JP2006095470A - Water-absorbing medium, and method for concentrating suspension using it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a new water-absorbing medium and a method for concentrating a suspension using it. <P>SOLUTION: The water-absorbing medium is a cross-linked polymer cross-linked with a layered clay mineral, includes a thermosensitive polymer gel having hydrophilicity/hydrophobicity reversibly changing at the phase transition point. In the method for concentrating the suspension, the water-absorbing medium and the suspension are brought into contact with each other in a temperature zone in which the thermosensitive polymer gel shows hydrophilicity, so that the suspension is concentrated. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention particularly relates to a water-absorbing medium using a thermosensitive polymer gel suitable for a suspension concentration method.

Waste liquids in which inorganic fine particles such as abrasives are suspended are discharged from semiconductor factories and glass factories. These waste liquids are usually subjected to a coagulation-precipitation treatment using various inorganic or organic flocculants to concentrate the waste liquid, or directly processed as industrial waste.
However, in the case of this coagulation-precipitation treatment, there is a problem that the cost of chemicals such as the coagulant is large, and a large amount of sludge is generated, so that the treatment cost increases.

Further, in the production process of a solution containing inorganic fine particles, such as a suspension of fine silica particles coated as an ink receiving layer in the production of an ink jet recording sheet, for example, concentration of the solution using a film, Evaporation concentration is performed.
However, in the concentration using the above-mentioned membrane, membrane clogging may occur due to fine particles suspended in the solution, and in the case of evaporation concentration, the initial cost and running cost increase, and the economic burden is increased. There is a problem of being big.

For this reason, there is a need for a processing method that is simple in operation and low in processing cost for dehydrating and concentrating a suspension in which inorganic fine particles are suspended.
On the other hand, for example, in order to efficiently dehydrate moisture adhering to the surface of a metal strip, a polymer compound that reversibly changes hydrophilicity and hydrophobicity at the phase transition point, specifically, polyvinylmethyl A draining method using ether, methylcellulose, polyethylene oxide, poly-N-isopropylacrylamide, partially saponified polyvinyl acetate or the like as a water-absorbing medium is known (see Patent Document 1).

In this prior art, in the temperature range where the water absorbing medium is hydrophilic (low temperature), the water absorbing medium and the metal strip are brought into contact with each other to dehydrate the water adhering to the metal strip, and then the temperature range where the water absorbing medium is hydrophobic. The metal strip is drained by repeating the treatment of transporting to (high temperature) and discharging the water absorbed there.
Japanese Patent Publication No. 6-46134

However, there has been no report to date of a case where water in a suspension is absorbed using a water-absorbing medium having temperature sensitivity as disclosed in Patent Document 1 to concentrate the suspension.
In light of the above, the present inventor uses a water-absorbing medium as described above when concentrating a suspension, so that, for example, the thermal energy for heating is significantly less than that in the evaporation concentration method. The idea is that mechanical energy such as driving a pump for pressure filtration is also unnecessary, and therefore the running cost can be reduced.

In this case, it is preferable that the water-absorbing medium has a water absorption speed as high as possible and that it should have a mechanical strength (shape holding force) that does not collapse when mixed with a suspension. The inventors have made extensive studies on the water-absorbing medium that should satisfy the requirements, and have developed a novel water-absorbing medium of the present invention described later.
That is, an object of the present invention is to provide a novel water-absorbing medium having a high water-absorbing speed and appropriate mechanical strength, and a suspension concentration method using the water-absorbing medium.

In order to achieve the above object, the present invention according to claim 1 is a crosslinked polymer crosslinked with a lamellar clay mineral, and the hydrophilicity and hydrophobicity are reversibly bordered on the phase transition point. A water-absorbing medium comprising a temperature-sensitive polymer gel that changes is provided.
Although the layered clay mineral is not particularly limited, smectite is suitable (Claim 2), and the thermosensitive polymer gel is one or more polymer cross-links selected from acrylamide derivatives and methacrylamide derivatives. It is preferable that it is a body (Claim 3). Of the acrylamide derivatives and methacrylamide derivatives, N-isopropylacrylamide is particularly preferred (Claim 4).

In addition, as the thermosensitive polymer gel, a water-soluble vinyl-based nonionic monomer and / or a water-soluble vinyl-based anionic monomer are copolymerized with one or more selected from the acrylamide derivatives and methacrylamide derivatives. A polymer cross-linked product is preferred (Claim 5).
Further, in the present invention according to claim 6, the water-absorbing medium containing the temperature-sensitive polymer gel and a suspension are brought into contact with each other in a temperature range in which the temperature-sensitive polymer gel exhibits hydrophilicity. There is provided a method for concentrating a suspension, characterized by concentrating the suspension.

In this water-absorbing medium, the layered clay mineral used as a cross-linking agent when synthesizing the thermosensitive polymer gel (polymer cross-linked product) is made uniform in the crosslink density in the thermosensitive polymer gel and its mechanical strength Since (form retention power) is increased, it does not collapse when it is brought into contact with the suspension, and can withstand repeated use.
When the water-absorbing medium is brought into contact with the suspension in a temperature range where the water-absorbing medium is hydrophilic, the water-absorbing medium selectively absorbs water from the suspension automatically. As a result, the suspension is concentrated. When the water absorbing medium is heated to a temperature exhibiting hydrophobicity, the stored water is automatically released, and the water absorbing medium is restored to a water absorbing state.

  In this process, for example, compared with the evaporation concentration method, the thermal and mechanical energy required is greatly reduced, so the running cost required for concentration is greatly reduced.

The water-absorbing medium of the present invention is basically composed of a temperature-sensitive polymer gel in which hydrophilicity and hydrophobicity reversibly change with a phase transition point (temperature) as a boundary.
And this thermosensitive polymer gel is characterized by being a crosslinked polymer crosslinked using a lamellar clay mineral described later.
As a thermosensitive polymer gel, it has a temperature sensitivity in which hydrophilicity and hydrophobicity reversibly change at the above-described phase transition point, and a lamellar clay mineral described later is used as a crosslinking agent. There is no particular limitation as long as it is a crosslinked polymer.

Among such thermosensitive polymer gels, in the present invention, for example, a cross-linked product of an acrylamide derivative, a cross-linked product of a methacrylamide derivative, or a copolymer of an acrylamide derivative and a methacrylamide derivative is given as a preferred example. Can do.
In this case, examples of the acrylamide derivative include N-methylacrylamide, N-methyl-N-ethylacrylamide, N-acryloylpyrrolidine, N-dichloropropylacrylamide, N-isopropylacrylamide, N, N-diethylacrylamide, N-methyl- N-isopropylacrylamide, N-normalpropyl acrylamide, N-methyl-N-normal acrylamide, N-acryloylpiperidine, and the like can be used.

Moreover, as a methacrylamide derivative, N-cyclopropyl methacrylamide, N-ethyl methacrylamide, N-isopropyl methacrylamide, N-normal propyl methacrylamide, etc. can be used, for example.
Among these derivatives, N-isopropylacrylamide is preferable in that it has a high polymerization rate, can have a high molecular weight, and has good copolymerizability with other monomers.

By selecting one or more of the above acrylamide derivatives as appropriate and crosslinking them, a polymer cross-linked product of the acrylamide derivative can be obtained, and one or more of the above methacrylamide derivatives are selected as appropriate. In addition, a crosslinked polymer of methacrylamide derivatives can be obtained by crosslinking them.
In addition, one or more of the above acrylamide derivatives are appropriately selected, one or more of the above methacrylic derivatives are appropriately selected, and both are copolymerized, whereby the acrylamide derivative and the methacrylamide derivative are co-polymerized. A crosslinked polymer containing a polymer can also be obtained.

The temperature-sensitive polymer gel of the present invention includes an acrylamide derivative or a methacrylamide derivative crosslinked, an aqueous vinyl nonionic monomer such as acrylamide or methacrylamide, and / or an aqueous solution such as acrylic acid or methacrylic acid. A crosslinked polymer obtained by copolymerizing a vinyl anionic monomer is preferred.
By copolymerizing these water-soluble vinyl-based nonionic monomers and water-soluble vinyl-based anionic monomers, it is possible to control the level of the phase transition point of the synthesized thermosensitive polymer gel and the magnitude of the water absorption / discharge rate.

  When copolymerizing the above water-soluble vinyl-based nonionic monomer and / or water-soluble vinyl-based anionic monomer, it is necessary to maintain the temperature sensitivity of the thermosensitive polymer gel, and the balance between water absorption and water discharge rate From the standpoints of maintaining an appropriate phase transition point, and the like, it is preferable to introduce 0.1 to 30% by mass with respect to the acrylamide derivative or methacrylamide derivative used.

  If the type of acrylamide derivative or methacrylamide derivative used, or the type of aqueous vinyl nonionic monomer or aqueous vinyl anion monomer to be copolymerized or the copolymerization ratio thereof are changed, the phase of the synthesized thermosensitive polymer gel is changed. Since the transition point also changes, it is necessary to appropriately select the type of each component described above in relation to the use temperature of the thermosensitive polymer gel.

  In addition, as these polymer cross-linked products, those having a molecular weight of about 10 to 20 million can be used normally, but the higher the molecular weight, the lower the cross-linking density, so the water absorption / discharge rate is large. Therefore, in the present invention, it is preferable to use one having a molecular weight of 2 million or more. However, when the molecular weight exceeds 20 million, problems such as a decrease in response speed occur due to entanglement of polymer chains in the polymer crosslinked product.

These polymer crosslinked products are produced by using a layered clay mineral as a crosslinking agent at the time of crosslinking of the above-described derivatives.
The layered clay mineral is not particularly limited, and examples thereof include smectites such as 2-octahedral smectite and 3-8-hedron smectite, and these have swelling properties (having Na ⁺ as an exchangeable cation). The organic substance can be intercalated (taken between layers). By using these layered clay minerals as cross-linking agents, the cross-link density of the synthesized polymer cross-linked product (temperature-sensitive polymer gel) becomes uniform, and its mechanical strength (form retention) increases. The effect of increasing the water discharge speed can be obtained. The water-absorbing medium used in contact with the suspension is particularly required to have a high mechanical strength of the thermosensitive polymer gel.

Smectite is useful in that the above-described effects can be effectively imparted to the thermosensitive polymer gel.
Examples of the 2-octahedral smectite include montmorillonite and beidellite, and examples of the 3-8-hedral type smectite include saphonite, hectorite, and soconite. Some of these smectites have been synthesized as natural products, but it is possible to increase the strength of the thermosensitive polymer gel synthesized by homogenizing the crosslink density and to increase the water absorption / discharge rate. In this respect, synthetic smectite having a particle size of about 10 nm to 1 μm is preferable.

  If the amount of layered clay mineral used in the synthesis of the polymer crosslinked product is too small, the number of crosslinking points will be reduced, so a crosslinked product with high mechanical strength cannot be obtained, and if the amount used is too large, the strength of the crosslinked product will be Although it increases, the water absorption / discharge rate of the crosslinked product tends to decrease, so the amount of layered clay mineral used is 1 to 50 mass relative to the amount of monomer of the acrylamide derivative or methacrylamide derivative to be crosslinked. % Is preferred.

The temperature-sensitive polymer gel of the present invention is produced by a radical polymerization method for a reaction system containing the above-described components.
In the case of a photopolymerization method, it can be further produced by using benzoin, benzoin ethyl ether, benzoin isopropyl ether or the like as a photopolymerization initiator and irradiating the reaction system with ultraviolet light having a wavelength of 365 nm.

In the case of the polymerization acceleration method, it can be produced using, for example, N, N, N, N-tetramethylethylenediamine as a polymerization accelerator, or using ammonium persulfate, sodium persulfate, potassium persulfate, or the like as a polymerization initiator. It is.
In these radical polymerization methods, the degree of polymerization and the molecular weight of the synthesized thermosensitive polymer gel can be adjusted by controlling the amount of each chemical used, the intensity of the irradiated ultraviolet rays, the polymerization temperature, and the like.

In the present invention, the suspension is concentrated by using the above-described thermosensitive polymer gel as a water-absorbing medium.
Specifically, the water-absorbing medium is introduced into the suspension and brought into contact with the suspension at a temperature below the phase transition point and in a temperature range showing hydrophilicity. Since the water in the suspension is stored in the water-absorbing medium, the suspension is concentrated.

At this time, the concentration of the suspension can be adjusted by appropriately selecting the amount of the water-absorbing medium used.
Then, after separating the suspension and the water-absorbing medium, the water-absorbing medium is heated at a temperature higher than the phase transition point and exhibiting hydrophobicity. As a result, the moisture stored in the water absorbing medium is released. As the heating means, for example, appropriate means such as hot water, hot air, and heater means may be used.

The water-absorbing medium after water discharge can be returned to the suspension concentration step and reused again by cooling to the air and cooling to a temperature range that exhibits hydrophilicity below the phase transition point.
In addition, the shape of the water absorption medium to be used can be arbitrarily selected and used. For example, when the concentration step is performed in a continuous manner, the water-absorbing medium can be moved in a suspension tank in a state where the water-absorbing medium is formed in a plate shape and disposed on the surface of the belt conveyor. Moreover, when performing a concentration process by a batch system, a water absorption medium can be used in a granular form.

(Sample preparation)
To 90 g of deionized water, 10 g of N-isopropylacrylamide and 3 g of synthetic smectite hectorite (Rockwood, particle size 72 to 148 nm) were added to 10 mg of benzoin isopropyl ether (photopolymerization initiator). After adding a solution dissolved in 0.1 g of acetone, nitrogen gas was fed at a flow rate of 100 mL / min for 2 hours, and the mixture was sufficiently stirred, and then sealed with a transparent glass lid. It was poured into a stainless steel container 10 cm long, 20 cm long and 5 cm high.

Next, ultraviolet rays having a wavelength of 365 nm were irradiated for 2 hours from the top of the lid, and photopolymerization was advanced to synthesize a thermosensitive polymer gel. This is designated as Example Sample 1.
To a solution obtained by adding 9.9 g of N-isopropylacrylamide and 3 g of synthetic smectite to 90 g of deionized water, a solution obtained by dissolving 10 mg of benzoin isopropyl ether in 0.1 g of acrylic acid (water-soluble vinyl anionic monomer) is added. Then, sodium hydroxide was further added to neutralize, and nitrogen gas was fed into the container at a flow rate of 100 mL / min for 2 hours, and then poured into the stainless steel container sealed with a glass lid. It is.

Then, photopolymerization proceeded by irradiating ultraviolet rays having a wavelength of 365 nm for 2 hours from the top of the lid. The obtained thermosensitive polymer gel is referred to as Example Sample 2.
A thermosensitive polymer gel was synthesized under the same conditions as in Example Sample 1 except that ethylene bisacrylamide was used as a cross-linking agent instead of synthetic smectite. This is a comparative sample.
(Mechanical strength of sample, water absorption speed)
As described above, the performance of the three types of thermosensitive polymer gels was investigated. As a result, Example Sample 1 had a uniform cross-linking density, so that the whole was transparent, the mechanical strength was high, and the water absorption rate was 4 g / g-gel · hr.

Further, in the case of Example Sample 2, the water absorption rate was remarkably large at 50 g / g-gel · hr. This is clearly the effect of copolymerizing acrylic acid (water-soluble vinyl anionic monomer) during the crosslinking of N-isopropylacrylamide.
On the other hand, the comparative sample that does not use synthetic smectite as a cross-linking agent has a non-uniform cross-link density, and therefore the whole is cloudy, and even if a little external force is applied, it collapses brittlely, and the water absorption rate Also, it was a very small value of 0.4 g / g-gel · hr.

Here, when Example Sample 1 is compared with Comparative Example Sample, the usefulness of using synthetic smectite as a crosslinking agent is obvious. When synthetic smectite is used as the cross-linking agent, the effectiveness of copolymerizing a water-soluble vinyl-based anionic monomer with an acrylamide derivative is clear, as is clear by comparing Example Sample 1 and Example Sample 2. is there.
(Suspension concentration test)
Using Example Sample 2, the suspension was concentrated as follows.

5 g (as dry weight) of Example Sample 2 was added to 300 mL of a suspension in which silicate fine particles were suspended at a concentration of 13%, and left for 1 hour. I investigated.
The amount of water absorption was 150 mL. The suspension was concentrated to a concentration of 26.0%.
Example Sample 2 was taken out from the concentrated solution, heated at a temperature of 60 ° C. for 30 minutes and allowed to drain, and then subjected to the same concentration treatment as described above. As a result, no change was observed in the concentration performance.

In addition, 3 g (as dry weight) of Example Sample 2 was added to 300 mL of suspension in which abrasive fine particles were suspended at a concentration of 6% and left for 1 hour, and then the water absorption and suspension of Example Sample 2 were suspended. The liquid concentration was examined.
The amount of water absorption was 150 mL. The suspension was concentrated to a concentration of 12.0%.
Example Sample 2 was taken out from the concentrated solution, heated at a temperature of 60 ° C. for 30 minutes and allowed to drain, and then subjected to the same concentration treatment as described above. As a result, no change was observed in the concentration performance.

  Since this water-absorbing medium is synthesized using a layered clay mineral as a cross-linking agent, it has a large form-retaining power, so it can retain its form without collapsing even when contacted with a suspension. Is possible. And since it has the property of absorbing water in the temperature range below the phase transition point and discharging water in the temperature range above the phase transition point, it simply absorbs and concentrates the water content of the suspension just by contacting with the suspension. be able to.

  For this reason, the suspension concentration method using this method uses less thermal and mechanical energy than the conventional suspension concentration method, and the running cost is greatly reduced. Industrially useful.

Claims (6)

  A water-absorbing medium, which is a crosslinked polymer obtained by crosslinking with a layered clay mineral and includes a temperature-sensitive polymer gel that reversibly changes its hydrophilicity and hydrophobicity with a phase transition point as a boundary.   The water-absorbing medium according to claim 1, wherein the layered clay mineral is smectite.   The water-absorbing medium according to claim 1 or 2, wherein the temperature-sensitive polymer gel is one or two or more kinds of crosslinked polymers selected from acrylamide derivatives and methacrylamide derivatives.   The water-absorbing medium according to claim 3, wherein the thermosensitive polymer gel is N-isopropylacrylamide alone or a polymer crosslinked product containing the same.   A crosslinked polymer in which the thermosensitive polymer gel is obtained by copolymerizing one or more selected from the acrylamide derivative or the methacrylamide derivative with a water-soluble vinyl nonionic monomer and / or a water-soluble vinyl anionic monomer. The water-absorbing medium according to claim 3 or 4, wherein   The water-absorbing medium and the suspension according to any one of claims 1 to 5 are brought into contact with each other in a temperature range where the temperature-sensitive polymer gel of the water-absorbing medium exhibits hydrophilicity to concentrate the suspension. A method for concentrating a suspension.