JP6598836B2 - Method for collecting organic acid and excreta, and method for producing recycled pulp fiber - Google Patents

Description

  The present disclosure relates to a method for recovering organic acid and excrement from an inactivated aqueous solution for superabsorbent polymer containing excrement and organic acid, and organic to inactivate superabsorbent polymer from used absorbent articles. The present invention relates to a method for producing recycled pulp fiber while reusing an acid.

A method for recovering recycled pulp fibers from used absorbent articles is known.
For example, Patent Document 1 discloses a method of recovering pulp fibers from used sanitary products including pulp fibers and a superabsorbent polymer, and producing recycled pulp that can be reused as sanitary products. The used sanitary article is made into pulp fiber and other substances by applying physical force to the used sanitary article in an aqueous solution containing a polyvalent metal ion or an acidic aqueous solution having a pH of 2.5 or less. Including a step of decomposing into raw materials, a step of separating pulp fibers from a mixture of pulp fibers and other materials generated in the decomposing step, and a step of treating the separated pulp fibers with an ozone-containing aqueous solution having a pH of 2.5 or less. A method characterized by this is disclosed.

  In Patent Document 1, the acidic aqueous solution having a pH of 2.5 or less contains an organic acid, and the organic acid is selected from the group consisting of tartaric acid, glycolic acid, malic acid, citric acid, succinic acid, and acetic acid. It is described that it is at least one.

Japanese Patent Laid-Open No. 2006-881

  Since many organic acids function as weak acids and have a small environmental load, it is preferable to inactivate the superabsorbent polymer using organic acids. On the other hand, when the superabsorbent polymer containing the wearer's excrement is inactivated, the excrement retained by the superabsorbent polymer is discharged into the inactivated aqueous solution, so that the inactivated aqueous solution containing the excrement is discarded. In this case, treatment such as sterilization is required. In consideration of the environment, it is preferable to recover each of the organic acid and the excrement from the inactivated aqueous solution containing the excrement and the organic acid.

Therefore, this indication aims at providing the collection method of organic acid and excrement which can collect each of organic acid and excrement from inactivation aqueous solution containing excrement and organic acid.
Another object of the present disclosure is to provide a method for producing recycled pulp fibers from a used absorbent article while collecting each of the organic acid and excrement and reusing the organic acid.

  The present disclosure is a method for recovering an organic acid and excrement from an inactivated aqueous solution for a superabsorbent polymer containing an organic acid and excreta, wherein a divalent or higher-valent metal is added to the inactivated aqueous solution. A precipitation step of precipitating a water-insoluble salt of an organic acid by adding a metal salt containing or a base containing a metal having a valence of 2 or more, and the water-insoluble property of the organic acid from the inactivated aqueous solution having undergone the precipitation step A mixture collecting step for collecting a mixture of salt and solid excreta derived from the excrement, adding an acid capable of forming a free organic acid, a water-insoluble salt, and water to the mixture; and An organic acid generating step for forming an aqueous solution containing an organic acid, the water-insoluble salt and the solid excrement, an organic acid containing the organic acid by removing the water-insoluble salt and the solid excrement from the aqueous solution Organic acid aqueous solution to obtain acid aqueous solution Comprise obtained step found a method characterized by.

The organic acid and excrement recovery method of the present disclosure can recover each of the organic acid and excrement from the inactivated aqueous solution containing the excrement and the organic acid.
Further, the method for producing recycled pulp fiber from the used absorbent article of the present disclosure can produce recycled pulp fiber while recovering each of the organic acid and excrement and reusing the organic acid. .

FIG. 1 is a diagram illustrating a flowchart for explaining the collection method of the present disclosure. FIG. 2 is a diagram illustrating a flowchart for explaining an additional step in the collection method of the present disclosure. FIG. 3 is a diagram illustrating a flowchart for explaining a method for manufacturing recycled pulp fiber according to the present disclosure. FIG. 4 is a block diagram illustrating an example of a system 1 for carrying out the present disclosure. FIG. 5 is a schematic diagram illustrating a configuration example of the bag breaking device 11 and the crushing device 12 of FIG. 4. FIG. 6 is a diagram showing the results of Examples 1 and 2.

[Definition]
・ "Water-insoluble salt"
In the present specification, “water-insoluble” relating to “water-insoluble salt” means “not easily soluble”, “extremely insoluble” or “almost insoluble” in “general rule 29” of “15th revised Japanese Pharmacopeia”. ”, More preferably“ very hardly soluble ”or“ little soluble ”, and even more preferably“ very little soluble ”.

Specifically, “water-insoluble salt” means that 1 g of salt as a solute is placed in water as a solvent and shaken vigorously at 20 ± 5 ° C. every 5 minutes for 30 seconds. It means that the amount of water dissolved within is as follows.
・ Slightly soluble: 100 mL or more and less than 1,000 mL ・ Extremely difficult to dissolve: 1,000 mL or more and less than 10,000 mL ・ Almost insoluble: 10,000 mL or more

・ "Water-soluble salt"
In this specification, “water-soluble” related to “water-soluble salt” is “slightly soluble”, “easily soluble”, or “extremely soluble” in “general rule 29” of “15th revised Japanese Pharmacopoeia”. It is preferably classified, more preferably classified as “easily soluble” or “extremely soluble”, and more preferably classified as “extremely soluble”.

Specifically, “water-soluble salt” means that when 1 g of salt as a solute is placed in water as a solvent and shaken vigorously at 20 ± 5 ° C. every 5 minutes for 30 seconds, 1 g of salt is within 30 minutes. It means that the amount of water dissolved in is as follows.
・ Very easy to dissolve: Less than 1 mL ・ Easily soluble: 1 mL or more and less than 10 mL ・ Slightly soluble: 10 mL or more and less than 30 mL Note that “General Rules 29” in “Fifteenth Revised Japanese Pharmacopoeia” includes the following classifications: Exists.
・ Slightly difficult to dissolve: 30 mL or more and less than 100 mL

・ "Inactivation" for superabsorbent polymers
In the present specification, "inactivated" to high absorption water soluble polymer (Super Absorbent Polymer, SAP) is superabsorbent polymer holding the excrement is preferably 50 times or less, more preferably 30 times or less, More preferably, it means adjusting to have an absorption ratio of 25 times or less, for example, releasing retained excrement, suppressing absorption of inactivated aqueous solution, and the like.
The said absorption rate is measured as follows.
(1) Put the inactivated superabsorbent polymer in a mesh and suspend it for 5 minutes to remove the water adhering to the surface, and measure the mass before drying: m ₁ (g).

(2) The inactivated superabsorbent polymer is dried at 120 ° C. for 10 minutes, and the mass after drying is measured: m ₂ (g).
(3) Absorption capacity (g / g) is expressed by the following formula:
Absorption capacity (g / g) = 100 × m ₁ / m ₂
Calculated by
The inactivated aqueous solution means an aqueous solution for inactivating the superabsorbent polymer.

Specifically, the present disclosure relates to the following aspects.
[Aspect 1]
A method for recovering organic acid and excrement from an inactivated aqueous solution for superabsorbent polymer containing organic acid and excrement,
A precipitation step of precipitating a water-insoluble salt of an organic acid by adding a metal salt containing a divalent or higher metal or a base containing a divalent or higher metal to the inactivated aqueous solution;
A mixture collecting step for collecting a mixture of the water-insoluble salt of the organic acid and the solid excreta derived from the excrement from the inactivated aqueous solution that has undergone the precipitation step;
An organic compound that forms an aqueous solution containing the organic acid, the water-insoluble salt, and the solid excrement by adding water and an acid capable of forming a free organic acid and a water-insoluble salt to the mixture. Acid generation step,
An organic acid aqueous solution obtaining step for removing the water-insoluble salt and the solid excrement from the aqueous solution to obtain an organic acid aqueous solution containing the organic acid,
A method as described above, comprising:

  As a method for recovering an organic acid such as citric acid from an aqueous solution containing an organic acid, a method using an electrodialysis method is known. However, in the recycling of used absorbent articles, the inactivated aqueous solution containing the organic acid used to inactivate the superabsorbent polymer contains excrement derived from the wearer in addition to the organic acid. Therefore, when organic acid is purified from an inactivated aqueous solution by electrodialysis and reused, solid excreta derived from the excrement may clog the ion exchange membrane used in electrodialysis. is there. On the other hand, in order to prevent clogging of the ion exchange membrane, if an inactivated aqueous solution containing organic acid and excrement is filtered through a filtration membrane or the like before electrodialysis, fine solid excrement clogs the filtration membrane. Or the filtration tends to be very time consuming.

In the above method, when the organic acid is precipitated and collected as a water-insoluble salt of the organic acid, fine solid excreta can be aggregated and collected, and in the organic acid aqueous solution forming step, the organic acid can be collected. And solid excreta can be separated. In the above method, the liquid excreta derived from the excrement can be recovered as a liquid in the mixture collecting step.
Therefore, the said method can each collect | recover an organic acid and excrement from the inactivation aqueous solution containing excrement and an organic acid.

[Aspect 2]
The method according to aspect 1, wherein the organic acid is an organic acid having a carboxyl group.
In the above method, since the organic acid is an organic acid having a carboxyl group, in the organic acid generation step, it is possible to expand the choice of acids that can generate a free organic acid and a water-insoluble salt. It is possible to improve the recoverability.

[Aspect 3]
The method according to aspect 1 or 2, wherein in the precipitation step, the water-insoluble salt of the organic acid is precipitated by adding the metal salt to the inactivated aqueous solution after neutralizing the inactivated aqueous solution. .

In the above method, since the metal salt is added to the deactivated aqueous solution after neutralizing the deactivated aqueous solution in the precipitation step, the organic acid is difficult to form a chelate complex with the metal constituting the metal salt. The recoverability of is improved.
The above method is particularly useful when the organic acid is an organic acid capable of forming a chelate complex with a metal.

[Aspect 4]
Aspect 1 in which the organic acid is an organic acid that does not form a chelate complex with a metal, and in the precipitation step, the water-insoluble salt of the organic acid is precipitated by adding the base to the inactivated aqueous solution. Or the method of 2.

  In the above method, since the organic acid is an organic acid that does not form a chelate complex with a metal, in the precipitation step, the base is directly added to the deactivated aqueous solution without neutralizing the deactivated aqueous solution, Water-insoluble salts of organic acids can be precipitated. Therefore, in the above method, the organic acid and the excrement can be recovered from the inactivated aqueous solution containing the excrement and the organic acid in a small number of steps.

[Aspect 5]
The said bivalent or more metal is as described in any one of aspects 1-4 selected from the group which consists of Mg, Ca, Ba, Fe, Ni, Cu, Zn, and Al, and those arbitrary combinations. Method.

  In the above method, since the divalent or higher metal is selected from predetermined ones, the water-insoluble salt of the organic acid formed is less water-soluble, and in the subsequent mixture collecting step, the water-insoluble salt of the organic acid And it becomes easy to isolate | separate the mixture with a solid excrement from a water-soluble salt.

[Aspect 6]
The acid in the organic acid production step is an acid having an acid dissociation constant of the organic acid (pK _a, water) smaller acid dissociation constant than (pK _a, water), one of the aspects 1 to 5 The method described in 1.

In the method, the acid is the acid dissociation constant of the organic acid (pK _a, water) smaller acid dissociation constant (pK _a, water) than for an acid having, in organic acid production step, the free organic acids It becomes easy to generate.

[Aspect 7]
The method according to any one of aspects 1 to 6, wherein the acid in the organic acid generation step is selected from the group consisting of sulfuric acid, hydrochloric acid, nitric acid, iodic acid, and bromic acid.

  In the above method, since the acid in the organic acid generation step is selected from the group consisting of sulfuric acid, hydrochloric acid, nitric acid, iodic acid and bromic acid, a free organic acid is easily generated in the organic acid generation step.

[Aspect 8]
Before the precipitation step, the organic acid is added to the inactivated aqueous solution, the pH adjusting substep for adjusting the inactivated aqueous solution to a predetermined pH, and the inactivated aqueous solution after the pH adjusting substep, Aspect 1 further comprising a concentration step for increasing the concentration of the organic acid and the excrement in the inactivated aqueous solution by alternately repeating an inactivation substep for inactivating a new superabsorbent polymer. The method as described in any one of -7.

The method includes a concentration step of increasing the concentration of organic acid and excrement in the inactivated aqueous solution while inactivating the superabsorbent polymer in the inactivated aqueous solution before the precipitation step.
By adjusting the inactivated aqueous solution to a predetermined pH, the present inventors can inactivate the superabsorbent polymer even if the concentration of excreta containing a basic substance in the inactivated aqueous solution increases. I found.
Therefore, by increasing the concentration of the organic acid and excrement in the inactivated aqueous solution, the organic acid and excrement can be efficiently recovered while maintaining the inactivation of the superabsorbent polymer.

[Aspect 9]
The method according to aspect 8, wherein the concentration step further includes a sterilization substep of sterilizing the inactivated aqueous solution.

The inactivated aqueous solution containing excrement becomes easy to propagate with the passage of time and with increasing concentration of organic acid and excrement, bacteria that existed in the excrement, bacteria that exist in the environment, etc. .
In the above method, since the high concentration step further includes a sterilization substep, the bacteria in the inactivated aqueous solution can be suppressed to a predetermined amount.

[Aspect 10]
The method according to aspect 9, wherein, in the sterilization sub-step, the inactivated aqueous solution is sterilized using ozone, chlorine dioxide, hydrogen peroxide, ultraviolet light, radiation, or any combination thereof.

  In the above method, in the sterilization sub-step, the inactivated aqueous solution is sterilized using a predetermined sterilization means, so that the bacteria in the inactivated aqueous solution can be suppressed to a predetermined amount, and the inactivated aqueous solution is decolorized and deodorized. be able to. Further, in the above method, since the predetermined sterilization means is a sterilization means that does not substantially remain in the inactivated aqueous solution, the sterilization means hardly remains in the recovered organic acid aqueous solution, and a step of separating the sterilization means is unnecessary. It becomes.

[Aspect 11]
A method of producing recycled pulp fiber from a used absorbent article while reusing an organic acid that inactivates a superabsorbent polymer,
Inactivation to inactivate the superabsorbent polymer by immersing the material containing pulp fibers and superabsorbent polymer derived from the used absorbent article in an inactivated aqueous solution containing an organic acid having a predetermined pH Step,
From the material that has undergone the inactivation step, a recycled pulp fiber forming step for forming the recycled pulp fiber,
Taking out the material from the inactivated aqueous solution that has undergone the inactivation step, and adding a metal salt containing a divalent or higher metal or a base containing a divalent or higher metal to the inactivated aqueous solution from which the material has been taken out. A precipitation step of precipitating a water-insoluble salt of the organic acid,
A mixture collecting step for collecting a mixture of the water-insoluble salt of the organic acid and the solid excreta derived from the excrement from the inactivated aqueous solution that has undergone the precipitation step;
An organic compound that forms an aqueous solution containing the organic acid, the water-insoluble salt, and the solid excrement by adding water and an acid capable of forming a free organic acid and a water-insoluble salt to the mixture. Acid generation step,
An organic acid aqueous solution obtaining step for removing the water-insoluble salt and the solid excrement from the aqueous solution to obtain an organic acid aqueous solution containing the organic acid,
A reactivation step for performing the deactivation step using the organic acid aqueous solution as the deactivation aqueous solution,
A method as described above, comprising:

  The above method can produce recycled pulp fibers while recovering each of the organic acid and excrement from the used absorbent article and reusing the organic acid.

[Aspect 12]
After the inactivation step and before the precipitation step, the organic acid is added to the inactivated aqueous solution, the pH adjustment substep for adjusting the inactivated aqueous solution to a predetermined pH, and the pH adjustment substep. By increasing the concentration of the organic acid and the excrement in the inactivated aqueous solution by alternately repeating the inactivation substep for inactivating a new superabsorbent polymer in the inactivated aqueous solution. The method of embodiment 11, further comprising a step.

The method further includes a predetermined concentration step after the inactivation step and before the precipitation step.
By disclosing the inactivated aqueous solution to a predetermined pH, the present disclosure can inactivate the superabsorbent polymer even if the concentration of excreta containing a basic substance in the inactivated aqueous solution increases. I found.
Therefore, by increasing the concentration of the organic acid and excrement in the inactivated aqueous solution, the organic acid and excrement can be efficiently recovered while maintaining the inactivation of the superabsorbent polymer.

[Aspect 13]
The method according to aspect 12, wherein the concentration step further includes a sterilization substep of sterilizing the inactivated aqueous solution.

The inactivated aqueous solution containing excrement tends to propagate bacteria that existed in the excrement, bacteria that exist in the environment, etc. with the passage of time and with increasing concentrations of organic acid and excrement.
In the above method, since the high concentration step further includes a sterilization substep, the bacteria in the inactivated aqueous solution can be suppressed to a predetermined amount.

[Aspect 14]
14. The method according to aspect 13, wherein, in the sterilization substep, the inactivated aqueous solution is sterilized using ozone, chlorine dioxide, hydrogen peroxide, ultraviolet light, radiation, or any combination thereof.

  In the above method, in the sterilization sub-step, the inactivated aqueous solution is sterilized using a predetermined sterilization means, so that the amount of bacteria contained in the recycled pulp fiber can be reduced, and the recycled pulp fiber can be reduced by the inactivated aqueous solution. It is possible to suppress coloring and smelling, and to reduce man-hours for washing recycled pulp fibers. In the above method, since the predetermined sterilization means is a sterilization means that does not substantially remain in the inactivated aqueous solution, the sterilization means hardly remains in the recycled pulp fiber, and a step of separating the sterilization means from the recycled pulp fiber is unnecessary. It becomes.

  Method of recovering organic acid and excrement from inactivated aqueous solution for superabsorbent polymer containing excrement and organic acid of present disclosure (hereinafter, “method of recovering organic acid and excrement”, or simply “method of recovery”) And a method for producing recycled pulp fiber from used absorbent articles while reusing an organic acid that inactivates the superabsorbent polymer (hereinafter referred to as “recycled pulp fiber production method”). Will be described in detail below.

<< Organic acid and excrement recovery method >>
The organic acid and excrement recovery method of the present disclosure includes the following steps.
(A1) A precipitation step for depositing a water-insoluble salt of an organic acid by adding a metal salt containing a divalent or higher metal or a base containing a divalent or higher metal to the inactivated aqueous solution (hereinafter referred to as “precipitation”). Sometimes referred to as a step)
(A2) A mixture collection step for collecting a mixture of a water-insoluble salt of an organic acid and solid excreta derived from excrement from an inactivated aqueous solution that has undergone the precipitation step (hereinafter sometimes referred to as “mixture collection step”). is there)
(A3) An organic acid which forms an aqueous solution containing an organic acid, a water-insoluble salt and solid excrement by adding water and an acid capable of forming a free organic acid and a water-insoluble salt to the mixture Generation step (hereinafter sometimes referred to as “organic acid generation step”)
(A4) An organic acid aqueous solution acquisition step for removing an insoluble salt and solid excrement from the aqueous solution to obtain an organic acid aqueous solution containing an organic acid (hereinafter sometimes referred to as “organic acid aqueous solution acquisition step”)
FIG. 1 is a flowchart for explaining the collection method of the present disclosure.

<Precipitation step S1>
In the precipitation step S1, an inactivated aqueous solution for a superabsorbent polymer containing excrement and organic acid, a metal salt containing a divalent or higher metal or a base containing a metal higher than a divalent (hereinafter referred to as “water-insoluble In some cases, a water-insoluble salt of an organic acid is precipitated. Specifically, in the precipitation step S1, by adding a metal salt containing a divalent or higher metal or a base containing a divalent or higher metal to the inactivated aqueous solution, (i) a water-insoluble salt of an organic acid And an excretion [(ii) solid excretion and (iii) liquid excrement] and (iv) an aqueous solution salt.

The inactivated aqueous solution for superabsorbent polymer containing excrement and organic acid can be obtained by inactivating the superabsorbent polymer that has absorbed excreta in the inactivated aqueous solution containing organic acid.
The inactivated aqueous solution for superabsorbent polymer containing excrement and organic acid contains excrement such as organic acid, feces and urine. The organic acid is mainly dissolved in the inactivated aqueous solution, and among the excreta, liquid (iii) liquid excreta such as urine is mainly dissolved in the inactivated aqueous solution, and feces. The solid excreta such as (ii) is mainly dispersed in the inactivated aqueous solution.

  The organic acid is not particularly limited as long as the inactivated aqueous solution can be adjusted to a predetermined pH that can inactivate the superabsorbent polymer, but the organic acid includes an acid group, For example, what has a carboxyl group, a sulfo group, etc. is mentioned. An organic acid having a sulfo group is referred to as a sulfonic acid, and an organic acid having a carboxyl group and not having a sulfo group is referred to as a carboxylic acid. As the organic acid, from the viewpoint of carrying out the organic acid and excrement recovery method of the present disclosure, in particular, in the organic acid generation step, there are choices of acids that can generate a free organic acid and a water-insoluble salt. From the viewpoint of expansion, an organic acid having a carboxyl group, particularly a carboxylic acid is preferable.

  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, it becomes easier for the organic acid to form a chelate complex with a bivalent or higher-valent metal contained in excreta, such as calcium, and lowers the ash content of recycled pulp fibers produced from used absorbent articles. It becomes easy.

Examples of the organic acid include citric acid, tartaric acid, malic acid, succinic acid, oxalic acid (above, carboxylic acid having a plurality of carboxyl groups), gluconic acid (C ₆ ), pentanoic acid (C ₅ ), butanoic acid. (C ₄ ), propionic acid (C ₃ ), glycolic acid (C ₂ ), acetic acid (C ₂ ), formic acid (C ₁ ) (a carboxylic acid having one carboxyl group), methanesulfonic acid, trifluoromethanesulfone An acid, benzenesulfonic acid, p-toluenesulfonic acid (above, sulfonic acid) is mentioned.

  In the precipitation step S1, by adding a metal salt containing a metal having a valence of 2 or more (hereinafter sometimes simply referred to as “metal salt”) to the inactivated aqueous solution, (i) a water-insoluble salt of an organic acid is obtained. In the case of precipitation, the neutralized aqueous solution may be neutralized or not neutralized before adding the metal salt, but before the metal salt is added, the neutralized aqueous solution is neutralized. It is preferred to neutralize the inactivated aqueous solution by adding a base (hereinafter sometimes referred to as “neutralizing base”). By doing so, since it becomes difficult for an organic acid to form a chelate complex with a metal, the recoverability of the organic acid is improved. The method of adding a metal salt after neutralization is particularly useful when the organic acid is an organic acid that can form a chelate complex with the metal.

In the present specification, the base (the neutralizing base and the water-insoluble salt-forming base) is preferably a base based on the Bronsted Lowry definition, that is, a substance capable of receiving proton H ⁺ .

  When the organic acid is an organic acid that can form a chelate complex with a metal, the neutralizing base is a base containing a monovalent metal, such as lithium hydroxide, sodium hydroxide, or potassium hydroxide. Preferably there is. This is to prevent the organic acid from forming a chelate complex.

  The inactivated aqueous solution for superabsorbent polymer containing excrement and organic acid is preferably 5.0 to 10.0, more preferably 6.0 to 9.0, by adding a neutralizing base. More preferably, it can be neutralized to a pH of 6.5 to 8.0. By doing so, when an organic acid is an organic acid which can form a chelate complex with a metal, it can suppress that an organic acid forms a chelate complex.

The metal salt is not particularly limited as long as it can generate (i) a water-insoluble salt of an organic acid and (iv) a water-soluble salt by reacting with the organic acid.
The above-mentioned metal salt has a solubility classified as “very easy to dissolve”, “easy to dissolve”, “slightly soluble” or “slightly difficult to dissolve” in “General Rules 29” of “Fifteenth revised Japanese Pharmacopoeia”. It is preferable to have. This is because, for example, the reaction time with the organic acid is shortened, and the unreacted metal salt is difficult to remain in the water-insoluble salt of the organic acid (i).

The metal salt is preferably a salt of an acid and a base containing a divalent or higher metal.
When the metal salt is added after neutralizing the inactivated aqueous solution, the divalent or higher metal constituting the metal salt preferably has an ionization tendency close to that of the metal constituting the neutralizing base. By doing so, the organic acid in the inactivated aqueous solution can be changed to (i) a water-insoluble salt of the organic acid in a high yield.

  The acid that can constitute the metal salt is preferably water-soluble, can be an organic acid or an inorganic acid, and is preferably an inorganic acid. This is from the viewpoint of organic acid recoverability. Examples of the inorganic acid include hydrochloric acid, sulfuric acid, nitric acid, iodic acid, and bromic acid.

  Examples of the divalent or higher metal constituting the metal salt include Mg, Ca, Ba, Fe, Ni, Cu, Zn, Al, and a group consisting of any combination thereof. (I) a water-insoluble salt of an organic acid (an organic acid and a divalent or higher valent metal). (Composed of metal) tends to precipitate in the inactivated aqueous solution, and in the subsequent mixture collection step, (i) facilitates collection of the water-insoluble salt of the organic acid.

The metal salt is added in an amount that is preferably 0.8 times equivalent or more, more preferably 0.9 times equivalent or more, and still more preferably 1.0 times equivalent or more with respect to the organic acid. In addition, the metal salt is added in an amount that is preferably 3.0 times equivalent or less, more preferably 2.5 times equivalent or less, and even more preferably 2.0 times equivalent or less with respect to the organic acid. The (I) From the viewpoint of efficiently forming a water-insoluble salt of an organic acid.
In addition, the said equivalent means the equivalent between the valence of the metal which comprises a metal salt, and the number of the acid groups which comprise an organic acid.

In order to determine the addition amount of the metal salt, it is preferable to grasp the amount of the organic acid in the inactivated aqueous solution. The amount of organic acid in the deactivated aqueous solution can be determined by directly measuring the concentration of the organic acid in the deactivated aqueous solution to which the metal salt is added, and the total amount of organic acid added to the deactivated aqueous solution It can also be grasped by subtracting the amount of the inactivated aqueous solution discharged together with the superabsorbent polymer, pulp fiber, etc. (the amount of discharged organic acid) from (history).
Also, if the amount of organic acid in the inactivated aqueous solution is unknown, add a metal salt that seems to be excessive with respect to the organic acid, and then add the excess metal salt to the subsequent mixture collection step. In the step or the like, the organic acid aqueous solution may be separated.

  When the organic acid is an organic acid having a carboxyl group, the acid can be, for example, hydrochloric acid, sulfuric acid, nitric acid or the like.

  In addition, when the organic acid is an organic acid that does not form a chelate complex with a metal, the precipitation step S1 includes a divalent or higher-valent metal in the inactivated aqueous solution without neutralizing the inactivated aqueous solution. By adding a water-soluble salt-generating base, (i) a water-insoluble salt of an organic acid can be precipitated. By doing so, an organic acid and excrement can each be collect | recovered from the inactivation aqueous solution containing excrement and an organic acid with few processes.

Examples of the divalent or higher metal constituting the base for forming a water-insoluble salt include Mg, Ca, Ba, Fe, Ni, Cu, Zn, Al, and a group consisting of any combination thereof.
Examples of the water-insoluble salt generating base include magnesium hydroxide, calcium hydroxide, copper hydroxide, and zinc hydroxide.

The amount of the water-insoluble salt generating base is preferably 0.8 times equivalent or more, more preferably 0.9 times equivalent or more, and further preferably 1.0 times equivalent or more, relative to the organic acid. Added at. The water-insoluble salt generating base is preferably 3.0 times equivalent or less, more preferably 2.5 times equivalent or less, and even more preferably 2.0 times equivalent or less with respect to the organic acid. In small amounts. (I) From the viewpoint of forming a water-insoluble salt of an organic acid.
In addition, the said equivalent means the equivalent between the valence of the bivalent or more metal which comprises the base for water-insoluble salt production | generation, and the number of the acid groups which comprise an organic acid.

Examples of the organic acid that does not form a chelate complex with a metal include pentanoic acid (C ₅ ), butanoic acid (C ₄ ), propionic acid (C ₃ ), acetic acid (C ₂ ), formic acid (C ₁ ), and the like. .
Examples of the organic acid that can form a chelate complex with a metal include citric acid, oxalic acid, tartaric acid, and gluconic acid.

  In the precipitation step S1, (i) a water-insoluble salt of an organic acid is formed, which crystallizes and precipitates. At that time, among the (ii) solid excreta dispersed in the inactivated aqueous solution, fine ones adhere to the surface of the water-insoluble salt of the organic acid, and (i) the water-insoluble water of the organic acid. It is taken up and aggregated by the crystalline salt. Thus, in the mixture collection step S2, fine (ii) solid excreta are collected as solids [i.e. (i) water-insoluble salts of organic acids and (ii) solid excreta] and liquids [i.e. (Iii) liquid excrement and (iv) water-soluble salt]. As a result, the concentration of suspended solids (SS) in the liquid becomes low, clogging of the filter or the like is difficult to clog at the time of solid-liquid separation that separates the liquid and solid, and the liquid is treated with microorganisms. In this case, the amount of sludge generated is reduced.

  The inactivated aqueous solution that has undergone the precipitation step S1 includes (i) a water-insoluble salt of an organic acid, (ii) a solid excrement, (iii) a liquid excrement, and (iv) a water-soluble salt.

<Mixture collection step S2>
In the mixture collection step S2, a mixture of a water-insoluble salt of organic acid and solid excrement is collected from the inactivated aqueous solution that has undergone the precipitation step S1.
Specifically, in the mixture collection step S2, inactivation including (i) a water-insoluble salt of an organic acid, (ii) a solid excrement, (iii) a liquid excrement, and (iv) a water-soluble salt. The aqueous solution is separated into solids [ie (i) water-insoluble salts of organic acids and (ii) solid excreta] and liquids [ie (iii) liquid excreta and (iv) water-soluble salts]. To do.

<Organic acid generation step S3>
In the organic acid generation step S3, an acid capable of generating a free organic acid and a water-insoluble salt (hereinafter sometimes referred to as “free organic acid-generating acid”) and water are added to the above mixture, and water. An aqueous solution containing an organic acid and a water-insoluble salt and solid excreta is formed. Specifically, in the organic acid generation step S3, the free organic acid-generating acid and water are added to the solid [that is, (i) the water-insoluble salt of organic acid and (ii) solid excreta], and (v Forming an aqueous solution comprising :) an organic acid; (vi) a water-insoluble salt; and (ii) solid excreta.

The free organic acid-forming acid is not particularly limited as long as it can liberate the organic acid from the water-insoluble salt of the organic acid and form a water-insoluble salt. (pK _a, water) is preferably an acid having a smaller acid dissociation constant than (pK _a, water). By doing so, the organic acid is easily liberated in the organic acid generation step.

In the case where the organic acid has a plurality of acid groups, for example, when the organic acid is a dibasic acid or tribasic acid, the free organic acid produced acid, acid dissociation constant of the organic acid (pK _a, water smallest acid dissociation constant (pK _a of) preferably has a smaller acid dissociation constant than water) (pK _a, water). This is from the viewpoint of easily forming a free organic acid.

Further, when the free organic acid-forming acid has a plurality of acid groups, for example, when the free organic acid-generating acid is a dibasic acid or a tribasic acid, the acid dissociation constant ( pK _a, the greatest acid dissociation constant (pK _a of water), water) is the acid dissociation constant of the organic acid (pK _a, the smallest acid dissociation constant (pK _a of the water), is less than water) preferable. This is from the viewpoint of the efficiency of the free organic acid-generating acid.

Acid dissociation constant (pK _a, water) of the organic acids acid having a smaller acid dissociation constant than (pK _a, water) can be organic or inorganic acids, and is preferably an inorganic acid. Examples of the inorganic acid include hydrochloric acid, sulfuric acid, nitric acid, iodic acid, and bromic acid.

In this specification, the value described in the electrochemical handbook edited by the Electrochemical Society can be adopted as the acid dissociation constant (pk _a , in water).
According to the electrochemical handbook, the acid dissociation constants (pk _a , in 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 (pK _a2 )

The acid dissociation constant (pk _a , in water) of an acid not described in the electrochemical handbook can be determined by measurement. Examples of the instrument that can measure the acid dissociation constant (pk _a , in water) of an acid include a compound physical property evaluation / analysis system T3 manufactured by Sirius.

  The free organic acid-forming acid is added in an amount that is preferably 0.8 times equivalent or more, more preferably 0.9 times equivalent or more, and further preferably 1.0 times equivalent or more, relative to the organic acid. The (I) It is from a viewpoint which makes the water-insoluble salt of an organic acid into the (v) organic acid in a free state.

The free organic acid-forming acid is preferably in an amount that is 2.0 times equivalent or less, more preferably 1.5 times equivalent or less, and still more preferably 1.3 times equivalent or less with respect to the organic acid. Added. (Vii) From the viewpoint of making the free organic acid-forming acid difficult to remain in the organic acid aqueous solution to be recovered, making it difficult to corrode equipment, and the like.
In addition, the said equivalent means the equivalent between the number of acid groups of a free organic acid production | generation acid, and the number of acid groups which comprise an organic acid.

The addition amount of the free organic acid-forming acid can be determined based on (i) the composition of the water-insoluble salt of the organic acid and its dry mass.
Further, the free organic acid-generating acid and water added in the organic acid generation step S3 may be added separately to the above mixture, and are added together to the above mixture as an aqueous solution of the free organic acid generating acid. May be.

<Organic acid aqueous solution acquisition step S4>
In the organic acid aqueous solution acquisition step S4, the water-insoluble salt and solid excrement are removed from the aqueous solution to obtain an organic acid aqueous solution containing an organic acid. Specifically, in the organic acid aqueous solution acquisition step S4, from the aqueous solution containing (v) an organic acid, (vi) a water-insoluble salt, and (ii) solid excreta, The water-soluble salt and (ii) solid excreta are removed to obtain a liquid, that is, (v) an organic acid aqueous solution containing (v) an organic acid.

The organic acid and excrement recovery method of the present disclosure may further include the following additional steps.
(A5) a pH adjustment sub-step (hereinafter sometimes referred to as “pH adjustment sub-step”) of adding an organic acid to the inactivated aqueous solution before the precipitation step and adjusting the inactivated aqueous solution to a predetermined pH; By alternately repeating an inactivation sub-step for inactivating a new superabsorbent polymer (hereinafter sometimes referred to as “inactivation sub-step”) in the inactivation aqueous solution that has undergone the pH adjustment sub-step, Concentration step for increasing the concentration of organic acids and excreta in the activated aqueous solution (hereinafter sometimes referred to as “high concentration step”)
The concentration-enhancing step can include a sterilization sub-step for sterilizing the inactivated aqueous solution (hereinafter sometimes referred to as “sterilization sub-step”).
FIG. 2 shows a flowchart for explaining the additional steps.

<High concentration step S5>
In the high concentration step S5, the pH adjustment substep S5a and the inactivation substep S5b are alternately repeated to increase the concentration of the organic acid and excrement in the inactivated aqueous solution.
By repeating the inactivation substep S5b, the excrement retained by the superabsorbent polymer is repeatedly released into the inactivated aqueous solution, and the excrement in the inactivated aqueous solution is increased in concentration. In addition, since the pH of the inactivated aqueous solution increases in accordance with the increase in the concentration of excrement, an organic acid is added to adjust the inactivated aqueous solution to a predetermined pH in the pH adjustment substep S5a. The concentration of organic acid in the inactivated aqueous solution increases.

  In the pH adjustment sub-step S5a, the organic acid is added to the inactivated aqueous solution for the superabsorbent polymer containing the organic acid and excrement, and the inactivated aqueous solution is adjusted to a predetermined pH. Generally, since the excrement contains a basic component such as ammonia, when the superabsorbent polymer is inactivated in the inactivated aqueous solution and the excrement is released into the inactivated aqueous solution, the inactivated aqueous solution There is a tendency for the pH of the solution to increase. Therefore, an organic acid is added and the inactivated aqueous solution is adjusted to a predetermined pH.

The predetermined pH described above 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, inactivation of the superabsorbent polymer may be insufficient.
Further, the predetermined pH is preferably 0.5 or more, and more preferably 1.0 or more. When the predetermined pH is too low, for example, when the superabsorbent polymer is inactivated and removed from the material containing the pulp fiber and the superabsorbent polymer, the recycled pulp fiber is produced from the pulp fiber. The fiber may be damaged.

In the inactivation substep S5b, the superabsorbent polymer holding excrement is inactivated. The inactivation substep S5b is preferably performed at the predetermined pH described above.
In the inactivation substep S5b, only the superabsorbent polymer can be inactivated, and the superabsorbent polymer in the material including the superabsorbent polymer and the pulp fiber can be inactivated. Examples of the material include materials composed of a superabsorbent polymer and pulp fibers, such as an absorbent core and absorbent articles (for example, crushed absorbent articles).

The concentration increasing step S5 may further include a sterilization sub-step S5c for sterilizing the inactivated aqueous solution. The inactivated aqueous solution containing excrement tends to propagate bacteria that existed in the excrement, bacteria that exist in the environment, etc. with the passage of time and with increasing concentrations of organic acid and excrement. The sterilization sub-step S5c can be performed using sterilization means known in the art, such as sterilization agents, ozone, chlorine dioxide, hydrogen peroxide, ultraviolet light and radiation, and any of them. Combinations are listed.
Examples of the radiation include electromagnetic radiation (X-ray and γ-ray), particle beam (β-ray, electron beam, proton beam, deuteron beam, α-ray and neutron beam).

The sterilization sub-step S5c may sterilize the inactivated aqueous solution so that the number of general bacteria is preferably 100 / mL or less, more preferably 50 / mL or less, and even more preferably 20 / mL or less. it can.
In addition, the number of general bacteria is measured according to JIS K0350-10-10: 2002 “General bacteria test method in water and wastewater”.

The sterilizing means is preferably a sterilizing means that does not substantially remain in the inactivated aqueous solution after the sterilization sub-step S5c. This is because the organic acid should be recovered (vii) so that the sterilizing means does not remain in the organic acid aqueous solution. In addition, in the inactivation substep S5b, when the superabsorbent polymer in the material containing the superabsorbent polymer and the pulp fiber is inactivated and the recycled pulp fiber is manufactured, the sterilization means may remain in the recycled pulp fiber. And there may be a need to remove sterilization means from recycled pulp fibers.
Examples of sterilizing means that do not substantially remain in the inactivated aqueous solution include sterilizing agents, ozone, chlorine dioxide, hydrogen peroxide, ultraviolet rays and radiation, and any combination thereof.

  The concentration increasing step S5 may further include a decoloring step for decoloring the inactivated aqueous solution using a decoloring unit, a deodorizing step for deodorizing the inactivated aqueous solution using a deodorizing unit, and the like. This is because the inactivated aqueous solution tends to cause coloring, odor, and the like derived from excrement as the excrement increases in concentration.

  The decoloring means is preferably a decolorizing means that does not substantially remain in the inactivated aqueous solution after the decolorizing step. The deodorizing means is preferably a deodorizing means that does not substantially remain in the inactivated aqueous solution after the deodorizing step. Furthermore, it is preferable that the sterilizing unit also serves as a decoloring unit and a deodorizing unit.

  As the sterilizing means (decoloring means and deodorizing means) which can be sterilized, decolorized and deodorized, and can be sterilized, decolorized and deodorized, and not substantially remain in the inactivated aqueous solution after the sterilizing sub-step S5c. Ozone, chlorine dioxide, hydrogen peroxide, ultraviolet light and radiation, and any combination thereof.

  The sterilization sub-step S5c can be performed at any position of the concentration-enhancing step S5, for example, before the pH adjustment sub-step S5a and / or after the pH adjustment sub-step S5a. In addition, the sterilization sub-step S5c can be performed once per cycle of the pH adjustment sub-step S5a and the inactivation sub-step S5b. Accordingly, for example, it can be carried out once per 5 cycles of pH adjustment sub-step S5a and inactivation sub-step S5b.

  In the concentration step S5, the concentration of the organic acid in the inactivated aqueous solution is finally preferably 1.5 to 10.0% by mass, more preferably 2.0 to 8.0% by mass, and still more preferably. The cycle of pH adjustment sub-step S5a and inactivation sub-step S5b can be repeated until is 2.3-6.0 mass%. By doing so, in the inactivation substep S5b, the inactivation of the superabsorbent polymer is inhibited, and the organic acid and excrement are efficiently controlled while suppressing the precipitation of the organic acid in the inactivated aqueous solution. It can be recovered well.

<< Method for producing recycled pulp fiber >>
The manufacturing method of the recycled pulp fiber of this indication includes the following steps.
(B1) A material containing pulp fibers derived from a used absorbent article and a superabsorbent polymer is immersed in an inactivated aqueous solution containing an organic acid having a predetermined pH, and the superabsorbent polymer is inactivated. Activation step (hereinafter sometimes referred to as “inactivation step”)
(B2) Recycled pulp fiber forming step for forming recycled pulp fiber from the material that has undergone the inactivation step (hereinafter sometimes referred to as “recycled pulp fiber forming step”)

(B3) Taking out the material from the inactivated aqueous solution that has passed through the inactivation step, and adding a metal salt containing a divalent or higher metal or a base containing a divalent or higher metal to the inactivated aqueous solution from which the material has been taken out. To precipitate a water-insoluble salt of an organic acid (hereinafter sometimes referred to as “precipitation step”)
(B4) A mixture collection step for collecting a mixture of a water-insoluble salt of an organic acid and solid excrement derived from excrement from an inactivated aqueous solution that has undergone the precipitation step (hereinafter sometimes referred to as “mixture collection step”). is there)
(B5) An organic acid generating step of adding an acid capable of forming an organic acid and a water-insoluble salt and water to the mixture to form an aqueous solution containing the organic acid, the water-insoluble salt and solid excreta (Hereinafter, sometimes referred to as “organic acid generation step”)

(B6) An organic acid aqueous solution acquisition step for removing an insoluble salt and solid excrement from the aqueous solution to obtain an organic acid aqueous solution containing an organic acid (hereinafter sometimes referred to as “organic acid aqueous solution acquisition step”)
(B7) Reactivation step for performing an inactivation step using an organic acid aqueous solution as the inactivation aqueous solution (hereinafter may be referred to as “reactivation step”).

The manufacturing method of the recycled pulp fiber of this indication can further include the following additional steps.
(B8) After the inactivation step and before the precipitation step, an organic acid is added to the inactivated aqueous solution to adjust the inactivated aqueous solution to a predetermined pH (hereinafter referred to as “pH adjustment substep”). And inactive aqueous solution that has undergone pH adjustment sub-step, and inactive sub-step for inactivating a new superabsorbent polymer (hereinafter sometimes referred to as “inactive sub-step”). Repeating the concentration step to increase the concentration of the organic acid and excrement in the inactivated aqueous solution by repeating (hereinafter, may be referred to as "concentration step")

The concentration-enhancing step can include a sterilization sub-step for sterilizing the inactivated aqueous solution (hereinafter sometimes referred to as “sterilization sub-step”).
In FIG. 3, the flowchart for demonstrating the manufacturing method of the recycled pulp fiber of this indication is shown.

<Inactivation step S101>
In the inactivation step S101, the material containing the pulp fiber derived from the used absorbent article and the superabsorbent polymer is immersed in an inactivated aqueous solution containing an organic acid having a predetermined pH, and the superabsorbent polymer is inactivated. Activate.
As described above, materials including pulp fibers and superabsorbent polymers derived from used absorbent articles include materials composed of superabsorbent polymers and pulp fibers (for example, absorbent core), absorbent articles (for example, Crushed absorbent articles) and the like.

The predetermined pH described above 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, inactivation of the superabsorbent polymer may be insufficient.
Further, the predetermined pH is preferably 0.5 or more, and more preferably 1.0 or more. When the predetermined pH is too low, for example, when the superabsorbent polymer is inactivated and removed from the material containing the pulp fiber and the superabsorbent polymer, the recycled pulp fiber is produced from the pulp fiber. The fiber may be damaged.

  In the inactivation step S101, for example, in the inactivation tank containing the inactivated aqueous solution, the material containing pulp fibers and the superabsorbent polymer is stirred at room temperature for about 5 to 60 minutes, so that the superabsorbent polymer is obtained. Can be inactivated.

The superabsorbent polymer is not particularly limited as long as it is used as a superabsorbent polymer in the technical field, and examples thereof include those containing an acid group such as a carboxyl group and a sulfo group. Those containing a carboxyl group are preferred.
Examples of the superabsorbent polymer containing a carboxyl group include polyacrylates and polyanhydride maleates, and examples of superabsorbent polymers containing a sulfo group include polysulfonates. Can be mentioned.

<Recycled pulp fiber formation step S102>
In the recycled pulp fiber forming step S102, recycled pulp fibers are formed from the material that has undergone the inactivation step S101. The specific means for forming the recycled pulp fiber is not particularly limited, and can be carried out by a method known in the art.
For example, as described in Patent Document 1, ozone gas is blown into an aqueous solution (for example, an inactivated aqueous solution) containing a material containing pulp fibers and an inactivated superabsorbent polymer that has undergone the inactivation step S101. Thus, the inactivated superabsorbent polymer can be solubilized, and the pulp fiber can be sterilized, bleached, deodorized and the like to form a recycled pulp fiber.

  Concentration step S103 (pH adjustment sub-step S103a, inactivation sub-step S103b, and sterilization sub-step S103c), precipitation step S104, mixture collection step S105, organic acid generation step S106, and organic acid aqueous solution acquisition step S107 are respectively In the organic acid and excrement recovery method of the present disclosure, the concentration step S5 (pH adjustment sub-step S5a, inactivation sub-step S5b, and sterilization sub-step S5c), precipitation step S1, mixture collection step S2, organic acid Since it is the same as that of production | generation step S3 and organic acid aqueous solution acquisition step S4, description is abbreviate | omitted.

<Reactivation step S108>
In the reactivation step S108, the organic acid aqueous solution obtained in the organic acid aqueous solution acquisition step S107 is used as the inactivation aqueous solution, and the inactivation treatment is performed in the same manner as in the inactivation step S101.
When the organic acid aqueous solution obtained in the organic acid aqueous solution acquisition step S107 does not have the above-mentioned predetermined pH, the organic acid aqueous solution is adjusted to the above-mentioned predetermined pH and used as the inactivated aqueous solution in the re-inactivation step S108. preferable.

  Further, the organic acid aqueous solution obtained in the organic acid aqueous solution acquisition step S107 may be partially removed together with the material containing pulp fibers and the superabsorbent polymer. In that case, the organic acid aqueous solution acquisition step The organic acid aqueous solution obtained in S107 can be supplemented with new organic acid and water, and used as the inactivated aqueous solution in the reactivation step S108.

  In the re-inactivation step S108, a new material containing pulp fibers derived from a used absorbent article and a superabsorbent polymer, which is different from the inactivation step S101, is added to a non-containing material containing an organic acid having a predetermined pH. Immerse in an activated aqueous solution to inactivate the superabsorbent polymer.

FIG. 4 is a block diagram illustrating an example of a system 1 for carrying out the present disclosure.
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 ozone treatment device 19, a fourth separation device 20, a fifth separation device 21, an ozone treatment device 22, a pH adjustment device 23, and a water storage tank 24 are provided.

  The bag breaking apparatus 11 opens a hole in the collection bag containing the used absorbent article in the inactivated aqueous solution. The crushing device 12 crushes the used absorbent article in the inactivated aqueous solution that has submerged under the surface of the inert aqueous solution together with the collection bag. FIG. 5 is a schematic diagram illustrating a configuration example of the bag breaking device 11 and the crushing device 12 of FIG. 4.

  The bag breaking device 11 is filled with the inactivated aqueous solution B, and a hole is made in the collection bag A that has settled in the inactivated aqueous solution B. The bag breaking device 11 includes a solution tank V and a punching unit 50. The solution tank V stores an inactivated aqueous solution B. The perforating part 50 is provided in the solution tank V, and when the collection bag A is put in the solution tank V, a hole is made in the surface of the collection bag A in contact with the inactivated aqueous solution B.

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

  The bag breaking portion 40 is disposed at the lower portion (preferably the bottom portion) of the solution tank V, and has a bag breaking blade 41, a support shaft (rotating shaft) 42 for supporting the bag breaking blade 41, and the support shaft 42 as axes. And a drive device 43 that rotates along the axis. The bag breaking blade 41 is rotated around the rotation shaft (support shaft 42) by the driving device 43, thereby making a hole in the collection bag A moved to the lower part of the inactivated aqueous solution B (solution tank V).

  The crushing device 12 crushes the used absorbent article in the collection bag A that has submerged under the surface of the inactivated aqueous solution B together with the collection bag A. The crushing device 12 includes a crushing unit 60 and a pump 63. The crushing unit 60 is connected to the solution tank V by a pipe 61, and the used absorbent article (mixed liquid 91) in the collection bag A sent together with the inactivated aqueous solution B from the solution tank V is collected together with the collection bag A. Crush in inactivated aqueous solution B.

  Examples of the crushing unit 60 include a biaxial crusher (for example, a biaxial rotary crusher, a biaxial differential crusher, and a biaxial shear crusher). For example, a Sumi cutter (Sumitomo Heavy Industries Environment Co., Ltd.) Company-made). The pump 63 is connected to the crushing part 60 by a pipe 62, and the crushed material obtained in the crushing part 60 is drawn out from the crushing part 60 together with the inactivated aqueous solution B (mixed liquid 92) and sent to the next step. However, the crushed material contains materials including pulp fiber, super absorbent polymer, material of collection bag A, film, nonwoven fabric, elastic body and the like.

  The first separation device 13 agitates the mixed liquid 92 containing the crushed material obtained by the crushing device 12 and the inactivated aqueous solution, and performs cleaning while removing dirt (excrement etc.) from the crushed material. An inactivated aqueous solution 93 containing pulp fibers and a superabsorbent polymer is separated from the liquid 92 and sent to the first dust removing device 14.

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

  The first dust removing device 14 uses a screen having a plurality of openings to remove foreign matters present in the inactivated aqueous solution 93 containing pulp fibers and highly water-absorbing polymers, and to remove non-containing materials containing pulp fibers and highly water-absorbing polymers with little foreign matter. An activated aqueous solution 94 is formed. Examples of the first dust removing device 14 include a screen separator (coarse screen separator). Specifically, for example, a pack pulper (manufactured by Satomi Manufacturing Co., Ltd.) can be used.

  The second dust removing device 15 removes finer foreign substances from the inactivated aqueous solution 94 containing pulp fibers and a superabsorbent polymer, which are sent from the first dust removing apparatus 14 and are sent from the first dust removing device 14, by a screen having a plurality of openings. Further, an inactivated aqueous solution 95 containing pulp fibers and a highly water-absorbing polymer with less foreign matters is formed. Examples of the second dust removing device 15 include a screen separator, specifically, a lamo screen (manufactured by Aikawa Tekko Co., Ltd.).

  The third dust removing device 16 is sent from the second dust removing device 15 by centrifugal separation, from the inactivated aqueous solution 95 containing pulp fibers and a highly water-absorbing polymer with less foreign matters, pulp fibers and An inactivated aqueous solution 96 containing a superabsorbent polymer is formed. Examples of the third dust removing device 16 include a cyclone separator, specifically, an ACT low concentration cleaner (manufactured by Aikawa Tekko Co., Ltd.).

  The second separation device 17 is inactivated by the screen having a plurality of openings from the inactivated aqueous solution 96 containing the pulp fibers and the superabsorbent polymer, which is sent from the third dust removing device 16 and has much less foreign matter. It isolate | separates into the pulp fiber 97 containing aqueous solution and a super absorbent polymer, and the inactivation aqueous solution 100 containing super absorbent polymer. Examples of the second separator 17 include a drum screen separator, specifically, a drum screen dehydrator (manufactured by Toyo Screen Co., Ltd.).

  The third separation device 18 is configured such that the pulp fiber 97 delivered from the second separation device 17 is separated from the solid 98 containing the pulp fiber and the superabsorbent polymer by the screen having a plurality of openings, and the superabsorbent polymer remaining. In addition, pressure is applied to the solid while separating it from the liquid containing the inactivated aqueous solution to crush the superabsorbent polymer in the solid. Examples of the third separation device 18 include a screw press dehydrator, specifically, a screw press dehydrator (manufactured by Kawaguchi Seiki Co., Ltd.).

  The ozone treatment device 19 treats the solid 98 sent from the third separation device 18 with an ozone aqueous solution containing ozone. Thereby, the superabsorbent polymer is oxidatively decomposed, the superabsorbent polymer is removed from the pulp fiber, and the aqueous ozone solution 99 containing the recycled pulp fiber is discharged.

  The fourth separation device 20 separates the recycled pulp fiber from the ozone aqueous solution 99 treated by the ozone treatment device 19 using a screen having a plurality of openings. Examples of the fourth separation device 20 include a screen separator.

The fifth separation device 21, the ozone treatment device 22, the pH adjustment device 23, and the water storage tank 24 are devices for regenerating and reusing the inactivated aqueous solution used in the system 1.
The fifth separator 21 forms the inactivated aqueous solution 101 from which the superabsorbent polymer is removed from the inactivated aqueous solution 100 containing the superabsorbent polymer using a screen separator or the like.
The ozone treatment device 22 sterilizes the inactivated aqueous solution 101 from which the superabsorbent polymer has been removed with ozone to form a sterilized inactivated aqueous solution 102. The pH adjuster 23 adjusts the sterilized inactivated aqueous solution 102 to a predetermined pH to form a regenerated inactivated aqueous solution 103. The water storage tank 24 stores an excess of the regenerated inactivated aqueous solution 103.

Hereinafter, although an example is given and this indication is explained, this indication is not limited to these examples.
[Production Example 1]
In accordance with the flowchart shown in FIG. 3, the inactivated aqueous solution No. 1 was subjected to a total of 10 inactivation steps (inactivation step S101 × 1 time, inactivation substep S103b × 9 times in the concentration step S103). 1 was obtained. The organic acid was citric acid, the absorbent article was a used disposable diaper, and the superabsorbent polymer was sodium polyacrylate. In addition, the initial pH of the inactivated aqueous solution (first time) was adjusted to 2.0, and in the pH adjustment substep S103a, the pH of the inactivated aqueous solution (second time to 10th time) was adjusted to about 3.0.

Inactivated aqueous solution no. 1 is that the inactivated aqueous solution is ozone after the inactivation step S101 and after the inactivation substep S103b in each of the concentration step S103 so that the number of general bacteria is less than 10 / mL. After performing the sterilization step (sterilization sub-step S103c) and finishing the first, fifth and tenth sterilization steps, the inactivated aqueous solution No. 1 was used. One time-lapse sample (1 time, 5 times, 10 times) was sampled. In each of the first to tenth inactivation steps, the inactivated superabsorbent polymer was sampled.
As a result of the analysis, the inactivated aqueous solution No. 10 after a total of 10 inactivation steps was obtained. 1 contained 2.7% by mass of citric acid.

[Production Example 2]
Except that the sterilization step (sterilization substep S103c) was not performed, the inactivated aqueous solution No. 1 was prepared in the same manner as in Production Example 1. 2 was prepared.
Inactivated aqueous solution No. 2, after finishing the first, fifth and tenth inactivation steps, the inactivated aqueous solution No. 2 was used. Two time-lapse samples (1 time, 5 times, 10 times) were sampled.
As a result of analysis, an inactivated aqueous solution No. 1 was used. 2 contained 2.3% by weight of citric acid.

[Examples 1 and 2]
Inactivated aqueous solution no. 1 and inactivated aqueous solution No. 1 The number of general bacteria in each of the time-lapse samples (1, 5, and 10 times) was measured. The results are shown in FIG.
Moreover, the absorptivity (mass ratio) of the inactivated superabsorbent polymer sampled in Production Example 1 was as follows.
First inactivation step S101: about 7.0 times Second to tenth inactivation substep S103b: about 22.0 times

As shown in FIG. No. 1 showed that the number of general bacteria was 0 / g in any of the time-lapse samples (the number of general bacteria in the undiluted sample itself was 0 / g). Inactivated aqueous solution No. 1 samples (1 time, 5 times, 10 times) were deactivated aqueous solution No. 1; Compared to each of the two time-lapse samples (1 time, 5 times, 10 times), there was less coloring and odor.
Therefore, it is suggested that the concentration step preferably includes a sterilization substep when the number of concentration steps increases and when manufacturing recycled pulp fibers.

  Further, the absorption ratio of the deactivated superabsorbent polymer in each of the second to tenth inactivation substeps S103b of Production Example 1 was about 22.0 times. From this, it can be seen that the inactivation of the superabsorbent polymer is determined by the pH of the inactivated aqueous solution and is not easily affected by the concentration step S103 (effect of discharged excrement).

[Example 3]
<Precipitation step S104>
Sodium hydroxide (solid) was added to 2,000 g of the inactivated aqueous solution No. 1 to adjust the pH to 7. Next, while stirring the inactivated aqueous solution No. 1, the inactivated aqueous solution No. 1 was used. First, 32 g of calcium chloride as a metal salt was dissolved, and (i) calcium citrate as a water-insoluble salt of an organic acid was precipitated, and fine (ii) solid excreta were aggregated.

<Mixture collection step S105>
After leaving still for 24 hours from the addition of calcium chloride, using a mesh filter, the inactivated aqueous solution no. 1 was solid-liquid separated to obtain a mixture (wet state) of (i) calcium citrate (tetrahydrate) as a water-insoluble salt of organic acid and (ii) solid excreta, The (wet state) was dried at 120 ° C. for 10 minutes to obtain 120 g of a mixture (dry state).

<Organic acid generation step S106>
(I) A mixture of calcium citrate as a water-insoluble salt of an organic acid and (ii) solid excrement is mixed with 30% by mass sulfuric acid aqueous solution as a free organic acid-generating acid, and calcium citrate (tetrahydrate) ) 120 g and 1.0 equivalent. Specifically, assuming that 120 g of the mixture (dry state) is all calcium citrate (tetrahydrate) (= 0.21 mol), a 30% by mass sulfuric acid aqueous solution has a total mole number of H ⁺ of 1.26 mol, which is the total number of moles of carboxyl groups present in 0.21 mol of calcium citrate (tetrahydrate), and 1.26 mol of 1.0 times equivalent (the number of moles of sulfuric acid is 0.63 mol) To the above mixture (dry state).
In the mixture aqueous solution, with addition of 30% by mass sulfuric acid aqueous solution, (vi) precipitation of calcium sulfate as a water-insoluble salt was formed.

<Organic acid aqueous solution acquisition step S107>
The mixture aqueous solution was subjected to solid-liquid separation using a mesh filter to obtain about 65 g of an aqueous citric acid solution as (vii) an organic acid aqueous solution. The pH of the citric acid aqueous solution was 2.1.

S1 Precipitation step S2 Mixture collection step S3 Organic acid generation step S4 Organic acid aqueous solution acquisition step S5 Concentration step S5a pH adjustment substep S5b Deactivation substep S5c Sterilization substep S101 Deactivation step S102 Recycled pulp fiber formation step S103 High concentration Step S103a pH adjustment substep S103b Inactivation substep S103c Sterilization substep S104 Precipitation step S105 Mixture collection step S106 Organic acid generation step S107 Organic acid aqueous solution acquisition step S108 Reactivation step 11 Bag breaking device 12 Crushing device 13 First separation device 14 1st dust removing device 15 2nd dust removing device 16 3rd dust removing device 17 2nd separating device 18 3rd separating device 19 Ozone processing device 20 4th separation Location 21 fifth separator 22 ozone treatment apparatus 23 pH adjuster 24 reservoir

Claims (14)

A method for recovering organic acid and excrement from an inactivated aqueous solution for superabsorbent polymer containing organic acid and excrement,
A precipitation step of precipitating a water-insoluble salt of an organic acid by adding a metal salt containing a divalent or higher metal or a base containing a divalent or higher metal to the inactivated aqueous solution;
A mixture collecting step for collecting a mixture of the water-insoluble salt of the organic acid and the solid excreta derived from the excrement from the inactivated aqueous solution that has undergone the precipitation step;
To the mixture, a free organic acid, an acid capable of forming a water-insoluble salt, and water are added, and an organic solution that forms the aqueous solution containing the organic acid, the water-insoluble salt, and the solid excreta is added. Acid generation step,
An organic acid aqueous solution obtaining step of removing the water-insoluble salt and the solid excrement from the aqueous solution to obtain an organic acid aqueous solution containing the organic acid,
The method comprising the steps of:   The method according to claim 1, wherein the organic acid is an organic acid having a carboxyl group.   3. The water-insoluble salt of the organic acid is precipitated in the precipitation step by adding the metal salt to the inactivated aqueous solution after neutralizing the inactivated aqueous solution. Method.   The organic acid is an organic acid that does not form a chelate complex with a metal, and in the precipitation step, the water-insoluble salt of the organic acid is precipitated by adding the base to the inactivated aqueous solution. The method according to 1 or 2.   5. The metal according to claim 1, wherein the metal having a valence of 2 or more is selected from the group consisting of Mg, Ca, Ba, Fe, Ni, Cu, Zn, and Al, and any combination thereof. the method of. Wherein the acid in organic acid production step, acid dissociation constant (pK _a, water) of the organic acid is an acid having a smaller acid dissociation constant than (pK _a, water), either of claims 1 to 5 one The method according to item.   The method according to any one of claims 1 to 6, wherein the acid in the organic acid generating step is selected from the group consisting of sulfuric acid, hydrochloric acid, nitric acid, iodic acid and bromic acid.   Before the precipitation step, the organic acid is added to the inactivated aqueous solution, the pH adjusting substep for adjusting the inactivated aqueous solution to a predetermined pH, and the inactivated aqueous solution that has undergone the pH adjusting substep, The method further includes a concentration step of increasing the concentration of the organic acid and the excrement in the inactivated aqueous solution by alternately repeating an inactivation substep of inactivating a new superabsorbent polymer. The method as described in any one of 1-7.   The method of claim 8, wherein the concentration step further comprises a sterilization substep of sterilizing the inactivated aqueous solution.   10. The method of claim 9, wherein in the sterilization substep, the inactivated aqueous solution is sterilized using ozone, chlorine dioxide, hydrogen peroxide, ultraviolet light or radiation, or any combination thereof. A method of producing recycled pulp fiber from a used absorbent article while reusing an organic acid that inactivates a superabsorbent polymer,
Inactivation to inactivate the superabsorbent polymer by immersing a material containing pulp fibers and superabsorbent polymer derived from the used absorbent article in an inactivated aqueous solution having a predetermined pH and containing an organic acid Step,
From the material that has undergone the inactivation step, a recycled pulp fiber forming step for forming the recycled pulp fiber,
Removing the material from the inactivated aqueous solution that has undergone the inactivation step, and adding a metal salt containing a divalent or higher metal or a base containing a divalent or higher metal to the inactivated aqueous solution from which the material has been removed. A precipitation step of precipitating a water-insoluble salt of the organic acid,
A mixture collecting step for collecting a mixture of the water-insoluble salt of the organic acid and the solid excreta derived from the excrement from the inactivated aqueous solution that has undergone the precipitation step;
To the mixture, a free organic acid, an acid capable of forming a water-insoluble salt, and water are added, and an organic solution that forms the aqueous solution containing the organic acid, the water-insoluble salt, and the solid excreta is added. Acid generation step,
An organic acid aqueous solution obtaining step of removing the water-insoluble salt and the solid excrement from the aqueous solution to obtain an organic acid aqueous solution containing the organic acid,
Reactivation step for performing the deactivation step using the organic acid aqueous solution as the deactivation aqueous solution,
The method comprising the steps of:   After the inactivation step and before the precipitation step, the organic acid is added to the inactivation aqueous solution, and the pH adjustment substep for adjusting the inactivation aqueous solution to a predetermined pH and the pH adjustment substep are performed. By increasing the concentration of the organic acid and the excrement in the inactivated aqueous solution by alternately repeating the inactivation substep for inactivating a new superabsorbent polymer in the inactivated aqueous solution. The method of claim 11, further comprising a step.   The method of claim 12, wherein the concentration step further comprises a sterilization substep of sterilizing the inactivated aqueous solution.   14. The method of claim 13, wherein in the sterilization substep, the inactivated aqueous solution is sterilized using ozone, chlorine dioxide, hydrogen peroxide, ultraviolet light or radiation, or any combination thereof.

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