Method for dissolving water-soluble polymers

Abstract

The objective is to provide a method for dissolving water-soluble polymers that improves insufficient dissolution and the solution stability of the water-soluble polymer solution. [Solution] By using water containing ultrafine bubbles as dissolution water, the repulsion between the ultrafine bubbles and the gaps created by the presence of microbubbles improve the dispersibility of water-soluble polymers when they are added to this water, promoting the swelling of the water-soluble polymers and shortening the dissolution time. Furthermore, the surface adsorption of ionic components that cause viscosity deterioration due to the negative charge of ultrafine bubbles in water, and the surface repulsion effect, suppress reactions with water-soluble polymers, thereby improving the solution stability of the water-soluble polymer solution.

Description

【Technical Field】 【0001】 The present invention relates to a method for dissolving a water-soluble polymer using water containing ultrafine bubbles as dissolution water. 【Background Art】 【0002】 Conventionally, water-soluble polymers are used in a wide range of applications such as polymer flocculants for water treatment, yield improvers for papermaking, thickeners, and paper strength enhancers in the state of a dilute aqueous solution. 【0003】 Water-soluble polymers are usually supplied in product forms with relatively high concentrations of 10 to 100% by mass, such as powders, liquids (emulsions, dispersions), or pastes. Therefore, when these powders, liquids, or pastes of water-soluble polymers are used in the above applications, they are diluted with water to a concentration suitable for each application before use. 【0004】 Basically, about 30 minutes to 1 hour is required as the dissolution time to dilute the above water-soluble polymer to the concentration for use with water. However, depending on the type of water-soluble polymer, it may take several hours for dissolution, which may cause problems such as being used in a state of insufficient dissolution. 【0005】 Furthermore, a water-soluble polymer solution obtained by diluting and dissolving a water-soluble polymer with dissolution water has a short solution stability time because the viscosity decreases over time, and a decrease in the aggregation effect due to changes over time occurs. 【0006】 For example, in Patent Document 1, as a method for generating a dissolution solution of a polymer flocculant in a short time and with a high dissolution rate, an example of an apparatus equipped with a stirrer in a polymer flocculant mixing and dissolution system, in which a mixing tank has a stirrer with propeller blades and turbine blades arranged in upper and lower stages on a rotating shaft, is described. Patent Document 2 describes an example in which a coagulation agent and an aqueous solution of the coagulation agent are stabilized by an aqueous solution in which a coagulation agent is dissolved, comprising a polymer coagulant, a reducing agent, and an amount of acidic substance that reduces the pH of the solution to 6 or less when the polymer coagulant is dissolved in 0.1% by mass or more. However, mechanical technology has challenges in terms of costs such as installation and maintenance, while chemical additive technology has challenges in terms of a decrease in purity due to the reduction in the proportion of water-soluble polymers depending on the proportion of additives. 【0007】 [Patent Document 1] Japanese Patent Publication No. 2017-80686 [Patent Document 2] Japanese Patent Publication No. 2008-18344 [Overview of the project] [Problems that the invention aims to solve] 【0008】 The present invention aims to provide a method for dissolving water-soluble polymers that improves the dissolution rate and solution stability of the water-soluble polymer, and to provide the solution therefor. 【0009】 In order to solve the above-mentioned problems, the inventors focused on the dissolution water and conducted various studies, resulting in the invention described below. Specifically, the invention is a method for dissolving a water-soluble polymer and a solution thereof, using water containing ultrafine bubbles, which has been generated, as the dissolution water. [Effects of the Invention] 【0010】 By using water containing ultrafine bubbles in this invention to dissolve water-soluble polymers, it is possible to improve the dissolution rate and reduce the viscosity of the water-soluble polymer solution compared to conventional methods. As a result, running costs can be reduced by shortening the dissolution time of water-soluble polymers, the amount of water-soluble polymer used can be reduced by suppressing the generation of undissolved substances, and the shelf life of the water-soluble polymer solution can be extended by improving solution stability, while also suppressing the decrease in flocculation effect. [Modes for carrying out the invention] 【0011】 In this invention, ultrafine bubbles specifically refer to fine bubbles with a diameter of less than 1 μm. Water containing a large number of such ultrafine bubbles is transparent, does not float to the surface, and remains stable in the water for a long period of time. While fine bubbles with a diameter of 1 μm to 1000 μm are defined as microbubbles, the water used in this invention contains ultrafine bubbles. Fine bubbles, including ultrafine bubbles, possess various properties that differ from ordinary bubbles, such as surfactant activity, i.e., negative surface charge, surface adsorption, surface repulsion, and hydrophobic interactions. 【0012】 There are no particular limitations on the method for generating microbubbles with a diameter of less than 1 μm, such as ultrafine bubbles, in a liquid, but methods such as those published by the Fine Bubble Industry Association, such as the following, can be used. 【0013】 High-speed swirling flow method: A method in which liquid is injected under pressure into a cylindrical generator body using a pump, generating high-speed commutation inside to crush air bubbles and produce fine bubbles and ultrafine bubbles, the fine bubbles are separated by flotation, and the ultrafine bubbles are left to remain in the liquid. 【0014】 Pressurized dissolution method: A method in which a gas-liquid mixture is pressurized with a pump, the gas is dissolved in the liquid to a supersaturated state, fine bubbles and ultrafine bubbles are generated by rapid depressurization, the fine bubbles are separated by flotation, and the ultrafine bubbles remain in the liquid. 【0015】 Surfactant-added micropore method: A method in which a sufficient amount of surfactant is added to a liquid to reduce the gas-liquid interface tension and separate ultrafine bubbles from very small gas dispersion pores. 【0016】 Ultrasonic cavitation: A method of generating ultrafine bubbles from dissolved gases in a liquid through cavitation (a phenomenon in which tiny cavities are formed in a liquid due to rapid pressure fluctuations, and these cavities rapidly collapse). 【0017】 Ultrafine bubbles can be obtained using commercially available ultrafine bubble generators, and commonly used devices can be used. For example, the high-speed swirling flow type nanobubble generation kit ND-NBZS (manufactured by Nippon Denko Co., Ltd.) and the pressurized dissolution type GaLF (manufactured by IFB Technologies Co., Ltd.) can also be used. 【0018】 In the present invention, commercially available polymers can be used as the water-soluble polymer, but dimethylaminoethyl (meth)acrylate polymers are preferred because the ion density and molecular weight of the polymer can be easily adjusted. 【0019】 Examples of tertiary amino group-containing cationic monomers used in the production of dimethylaminoethyl (meth)acrylate polymers include dimethylaminoethyl (meth)acrylate, diethylaminoethyl (meth)acrylate, dimethylaminopropyl (meth)acrylamide, diethylaminopropyl (meth)acrylamide, and their salts. Examples of quaternary ammonium base-containing cationic monomers include (meth)acryloyloxyethyltrimethylammonium chloride, (meth)acryloyloxyethyldimethylbenzylammonium chloride, (meth)acryloylaminopropyltrimethylammonium chloride, (meth)acryloylaminopropyldimethylbenzylammonium chloride, and (meth)acryloyloxy 2-hydroxypropyltrimethylammonium chloride. These can be polymers of cationic monomers alone, polymers of two or more cationic monomers, copolymers of cationic monomers and nonionic monomers, copolymers of cationic monomers and anionic monomers, or copolymers of cationic monomers, anionic monomers and nonionic monomers. Examples of nonionic monomers include (meth)acrylamide, N,N'-dimethylacrylamide, vinyl acetate, acrylonitrile, methyl acrylate, 2-hydroxyethyl (meth)acrylate, diacetoneacrylamide, N-vinylpyrrolidone, N-vinylformamide, N-vinylacetamide, acryloylmorpholine, etc., and one or more of these can be used. Examples of anionic monomers include (meth)acrylic acid, itaconic acid, 2-acrylamido-2-methylsulfonic acid, maleic acid, and salts thereof, and one or more of these can be used. 【0020】 When producing the water-soluble polymer in the present invention, a crosslinkable monomer may be used as a structure modifier during or after polymerization. When using it, the crosslinkable monomer is present in the range of 0.00005 to 0.050% by mass based on the total amount of monomers. Although it varies depending on the monomer composition and polymerization conditions, if it exceeds 0.050% by mass, crosslinking proceeds too much and it becomes water-insoluble, which is not preferable for the use of the present invention. Examples of the crosslinkable monomer include N,N'-methylenebis(meth)acrylamide, triallylamine, ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, triethylene glycol dimethacrylate, tetraethylene glycol dimethacrylate, 1,3-butylene glycol dimethacrylate, polyethylene glycol di(meth)acrylate, N-vinyl(meth)acrylamide, N-methylallylacrylamide, glycidyl acrylate, polyethylene glycol diglycidyl ether, acrolein, glyoxal, vinyltrimethoxysilane, etc., and N,N'-methylenebis(meth)acrylamide is preferably applied. 【0021】 In addition, an amidine-based polymer can be used as the water-soluble polymer. As the amidine-based polymer, known ones can be used, for example, those produced by the method disclosed in JP-A-5-192513 and the like. 【0022】 The weight average molecular weight of the water-soluble polymer in the present invention is in the range of 1 million to 30 million, and preferably 3 million to 20 million. 【0023】 The dissolution of the water-soluble polymer using the water containing ultrafine bubbles in the present invention as dissolution water is as follows. First, due to the repulsion between ultrafine bubbles caused by the negatively charged ultrafine bubbles in water generated by any of the above methods or the gaps due to the presence of fine bubbles, the dispersibility of the water-soluble polymer in this water is improved when the water-soluble polymer is added to this water, promoting the swelling of the water-soluble polymer. As a result of the effective action of ultrafine bubbles, it is considered that the dissolution time is shortened. 【0024】 The improvement of the solution stability of a water-soluble polymer solution obtained by using water containing ultra-fine bubbles in the present invention as dissolution water is considered to suppress the reaction with the water-soluble polymer by surface adsorption and surface repulsion of ionic components that cause viscosity deterioration due to the negatively charged ultra-fine bubbles in water. 【0025】 Water-soluble polymers are usually used in applications such as polymer flocculants, polymer dehydrating agents, yield improvers, thickeners, etc. In the present invention, these commercially available water-soluble polymers can also be used. 【0026】 In the present invention, the above water-soluble polymer is dissolved in water to prepare a water-soluble polymer solution of 0.01 to 0.8% by mass, preferably 0.05 to 0.4% by mass. 【0027】 As a dissolution method, a method of gradually adding a calculated amount of the water-soluble polymer while stirring a calculated amount of water to dissolve it is desirable. Examples of the stirring method include using an impeller or an in-line mixer. Dissolution to the target dilution concentration may be not only one-step dilution but also stepwise dilution. The dissolution time is usually 30 minutes or more, and may require about 2 to 3 hours in some cases. 【Examples】 【0028】 Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to the following examples as long as the gist thereof is not exceeded. 【0029】 First, 1 to 5 were prepared and prepared as water-soluble polymers. Their compositions and physical properties are shown in Table 1. 【0030】 As a means of generating ultrafine bubbles, a high-speed swirling method was adopted, and a structure disclosed in Japanese Patent Application Publication No. 2018-58038 was used, namely, a cylindrical body and a flange, wherein the flange and the cylindrical body have through holes, the cross-sectional shape of the through holes is a constricted shape that narrows in the middle, and the through holes are engraved in a spiral pattern as they extend along the longitudinal direction within the cylindrical body. In the generation method, an apparatus conforming to the structure consisting of a cylindrical body and a flange, wherein the flange and the cylindrical body have through holes, the cross-sectional shape of the through holes is a constricted shape that narrows in the middle, and the through holes are engraved in a spiral pattern as they extend along the longitudinal direction within the cylindrical body was used. 【0031】 (Table 1) Composition and physical properties of water-soluble polymers TIFF2026095794000001.tif47105 【0032】 (Examples 1-3) Dissolution rate tests were conducted using tap water containing ultrafine bubbles generated by the aforementioned generating device under the conditions described in Table 2. Specifically, aqueous solutions of water-soluble polymers with a concentration of 0.2% by mass were prepared using the water-soluble polymers of samples 1 to 3. At this time, the viscosity of the aqueous solution of the water-soluble polymer solution was measured and recorded as a function of the elapsed time after the start of dissolution. These results are shown in Table 3. 【0033】 (Comparative Examples 1-3) Dissolution rate tests similar to those in Examples 1-3 were conducted using tap water under the conditions described in Table 2. The results are shown in Table 3. 【0034】 (Table 2) Test conditions for dissolution rate TIFF2026095794000002.tif65116 【0035】 (Table 3) Results of dissolution rate measurement JPEG2026095794000003.jpg52116 【0036】 In Examples 1-3 of the present invention, which used tap water without ultrafine bubbles as dissolving water, the viscosity of the aqueous solution increased rapidly from 10 minutes after the start of dissolution. Furthermore, there was no residue on the 60-mesh sieve when the viscosity of the aqueous solution stabilized, and the water-soluble polymer was completely dissolved faster than in the comparative examples, thus confirming an improvement in the dissolution rate. 【0037】 (Examples 4-8) Solution stability tests were conducted using tap water containing ultrafine bubbles generated by the aforementioned generating device under the conditions described in Table 4. Specifically, 0.2% by mass aqueous polymer solutions were prepared using the aqueous polymers of samples 1 to 5. At this time, the viscosity of the aqueous solution of the aqueous polymer solution was measured and recorded as a function of the elapsed time after complete dissolution. These results are shown in Table 5. 【0038】 (Comparative Examples 4-8) Solution stability tests similar to those in Examples 4-8 were conducted using tap water under the conditions described in Table 4. The results are shown in Table 5. 【0039】 (Table 4) Test conditions for solution stability TIFF2026095794000004.tif51118 【0040】 (Table 5) Measurement results of solution stability TIFF2026095794000005.tif53100 【0041】 Compared to Comparative Examples 4-8, which used tap water without ultrafine bubbles as dissolution water, Examples 4-8 of the present invention, which used tap water containing ultrafine bubbles, showed a lower rate of decrease in aqueous solution viscosity after complete dissolution. In particular, the crosslinked products of Sample 1 and Sample 2 demonstrated a good effect in suppressing the decrease in aqueous solution viscosity. Aqueous solution viscosity is a numerical value that serves as a criterion for judging performance degradation due to cleavage of molecular chains of water-soluble polymers, and suppressing the decrease in aqueous solution viscosity can be said to have an effect of improving solution stability.

Claims

[Claim 1] A method for dissolving water-soluble polymers, using water containing ultrafine bubbles generated by an ultrafine bubble generating device as dissolving water. [Claim 2] The method for dissolving a water-soluble polymer according to claim 1, characterized in that the water-soluble polymer is one or more selected from dimethylaminoethyl (meth)acrylate polymers and amidine polymers. [Claim 3] The method for dissolving a water-soluble polymer according to claim 1, wherein the ultrafine bubble generating means is any of the following: high-speed swirling liquid flow type, pressurized dissolution type, surfactant-added micropore type, or ultrasonic cavitation type. [Claim 4] A water-soluble polymer solution obtained by the dissolution method described in claims 1 to 3.

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