KR100994217B1 - method of eliminated acrylic acid and moisture from super-absorbent polymer - Google Patents

Abstract

A process for preparing superabsorbent polymers from which acrylic acid and water have been removed using pressurized liquids, supercritical fluids and mixtures thereof is disclosed. To accomplish this, the superabsorbent polymer formed by the polymerization reaction is provided with a pressurized liquid, a supercritical fluid or a mixture thereof. Thereafter, an extraction process using a pressurized liquid, a supercritical fluid or a mixture thereof is performed to extract acrylic acid and water remaining in the superabsorbent polymer formed by the polymerization reaction. For this reason, the superabsorbent polymer formed by the extraction process is formed of a superabsorbent polymer having a residual amount of acrylic acid of 20 to 500 ppm.

Super Absorbent Polymer, Residual Solvent, Supercritical, Carbon Dioxide

Description

Method for eliminating acrylic acid and moisture from super-absorbent polymer

The present invention relates to a process for producing a superabsorbent polymer from which acrylic acid and water are removed. More particularly, the present invention relates to a method for producing a superabsorbent polymer from which acrylic acid and water are removed using a supercritical fluid.

Super absorbent polymers (SAP) can absorb and retain aqueous fluids in amounts of hundreds to thousands of times their weight, as is well known in the art. Accordingly, the superabsorbent polymer can be used in infant diapers, adult incontinence products, feminine hygiene products, paper towels, surgical sponges, meat dishes, disposable mats outside doors and bathrooms, pet rugs, bandages and wound dressings, controlled drugs It is used in delivery, humidity control products, soil conditioners, controlled release of fertilizers, thickeners to harden cosmetics, underground cable sealing, snow, sensors, waste disposal and gelling agents.

The superabsorbent polymer used for such a wide range of applications is represented by the following chemical formula, and is prepared through crosslinking reaction after polymerization of acrylic acid and acrylate monomer and contains a large amount of acrylic acid and water after polymerization.

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Since the residual acrylic acid causes a problem of skin rash in contact with the skin, a process for removing these acrylic acid residues after the preparation of the super absorbent polymer is essential. Steam stripping has been applied as a method for removing the acrylic acid, but this process requires increasing the temperature and increasing the time in order to lower the residual acrylic acid concentration below an acceptable standard. At this time, the problem of thermal decomposition of acrylic acid and acrylate bonded in the superabsorbent polymer is caused, and it is difficult to lower the concentration of residual acrylic acid below a certain concentration.

An object of the present invention for solving this problem is to provide a method for producing a super absorbent polymer from which acrylic acid and water are removed using a pressurized solvent or a supercritical fluid.

In order to carry out the method for preparing a superabsorbent polymer according to an embodiment of the present invention for achieving the above object, first, a pressurized liquid, a supercritical fluid, or a mixture thereof is provided to a superabsorbent polymer formed by a polymerization reaction of an acrylate monomer. do. Thereafter, an extraction process using a pressurized liquid, a supercritical fluid or a mixture thereof is performed to remove (extract) acrylic acid remaining in the superabsorbent polymer formed by the polymerization reaction. The superabsorbent polymer formed by the extraction process is formed non-toxic with an acrylic acid residual amount of 20 to 500 ppm.

In the extraction process of the superabsorbent polymer, the water remaining in the superabsorbent polymer upon removal of residual acrylic acid may be removed at the same time.

As one example, the pressurized liquid and the supercritical fluid may include carbon dioxide, dimethyl ether, nitrous oxide, HFC-134a, HFC-125, propane and butane.

As one example, the pressurized liquid, supercritical fluid, or mixtures thereof may be used at 120 to 320 times the total weight of the superabsorbent polymer to remove the residual acrylic acid.

As an example, the acrylic acid may be removed at a temperature of 20 to 150 ° C. and a pressure of 50 to 700 bar.

Extraction processes using pressurized liquids, supercritical fluids, and mixtures thereof, as disclosed herein, can effectively remove toxic acrylic acid remaining in the superabsorbent polymer. That is, when the acrylic acid remaining in the existing superabsorbent polymer is removed by performing an extraction process using a pressurized liquid, a supercritical fluid, and a mixture thereof, the residual amount of the acrylic acid is reduced without causing a problem of thermal decomposition of the superabsorbent polymer. It can be reduced below the acceptable threshold. In addition, acrylic acid remaining in the superabsorbent polymer can be removed in a faster time under low temperature conditions than the existing process, and acrylic acid is removed to 500 ppm or less without discoloration, curing and deterioration of the superabsorbent polymer that may occur during the extraction process. can do. In addition, not only an acrylic acid monomer but also a dimer formed by the combination of monomers can be extracted together.

Hereinafter, with reference to the accompanying drawings will be described in detail a method for producing a super absorbent polymer according to embodiments of the present invention. However, the present invention is not limited to the following embodiments, and a person of ordinary skill in the art may implement the present invention in various other forms without departing from the technical spirit of the present invention. The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting of the present invention.

Singular expressions include plural expressions unless the context clearly indicates otherwise, and the terms "comprises" or "consists of" include, but are not limited to, features, numbers, steps, operations, components, parts or parts described in the specification. It is to be understood that the present invention is intended to indicate that there is a combination of and does not preclude the presence or addition of one or more other features or numbers, steps, operations, components, parts or combinations thereof.

Unless defined otherwise, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art. Terms such as those defined in the commonly used dictionaries should be construed as having meanings consistent with the meanings in the context of the related art, and are not construed in ideal or excessively formal meanings unless expressly defined in this application. Do not.

Method for preparing super absorbent polymer from which acrylic acid and water are extracted

The superabsorbent polymer of the present embodiment is formed by extracting (removing) acrylic acid and water remaining in the superabsorbent polymer formed through a polymerization reaction using a pressurized liquid, a supercritical fluid or a mixture thereof.

To do this, a pressurized liquid, a supercritical fluid, or a mixture thereof is first provided to a superabsorbent polymer comprising water formed by the polymerization reaction of an acrylate monomer. In this embodiment, the material to be removed from the super absorbent polymer formed by the polymerization reaction is acrylic acid and moisture. Acrylic acid is well dissolved in the supercritical fluid and the pressurized liquid, whereas the superabsorbent polymer itself is not dissolved, and thus it is possible to selectively separate and remove only residual acrylic acid and water.

The superabsorbent polymer is prepared by dissolving acrylic acid, an acrylate monomer and a crosslinking monomer in a solvent, followed by a polymerization-crosslinking reaction of the acrylic acid and the acrylate monomer. At this time, the superabsorbent polymer formed by the polymerization reaction contains moisture and a large amount of harmful acrylic acid remains. Here, the method for forming the super absorbent polymer is a technique known to those skilled in the art, and thus a detailed description thereof will be omitted.

Unlike the incompressible liquid solvents that are generally used, the supercritical fluids have various density changes depending on temperature and pressure conditions near the critical point, and thus can be controlled to have a relatively higher diffusivity and solubility than conventional solvents. That is, supercritical fluids have the ability to dissolve solids and liquids as well as liquid solvents. Supercritical carbon dioxide etc. are mentioned as an example of the supercritical fluid applied by a present Example.

As an example, the supercritical fluid may be used alone or in combination with the pressurized liquid. Examples of the pressurized liquid include carbon dioxide pressurized to have a subcritical or supercritical state, dimethyl ether, nitrous oxide, HFC-134a, HFC-125, propane and butane. As one example, the pressurized liquid may be used alone or in combination with the fluid. In addition, a co-solvent may be used when the acrylic acid is extracted, and examples of the co-solvent may include methanol, ethanol, propanol, butanol, and acetone. These may be used alone or in combination of two or more.

 As an example, the supercritical fluid or pressurized liquid may be provided at about 120 to 360 times the total weight of the superabsorbent polymer. When the amount of the supercritical fluid or the pressurized liquid is less than 120 times, the removal of residual acrylic acid is not easy, and when it exceeds 320 times, the effect is insignificant.

Subsequently, the acrylic acid remaining in the superabsorbent polymer polymerized using the pressurized liquid, the supercritical fluid or a mixture thereof is removed to 500 ppm or less. At this time, not only an acrylate monomer included in acrylic acid but also a dimer formed by the combination of monomers can be extracted together.

As an example, the removal of acrylic acid may be performed under an extraction temperature of about 20 to 150 ° C. and a pressure of 50 to 700 bar. At this time, the acrylic acid remaining in the super absorbent polymer is dissolved in the pressurized liquid and the supercritical fluid in the extractor and discharged through the pressure reducer, and the moisture is also discharged together. As a result, the superabsorbent polymer including water may be formed of a superabsorbent polymer having a dried state and having an acrylic acid residual amount of 20 to 500 ppm.

That is, the process of recovering the supercritical carbon dioxide provided into the extractor after removing the acrylic acid and water remaining in the superabsorbent polymer by adding a predetermined amount to the extractor, adding supercritical carbon dioxide at a desired temperature and pressure conditions at a constant flow rate It includes. Accordingly, the residual amount of acrylic acid included in the superabsorbent polymer after the extraction process may vary depending on the amount of the supplied supernatant liquid or supercritical fluid, the extraction time, and the extraction temperature, and the amount of the superabsorbent polymer filled in the extractor. .

As an example, when the extraction is performed by filling the superabsorbent polymer in the extractor included in the extraction apparatus and providing supercritical carbon dioxide for 120 minutes at 70 ° C. and 200 atm, the residual acrylic acid is 50 ppm or less from the superabsorbent polymer, Residual moisture can be removed to levels up to 15% by weight.

In another embodiment, after filling the superabsorbent polymer in the extractor included in the extraction device for 180 minutes at 70 ℃, 200 atm under conditions of extraction, the extraction is carried out, the residual acrylic acid from the super absorbent polymer 70ppm or less Residual moisture can be removed to levels below 5% by weight.

As another embodiment, the superabsorbent polymer is filled in the extractor included in the extraction apparatus, and when extraction is performed by providing nitrous oxide for 180 minutes at a temperature of 70 ° C. and 200 atm, the residual acrylic acid is 190 ppm or less and the residual moisture is 12 weight. Up to levels below% could be removed.

1 is a block diagram showing an extraction apparatus for performing the extraction process of the super absorbent polymer of the present invention.

Referring to FIG. 1, the superabsorbent polymer extraction apparatus 110 of the present embodiment includes a fluid supply unit 40 and a preheater including at least one container 10 containing a fluid, a precooler 20, and a pump 30. Extraction unit 90 including the 50 and the extractor 60 and the pressure reducer 70, has a configuration consisting of a separation unit 100 including a separator (80).

Fluid such as carbon dioxide contained in the container 10 is supplied to the extraction unit 90 in a liquid state having a constant temperature and pressure while passing through the precooler 20 and the piston pump 20, and the preheater 50. As it passes, it has a fixed temperature. Fluid such as carbon dioxide maintains a constant temperature and pressure in the extractor 60, and the carbon dioxide, which is in a supercritical state, extracts acrylic acid and water from the superabsorbent polymer filled in the extractor 60, and the pressure is higher than the set pressure. When the pressure exceeds a certain pressure is released to the gas state through the pressure reducer. Hereinafter, a method of manufacturing the superabsorbent polymer using the apparatus shown in FIG. 1 will be described in detail.

In order to prepare a super absorbent polymer with sufficient water and acrylic monomer removed, (A) raw material filling process, (B) extraction solvent supply process, (C) acrylic acid and water extraction process, and (D) super absorbent polymer with acrylic acid and water removed This can be done by carrying out the recovery process of the polymer sequentially.

In order to perform the (A) raw material filling process, about 20 g of the super absorbent polymer is filled into the extractor 60. In order to perform the (b) extraction solvent supply process, silver carbon dioxide is used as the extraction solvent, and the temperature of the preheater 50 is set to 70 ° C., and the precooler 20 is set to −10 ° C. The carbon dioxide from the vessel 10 is fed to the pump 30 in a complete liquid state at −10 ° C. via the precooler 20. In the pump 30, the liquid carbon dioxide is supplied to the extractor 60 and is primarily heated while passing through the preheater 50. In the state where the allowable pressure of the pressure reducing device 70 is set to 200 atmospheres, the carbon dioxide inside the extractor 60 is heated and pressurized until it becomes a supercritical state at 200 atmospheres of 70 캜, and the pressure inside the extractor 60 is 200. When the pressure is reduced, the pressure reduction device 70 discharges a predetermined pressure or more to the outside so that the pressure inside the extractor 60 is maintained at 200 atmospheres.

Subsequently, in order to perform the (c) acrylic acid and water extraction process, the supercritical carbon dioxide at 200 atm and 70 ° C. is continuously supplied and discharged during the extraction process. As a result, the supercritical carbon dioxide extracts acrylic acid and water in the superabsorbent polymer. At this time, not only an acrylate monomer included in acrylic acid but also a dimer formed by the combination of monomers can be extracted together.

Subsequently, (d) supercritical carbon dioxide containing acrylic acid and water is discharged through the decompression device 70 to the separator to perform a recovery process of the superabsorbent polymer from which acrylic acid and water have been removed. At this time, at room temperature and atmospheric pressure, the carbon dioxide loses its dissolving power in the supercritical state and is separated into gaseous carbon dioxide, liquid acrylic acid, and water. Thereafter, the superabsorbent polymer from which acrylic acid and water are removed may be recovered through the extractor 60.

Hereinafter, the present invention will be described with reference to the embodiments disclosed below. Since the above examples correspond to experiments in which the conditions in which the acrylic acid remains in the superabsorbent polymer is minimal, the numerical limitations disclosed in the examples do not limit the present invention.

Examples 1 to 21

About 20 g of a sample containing a super absorbent polymer (SAP) is filled in the extractor included in the extraction apparatus, followed by providing supercritical carbon dioxide under the conditions described in Table 1, followed by drying to remove acrylic acid and water from the super absorbent polymer. Was performed respectively. Thereafter, liquid chromatography (Liquid Chromatography) was used to measure the residual amount and the water content of acrylic acid (AA) contained in the super absorbent polymer subjected to the extraction process. The results are shown in Table 1. Here, the superabsorbent polymer filled in the extractor contains 46000 ppm of residual acrylic acid and 48% by weight of water.

TABLE 1

Referring to Table 1, the acrylic acid removal process using supercritical carbon dioxide is carried out at a temperature of 50 ° C. or more, pressure of 100 bar or more, extraction time of 90 minutes or more, and process conditions using supercritical carbon dioxide of 120 times or more of the amount of SAP used. The residual amount of was confirmed to be 500 ppm or less. In particular, it was confirmed that the residual amount of acrylic acid was 100 ppm or less when using a temperature of 70 ° C. or more, a pressure of 200 bar or more, an extraction time of 120 minutes or more, and a supercritical carbon dioxide of 200 times or more of the amount of SAP.

2 is a graph showing a change in the amount of acrylic acid remaining in the super absorbent polymer according to the amount of carbon dioxide used in the present embodiments.

Referring to FIG. 2, it can be seen that as the amount of supercritical carbon dioxide increased, the concentration of residual acrylic acid decreased. In particular, when the amount of supercritical carbon dioxide is more than 120 times, it was confirmed that the residual amount of acrylic acid was significantly reduced. In addition, it was confirmed that the concentration of acrylic acid also decreases as the pressure increases.

3 is a graph showing the change in the content of water remaining in the super absorbent polymer according to the amount of carbon dioxide used in the present embodiment.

Referring to FIG. 3, it can be seen that as the amount of supercritical carbon dioxide is increased, the content of remaining moisture decreases.

Examples 22-23

20 g of superabsorbent polymer (SAP) was charged into the extractor included in the extraction apparatus, and then dimethyl ether (DME) or nitrous oxide (N ₂ O) was provided under the conditions described in Table 2 to extract acrylic acid from the superabsorbent polymer and to obtain moisture. Each drying process to remove was performed. Then, the amount of residual acrylic acid (AA) and water content of the superabsorbent polymer, which was extracted using liquid chromatography, was measured using liquid chromatography. The results are shown in Table 2. Here, the superabsorbent polymer filled in the extractor contains 46000 ppm of residual acrylic acid and 48% by weight of water.

TABLE 2

Referring to Table 2, it was also confirmed that acrylic acid and water remaining in the superabsorbent polymer may be effectively removed from the acrylic acid removal process using dimethyl ether or nitrous oxide.

As described above, the present invention can effectively remove toxic acrylic acid remaining in the superabsorbent polymer. In other words, by performing an extraction process using a pressurized solvent or a supercritical fluid, the residual amount of acrylic acid is reduced below an acceptable standard without causing a problem of thermal decomposition of the superabsorbent polymer when removing the acrylic acid remaining in the existing superabsorbent polymer. You can. In addition, acrylic acid remaining in the superabsorbent polymer can be removed in a faster time under low temperature conditions than the existing process, and acrylic acid is removed to 500 ppm or less without discoloration, curing and deterioration of the superabsorbent polymer that may occur during the extraction process. can do. In addition, not only an acrylate monomer included in acrylic acid, but also a dimer formed by the combination of monomers can be extracted together.

Although described with reference to the embodiments above, those skilled in the art can variously modify and change the present invention without departing from the spirit and scope of the invention described in the claims below. You will understand.

BRIEF DESCRIPTION OF THE DRAWINGS It is a block diagram which shows the extraction apparatus for carrying out the extraction process of the superabsorbent polymer of this invention.

2 is a graph showing a change in the amount of acrylic acid remaining in the super absorbent polymer according to the amount of carbon dioxide used in the present embodiments.

3 is a graph showing the change in the content of water remaining in the super absorbent polymer according to the amount of carbon dioxide used in the present embodiment.

<Description of the symbols for the main parts of the drawings>

10 fluid container 20 precooler

30: pump 40: fluid supply

50: preheater 60: extractor

70: pressure reducer 80: separator

90: extraction unit 100: separation unit

Claims (7)

(a) providing a pressurized liquid or supercritical fluid or mixtures thereof to a superabsorbent polymer formed by polymerizing acrylic acid, acrylate monomers and crosslinking monomers dissolved in a solvent; (b) extracting acrylic acid remaining in the polymerized superabsorbent polymer using the pressurized liquid, supercritical fluid or mixtures thereof; (c) separating the pressurized liquid, supercritical fluid or mixtures thereof in which acrylic acid is dissolved under reduced pressure; And (d) recovering the super absorbent polymer from which acrylic acid has been removed. The method of claim 1, wherein the acrylic acid is obtained in a super absorbent polymer having a residual amount in the range of 20 to 500 ppm.         The method of claim 1, wherein the water or the solvent remaining in the super absorbent polymer is removed together when the acrylic acid is removed. The method of claim 1, wherein the pressurized liquid or supercritical fluid is at least one selected from the group consisting of carbon dioxide, dimethyl ether, nitrous oxide, HFC-134a, HFC-125, propane and butane Method for producing a super absorbent polymer, characterized in that it comprises. The method of claim 1, wherein a co-solvent is used to extract the acrylic acid, and the co-solvent comprises at least one selected from the group consisting of methanol, ethanol, propanol, butanol and acetone. The method of claim 1, wherein the acrylic acid is removed at a temperature of 20 to 150 ° C. and a pressure of 50 to 700 bar. The method of extracting superabsorbent polymer according to claim 1, wherein the acrylic acid is removed together with the acrylic acid monomer and dimer thereof.

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