before the separation step, the method further includes a removal step of removing foreign substances present in the solution using a dust removal device.
A method according to any one of claims 1 to 8 . 10. The method of claim 9 , wherein the dust removal device is a screen separator.

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