TWI683840B - Treatment method of water-absorbent resin - Google Patents

Abstract

Provide a treatment method for reusing the water-absorbent resin powder contained in the absorbent article after use.

The method for processing a water-absorbent resin of the present invention is characterized in that an alkali metal salt of a weak acid is added to agglomerates of a water-absorbent resin powder formed by water absorption and aggregation of water-absorbent resin powder by adding weak acid.

Description

Treatment method of water-absorbent resin

The present invention relates to a method of treating water-absorbent resin contained in an absorbent article after use.

Due to aging, the number of people using disposable diapers for nursing care is increasing. Moreover, from a global perspective, the population of children using disposable diapers has also increased. In recent years, the use of disposable paper diapers has rapidly increased. Because the used paper diapers are contaminated with dirt, they are discarded without reuse. Discarded paper diapers are usually incinerated. However, with the increase in the amount of paper diapers discarded, from the viewpoint of environmental protection, it has been studied to reuse the materials constituting the paper diapers.

Patent Document 1 discloses a separation method of a used paper diaper that separates the used paper diaper into vinyl plastic and other components, and is characterized by the following steps: adding water to the cut or crushed used paper diaper The reaction step of mixing the dehydrating agent to make the water-absorbent polymer contained in the used paper diaper react with the dehydrating agent to dehydrate it; put the dehydrated mixture into a drum to dissolve it, and precipitate the dissolved matter other than vinyl plastic. The separation step of discharging to the outside of the drum to make the vinyl plastic remain in the drum; and the recovery step of attracting the remaining vinyl plastic to the outside of the drum for recovery.

Patent Document 2 discloses a treatment device for a used paper diaper, which includes: receiving the cut-off used paper diaper and the treatment liquid, stirring it, and Recycling substance containing the base material component of the paper diaper and the water-absorbing substance component, and a stirring separation tank separated from the plastic component; receiving the first recovery of the processing liquid containing the regeneration substance discharged from the stirring separation tank A tank; and a second recovery tank that receives the processing liquid containing the regeneration substance discharged from the agitating separation tank, and is different from the second recovery tank of the first recovery tank.

Patent Document 3 discloses a paper diaper processing device, including: a drum for receiving used paper diapers; a water tank portion that stores at least the lower end portion of the drum and water inside; a water supply device that supplies water into the water tank portion; rotation Drive the drum to separate and disintegrate the paper diapers immersed in water into water-soluble and insoluble materials; and a discharge device that simultaneously discharges the water-soluble and water-dissolved materials separated and disintegrated to the sewage treatment equipment side.

Patent Document 4 discloses a method of recovering materials from a contaminated sanitary product containing water-absorbent resin, which is to pulverize the contaminated sanitary product containing water-absorbent resin that has absorbed water into a gel form, and to make the pulverized sanitary product The sanitary products are dispersed in the water containing the disinfectant, and the contaminated part of the sanitary products is separated from the crushed product of the foregoing sanitary products.

Patent Document 5 discloses a granular excrement disposal material, which is characterized by containing a water-absorbent resin recovered from a dried powdered plastic material and a water-absorbent resin after water absorption to form a granular material having a particle size of 1 mm or more.

【Prior Technical Literature】 【Patent Literature】

[Patent Document 1] Japanese Unexamined Patent Publication No. 2012-81433

[Patent Document 2] Japanese Unexamined Patent Publication No. 2012-170918

[Patent Document 3] Japanese Patent Laid-Open No. 2004-104929

[Patent Document 3] Japanese Patent Laid-Open No. 2009-73198

[Patent Document 4] Japanese Patent Laid-Open No. 2005-304506

The water-absorbent resin powder has a problem that it is difficult to dry because the aggregate of the water-absorbent resin formed by absorbing water and coagulating absorbs a large amount of water and has a small surface area. In particular, when a water-absorbent resin that absorbs water and swells is added with a dehydrating agent (for example, calcium chloride) and is subjected to dehydration treatment, although the water content is slightly reduced, the water content is still high and it is difficult to dry the aggregate of the water-absorbent resin . Therefore, in the case of reusing disposable paper diapers, an efficient treatment method for water-absorbing and coagulated water-absorbing resin is required.

The present invention has been made in view of the foregoing circumstances, and it is a problem to provide a treatment method for reusing the water-absorbent resin powder contained in the absorbent article after use.

The method for treating a water-absorbent resin of the present invention that solves the aforementioned problems is characterized in that a weak acid alkali metal salt is added to agglomerates of a water-absorbent resin powder obtained by water absorption and aggregation of water-absorbent resin powder.

As a result of intensive research, the inventors found that the water-absorbent resin after dehydration treatment using a dehydrating agent (for example, calcium chloride) constitutes the carboxyl group of acrylic acid of the water-absorbing resin because the divalent metal ion of the dehydrating agent forms a cross-linked structure. Strong cohesion and cohesion. Therefore, by adding a weak acid alkali metal salt to the aggregate of the water-absorbent resin powder formed by the crosslinking of the divalent metal ion, the dehydrating agent Ion exchange of divalent metal ions with alkali metal ions. As a result, the crosslink formed by the divalent metal ion is cut. Since the cohesive force decreases when the metal crosslink is cut, the aggregate of the water-absorbent resin powder changes to the original granular form. The particulate water-absorbing resin has a large surface area and is easy to dry.

According to the present invention, the water-absorbent resin powder contained in the absorbent article after use can be recycled. The obtained water-absorbent resin powder can be suitably used as a soil improver, solid fuel, or the like.

1‧‧‧Water-absorbent resin powder

Figure 1 is a flow chart showing the processing steps of an absorbent article.

Fig. 2 is a graph showing changes in the aggregation state of the water-absorbent resin powder.

Fig. 3 is a diagram instead of a photograph showing the aggregation state of the water-absorbent resin powder.

Fig. 4 is a diagram instead of a photograph showing the aggregation state of the water-absorbent resin powder.

Fig. 5 is a diagram instead of a photograph showing the aggregation state of the water-absorbent resin powder.

[Forms for carrying out the invention]

The method for processing a water-absorbent resin of the present invention is characterized in that a weak acid alkali metal salt is added to agglomerates of a water-absorbent resin powder obtained by absorbing and coagulating water-absorbent resin powder.

First, the processing procedure of the absorbent article is explained with reference to the drawings, but The present invention is not limited by the processing steps shown in the drawings. Fig. 1 shows an example of the processing procedure of the absorbent article. The first step is a washing step of the absorbent article to which dirt is attached. First, put the absorbent article after use after the cut into the treatment liquid. As a processing liquid, water is suitable. By performing the stirring treatment in the treatment liquid, the dirt adhering to the absorbent article can be washed. In addition, it can be separated by the specific gravity of the materials constituting the absorbent article.

The second step is the dehydration treatment of the water-absorbing resin. By this dehydration treatment, the water absorption of the water-absorbent resin is lost. As a dehydrating agent, a divalent metal salt is suitably used, and calcium chloride can be more suitably used. By treatment with a divalent metal salt, the carboxyl group of acrylic acid constituting the water-absorbent resin powder is cross-linked. As a result, the volume of the aggregate of the water-absorbent resin powder is reduced. As the volume of the condensate changes, water is discharged from the condensate. By this dehydration treatment, the water content of the water-absorbent resin powder is reduced from about 98% by mass to about 70% by mass.

The third step is the plastic component recovery step. Recycle plastic components such as nonwoven fabrics and films used in absorbent articles. The recycled plastic components are further washed and reused as oil. Carbonized raw materials are preferred. The fourth step is the pulp recovery step. In the fourth step, the pulp constituting the absorber is recovered. The recovered pulp is further washed and reused.

The fifth step is the wastewater treatment step after pulp recovery. This sewage contains a large amount of water-absorbent resin powder used as an absorbent article, and contains pulp residues, feces, and the like. Sediment and sewage concentrates are treated as sludge. The water-absorbent resin powder exists in the form of agglomerates in the sludge. However, since the sludge contains a large amount of aggregates of water-absorbent resin powder, there is a problem that it is not easy to dry the sludge. Especially if you do it directly Dryness also has the problem that only the surface is dry and the interior of the aggregate is not dry. In the treatment method of the present invention, a weak acid alkali metal salt is added to the sludge. The weakly acidic alkali metal salt acts on the aggregates of the water-absorbent resin powder contained in the sludge. By processing with alkali metal salt of weak acid, ion exchange reaction occurs between divalent metal ion and alkali metal ion. As a result, since the metal crosslink is cut, the aggregate of the water-absorbent resin powder can be easily granulated. The granulated water-absorbent resin can be easily dried because of the increased surface area.

Fig. 2 is a graph showing the change of the aggregation state of the water-absorbent resin powder. Fig. 2(a) shows the aggregate of the water-absorbent resin powder 1. ^{(- .M 2+ -. -COO OOC-} ) water absorbent resin powder 1 based metal produced by crosslinking divalent metal ion of a dehydrating agent and cohesion. The divalent metal ion M ²⁺ and the alkali metal ion M ⁺ cut off the metal crosslink (-COO ^- M ⁺ M ^+- OOC-) by ion exchange. As a result, the aggregate of the absorbent resin powder changes into a granular shape (Figure 2 (b)).

The addition amount of the alkali metal salt of the weak acid is preferably 1 part by mass or more, preferably 3 parts by mass or more, and 100 parts by mass or less with respect to 100 parts by mass of the water-absorbent resin in the water-containing state treated with the dehydrating agent. Preferably, 30 parts by mass or less is preferable.

The mixture of the water-absorbent resin powder after water absorption and the alkali metal salt of the weak acid are not particularly limited. For example, ROCKING MIXER BHR type manufactured by Aichi Electric Co., Ltd. can be used. The aforementioned mixing is not particularly limited, and it is preferably performed in a temperature range of 5°C or more and 130°C or less for 5 minutes to 6 hours. It can also be dehydrated while mixing. The mixed dehydration is not particularly limited, and it is preferably performed in a temperature range of 80°C or more and 130°C or less for 5 minutes to 6 hours. It can also be carried out under any conditions of normal pressure, reduced pressure, and increased pressure.

By the aforementioned mixing, the aggregate of the absorbent resin powder changes into a granular or powdery absorbent resin. Because the surface area of the particulate or powdery absorbent resin powder is large, it can be easily dried.

The weak acid component of the alkali metal salt of the weak acid is preferably an acid of the same level as the acrylic acid constituting the water-absorbent resin powder or a weaker acid. That is, it is preferable to use an acid having an acid dissociation constant equal to or higher than that of acrylic acid as the weak acid component. By using the metal salt of the same or weaker acid as acrylic acid, it is easy to produce ion exchange reaction with the divalent metal salt used as a dehydrating agent. The acid dissociation constant of acrylic acid at 25°C in water is 4.26. That is, in the present invention, it is preferable to use an acid having an acid dissociation constant of 4.26 or more at 25°C in water as the weak acid component. It is more preferable to use an acid of 4.30 or more, and it is more preferable to use an acid of 4.50 or more. The upper limit of the acid dissociation constant of the weak acid is not particularly limited, but 12 is preferred, and 10 is preferred. For example, phenol with an acid dissociation constant of 9.95 is considered effective, but ethanol with an acid dissociation constant of 16 is not considered effective.

The acid dissociation constant pKa of the acid (H _n X ^n- ) can be expressed by the following formula.

pKa=-log(1/Ka),Ka=[H ⁺ ] ⁿ . [X ^n- ]/[H _n X ^n- ]

When dissociating acid in multiple stages, the acid dissociation constant of at least one stage is preferably in the range of 4.26-12, preferably in the range of 4.3-11, and more preferably in the range of 4.5-10. In addition, the dissociation constant in all stages is preferably in the range of 4.26 to 12, preferably in the range of 4.3 to 11, and more preferably in the range of 4.5 to 10.

Specific examples of acids having an acid dissociation constant of 4.26 or more at 25°C in water include adipic acid (4.26), azelaic acid (4.39), p-anisic acid (4.48), and o-aminobenzoic acid. (2nd stage: 4.95), p-aminobenzoic acid (4.85), isovaleric acid (4.58), isonicotinic acid (2nd stage: 4.87), isobutyric acid (4.63), caprylic acid (4.89), valeric acid (4.64), 2-quinodic acid (stage 2: 4.75), citric acid (stage 2: 4.35), crotonic acid (4.69), cinnamic acid (Trans) (4.44), acetic acid (4.56), cyclohexane carboxylic acid (4.70), (R,R)-tartaric acid (stage 2: 4.44), p-hydroxybenzoic acid (4.58), pimelic acid (4.31 ), 2,6-pyridinedicarboxylic acid (stage 3: 4.68), propionic acid (4.67), hexanoic acid (4.63), heptanoic acid (4.66), phthalic acid (stage 2: 4.93), propylene Diacid (stage 2: 5.28), butyric acid (4.63), malic acid (3.24), levulinic acid (4.44), carbonic acid (6.35), etc.

Examples of the alkali metal include lithium, sodium, and potassium. Specific examples of the alkali metal salt of the weak acid include, for example, sodium carbonate, sodium bicarbonate, potassium carbonate, potassium bicarbonate, sodium citrate acetate, and sodium succinate acetate. In addition, the alkali metal salt of the weak acid is preferably solid. The addition of a solid weak acid alkali metal salt mix makes it easy to discharge osmotic pressure water from the aggregates of the water-absorbent resin powder.

By drying the particulate water-absorbent resin obtained using the aforementioned processing method, the particulate water-absorbent resin powder can be regenerated. The regenerated water-absorbent resin powder also has excellent absorption performance. For example, the regenerated water-absorbent resin powder has an absorption ratio of 15 g/g or more.

The regenerated water-absorbent resin powder can be used, for example, as a soil amendment or as a solid fuel. Therefore, the present invention includes a method for drying a regenerated water-absorbent resin powder characterized by the particulate absorbent resin powder obtained by the aforementioned processing method, a method for producing a soil improver, and a method for producing solid fuel.

The water-absorbent resin powder to be treated by the present invention is not particularly As a limitation, a cross-linked polymer having acrylic acid as a constituent component, it is preferable that at least a part of its carboxyl group is neutralized. The content of the acrylic component constituting the crosslinked polymer is preferably 90% by mass or more, preferably 95% by mass or more, preferably 99% by mass or less, and more preferably 97% by mass or less.

The cation that neutralizes at least a part of the carboxyl group of the crosslinked polymer is not particularly limited, and examples thereof include alkali metal ions such as lithium, sodium, and potassium, and alkaline earth metal ions such as magnesium and calcium. Among these, it is preferable that at least a part of the carboxyl group of the cross-linked polymer is neutralized by sodium ions. In addition, the carboxyl group of the cross-linked polymer is neutralized, and the carboxyl group of the cross-linked polymer obtained by polymerization may be neutralized, or the monomer after neutralization may be used in advance to form a cross-linked polymer.

The degree of neutralization of the carboxyl group of the cross-linked polymer is preferably 60 mol% or more, and preferably 65 mol% or more. When the degree of neutralization is too low, the absorption performance of the resulting water-absorbent resin powder may be reduced. In addition, the upper limit of the degree of neutralization is not particularly limited, and all of the carboxyl groups may be neutralized. In addition, the degree of neutralization can be obtained by the following formula.

Neutralization degree (mol %) = 100 × "number of carboxyl groups of the cross-linked polymer neutralized" / "total number of carboxyl groups of the cross-linked polymer (including neutralized and unneutralized) "

The absorbent article to be treated in the present invention is not particularly limited as long as it uses water-absorbent resin powder, and examples thereof include disposable diapers, incontinence pads, light incontinence pads, sanitary napkins, and breast milk pads. . Among these, disposable paper diapers with a large amount of water-absorbent resin powder used are suitable.

[Example]

Hereinafter, the present invention will be described in detail by examples, but the present The invention is not limited by the following examples, and any change or embodiment that does not deviate from the scope of the invention is included in the scope of the invention.

[Processing examples 1 to 10]

The pulverized product of the commercially available disposable paper diaper was put into treated water containing calcium chloride as a dehydrating agent, and dehydrated by a water-absorbent resin. The non-woven fabrics, films and other plastic components used in absorbent articles are separated and recovered from the treated water, and then the pulp is separated and recovered. The separated and recovered sewage is dehydrated by a dehydrator to recover sludge (agglomerates of water-absorbent resin).

[Processing Examples 11 to 13]

100 parts by mass of fluff pulp and 60 parts by mass of water-absorbent resin powder (AQUAPEARL DS560 manufactured by Sundia Polymer Co., Ltd.: a cross-linked polymer composed of acrylic acid) as an air-flow mixing device (PAD FORMER manufactured by AUTECH Co., Ltd.) ) Mixing, the resulting mixture is evenly laminated on an acrylic plate (thickness 4mm) with a weight per unit area of about 500g/m ² and pressurized under a pressure of 5kg/cm ² After 30 seconds, the absorber was obtained. The absorbent body was cut into a rectangular shape of 14 cm×36 cm, and water absorbing paper of the same size as the absorbent body (weight per unit area 15.5 g/m ² , manufactured by ADVANTEC, FILTER PAPER No. 2) was placed above and below the polyethylene sheet. (Polyethylene film UB-1 manufactured by Tamapoly) is arranged on the back, and a non-woven fabric (weight 20g/m ² per unit area, ELTAS GUARD manufactured by Asahi Kasei Corporation) is arranged on the surface to manufacture absorbent articles.

The absorbent article was immersed in physiological saline for 60 minutes, and then placed on a wire mesh for 60 minutes to remove water. Use the high-speed shredder RSC-500 (R-ing Co., Ltd.) to carry out the dehydrated absorbent articles Smash. The pulverized product was immersed in a 5% by mass calcium chloride solution and dehydrated. After the dehydration treatment, the sediment (agglomerate of water-absorbent resin) is recovered. The water content of the water-absorbent resin before the dehydration treatment was 98% by mass, and the water content of the sediment (agglomerate of the water-absorbent resin) was 72% by mass.

<Treatment of aggregates of water-absorbent resin after water absorption>

Into a 200 mL beaker, 10 g of the obtained sludge or sediment (agglomerate of water-absorbent resin powder) and a predetermined amount of treatment agent were placed, and mixed with a medicine spoon for 60 minutes. The resulting mixture was evenly spread in an aluminum standard container (width: 276 mm, depth: 211 mm, height: 35 mm). Put an aluminum standard container into a blower thermostat (YAMATO Scientific Co., Ltd. DKM600) at 100°C for 3 minutes to dry the mixture. Table 1 summarizes the obtained results. In the dryness in the table, "○" indicates that it can be easily dried, and "×" indicates that only the surface is dry and the inside is not dry. The absorption ratio is the absorption ratio measured by taking out the dried absorbent resin powder and adjusting it to a particle size of 250 μm to 500 μm. The absorption ratio is measured using the following method.

(Measurement method of absorption rate)

The measurement of the absorption rate is performed in accordance with JIS K 7223 (1996). A nylon mesh (JIS Z8801-1: 2000) with a mesh size of 63 μm was cut into a rectangle with a width of 10 cm and a length of 40 cm, and folded in the center in the longitudinal direction, and both ends were heat-sealed to produce a width of 10 cm (internal size: 9 cm) and length. 20cm nylon bag. Measure exactly 1.00 g of the test sample and fill it evenly into the bottom of the manufactured nylon bag. The nylon bag containing the sample was immersed in physiological saline. After 60 minutes from the start of immersion, the nylon bag was taken out of physiological saline and hung vertically for 1 hour to remove water, and then the mass of the sample was measured (F1). Also, do the same without using samples Make and measure the mass F0(g) at this time. Then, from the masses F1, F0 and the mass of the sample, the target absorption rate is calculated according to the following formula.

Absorption rate (g/g)=(F1-F0)/quality of sample

It is clear from the results in Table 1 that when the water-absorbent resin powder is mixed by adding the weak acid alkali metal salt to the aggregate of the water-absorbent resin powder formed by absorbing water and agglomeration, the aggregate of the water-absorbent resin powder becomes granular. . In addition, it can be seen that the particulate water-absorbent resin powder can be dried to a moisture content of about 3% by mass or less. On the other hand, the gel-like water-absorbent resin is in the original state where the surface is dry but the inside is not dried.

FIG. 3 is a diagram instead of a photograph showing a sediment (agglomerate of water-absorbent resin) after dehydration treatment. Figure 4 shows the settlement after dehydration The substance (agglomerate of water-absorbent resin) is an example after treatment using sodium bicarbonate as the alkali metal salt of weak acid. Fig. 5 shows an example in which the sediment after dehydration treatment (agglomerate of water-absorbent resin) is treated with potassium chloride. It can be clearly seen from FIG. 4 that when a weak acid alkali metal salt is used, the aggregate of the water-absorbent resin becomes granular. On the other hand, when potassium chloride is used as shown in Fig. 5, although water is discharged from the water-absorbent resin by osmotic pressure, it is still in the original state of the aggregate and drying is difficult.

【Industrial utilization possibilities】

The absorbent body of the present invention can be suitably used in absorbent articles used for absorbing body fluids discharged from the human body, and particularly can be suitably used in incontinence pads. Absorbent articles such as disposable diapers, sanitary napkins, breast pads, etc.

Claims (11)

A method for treating water-absorbent resin, characterized in that the water-absorbent resin powder used as an absorbent article is agglomerated by water-absorbent resin powder aggregated by water absorption, and is dehydrated by using a divalent metal salt as a dehydrating agent The agglomerate of the treated water-absorbent resin powder is added and mixed with an alkali metal salt of a weak acid to change the agglomerate of the water-absorbent resin powder into a granular form, and the resulting granular water-absorbent resin is dried. The method for processing a water-absorbent resin as described in item 1 of the patent application range, wherein the water-absorbent resin powder is a water-absorbent resin powder having acrylic acid as a main component. The method for processing a water-absorbent resin as described in item 1 of the patent application scope, wherein the water-absorbent resin powder used as an absorbent article is dehydrated by using a divalent metal salt as a dehydrating agent to obtain a product containing Sewage of aggregates of water-absorbent resin powder is treated by sedimentation or concentration of this sewage to obtain sludge of sewage sediments or sewage concentrates containing aggregates of water-absorbent resin powder, and the alkali metal salt of the above-mentioned weak acid is added to this sewage The sludge is mixed to make the aggregate of the water-absorbent resin powder contained in the sludge granular, and the obtained particulate water-absorbent resin is dried. The method for processing a water-absorbent resin as described in item 1 of the patent application, wherein the aforementioned divalent metal salt is calcium chloride. The method for processing a water-absorbent resin as described in item 1 of the patent application range, wherein the weak acid is an acid having an acid dissociation constant of 4.26 or more at 25°C in water. The treatment method of water-absorbent resin as described in item 1 of the patent application scope, wherein the alkali metal salt of the weak acid is selected from sodium carbonate, sodium bicarbonate, carbonic acid At least one of the group consisting of potassium, potassium bicarbonate, sodium citrate acetate, and sodium succinate acetate. The method for processing a water-absorbent resin as described in item 1 of the patent application scope, wherein the absorbent article is an absorbent article for absorbing body fluids discharged from the human body. The treatment method of the water-absorbent resin as described in item 3 of the patent application scope further includes: before the dehydration treatment step, the step of washing the contaminants attached to the aforementioned absorbent article; and in the aforementioned sedimentation treatment or concentration treatment Before the step, the plastic component and the pulp component used in the absorbent article are separately recovered from the sewage. A method for manufacturing a regenerated water-absorbent resin powder, characterized in that the regenerated water-absorbent resin powder is obtained by the processing method described in any one of patent application items 1 to 8. A method for producing a soil improvement material, characterized by using a particulate water-absorbent resin obtained by the treatment method described in any one of claims 1 to 8 to produce a soil improvement material. A method for manufacturing a solid fuel, characterized in that a particulate water-absorbent resin obtained by the processing method described in any one of claims 1 to 8 is used to manufacture a solid fuel.

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