JP2022145758A - Method for regenerating highly absorbent polymer, method for producing highly absorbent recycled polymer, and use of alkali metal supply source - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for regenerating a highly absorbent polymer deactivated by an acid, which can form a highly absorbent polymer having predetermined water absorptivity.

SOLUTION: Provided is a method for regenerating a highly absorbent polymer deactivated by an acid into a highly absorbent polymer having predetermined water absorptivity, comprising: a preparation step S1 of preparing a highly absorbent polymer having an acid group and deactivated by an acid; a step S3 of forming a highly absorbent recycled polymer where adding an alkali metal ion supply source, which can supply alkali metal ions, to a solution for regeneration containing the highly absorbent polymer deactivated by an acid, to form, from the highly absorbent polymer deactivated by an acid, the highly absorbent recycled polymer in a wet state; and a drying step of drying the highly absorbent recycled polymer in a wet state to form the highly absorbent polymer having predetermined water absorptivity.

SELECTED DRAWING: Figure 3

COPYRIGHT: (C)2023,JPO&INPIT

Description

The present disclosure provides a method for regenerating an acid-inactivated superabsorbent polymer into a superabsorbent recycled polymer having a predetermined water absorbency, from used sanitary articles comprising pulp fibers and superabsorbent polymers. , a method for producing a superabsorbent recycled polymer having a predetermined water absorbency, and an alkali metal ion source, an acid-inactivated superabsorbent polymer having a predetermined water absorbency; It relates to the use for regeneration into recycled polymer.

Methods for recovering superabsorbent polymers from used sanitary products are 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 removed from a used bodily fluid-absorbing article and subjected to washing and dehydration treatment. However, it describes a method for regenerating a water-absorbing resin, which includes an operation of placing the water-absorbing resin in an environment in which the liquid absorbed by the water-absorbing resin is discharged.

Further, in paragraph [0037] of Patent Document 1, the water absorbent resin after undergoing the regeneration treatment as exemplified above is the recycled water absorbent resin of the present invention (hereinafter referred to as the water absorbent resin of the present invention). It is described that it is preferable to add a basic compound again in order to adjust the pH if necessary, although it may be used as it is as an absorbent article.

Japanese Patent Application Laid-Open No. 2003-326161

In the recycling of used sanitary products, for example, when recycling disposable diapers, light incontinence pads, sanitary napkins, panty liners, etc. together, the superabsorbent polymer to be recycled has relatively high water absorbency. Superabsorbent polymers (e.g., those contained in disposable diapers) and superabsorbent polymers with relatively low water absorbency but excellent gel strength when wet (e.g., light incontinence pads, sanitary napkins, panty liners, etc.) Since the recycled superabsorbent polymer will be mixed, a superabsorbent polymer with relatively high water absorption and a superabsorbent polymer with relatively low water absorbency will be mixed. tend to be included.

In addition, even if the sanitary goods to be recycled are limited to, for example, only disposable diapers, in general, disposable diapers from different manufacturers contain superabsorbent polymers with different absorbency, so the high water content to be recycled is Absorbent polymers, as well as regenerated superabsorbent polymers, tend to include, in principle, superabsorbent polymers with different water absorbencies.

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 superabsorbent polymers recycled from used sanitary goods are reused for applications with a narrow tolerance for water absorption, such as sanitary goods, it is necessary to recycle them so as not to adversely affect the water absorption of the sanitary goods. It is thought that it is necessary to mix the superabsorbent polymer with a low ratio (for example, 10 to 30% by mass of the superabsorbent polymer contained in the sanitary goods) with the virgin superabsorbent polymer. At present, there is generally no business of reusing superabsorbent polymers recycled from used sanitary goods for sanitary goods.

In the regeneration method described in Patent Document 1, regeneration of the absorbent resin is completed by carrying out the "regeneration method" including predetermined "washing" and "dehydration treatment", and paragraph [0037] of Patent Document 1 is completed. ] adjusts the pH of the absorbent resin exhibiting acidity due to the acidic compound added in the "dehydration treatment" to shrink the gel, specifically for neutralization It is not for adjusting the water absorbency of the regenerated absorbent resin.
Therefore, since the absorbent resin regenerated by the regeneration method described in Patent Document 1 does not have adjusted water absorbency, in order to reuse it in sanitary goods, it is necessary not to hinder the water absorbency of the sanitary goods. In addition, it is necessary to mix in a low ratio, for example, 10 to 30% by mass.

In view of the above, it is an object of the present disclosure to provide a method for regenerating an acid-inactivated superabsorbent polymer that is capable of forming a superabsorbent recycled polymer having a predetermined absorbency.

The present disclosure discloses a method for regenerating an acid-inactivated superabsorbent polymer into a superabsorbent recycled polymer having a predetermined water absorbency, comprising: a preparatory step of preparing the superabsorbent polymer, adding an alkali metal ion supply capable of supplying alkali metal ions to the aqueous regeneration solution containing the acid-inactivated superabsorbent polymer, and inactivating with the acid; a superabsorbent recycled polymer forming step of forming the superabsorbent recycled polymer in a wet state from the obtained superabsorbent polymer, drying the superabsorbent recycled polymer in the wet state to have the predetermined water absorbency; A method has been found 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 absorbency.

FIG. 1 is a block diagram of a system 1 for implementing methods of manufacture, refurbishment 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 of FIG. FIG. 3 is a flow chart 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"
As used herein, "absorption capacity" is measured as follows.
(1) Put the wet superabsorbent polymer or superabsorbent recycled polymer in a mesh and hang it for 5 minutes to remove the moisture adhering to the surface, and measure the mass before drying: m ₁ (g) do.
(2) Dry the superabsorbent polymer or superabsorbent recycled polymer from which water adhering to the surface is removed at 50° C. for 180 minutes, and measure the mass after drying: m ₂ (g).
(3) The absorption capacity (g/g) is calculated by the following formula:
Absorption capacity (g/g) = m1 _{/ m2}
Calculated by

・"Deactivation" for superabsorbent polymers
As used herein, "inactivation" with respect to a super absorbent polymer (SAP) means that the super absorbent polymer retaining excrement or the like is preferably 50 times or less, more preferably 30 times or less, More preferably, it means to adjust the absorption capacity to be 25 times or less, for example, to release retained excrement, to suppress absorption of an acid-containing aqueous solution, and the like.

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

Since the above recycling method includes a predetermined superabsorbent recycled polymer forming step and a drying step, the regenerated superabsorbent recycled polymer can be used in various applications that require different absorbency and narrower tolerances for absorbency. can be used. Also, the regenerated superabsorbent recycled polymer can be used in a high proportion for various applications.

[Aspect 2]
The method according to aspect 1, wherein the predetermined water absorbency is an arbitrary value of 100 to 400 times (g/g) absorbency with respect to deionization.
In the above recycling method, since the predetermined water absorbency is an arbitrary value of the predetermined absorbency, the superabsorbent recycled polymer is replaced with a superabsorbent polymer with low water absorbency. napkins for personal use, etc.) to applications where a superabsorbent polymer with high water absorption is preferable (for example, disposable diapers, etc.).

[Aspect 3]
Aspect 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 an acid dissociation constant greater than that of the acid group of the superabsorbent polymer. The method described in .
In the above regeneration method, since the alkali metal ion supply source is a predetermined compound, the water absorbency of the regenerated superabsorbent recycled polymer can be easily adjusted.

[Aspect 4]
4. The method of any one of aspects 1-3, wherein the alkali metal ions are selected from the group consisting of lithium ions, sodium ions and potassium ions, and any combination thereof.
In the recycling method described above, the highly water-absorbent recycled polymer is excellent in water absorbency because it is selected from the predetermined group.

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

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

In the above regeneration method, since the pH of the aqueous solution for regeneration is adjusted to a predetermined range, the superabsorbent recycled polymer is selected from applications in which a superabsorbent polymer with low water absorption is preferred to applications in which a superabsorbent polymer with high water absorption is preferred. Up to, the water absorbency of the superabsorbent recycled polymer can be easily adjusted.

[Aspect 7]
A method for producing a superabsorbent recycled polymer having a predetermined water absorbency from a used sanitary product comprising pulp fibers and a superabsorbent polymer, the method comprising the steps of:
The sanitary article constituent material constituting the sanitary article, which contains the pulp fiber and the superabsorbent polymer having an acid group, is immersed in an acid-containing aqueous solution containing an acid, and the acid-inactivated superabsorbent polymer is added. forming inactivation step,
An alkali metal ion supply source capable of supplying alkali metal ions is added to the aqueous solution for regeneration containing the acid-inactivated superabsorbent polymer, and from the acid-inactivated superabsorbent polymer, in a wet state a superabsorbent recycled polymer forming step for forming the superabsorbent recycled polymer;
a drying step of drying the superabsorbent recycled polymer in a wet state to form a superabsorbent recycled polymer having the predetermined water absorbency;
The above method, characterized in that it comprises:

Since the above production method includes a predetermined superabsorbent recycled polymer forming step and a drying step, the produced superabsorbent recycled polymer can be used in various applications where different water absorbency and narrow tolerance water absorbency are required. can be used for In addition, the highly water-absorbent recycled polymer produced can be used in a high proportion for various applications.

[Aspect 8]
Aspect 7, wherein the alkali metal ion source is an alkali metal hydroxide or a salt of an alkali metal hydroxide and an acid having an acid dissociation constant greater than that of the acid groups of the superabsorbent polymer. the method of.
In the above production method, since the alkali metal ion supply source is a predetermined compound, the water absorbency of the regenerated superabsorbent recycled polymer can be easily adjusted.

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

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

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

In the above production method, the pH of the aqueous solution for regeneration is adjusted to a predetermined range, so that the superabsorbent recycled polymer is selected from applications where a superabsorbent polymer with low water absorption is preferred to applications where a superabsorbent polymer with high water absorption is preferred. Up to, the water absorbency of the superabsorbent recycled polymer can be easily adjusted.

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

In the above production method, in the superabsorbent recycled polymer forming step, an acid-containing aqueous solution is used as the aqueous solution for regeneration, and the pH of the aqueous solution for regeneration is adjusted to a predetermined range. A suitable superabsorbent recycled polymer can be easily produced.

[Aspect 12]
The aqueous solution for regeneration is a neutral aqueous solution or an alkaline aqueous solution, and in the superabsorbent recycled polymer forming step, the superabsorbent polymer deactivated by acid is immersed in the aqueous solution for regeneration, A method according to aspect 9 or 10, wherein the pH is adjusted to above 7.0 and below 9.0.

In the above production method, the aqueous solution for regeneration is a neutral aqueous solution or an alkaline aqueous solution, and in the superabsorbent recycled polymer forming step, the superabsorbent polymer deactivated by acid is immersed in the aqueous solution for regeneration, and the regeneration is performed. Since the pH of the aqueous solution for use is adjusted to a predetermined range, a highly water-absorbing recycled polymer suitable for applications in which a highly water-absorbing polymer is preferred can be easily manufactured by reducing the amount of the alkali metal ion source. can do.

[Aspect 13]
Use of an alkali metal ion source capable of supplying alkali metal ions for regenerating an acid-inactivated superabsorbent polymer into a superabsorbent recycled polymer having a predetermined water absorbency, comprising:
The alkali metal ion supply source is added to the aqueous solution for regeneration containing the acid-inactivated superabsorbent polymer having an acid group, and the acid-inactivated superabsorbent polymer is dehydrated in a wet state. a superabsorbent recycled polymer forming step for forming the superabsorbent recycled polymer;
Uses above, including;

Since the use includes a predetermined superabsorbent recycled polymer forming step, the formed superabsorbent recycled polymer can be used in various applications where different and narrow tolerances of water absorbency are required. In addition, the regenerated superabsorbent recycled polymer can be used in a high proportion for various applications.

[Aspect 14]
Aspect 13, wherein the alkali metal ion source is an alkali metal hydroxide, or a salt of an alkali metal hydroxide and an acid having an acid dissociation constant greater than the acid groups 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 regenerated superabsorbent recycled polymer can be easily adjusted.

(1) A method of recycling an acid-inactivated superabsorbent polymer of the present disclosure into a superabsorbent recycled polymer having a predetermined water absorbency (hereinafter, “method for regenerating a superabsorbent polymer”, “this (2) A method of producing a superabsorbent recycled polymer having a predetermined water absorbency from used sanitary goods containing pulp fibers and a superabsorbent polymer. (hereinafter sometimes referred to as a “method for producing a superabsorbent recycled polymer”, a “method for producing the present disclosure”, etc.); Use for regenerating an activated superabsorbent polymer into a superabsorbent recycled polymer having a predetermined water absorbency (hereinafter referred to as "use of an alkali metal ion source", "use of the present disclosure" ) will be described in detail below.
From the viewpoint of ease of explanation, first, (2) a method for producing a superabsorbent recycled polymer will be explained, (1) a method for regenerating a superabsorbent polymer, and (3) use of an alkali metal ion supply source. (2) Differences from the production method of superabsorbent recycled polymer will be explained.

<<Method for producing superabsorbent recycled polymer>>
A method for manufacturing a superabsorbent recycled polymer includes the following steps.
- A sanitary product component material comprising a pulp fiber and a super absorbent polymer having an acid group is immersed in an acid-containing aqueous solution to form an acid-inactivated super absorbent polymer. inactivation step (hereinafter sometimes referred to as "inactivation step")
- A superabsorbent recycled polymer that forms a superabsorbent recycled polymer in a wet state by adding an alkali metal ion supply capable of supplying alkali metal ions to an aqueous solution for regeneration containing a superabsorbent polymer deactivated by an acid. Formation step (hereinafter sometimes referred to as "superabsorbent recycled polymer formation step")
- A drying step of drying the superabsorbent recycled polymer in a wet state to form a superabsorbent recycled polymer having a predetermined water absorbency (hereinafter sometimes referred to as a "drying step")

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

Examples of the acid include, but are not limited to, inorganic acids and organic acids. Deactivating the superabsorbent polymer with acid has a higher effect on pulp fibers than deactivating the superabsorbent polymer with lime, calcium chloride, magnesium sulfate, magnesium chloride, aluminum sulfate, aluminum chloride, etc. Hard to leave ash.

Examples of the inorganic acid include sulfuric acid, hydrochloric acid and nitric acid. Sulfuric acid is preferable as the inorganic acid from the viewpoints of chlorine-free and cost. Examples of the organic acid include those having an acid group such as a carboxyl group and a sulfo group. 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. From the viewpoint of protecting equipment, the organic acid is preferably an organic acid having a carboxyl group, particularly a carboxylic acid.

When the organic acid has a carboxyl group, the organic acid can have one or a plurality of carboxyl groups per molecule, and preferably has a plurality of carboxyl groups. By doing so, the organic acid easily forms a chelate complex with a divalent or higher metal contained in excrement, such as calcium, and the ash content of recycled pulp fibers produced from used sanitary products is easily reduced. Become.

Examples of the organic acid include citric acid, tartaric acid, malic acid, succinic acid, oxalic acid (the above are carboxylic acids having a plurality of 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) (all carboxylic acids having one carboxyl group), methanesulfonic acid, trifluoromethanesulfonic acid, Examples include benzenesulfonic acid, p-toluenesulfonic acid (all referred to as sulfonic acid), and the like.

The acid-containing aqueous solution preferably has a predetermined pH, wherein the predetermined pH is preferably 4.5 or less, more preferably 4.0 or less, even more preferably 3.5 or less, and even more preferably 3 .0 or less. If the predetermined pH is too high, the superabsorbent polymer is not sufficiently inactivated, excrement held by the superabsorbent polymer tends to be insufficiently excreted, and separation from pulp fibers and the like tends to occur. tends to be difficult.

Also, the predetermined pH is preferably 0.5 or higher, and more preferably 1.0 or higher. If the predetermined pH is too low, the superabsorbent polymer is more inactivated, and the reaction between the inactivated superabsorbent polymer and the alkali metal ion source takes longer in the step of forming the superabsorbent recycled polymer. Tend. In addition to the recycling method of the present disclosure, when recycling pulp fibers contained in used sanitary goods to produce recycled pulp fibers, the recycled pulp fibers may be damaged.
In addition, in this specification, pH means the value in 25 degreeC. Also, the pH can be measured using, for example, twin pH meter AS-711 manufactured by Horiba, Ltd.

In the manufacturing method of the present disclosure, the acid-containing aqueous solution preferably satisfies the predetermined pH at least at the start of the inactivation step, for example, when immersing the constituent materials of sanitary goods in the acid-containing aqueous solution. This is for inactivating the superabsorbent polymer, and if the inactivation of the superabsorbent polymer is insufficient, the deactivation of the superabsorbent polymer is not sufficiently performed, and the body fluids retained by the superabsorbent polymer 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, the predetermined pH is preferably met at the end of the inactivation step. This is from the viewpoint of continuing to inactivate the superabsorbent polymer.

The superabsorbent polymer is not particularly limited as long as it is used as a superabsorbent polymer having an acid group in the technical field, 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 polyacrylates and polymaleic anhydrides, and examples of superabsorbent polymers containing sulfo groups and the like include polysulfonates. mentioned.
The pulp fiber is not particularly limited as long as it can be contained in sanitary goods.

In addition, the acid for inactivating the _{superabsorbent} polymer efficiently deactivates the superabsorbent polymer. It preferably has 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) is preferably smaller than the acid dissociation constant (pK _a , in water) of the acid groups of the superabsorbent polymer. 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 of the superabsorbent polymer. is preferred. This is from the viewpoint of the efficiency of inactivation of the superabsorbent polymer.

In this specification, the acid dissociation constant ( _pka , in water) can be the value described in the Electrochemical Handbook edited by the Electrochemical Society of Japan.
According to the Handbook of Electrochemistry, the acid dissociation constants ( _pka , in water, 25° C.) of major 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

Acid dissociation constants ( _pka in water) of acids that are not described in electrochemical handbooks can be determined by measurement. An example of an instrument capable of measuring the acid dissociation constant ( _pka , in water) of an acid is T3, a compound physical property evaluation analysis system manufactured by Sirius.

In the manufacturing method of the present disclosure, the specific method is not particularly limited as long as the constituent materials of sanitary articles can be immersed in the acid-containing aqueous solution. and the acid-containing aqueous solution may be introduced into the tank in which the sanitary article components are placed.

The sanitary products are not particularly limited as long as they contain a superabsorbent polymer, and examples thereof include disposable diapers, disposable shorts, sanitary napkins, panty liners, urine absorbing pads, bed sheets, and pet sheets. be done. The sanitary goods preferably contain pulp fibers and a superabsorbent polymer.
Examples of the sanitary goods include those including a liquid-permeable sheet, a liquid-impermeable sheet, and an absorbent body (absorbent core and core wrap) therebetween.

In the manufacturing method of the present disclosure, the sanitary article component in the deactivation step can be a mixture of pulp fibers and superabsorbent polymers, such as absorbent cores taken from used sanitary articles. Further, the sanitary product constituent material may be the sanitary product itself.

In addition to pulp fibers and superabsorbent polymers (hereinafter sometimes referred to as "specified materials"), the sanitary product constituent materials to be immersed in the acid-containing aqueous solution are additional materials (hereinafter referred to as "non-specified materials") ), for example, when a liquid-permeable sheet, a liquid-impermeable sheet, etc. are included, for example, when the sanitary product itself is immersed in an acid-containing aqueous solution as a constituent material of the sanitary product, after the inactivation step, A removal step (hereinafter sometimes referred to as a “removal step”) for removing non-specific materials may be further included. In addition, in the removing step, all of the non-specified materials may be removed, or part of the non-specified materials may be removed.

Specific examples of the above removal steps are described below in connection with the system 1 shown in FIG. 1 and the flow chart shown in FIG.

In the inactivation step, for example, in an inactivation bath containing an acid-containing aqueous solution, the constituent materials of sanitary goods are stirred for about 5 to 60 minutes, depending on the temperature, to inactivate the superabsorbent polymer and acidify it. 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 (for example, sodium salt) state to a free acid state, thereby reducing the water absorbency of the superabsorbent polymer.
The inventors of the present application found that when a superabsorbent polymer that has absorbed water is placed in an acid-containing aqueous solution, negatively charged hydrophilic groups (e.g., —COO ⁻ ) are neutralized by positively charged hydrogen ions (H ⁺ ). It has been found that the ionic repulsive force of the hydrophilic groups is weakened due to the addition (eg —COOH), the water absorbency 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 can 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 facilitates sterilization of bacteria derived from excrement and the like contained in the acid-containing aqueous solution.

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

The inventor of the present application contacted an acid-inactivated superabsorbent polymer in water or the like with an alkali metal ion supply source while adjusting the amount thereof to convert a part of the acid groups of the superabsorbent polymer into an alkali metal salt. Thus, it was found that the water absorption of the superabsorbent recycled polymer in a wet state (that is, the water absorbency of the superabsorbent recycled polymer in a dry state) can be controlled.

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") and the like.

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

The above salt may be an acid salt, a basic salt, or the like.
Alkali metal hydroxides in the above salts include lithium hydroxide, sodium hydroxide and potassium hydroxide, and any combination thereof.
The acid in the above salt is not particularly limited, and examples thereof include acids listed in the "inactivation step" (eg, hydrochloric acid, sulfuric acid), carbonic acid, and the like.

The acid is preferably an acid having a higher acid dissociation constant (pK _a in water) than the acid dissociation constant (pK _a in water) of the acid groups in the superabsorbent polymer. By doing so, the acid groups of the superabsorbent polymer tend 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) is preferably larger than the acid dissociation constant (pK _a , in water) of the acid groups of the superabsorbent polymer. 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 of the superabsorbent polymer. is preferred. This is from the viewpoint of facilitating conversion of the acid group of the superabsorbent polymer into an alkali metal salt.

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

Examples of the salt 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 forming step, the aqueous regeneration solution can be acidic (pH<7.0), neutral (pH=7.0) or alkaline (7.0<pH), neutral or It is preferably alkaline, preferably alkaline. This is from the viewpoint of the effects of the present disclosure.

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

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

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

The inventors of the present application also found that by adjusting the pH of the system containing the acid-inactivated superabsorbent polymer, i.e., the pH of the aqueous solution for regeneration, the water absorbency of the superabsorbent recycled polymer in the wet state (i.e., high It was found that the water absorbency of the water-absorbing recycled polymer) can be adjusted within a predetermined range.

In addition, the "superabsorbent recycled polymer in a wet state" formed in the superabsorbent recycled polymer forming step has the same water absorption as the "superabsorbent recycled polymer" obtained in the drying step, but the drying step Depending on the specific method, the water absorbency of the superabsorbent recycled polymer varies. For example, the reaction between the acid group of the superabsorbent recycled polymer and the alkali metal further progresses, and the absorbency of the superabsorbent recycled polymer increases. 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 pH is not particularly limited as long as the superabsorbent recycled polymer in a dry state can achieve a predetermined water absorbency (absorption capacity). The pH may be either pH (pH=7.0) or an alkaline pH range (7.0<pH), and the pH is preferably 5.0 to 9.0.

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

When the pH is adjusted within the range of neutral pH or alkaline pH, the aqueous regeneration solution can be an acidic aqueous solution, a generally neutral aqueous solution, or an alkaline aqueous solution, and a generally neutral aqueous solution, Alternatively, it is preferably an alkaline aqueous solution. This is from the viewpoint of efficiently using the alkali metal ion supply source to form the superabsorbent recycled polymer.
It is also preferred to form the superabsorbent recycled polymer in the wet state by adding the alkali metal ion source as such or in the form of an aqueous solution to the aqueous regeneration solution, which is generally neutral or alkaline.

The alkali metal ion source may be present in the aqueous regeneration solution, as described above, and the alkali metal ion source can be added to the aqueous regeneration solution either neat or as an aqueous solution.
When an alkali metal hydroxide is added to the regeneration aqueous solution as the alkali metal ion supply source, the alkali metal hydroxide is preferably an aqueous solution, and the aqueous solution has a hydroxide ion concentration of , 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. be done. This is from the standpoint of easiness in adjusting the pH of the aqueous solution for regeneration and, in turn, the water absorbency of the superabsorbent recycled polymer.

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 added to the aqueous solution for regeneration. May be immersed. Examples of the apparatus capable of solid-liquid separation include a rotary drum screen, an inclined screen, a vibrating screen, and the like.

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

<Drying step>
The drying step dries the superabsorbent recycled polymer in a wet state to form a superabsorbent recycled polymer having a predetermined water absorbency.
The predetermined water absorbency is not particularly limited, but considering the practicality of the superabsorbent recycled polymer, the absorbency is preferably 100 times (g / g) with respect to deionized water. or more, 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 when the superabsorbent recycled polymer swells, the absorbency is preferably 500 times (g /g), more preferably 450 times (g/g) or less, and even more preferably 400 times (g/g) or less.

In the drying step, the aqueous solution for regeneration 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 superabsorbent recycled polymer can be separated from the aqueous solution for regeneration containing the superabsorbent recycled polymer by using a device capable of solid-liquid separation. Examples of the apparatus capable of solid-liquid separation include a rotary drum screen, an inclined screen, a vibrating screen, and the like.

The separated superabsorbent recycled polymer may be washed with tap water, deionized water, or the like before drying to remove the aqueous solution for regeneration adhering to the surface of the superabsorbent recycled polymer.
In addition, the separated superabsorbent recycled polymer is contacted with a hydrophilic organic solvent (for example, immersed in a hydrophilic organic solvent) before drying, so that the water contained in the separated superabsorbent recycled polymer is It can be dehydrated 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 temperature of drying can be lowered and/or the time of drying can be reduced.

The hydrophilic organic solvent is preferably one that is miscible with water. Solvents (eg, acetone, methyl ethyl ketone), nitrile solvents (eg, acetonitrile), and the like can be mentioned.

In the drying step, the superabsorbent recycled polymer in wet state is dried at a drying temperature of preferably room temperature (eg, 25°C) to 120°C, more preferably 30-80°C, and preferably 40-60°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 undergo dehydration condensation, etc., 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 performed under reduced pressure, for example at 0.1 kPa or more and less than 100 kPa.
The drying step can be performed, for example, for 30-300 minutes.
The drying step is preferably carried out so that the drying weight loss of the superabsorbent recycled polymer is preferably 15% or less (2.0 g, 105° C., 3 hours). This is from the viewpoint of utilization of superabsorbent recycled polymer.
The above loss on drying is based on the "Material Standards for Sanitary Treatment Products" attached as an attachment to the "Standards for Materials for Sanitary Treatment Products" notified by the Ministry of Health, Labor and Welfare as PFSB Notification No. 0325-24 on March 25, 2015. <2. General Test Methods>, "7. Loss on Drying Test Method".

After the drying step, if the dried superabsorbent recycled polymer is fixed or integrated, the dried superabsorbent recycled polymer may be pulverized and classified.

<<Method for regenerating superabsorbent polymer inactivated by acid>>
A method of 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 superabsorbent recycled polymer that forms a superabsorbent recycled polymer in a wet state by adding an alkali metal ion supply capable of supplying alkali metal ions to an aqueous solution for regeneration containing a superabsorbent polymer deactivated by an acid. Formation step (hereinafter sometimes referred to as "superabsorbent recycled polymer formation step")
- A drying step of drying the superabsorbent recycled polymer in a wet state to form a superabsorbent recycled polymer having a predetermined water absorbency (hereinafter sometimes referred to as a "drying step")

<Preparation step>
In the preparation step, an acid-inactivated superabsorbent polymer having acid groups is provided.
The acid-inactivated superabsorbent polymer is not particularly limited as long as it is inactivated by an acid. can be prepared as described in
In addition to the above-mentioned acid-inactivated superabsorbent polymers, the superabsorbent polymers contained in used sanitary goods are inactivated with a polyvalent metal salt such as an alkaline earth metal salt. , and then those treated with acid are also included.

<Super absorbent recycled polymer forming step and drying step>
The “superabsorbent recycled polymer forming step” and the “drying step” in the recycling method of the present disclosure are respectively the “superabsorbent recycled polymer forming step” and the “drying step” in the “method for producing a superabsorbent recycled polymer”. Since it is the same, the explanation is omitted.

<Use of alkali metal ion supply source>
Use of an alkali metal ion source includes the following steps.
Add an alkali metal ion source capable of supplying alkali metal ions to an aqueous solution for regeneration containing an acid-inactivated superabsorbent polymer having acid groups to form a superabsorbent recycled polymer in a wet state. superabsorbent recycled polymer forming step (hereinafter sometimes referred to as “superabsorbent recycled polymer forming step”).

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 description is omitted.

FIG. 1 is a block diagram of a system 1 for implementing methods of manufacture, refurbishment and use according to one embodiment of the present disclosure. FIG. 1 is a diagram for explaining a manufacturing method, a recycling method, and a 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 oxidant treatment device 19 and a fourth separation device 20 are provided.

The bag-breaking device 11 is filled with an acid-containing aqueous solution and forms an opening in the acid-containing aqueous solution in the collection bag containing the used sanitary products. The crushing device 12 crushes the used sanitary goods submerged under the surface of the acid-containing aqueous solution together with the collection bag. FIG. 2 is a schematic diagram showing a configuration example of the bag breaking device 11 and the crushing device 12 of FIG.

The bag-breaking device 11 is filled with the acid-containing aqueous solution B, forms an opening in the collection bag A that has settled in the acid-containing aqueous solution B, and collects the used sanitary goods having the opening. 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 pore forming part 50 is provided in the solution tank V, and when the collection bag A is placed in the solution tank V, the pore forming part 50 is formed in the surface of the collection bag A in contact with the acid-containing aqueous solution B. .

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

The bag-breaking section 40 is arranged in the lower part (preferably the bottom) of the solution tank V, and has a bag-breaking blade 41, a support shaft (rotating shaft) 42 that supports the bag-breaking blade 41, and the support shaft 42 as an axis. and a drive 43 rotating along. The bag-breaking blade 41 is rotated around a rotating shaft (supporting shaft 42) by a driving device 43 to form an opening in the collecting bag A moved to the lower portion of the acid-containing aqueous solution B (solution tank V).

The crushing device 12 crushes the used sanitary goods in the collection bag A submerged under 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 the collection bag 91 containing the used sanitary goods discharged from the solution tank V and having an opening is crushed together with the collection bag A into the acid-containing aqueous solution. Crush in B to form an acid-containing aqueous solution 92 containing the crushed material.

The crushing unit 60 includes a twin-axis crusher (for example, a twin-axis rotary crusher, a twin-shaft differential crusher, a twin-shaft shear crusher), for example, SumiCutter (Sumitomo Heavy Industries Environment Co., Ltd. manufactured by the company). The pump 63 is connected to the crushing section 60 by a pipe 62, and draws out the acid-containing aqueous solution 92 containing the crushed matter obtained in the crushing section 60 from the crushing section 60 and delivers it to the next step. However, the crushed materials include materials including pulp fibers, acid-inactivated superabsorbent polymers, materials for the collection bag A, films, non-woven fabrics, elastic bodies, and the like.

The first separation device 13 agitates the acid-containing aqueous solution 92 containing the crushed matter obtained by the crushing device 12 to wash the crushed matter to remove dirt (excretion, etc.), while removing the acid containing the crushed matter. The first acid-containing aqueous solution 93 from which the foreign matter has been removed is separated from the containing aqueous solution 92 , and the first acid-containing aqueous solution 93 is sent to the first dust remover 14 . The acid-containing first aqueous solution 93 contains pulp fibers and acid-inactivated superabsorbent polymer.

As the first separation device 13, for example, a washing machine having a washing tub/drying tub and a tub surrounding it can be used. However, the washing tub and dewatering tub (rotary drum) is used as the washing tub and sieve tub (separation tub). Examples of the washing machine include a horizontal washing machine ECO-22B (manufactured by Inamoto Seisakusho Co., Ltd.).

The first dust remover 14 further removes foreign matter present in the acid-containing first aqueous solution 93 with a screen having a plurality of openings, and the second acid-containing aqueous solution from which foreign matter has been removed more than the acid-containing first aqueous solution 93 is removed. form 94; The acid-containing second aqueous solution 94 contains pulp fibers and acid-inactivated superabsorbent polymer. Examples of the first dust remover 14 include a screen separator (coarse screen separator), and more specifically, a pack pulper (manufactured by Satomi Seisakusho Co., Ltd.).

The second dust remover 15 removes finer foreign matter from the acid-containing second aqueous solution 94 delivered from the first dust remover 14 by using a screen having a plurality of openings, and removes more foreign matter than the acid-containing second aqueous solution 94. A second acid-containing third aqueous solution 95 is formed. The acid-containing third aqueous solution 95 contains pulp fibers and acid-inactivated superabsorbent polymer. As the second dust remover 15, for example, a screen separator, specifically, Lamo Screen (manufactured by Aikawa Iron Works Co., Ltd.) can be used.

The third dust remover 16 further removes foreign matter from the acid-containing third aqueous solution 95 sent from the second dust remover 15 by centrifugal separation, and removes more foreign matter from the acid-containing third aqueous solution 95 than the acid-containing third aqueous solution 95. A containing fourth aqueous solution 96 is formed. The acid-containing third aqueous solution 95 contains pulp fibers and acid-inactivated superabsorbent polymer. As the third dust remover 16, for example, a cyclone separator, specifically an ACT low-concentration cleaner (manufactured by Aikawa Iron Works Co., Ltd.) can be used.

The second separation device 17 separates the acid-containing fourth aqueous solution 96 sent from the third dust removal device 16 through a screen having a plurality of openings into an acid-containing aqueous solution containing an acid-inactivated superabsorbent polymer and mainly pulp fibers. and the acid-containing aqueous solution 97 contained therein. The acid-inactivated superabsorbent polymer also remains in the acid-containing aqueous solution 97 mainly containing pulp fibers.
The second separation device 17 is, for example, 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 polymer through a screen having a plurality of openings. 98 and a liquid containing the acid-inactivated superabsorbent polymer and the acid-containing aqueous solution, and pressurizing the solid 98 containing the pulp fibers and the acid-inactivated superabsorbent polymer to produce the pulp fibers and the acid-inactivated superabsorbent polymer. The acid-deactivated superabsorbent polymer is crushed in a solid 98 containing the organic polymer.
Examples of the third separation device 18 include a screw press dehydrator, specifically a screw press dehydrator manufactured by Kawaguchi Seiki Co., Ltd.

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

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

The fourth separation device 20 uses a screen having a plurality of openings to separate the recycled pulp fibers and the treatment liquid from the treatment liquid 99 containing the recycled pulp fibers treated by the oxidizing agent treatment device 19 . The fourth separation device 20 may be, for example, a screen separator.

FIG. 3 is a flow chart illustrating a method for producing recycled pulp fibers and superabsorbent recycled polymers from used sanitary products using the system 1 shown in FIG. The flow chart shown in FIG. 3 is exemplary and in no way limits the present disclosure.

FIG. 3 shows an inactivation step S1 (preparation step S1), a removal step S2, a superabsorbent recycled polymer forming step S3, and a recycled pulp fiber recovery step S4. The inactivation step S1 (preparation step S1) includes an opening formation 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 A dust removal step P15 and a third dust removal step P16 are included, the superabsorbent 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. A detailed description will be given below.

The opening forming step P11 is performed using the bag-breaking device 11 . A collection bag A containing used sanitary goods is put into a solution tank V containing an acid-containing aqueous solution B, and an opening is formed in the surface of the collection bag A that is in contact with the acid-containing aqueous solution B. The acid-containing aqueous solution B is spread around the collection bag A when the collection bag A is formed with the perforations so that dirt, fungi, odors, etc. of the used sanitary goods in the collection bag A are not released to the outside. Surround and seal. When the acid-containing aqueous solution enters the collection bag A through the openings, the gas in the collection bag A escapes to the outside of the collection bag A, the specific gravity of the collection bag A becomes heavier than that of the acid-containing aqueous solution B, and the collection bag A It settles in the acid-containing aqueous solution B. Also, the acid in the acid-containing aqueous solution B acts as an inactivating agent, inactivating the superabsorbent polymer in the used sanitary article in the collection bag A.

When the superabsorbent polymer in the used sanitary product is inactivated, its water absorption capacity is reduced, the superabsorbent polymer is dehydrated, and the particle size becomes smaller, making it easier to handle in subsequent steps. and improve processing efficiency. The use of acid for inactivation has the advantage that ash does not remain in the pulp fiber compared to the case of inactivating the superabsorbent polymer using lime, calcium chloride, etc., and the degree of inactivation (particle size, specific gravity etc.) can be easily adjusted by pH.

When the constituent materials of sanitary articles to be immersed in the acid-containing aqueous solution include non-specified materials such as liquid-permeable sheets, liquid-impermeable sheets, etc., for example, the sanitary article itself is used as the constituent material of the sanitary article in the acid-containing aqueous solution. When immersed in the water, it is preferable that the size, specific gravity, etc. of the pulp fibers constituting the specific material are relatively close 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-described predetermined pH in the inactivation step.

In the bag-breaking device 11 of FIG. 2, the rotation of the stirring blade 33 around the rotating shaft (supporting shaft 32) causes 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 in 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-breaking blade 41 due to the rotation of the bag-breaking blade 41 around the rotation shaft (support shaft 42), and an opening is formed in the collection bag A. .

The crushing process P12 is performed 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. Articles are crushed in an acid-containing aqueous solution B together with a collection bag A.

For example, in the crushing device 12 of FIG. It is crushed together with A in an acid-containing aqueous solution B (submerged crushing step). In the crushing apparatus 12 of FIG. 2, the acid-containing aqueous solution 92 containing the crushed material obtained in the crushing unit 60 (submerged crushing step) is drawn out from the crushing unit 60 (drawing step) by the pump 63 and sent to the next step. be done.

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

As a result, the acid-containing first aqueous solution 93 containing the pulp fibers and the acid-inactivated superabsorbent polymer is separated from the acid-containing aqueous solution 92 containing the crushed matter through the through-holes and delivered from the first separation device 13. be done. On the other hand, relatively large unspecified materials in the acid-containing aqueous solution 92 containing crushed materials cannot pass through the through-holes and remain in the first separation device 13 or are sent out through another route. Among the crushed non-specified materials, small ones 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 separating device 13, the size of the through-hole of the washing tub functioning as a sieve may be 5 mm to 20 mmφ in the case of a round hole. In some cases, the size of the area is 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, and the acid-containing aqueous solution containing pulp fibers and acid-inactivated superabsorbent polymer and crushed non-specific materials (foreign matter) are further separated. To separate. As a result, the crushed non-specified 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 remover 14 . On the other hand, the crushed non-specified material (foreign matter) cannot pass through the screen and remains in the first dust remover 14 or is sent out through another route. Among the crushed non-specified materials, smaller ones cannot be completely separated by the first dust remover 14 and are included in the acid-containing second aqueous solution 94 .

The second dust removal step P15 is performed by the second dust remover 15, and passes the acid-containing second aqueous solution 94 sent from the first dust remover 14 through a screen to remove the acid containing the pulp fibers and the acid-inactivated superabsorbent polymer. The contained aqueous solution and the crushed non-specified material (foreign matter) are further separated. As a result, the crushed non-specified 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 remover 15 . On the other hand, the crushed non-specified material (foreign matter) cannot pass through the screen and remains in the second dust remover 15 or is sent out through another route. Among the crushed non-specified materials, even smaller ones cannot be completely separated by the second dust remover 15 and are included in the acid-containing third aqueous solution 95 .

The third dust removal step P16 is performed by the third dust remover 16, and the acid-containing third aqueous solution 95 delivered from the second dust remover 15 is centrifuged in an inverted conical housing to remove pulp fibers and acid free. The acid-containing aqueous solution containing the activated superabsorbent polymer and the crushed non-specific material (foreign matter) are further separated. As a result, an acid-containing fourth aqueous solution 96 is delivered from the top of the third dust remover 16 (cyclone separator). On the other hand, crushed non-specific materials (foreign matter), particularly heavy materials such as metals, are delivered from the lower part of the third dust remover 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 a predetermined range.

The second separation process P17 is performed by the second separation device 17 . The fourth acid-containing aqueous solution 96 delivered from the third dust remover 16 is separated by a drum screen into an acid-containing aqueous solution containing 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, among the acid-containing fourth aqueous solution 96, the acid-containing aqueous solution 97 mainly containing pulp fibers cannot pass through the drum screen and is sent from the second separating device 17 through another route.

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

Further, 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 separation device such as a rotary drum screen, and separated. , The acid-inactivated superabsorbent polymer is moved to a stirring device filled with tap water, an alkaline aqueous solution, etc. as an aqueous solution for regeneration, and an alkali metal ion supply source is added to adjust the pH, and the superabsorbent in a wet state. can form organically recycled polymers.

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

A third separation process P18 is performed by the third separation device 18 . The acid-containing aqueous solution 97 mainly containing pulp fibers sent from the second separation device 17 is separated by a drum screen from solids 98 containing pulp fibers and acid-inactivated superabsorbent polymers, acid-inactivated superabsorbent polymers and and a liquid containing an acid-containing aqueous solution. Along with the separation, the acid-deactivated superabsorbent polymer in the solid 98 containing the pulp fibers and the acid-deactivated superabsorbent polymer is pressed and crushed. As a result, the liquid containing the acid-inactivated superabsorbent polymer and the acid-containing aqueous solution is separated from the acid-containing aqueous solution 97 mainly containing pulp fibers through the drum screen and discharged from the third separating device 18 . On the other hand, in the acid-containing aqueous solution 97 mainly containing pulp fibers, solids 98 containing pulp fibers and acid-inactivated superabsorbent polymer cannot be added to the drum screen, and the third It is delivered outside the separating device 18 .

The oxidant treatment process P19 is performed by the oxidant treatment device 19 . The pulp fibers and crushed acid-deactivated superabsorbent polymer in the solids 98 containing pulp fibers and acid-deactivated superabsorbent polymer delivered from the third separation device 18 are treated with an aqueous solution containing an oxidizing agent. be. The acid-inactivated superabsorbent polymer is thereby oxidatively degraded and removed from the pulp fibers. As a result, the acid-inactivated super-absorbent polymer adhering to the pulp fibers of the solid 98 containing the pulp fibers and the acid-inactivated super-absorbent polymer (eg, remaining on the surface of the pulp fibers) was removed by the aqueous solution containing the oxidizing agent. By being oxidatively decomposed and changed into low-molecular-weight organic substances soluble in aqueous solutions, they are removed from the pulp fibers to form a treatment liquid 99 containing recycled pulp fibers.

For example, in the oxidizing agent treatment device 19, a solid 98 containing pulp fibers and 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, the aqueous solution containing the oxidizing agent. to go On the other hand, ozone-containing gas is continuously discharged in the form of fine bubbles (for example, microbubbles or nanobubbles) into the processing liquid from nozzles in the processing bath. That is, the ozone-containing gas rises from the bottom of the processing liquid toward the top. Within the treatment liquid, the settling pulp fibers and the rising ozone-containing gas collide while advancing in opposite directions. Then, the ozone-containing gas adheres to the surfaces of the pulp fibers so as to wrap the pulp fibers. At that time, the ozone in the ozone-containing gas reacts with the acid-inactivated superabsorbent polymer in the pulp fibers to oxidatively decompose the acid-inactivated superabsorbent polymer and dissolve it in the treatment liquid. Thereby, the acid-inactivated super-absorbent polymer contained in the pulp fibers of the solid 98 containing the pulp fibers and the acid-inactivated super-absorbent polymer is oxidatively decomposed and removed from the pulp fibers, and the treatment liquid 99 containing the recycled pulp fibers is produced. Form.

The fourth separation step P20 is performed by the fourth separation device 20, and the treated liquid 99 containing recycled pulp fibers passes through a screen having a plurality of slits to separate the recycled pulp fibers from the treated liquid 99 containing recycled pulp fibers. and the processing liquid are separated. As a result, the treated liquid passes through the screen and is separated from the treated liquid 99 containing the recycled pulp fibers and is delivered 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 separator 20 or are sent out through another route.

The production method of the present disclosure, the recycling method of the present disclosure, and the superabsorbent recycled polymer formed by the use of the present disclosure can be used without particular limitation in applications where superabsorbent polymers are 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 improvers, and the like.

The present disclosure will be described below using examples, but the present disclosure is not limited to these examples.
[Example 1]
A polyacrylic acid-based super absorbent polymer (Sumitomo Seika Co., Ltd., Aqua Keep, unused product) is placed 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.
The absorption capacity (physiological saline) of the immersed superabsorbent polymer was measured according to the method described herein, and the absorption capacity (physiological saline) was 86.6 (g/g).
In addition, when the absorption capacity (deionized water) was measured by changing the "physiological saline solution with a mass ratio of 150 times" to "deionized water with a mass ratio of 1,000 times", the absorption capacity (deionized water) was about 600 times (g/g).

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

[Examples 2 to 6]
The aqueous solution for regeneration 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 absorption capacity (g/g) of the pH and superabsorbent polymer (recycled superabsorbent polymer) was measured. FIG. 4 shows the relationship between the added amount of NaOH aqueous solution, pH and absorption capacity (g/g), and FIG. 5 shows the relationship between pH and absorption capacity (g/g).

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

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

[Example 7]
An acid-inactivated superabsorbent polymer was prepared according to Example 1, 450 g of the prepared acid-inactivated superabsorbent polymer was placed in a polytetrafluoroethylene bag, and 500 mL of the acid-inactivated superabsorbent polymer was added to each bag. Place in a 1 L beaker filled with deionized water, add a predetermined amount of Na ₂ CO ₃ to the beaker while stirring the beaker, remove the bag from the beaker 10 minutes after the addition of Na ₂ CO ₃ , and place the bag inside the bag. was measured. The results are shown in FIG. In addition, in Example 7, a plurality of experiments were performed 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 superabsorbent recycled polymer.

[Example 8]
The absorption capacity of the superabsorbent polymer (superabsorbent 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 FIG. 6, the horizontal axis represents the molar concentration (mmol/L) of NaHCO ₃ .

[Examples 9 to 13]
Artificial urine (ion A container (prepared by dissolving 200 g of urea, 80 g of sodium chloride, 8 g of magnesium sulfate, 3 g of calcium chloride, and about 1 g of pigment: Blue No. 1) in 10 L of exchanged water (the container contains an unused artificial urine in an amount about 1000 times the mass ratio of the superabsorbent polymer) for 30 minutes, and the superabsorbent polymer after immersion was allowed to stand on the net for 10 minutes.

The superabsorbent polymer after standing is placed in a container filled with a 1% by mass aqueous citric acid solution (the container is filled with an aqueous citric acid solution that is about 1000 times the mass ratio of the unused superabsorbent polymer. ) for 30 minutes, and the superabsorbent polymer after immersion was allowed to stand on the net for 10 minutes. The superabsorbent polymer after standing is placed in a container filled with a 20mmol/L NaOH aqueous solution (the container is filled with an NaOH aqueous solution of about 1000 times the mass ratio of the unused superabsorbent polymer. ) for 30 minutes, and the superabsorbent polymer after immersion (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. A portion of the highly water-absorbent recycled polymer in a wet state was sampled, and the absorption capacity (after regeneration) was measured to be 201.0 times.

Part of the superabsorbent recycled polymer in the wet state is placed in each container filled with a hydrophilic organic solvent (each container contains a hydrophilic organic It is dehydrated by immersing it in a solvent filled) for 30 minutes, the superabsorbent recycled polymer after dehydration is left to stand on the net for 10 minutes, and the absorption capacity of the superabsorbent recycled polymer after standing (dehydrated after) were measured. Table 1 shows the results.
The hydrophilic organic solvent used was methanol, ethanol, acetone, or acetonitrile, and as a control, a sample was prepared without immersion in the hydrophilic organic solvent.

After standing, the wet superabsorbent recycled polymer was dried at 60° C. for 24 hours to obtain a dry superabsorbent recycled polymer.
A container filled with deionized water (the container is filled with about 1000 times the mass ratio of the unused superabsorbent polymer). The highly water-absorbent recycled polymer after immersion was left to stand on a net for 10 minutes, and the absorption capacity (after drying) was measured. The results are shown in Table 1.

From Table 1, the superabsorbent recycled polymers dehydrated with a hydrophilic solvent (Examples 9 to 12) had the same absorption capacity (Example 13) as the superabsorbent polymer not dehydrated with a hydrophilic solvent (Example 13). after drying).

1 system 11 bag breaking device 12 crushing device 13 first separating device 14 first dust removing device 15 second dust removing device 16 third dust removing device 17 second separating device 18 third separating device 19 oxidant treatment device 20 fourth separating device S1 Inactivation step S2 Removal step S3 Highly absorbent recycled polymer forming step S4 Recycled pulp fiber recovery step P11 Aperture forming 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 (14)

A method for regenerating an acid-inactivated superabsorbent polymer into a superabsorbent recycled polymer having a predetermined water absorbency, comprising:
a preparatory step of providing an acid-inactivated superabsorbent polymer having acid groups;
An alkali metal ion supply source capable of supplying alkali metal ions is added to the aqueous solution for regeneration containing the acid-inactivated superabsorbent polymer, and from the acid-inactivated superabsorbent polymer, in a wet state a superabsorbent recycled polymer forming step of forming the superabsorbent recycled polymer;
a drying step of drying the superabsorbent recycled polymer in a wet state to form a superabsorbent recycled polymer having the predetermined water absorbency;
The above method, comprising 2. The method according to claim 1, wherein the predetermined water absorbency is an arbitrary value of 100 to 400 times (g/g) absorbency with respect to deionization. 2. The alkali metal ion source is an alkali metal hydroxide, or a salt of an alkali metal hydroxide and an acid having an acid dissociation constant greater than that of the acid group of the superabsorbent polymer. 2. The method described in 2. The method of any one of claims 1-3, wherein the alkali metal ions are selected from the group consisting of lithium ions, sodium ions and potassium ions, and any combination thereof. The method according to any one of claims 1 to 4, wherein the predetermined water absorbency is adjusted by controlling the pH of the aqueous regeneration solution. The method according to claim 5, wherein the pH of the regeneration aqueous solution is adjusted to 5.0 to 9.0 (25°C). A method for producing a superabsorbent recycled polymer having a predetermined water absorbency from a used sanitary product comprising pulp fibers and a superabsorbent polymer, the method comprising the steps of:
The sanitary article constituent material constituting the sanitary article, which contains the pulp fiber and the superabsorbent polymer having an acid group, is immersed in an acid-containing aqueous solution containing an acid, and the acid-inactivated superabsorbent polymer is forming inactivation step,
An alkali metal ion supply source capable of supplying alkali metal ions is added to the aqueous solution for regeneration containing the acid-inactivated superabsorbent polymer, and from the acid-inactivated superabsorbent polymer, in a wet state a superabsorbent recycled polymer forming step of forming the superabsorbent recycled polymer;
a drying step of drying the superabsorbent recycled polymer in a wet state to form a superabsorbent recycled polymer having the predetermined water absorbency;
The method, characterized in that it comprises: 8. According to claim 7, wherein the alkali metal ion source is an alkali metal hydroxide or a salt of an alkali metal hydroxide and an acid having an acid dissociation constant greater than that of the acid group of the superabsorbent polymer. described method. 9. The method according to claim 7 or 8, wherein the predetermined water absorbency is adjusted by controlling the pH of the aqueous regeneration solution. The method according to claim 9, wherein the pH of the regeneration aqueous solution is adjusted to 5.0 to 9.0 (25°C). 10. or, in the superabsorbent recycled polymer forming step, the acid-containing aqueous solution is used as the aqueous solution for regeneration, and the pH of the aqueous solution for regeneration is adjusted to 5.0 to 7.0 (25° C.). 10. The method according to 10. The aqueous solution for regeneration is a neutral aqueous solution or an alkaline aqueous solution. 11. The method of claim 9 or 10, wherein the pH is adjusted to above 7.0 and below 9.0. Use of an alkali metal ion source capable of supplying alkali metal ions for regenerating an acid-inactivated superabsorbent polymer into a superabsorbent recycled polymer having a predetermined water absorbency, comprising:
The alkali metal ion source is added to the aqueous solution for regeneration containing the acid-inactivated superabsorbent polymer having an acid group, and the acid-inactivated superabsorbent polymer in a wet state a superabsorbent recycled polymer forming step of forming the superabsorbent recycled polymer;
the above uses, including 14. According to claim 13, 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. Use as indicated.

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