JP2011127077A - Method for producing acrylamide-based water-soluble polymer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing an acrylamide-based water-soluble polymer having a molecular weight of 2,000,000 to 25,000,000 and excellent water solubility, and to provide a method for producing the acrylamide-based water-soluble polymer, particularly, in which polymerization rate is sufficiently high even in polymerization in low monomer concentration and with which the acrylamide-based water-soluble polymer can be efficiently produced. <P>SOLUTION: In the method for producing the acrylamide-based water-soluble polymer, 15-50 mass% aqueous solution of a monomer composition comprising acrylamide and 0-5 mol% monomer copolymerizable with the acrylamide, is polymerized by redox polymerization using a reducing agent made of an amine or an inorganic salt and an oxidizing agent, or by photopolymerization, in the coexistence of 0.05-5 mol% hydroxycarboxylic acid and/or its salt on the basis of the monomer composition. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

    The present invention relates to a method for producing an acrylamide-based water-soluble polymer. More specifically, the present invention relates to a method for producing a water-soluble acrylamide polymer having a high molecular weight and excellent water solubility. In particular, the present invention relates to a method for producing an acrylamide-based water-soluble polymer having a sufficiently high polymerization rate even at a low monomer concentration.

    Polyacrylamide is widely used in various industries as a flocculant, a papermaking process chemical (for example, a papermaking viscosity agent or a yield improver), and a tertiary oil recovery chemical. The polyacrylamide used for these generally has higher performance as the molecular weight (referred to as a weight average molecular weight, hereinafter the same) is higher, and depending on the application, a very high molecular weight exceeding 10 million may be required.

    As polyacrylamide, polyacrylamide produced by homopolymerization of acrylamide, and nonionic or anionic polyacrylamide produced by copolymerization of acrylamide and neutralized acrylic acid or the like are widely used.

    Examples of the method for producing polyacrylamide include a method of radical polymerization of an aqueous monomer solution in the presence of a suitable initiator. Examples of the radical polymerization method include a polymerization method using a redox initiator and an azo initiator, and a photopolymerization method using a photoinitiator.

    Various methods have been conventionally used as a method for producing a high-molecular-weight polymer having high water solubility on an industrial scale on a large scale. As one of them, a method of polymerizing by lowering the monomer concentration is known. However, when the monomer concentration is lowered, the molecular weight is increased, but the polymerization rate is remarkably lowered to lower the productivity, or the residual monomer concentration of the obtained polymer is increased to deteriorate the quality.

    If the initiator concentration is lowered or the reaction initiation temperature is lowered, the molecular weight can be increased, but in this case, the water solubility becomes worse. In order to improve water solubility, various additives have been studied, but sufficient results have not been obtained. Therefore, conventionally, the industrial production of polyacrylamide usually uses an aqueous acrylamide solution of 30% by mass to a saturated concentration.

    Patent Document 1 discloses a polymerization initiator in which hydrogen peroxide and hydroxycarboxylic acid are combined, and is said to be useful as a method for introducing an active hydrogen group into the polymer terminal. However, the invention is mainly directed to polymerizing hydrophobic monomers, and there is no description regarding water solubility. Moreover, the molecular weight of the polymer is also targeted at 500 to 50,000, and no method for increasing the molecular weight is described.

    Patent Document 2 discloses the addition of hydroxycarboxylic acid as one component of a dental curing composition, and there is a description that the surface unpolymerized layer is reduced, but it relates to the polymerization of a hydrophobic monomer, In addition, the product is not sufficiently analyzed because it becomes a cured product.

    As described above, there is currently no satisfactory method for producing a high molecular weight acrylamide polymer having excellent water solubility on an industrial scale.

JP 2002-69112 A International Publication No. 2002-45660

    Provided is a method for producing an acrylamide-based water-soluble polymer having a molecular weight (referred to as a weight average molecular weight, hereinafter the same) of 2 million to 25 million and excellent water solubility. In particular, the present invention provides a method for producing an acrylamide-based water-soluble polymer that can be produced efficiently at a sufficiently high polymerization rate even when polymerization is performed at a low monomer concentration.

    As a result of repeated studies to solve the above-mentioned problems, the present inventors have produced a hydroxycarboxylic acid and / or a salt thereof (hereinafter collectively referred to as “hydroxyl”) when an acrylamide polymer is produced by an aqueous solution polymerization method. The inventors have come up with a method for polymerizing monomers in the presence of carboxylic acids). It has been found that this method has a sufficiently high polymerization rate even at a low monomer concentration. And it discovered that the improvement effect of the polymerization rate of this hydroxycarboxylic acid was expressed specifically only in the case of an acrylamide polymer. The acrylamide polymer produced in this way was found to have a large molecular weight and excellent water solubility. The present inventors have completed the present invention based on these findings.

    The present invention for solving the above problems is described below.

[1]
A 15 to 50% by weight aqueous solution of a monomer composition containing 0 to 5% by mole of acrylamide and a monomer copolymerizable with acrylamide is mixed with 0.05 to 5% by mole of hydroxycarboxylic acid and / or based on the monomer composition. The monomer composition is polymerized by redox polymerization or photopolymerization using a reducing agent comprising an amine or an inorganic salt and an oxidizing agent in the presence of the salt, and the weight average molecular weight is 2 million to 25 million. A method for producing a water-soluble acrylamide polymer.

    The present invention includes those to which the following configurations are added.

[2]
The method for producing an acrylamide-based water-soluble polymer according to [1], wherein the concentration of the aqueous solution of the monomer composition containing 0 to 5 mol% of acrylamide and a monomer copolymerizable with acrylamide is 20 to 40% by mass.

[3]
The method for producing an acrylamide-based water-soluble polymer according to [1], wherein the acrylamide-based water-soluble polymer has a weight average molecular weight of 3 million to 20 million.

[4]
The method for producing an acrylamide-based water-soluble polymer according to [1], wherein the monomer composition is polymerized without heating or removing heat from the reaction system.

[5]
The method for producing a water-soluble acrylamide polymer according to [1], wherein an azo compound is further allowed to coexist in the reaction system.

[6]
A 15 to 50% by weight aqueous solution of a monomer composition containing 0 to 5% by mole of acrylamide and a monomer copolymerizable with acrylamide is mixed with 0.05 to 5% by mole of hydroxycarboxylic acid and / or based on the monomer composition. In the presence of the salt, the monomer composition is polymerized by redox polymerization or photopolymerization using a reducing agent comprising an amine or an inorganic salt and an oxidizing agent, and then the resulting gel-like acrylamide-based water-soluble polymer is dissolved. The method for producing an acrylamide-based water-soluble polymer according to [1], wherein the coalescence is dried and then pulverized to obtain a powdery polymer having an average particle diameter of 1 to 100 μm.

  According to the method for producing an acrylamide-based water-soluble polymer of the present invention, it is difficult to lower the polymerization rate even when the monomer concentration is low. Therefore, even if the monomer concentration is lowered, the production can be performed efficiently. Since the monomer concentration can be reduced, the molecular weight of the resulting polymer can be increased. Moreover, the water solubility of the obtained polymer is excellent. Furthermore, since the concentration of the raw material monomer composition aqueous solution is low, it is easy to employ a method of polymerizing the reaction system without heating or heat removal. Therefore, this method is suitable for mass production.

    Hereinafter, the present invention will be described in detail.

(Monomer composition)
In the present invention, the monomer composition uses acrylamide as a main component. To this, monomers such as methacrylamide, acrylic acid, methacrylic acid, acrylamide-2-methylpropanesulfonic acid, and neutralized salts thereof can be appropriately blended. Further, other monomers, for example, monomers such as styrene, acrylonitrile, (meth) acrylic acid ester and the like may be appropriately blended so long as the water solubility of the monomer and the resulting polymer is not impaired. The content of these monomers is preferably 5 mol% or less.

(Hydroxycarboxylic acids)
In the present invention, hydroxycarboxylic acids are allowed to coexist in the reaction system during polymerization. Hydroxycarboxylic acids include hydroxycarboxylic acids and salts thereof. The hydroxycarboxylic acid and / or salt thereof added to the monomer aqueous solution at the time of polymerization is not particularly limited as long as it is aliphatic having 10 or less carbon atoms and has a carboxyl group and a hydroxyl group in the molecule. Examples of the hydroxycarboxylic acid include citric acid, malic acid, tartaric acid, glycolic acid, gluconic acid, lactic acid, mandelic acid, α-oxyisobutyric acid, 2-hydroxypropanoic acid, 3-hydroxybutanoic acid, dimethylolpropionic acid, α-Hydroxycarboxylic acid is preferred. These hydroxycarboxylic acids may be used as alkali metal salts such as sodium salt and potassium salt, alkaline earth metal salts such as calcium salt and magnesium salt, and the like. These hydroxycarboxylic acids may be used alone or in combination of two or more.

    The amount of the hydroxycarboxylic acid added to the monomer aqueous solution is 0.05 to 5.0 mol%, preferably 0.10 to 4.0 mol%, relative to 1 mol of the monomer. If it is less than 0.05 mol%, the polymerization rate is hardly improved and the solubility is not improved. On the other hand, when the addition exceeds 5.0 mol%, the polymerization rate is sufficiently improved, but the molecular weight of the resulting polymer does not increase.

    In adding the hydroxycarboxylic acid to the monomer aqueous solution, the hydroxycarboxylic acid may be added in a solid state or may be added after being dissolved in water. Hydroxycarboxylic acids also have a function as a pH buffer for the monomer aqueous solution described later.

(Initiator)
As the polymerization initiation method, a method using a redox initiator and a method of irradiating light in the presence of a photoinitiator are known, and any of them may be adopted in the present invention.

    As a polymerization initiation method using a redox initiator, a commonly used method is adopted. That is, polymerization is initiated by adding a redox initiator comprising an oxidizing agent and a reducing agent to the monomer solution. Examples of the oxidizing agent include ammonium persulfate, potassium persulfate, hydrogen peroxide, and tertiary butyl hydroperoxide. Examples of the reducing agent include inorganic salts such as ferrous sulfate, ammonium ferrous sulfate, and sodium bisulfite, and trimethylamine. The amount of redox initiator used is 1 to 200 ppm for both the oxidizing agent and the reducing agent with respect to the monomer composition. Polymerization is started by adding each aqueous solution of an oxidizing agent and a reducing agent to the aqueous monomer solution immediately before the start of polymerization. In the present invention, a polymerization initiation method using a redox initiator is simple and preferable.

    As a polymerization initiation method using a photoinitiator, a generally used method is employed. For example, a photoinitiator such as benzophenone, anthraquinone, acylphosphine oxide compound, or azo compound is added to the monomer aqueous solution, and the monomer aqueous solution is irradiated with light containing light having the maximum absorption wavelength of the photoinitiator. .

    An azo initiator may be added to the aqueous monomer solution in order to cause the polymerization at a high temperature to be performed quickly. As the azo initiator, 2,2′-azobis (4-methoxy-2,4-dimethylvaleronitrile), 4,4′-azobis (4-cyanovaleric acid, 2,2′-azobis (2,4 -Dimethylvaleronitrile), 2,2'-azobis (2-methylpropionitrile), 2,2'-azobis (2-methylbutyronitrile), 2,2'-azobis (2-amidinopropane) dihydrochloride Salt, 2,2′-azobis [2- (2-imidazolin-2-yl) propane] dihydrochloride, 2,2′-azobis [2- (3,4,5,6-tetrahydropyrimidin-2-yl] ) Propane] dihydrochloride, dimethyl 2,2′-azobis (2-methylpropionate), 4,4′-azobis (4-cyanopentanoic acid), 1,1′-azobis (cyclohexane-1-carbonitrile) ), 2, 2 -Azobis {2-methyl-N- [1,1-bis (hydroxymethyl) -2-hydroxylethyl] -propionamide, 2,2'-azobis [2-methyl-N- (2-hydroxyethyl) -propion Amide], 2,2′-azobis [N- (2-propenyl) -2-methylpropionamide] These may be used alone or in combination of two or more. The addition amount of the agent is 100 ppm or more with respect to the monomer mass, and preferably 200 to 10,000 ppm.

    The water-soluble azo compound may be added directly to the aqueous monomer solution or added as an aqueous solution. When the water-insoluble azo compound is added directly to the monomer aqueous solution, the effects of the present invention may not be sufficiently obtained. In such a case, the desired effect can be obtained by adding the azo compound dissolved in a polar organic solvent such as methanol, which has a relatively low chain mobility and is easily mixed with water.

    In addition to the monomer composition and azo compound described above, a chain transfer agent such as isopropyl alcohol, a pH buffering agent, and the like may be added to the aqueous monomer solution as necessary.

(Polymerization reaction)
In the present invention, the polymerization reaction can be initiated by adding a redox initiator to the monomer aqueous solution to which the hydroxycarboxylic acids are added, or by adding a photoinitiator and irradiating with light.

    Generally, in the polymerization reaction of acrylamide, when the monomer concentration is low, the molecular weight increases, but the polymerization rate decreases. On the other hand, when the monomer concentration is high, the polymerization rate increases, but the molecular weight decreases.

    The monomer concentration in the method for producing an acrylamide-based water-soluble polymer of the present invention is 15 to 50% by mass, preferably 20 to 40% by mass. When it is less than 15% by mass, the decrease in polymerization rate becomes remarkable. On the other hand, when it exceeds 50 mass%, the molecular weight of the polymer obtained does not increase. In the method for producing an acrylamide-based water-soluble polymer of the present invention, the decrease in polymerization rate is small even at a relatively low monomer concentration. Therefore, the monomer concentration can be set lower than usual. Therefore, it is easy to increase the molecular weight of the acrylamide-based water-soluble polymer.

    In the method for producing an acrylamide-based water-soluble polymer of the present invention, it is preferable to deoxidize the aqueous monomer solution through nitrogen gas or the like prior to the start of polymerization.

    The pH of the aqueous monomer solution during polymerization is preferably 4-9.

    In the present invention, the polymerization solution may be heated during the polymerization reaction to accelerate the polymerization reaction, or the reaction heat generated in the polymerization reaction may be removed to prevent the runaway of the polymerization reaction. However, the method for producing an acrylamide-based water-soluble polymer of the present invention targets an acrylamide-based water-soluble polymer having a molecular weight of 2 million to 25 million. Therefore, the viscosity of the polymerization solution is high and gelled, so that the heat exchange efficiency is poor. Therefore, in the method for producing an acrylamide-based water-soluble polymer of the present invention, it is preferable to use a so-called adiabatic polymerization method in which the acrylamide-based water-soluble polymer is left in an environmental atmosphere that is not artificially heated or removed from outside.

    In the adiabatic polymerization method, the reaction temperature (temperature of the aqueous solution) rises due to reaction heat as polymerization starts, and when the polymerization reaction is almost complete, the rise in reaction temperature stops and reaches the maximum temperature.

    In the method for producing an acrylamide-based water-soluble polymer of the present invention, the maximum temperature of the polymerization reaction is preferably 50 to 90 ° C, more preferably 60 to 80 ° C.

    In the adiabatic polymerization method, the maximum temperature of the polymerization reaction is adjusted to the above range by adjusting the monomer concentration in the aqueous solution and the polymerization start temperature. Although depending on the production amount and the type of monomer to be polymerized, the maximum concentration of the polymerization reaction is 50 to 50% when the monomer concentration is adjusted between 15 and 50% by mass and the polymerization start temperature is adjusted in the range of -5 to 30 ° C. It can be 90 degreeC. In the adiabatic polymerization method, the polymerization reaction usually reaches a maximum temperature of 50 to 90 ° C. in 30 minutes to 5 hours after the start of polymerization.

    By the polymerization reaction, the monomer aqueous solution becomes a gel-like acrylamide-based water-soluble polymer (hereinafter abbreviated as polymer gel).

    The polymerization can be carried out batchwise in a suitable reaction vessel, or can be carried out continuously by pouring onto a belt conveyor or the like.

    After the polymerization, heat treatment may be performed for the purpose of reducing the residual acrylamide monomer content. The heat treatment can be performed by performing a heat treatment in the reaction vessel or on the belt conveyor. Alternatively, the obtained polymer gel may be cut into an appropriate size, tightly packed in a vinyl bag or the like, and heat-treated in a hot water bath or the like. The heat treatment temperature is 70 to 100 ° C., and the heat treatment time is about 1 to 5 hours.

    The polymer gel can be powdered by drying and pulverizing by a known method. For drying, a known method such as heat drying or freeze drying can be applied. In drying, in order to increase the drying efficiency, the polymer gel may be cut in advance to about 1 to 10 mm. In this case, it may be possible to obtain a powder without going through the pulverization step. The pulverization can be performed using a known device such as a mill using a cutter, a hammer, or a roll. By the pulverization, a powdery polymer having an average particle diameter of 1 to 100 μm is obtained.

    The molecular weight of the acrylamide-based water-soluble polymer obtained by the production method of the present invention is 2 million to 25 million, preferably 3 million to 20 million. This molecular weight corresponds to about 1.3 to 7.3 (mPa · s) and 1.7 to 6.3 (mPa · s), respectively, when converted to a 0.10% salt viscosity (25 ° C.) described later. .

    Addition of hydroxycarboxylic acids to polymerize the monomer improves the solubility of the polymer in water. The insoluble content (described later) of the acrylamide-based water-soluble polymer obtained by the production method of the present invention is 5% by mass or less, preferably 3% by mass or less, and more preferably 2% by mass or less.

    EXAMPLES Next, the present invention will be specifically described with reference to examples, but the present invention is not limited to the following examples. The evaluation methods and measurement methods used in this example are as follows.

(Reaction rate)
The rate of the polymerization reaction in the case of adiabatic polymerization was determined by the time from the start of polymerization until reaching the maximum temperature (hereinafter referred to as “Tmax”) (hereinafter referred to as “TTmax”). The shorter this time (TTmax), the higher the polymerization rate.

(Molecular weight)
The molecular weight of the acrylamide-based water-soluble polymer was measured using 0.10% salt viscosity at 25 ° C. as an index. The larger this value (0.10% salt viscosity), the higher the molecular weight.

(0.10% salt viscosity)
While stirring 400 g of distilled water in a 500 ml beaker and stirring a screw type stirring blade at 400 rpm, 0.4 g of sample (in terms of solid content) was added and stirred for 90 minutes to dissolve. To this solution, sodium chloride was added and dissolved so as to have a concentration of 1 mol%, and the viscosity at 25 ° C. was measured.

(Insoluble matter)
While stirring the screw type stirring blade at 400 rpm in the same manner as described above, 0.4 g (in terms of solid content) of sample was added to distilled water, and the mixture was stirred for 90 minutes to be dissolved. The solution was filtered through a 150 mesh stainless steel wire mesh and washed with 200 mL deionized water. Thereafter, the wire mesh was dried at 105 ° C. for 180 minutes and weighed to calculate the insoluble content.

Example 1
0.67 g of trisodium citrate was added to 644 g of 50% by mass acrylamide aqueous solution, ion-exchanged water was added so that the total amount was 1400 g, and the pH was adjusted to 7 using dilute hydrochloric acid and caustic soda solution. To this, 700 ppm (mass, hereinafter the same) of 2,2′-azobis (2-amidinopropane) dihydrochloride (hereinafter abbreviated as V-50) was added with respect to the acrylamide monomer. Thereafter, the prepared liquid was cooled to 0 ° C. This mixed solution was put into a stainless steel dewar, and nitrogen was introduced at a rate of 5 L / min to sufficiently deoxygenate. Next, 5 per cent of ammonium persulfate (1% aqueous solution) in an amount corresponding to 5 ppm with respect to the acrylamide monomer, and 3 ppm of ferrous ammonium sulfate (1% aqueous solution) in an amount corresponding to 3 ppm with respect to the acrylamide monomer were each taken in a syringe. These were put into a dewar at the same time. These liquids were rapidly stirred to start the reaction, and the temperature in the reaction liquid was monitored. A maximum reaction temperature of 67 ° C. was reached 165 minutes after the start of the reaction. The mixture was allowed to stand for 60 minutes at the maximum reaction temperature, and the gel polymer obtained was taken out. The gel polymer was chopped and further chopped into granules having a diameter of about 2 to 3 mm with a meat grinder. Of these, about 50 g was taken in a petri dish, dried at 70 ° C. for 2 hours with a hot air circulating dryer, and then pulverized for 1 minute with a high-speed rotary blade pulverizer, with 20 to 60 mesh (20 mesh And acrylamide-based water-soluble polymer was obtained.

(Examples 2-6 and Comparative Examples 1-5)
According to the formulation and conditions described in Table 1, an acrylamide-based water-soluble polymer was produced in accordance with the method described in Example 1. These production results and sample physical properties are shown in Table 1. However, in Example 5, as Redox initiator, potassium persulfate (1% aqueous solution) was equivalent to 5 ppm with respect to the acrylamide monomer, and sodium bisulfite (1% aqueous solution) was 3 ppm with respect to the acrylamide monomer. A considerable amount was added and the polymerization was carried out at a starting temperature of 10 ° C.

    Since Comparative Examples 1 and 4, 5 do not contain a hydroxycarboxylic acid, TTmax is large, that is, the polymerization rate is slow. Moreover, the insoluble content of the obtained polymer is large. In Comparative Example 2, since the amount of hydroxycarboxylic acid added is too large, the 0.10% salt viscosity is small, that is, the molecular weight is low. In Comparative Example 3, hydrogen peroxide is used. However, since it did not contain hydroxycarboxylic acid, the polymerization was not completed.

  As apparent from Table 1, according to the method of the present invention, the molecular weight of the acrylamide-based water-soluble polymer can be increased, and the polymerization time can be greatly shortened. The resulting acrylamide-based water-soluble polymer has good water solubility. Hydroxycarboxylic acids are highly safe substances that exist in nature, including citric acid, and are excellent in terms of maintaining the environment.

Claims (6)

  A 15 to 50% by weight aqueous solution of a monomer composition containing 0 to 5% by mole of acrylamide and a monomer copolymerizable with acrylamide is mixed with 0.05 to 5% by mole of hydroxycarboxylic acid and / or based on the monomer composition. The monomer composition is polymerized by redox polymerization or photopolymerization using a reducing agent comprising an amine or an inorganic salt and an oxidizing agent in the presence of the salt, and the weight average molecular weight is 2 million to 25 million. A method for producing a water-soluble acrylamide polymer.   The method for producing an acrylamide-based water-soluble polymer according to claim 1, wherein the concentration of the aqueous solution of the monomer composition containing 0 to 5 mol% of acrylamide and a monomer copolymerizable with acrylamide is 20 to 40% by mass.   The method for producing an acrylamide-based water-soluble polymer according to claim 1, wherein the weight-average molecular weight of the acrylamide-based water-soluble polymer is 3 million to 20 million.   The method for producing an acrylamide-based water-soluble polymer according to claim 1, wherein the monomer composition is polymerized without heating or removing heat from the reaction system.     The method for producing an acrylamide-based water-soluble polymer according to claim 1, wherein an azo compound is further allowed to coexist in the reaction system. A 15 to 50% by weight aqueous solution of a monomer composition containing 0 to 5% by mole of acrylamide and a monomer copolymerizable with acrylamide is mixed with 0.05 to 5% by mole of hydroxycarboxylic acid and / or based on the monomer composition. In the presence of the salt, the monomer composition is polymerized by redox polymerization or photopolymerization using a reducing agent comprising an amine or an inorganic salt and an oxidizing agent, and then the resulting gel-like acrylamide-based water-soluble polymer is dissolved. The method for producing an acrylamide-based water-soluble polymer according to claim 1, wherein the polymer is dried and then pulverized to obtain a powdery polymer having an average particle diameter of 1 to 100 µm.