JP2017031255A - Method for producing acrylic acid based polymer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing an acrylic acid based polymer in which the content of a polymer high in a weight average molecular weight is low, and a molecular weight distribution is narrow, and useful as an inorganic pigment dispersant, a scale control agent or the like.SOLUTION: Provided is a method for producing an acrylic acid based polymer where, using a reactor 100 provided with a reaction tank 11, and an external circulation line including a heat exchanger 25, polymerization is performed while circulating a reaction liquid from the reaction tank to the external circulation line, in which the linear velocity of the reaction liquid in the heat exchanger is 0.1 to 1.0 m/s. Further, the polymerization is performed preferably in a batch process. Further, it is preferable that the temperature of the reaction liquid exhausted from the external circulation line to the reaction tank is lower than the temperature of the reaction liquid in the reaction tank, and a temperature difference therebetween is 15°C or lower. Further, it is preferable that at least one kind of chain transfer agent selected from hydrogensulfite, hypophosphorous acid and the salts thereof is used.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method for producing an acrylic acid polymer. More specifically, the present invention relates to a method for producing an acrylic acid polymer having a small content of a polymer having a large weight average molecular weight, a narrow molecular weight distribution, and useful as an inorganic pigment dispersant and a scale control agent.

  In order to increase productivity in the production of an acrylic acid polymer, it is necessary to sufficiently remove the generated heat of polymerization. In this case, heat can be efficiently removed by increasing the heat transfer area by providing an external circulation line including a heat exchanger in addition to the cooling jacket externally provided in the reaction vessel. In addition, low molecular weight acrylic acid polymers are used in various applications such as inorganic pigment dispersants and scale control agents. In order to achieve better performance, the content of a polymer having a large weight average molecular weight is required. The polymer is required to be small and have a narrow molecular weight distribution.

  However, in an external circulation line equipped with a heat exchanger, the fluidity of the reaction solution may decrease at the boundary film portion on the inner wall surface of the heat exchanger, and the reaction solution may stay in the boundary film portion. Moreover, since the staying reaction liquid reacts in a state with low fluidity, a polymer having a degree of polymerization different from that in the reaction tank is generated. In this case, the produced polymer is a polymer having a wide molecular weight distribution including a polymer having a large weight average molecular weight, which is insufficient in terms of performance in the various applications described above. In particular, in aqueous solution polymerization of acrylic acid monomers using sodium hydrogen sulfite, sodium hypophosphite, etc. as a chain transfer agent, the polymerization rate tends to be high, so there is a tendency for the polymer produced in the residence part to increase. It has been difficult to achieve both high productivity and obtaining a polymer with a small content of a polymer having a large weight average molecular weight and a narrow molecular weight distribution.

  As a method for producing an acrylic acid polymer using a reactor equipped with an external circulation line provided with a heat exchanger, the temperature is controlled using an external circulation device having a heat exchange function, A production method for carrying out aqueous polymerization is known (for example, see Patent Document 1). In addition, a method for continuously producing a water-soluble polymer using a reaction apparatus having a circulation line provided with a cooler at least at one place is known (for example, see Patent Document 2). Furthermore, a method for producing a carboxylic acid polymer by semi-batch operation while circulating a reaction solution in a reaction tank to an external circulation line is known (for example, see Patent Document 3). In addition, a method for producing a (meth) acrylic acid polymer in which a polymerization solution is externally circulated during polymerization and polymerized in a batch system is known (for example, see Patent Document 4).

JP 2004-244617 A JP 2007-217654 A JP 2010-150327 A JP 2011-63742 A

Patent Document 1 discloses a production method in which the temperature is controlled using an external circulation device having a heat exchange function and the monomer is subjected to aqueous solution polymerization. The polymerization temperature is 50 ° C. or higher and lower than the boiling point, It is described that the outlet temperature of the circulation device is preferably 10 to 90 ° C. However, in the examples, the difference between the polymerization temperature and the outlet temperature is 35 ° C. or 29 ° C., and the temperature difference is large. In Cited Document 3, when the polymer is used for a detergent builder, a dispersant, a scale inhibitor, etc., the weight average molecular weight is preferably 2000 to 30000, and the molecular weight distribution is preferably 7 or less. It is described that it is preferably 5 or less.
However, none of the cited references 1 to 4 describes the linear velocity of the reaction liquid in the heat exchanger.

  The present invention has been made in view of the above-described state of the art, and by specifying the linear velocity of the reaction liquid in the heat exchanger provided in the external circulation line, the weight average molecular weight (hereinafter referred to as “Mw”). An object of the present invention is to provide a method for producing an acrylic acid polymer having a small content of a large polymer, a narrow molecular weight distribution, and useful as an inorganic pigment dispersant and a scale control agent.

The present invention is as follows.
1. Using a reaction apparatus comprising a reaction tank and an external circulation line equipped with a heat exchanger, a method for producing an acrylic acid polymer that performs polymerization while circulating a reaction liquid from the reaction tank to the external circulation line There,
A method for producing an acrylic acid polymer, wherein a linear velocity of a reaction liquid in the heat exchanger is 0.1 to 1.0 m / s.
2. 1. The polymerization is carried out batchwise. A process for producing an acrylic acid polymer as described in 1.
3. The temperature of the reaction liquid discharged from the external circulation line to the reaction tank is lower than the temperature of the reaction liquid in the reaction tank, and the temperature difference is 15 ° C. or less. Or 2. A process for producing an acrylic acid polymer as described in 1.
4). 1. Use of at least one chain transfer agent selected from bisulfite and hypophosphorous acid and salts thereof. To 3. The manufacturing method of the acrylic acid type polymer of any one of these.
The “linear velocity (m / s)” is calculated by [flow rate of reaction liquid in external circulation line / cross-sectional area of heat exchanger channel]. The flow rate of the reaction solution is usually measured or set as a flow rate per unit time (m ³ / Hr), this flow rate is converted into a value per second, and this value is converted into a cross-sectional area of the heat exchanger flow path section. The linear velocity (m / s) is calculated by dividing by (unit: m ² ). The cross-sectional area of the heat exchanger is a cross-sectional area in a direction orthogonal to the direction in which the reaction liquid flows in the flow path of the reaction liquid. Furthermore, the heat exchanger often has a plurality of flow paths for the reaction liquid, for example, like a multi-tube heat exchanger, and in this case, the cross-sectional area of the heat exchanger flow path section has a plurality of flow path sections. Is the total cross-sectional area.

According to the method for producing an acrylic acid polymer of the present invention, by specifying the linear velocity of the reaction liquid in the heat exchanger provided in the external circulation line to 0.1 to 1.0 m / s, the high molecular weight polymer, For example, an acrylic acid polymer having a small content of a polymer having an Mw of 70000 or less and a narrow molecular weight distribution can be efficiently produced practically. The acrylic acid polymer can be suitably used as an inorganic pigment dispersant, a scale control agent, and the like.
In addition, when the polymerization is carried out batchwise, it is possible to easily produce an acrylic acid polymer having a low molecular weight content and a narrow molecular weight distribution.
Furthermore, when the temperature of the reaction liquid discharged from the external circulation line is lower than the temperature of the reaction liquid in the reaction tank and the temperature difference is 15 ° C. or less, the content of the high molecular weight polymer is sufficiently reduced. And an acrylic acid polymer having a narrow molecular weight distribution.
In addition, when at least one chain transfer agent selected from bisulfite and hypophosphorous acid and salts thereof is used, the reaction rate is usually large and the control of the molecular weight distribution is not easy, but the production of the present invention In the method, an acrylic acid polymer having a small content of high molecular weight polymer and a narrow molecular weight distribution can be obtained.

It is typical explanatory drawing of the reaction apparatus used in the manufacturing method of this invention.

  The present invention is a process for producing an acrylic acid-based polymer that performs polymerization while circulating a reaction liquid from a reaction tank to an external circulation line using a reaction apparatus including a reaction tank and an external circulation line equipped with a heat exchanger. It is a method, Comprising: The linear velocity of the reaction liquid in a heat exchanger is 0.1-1.0 m / s, It is characterized by the above-mentioned.

  The reaction apparatus used in the production method of the present invention comprises a reaction tank and an external circulation line equipped with a heat exchanger. Further, the polymerization may be carried out in any manner such as batch, semi-batch and continuous. This reaction apparatus will be described with reference to FIG. 1, but the reaction apparatus 100 in FIG. 1 is not an apparatus having a particularly limited configuration in the present invention, and can be appropriately provided with various equipment not shown. .

  The reaction tank 11 in the reaction apparatus 100 is a container for polymerizing or copolymerizing a monomer containing acrylic acid in the presence of water as a polymerization initiator, a chain transfer agent, and a reaction solvent. Stirring means 12 and raw material supply means 13 are provided. The raw material supply means 13 is a means for supplying a monomer, a polymerization initiator, a chain transfer agent, water and the like to the reaction tank 11. In the production of the acrylic acid polymer, each raw material is usually supplied separately, but specific raw materials may be combined and supplied simultaneously.

  Moreover, the supply method of each raw material is not specifically limited, It can supply to the reaction tank 11 continuously or intermittently. Furthermore, the monomer is supplied so that the concentration of the acrylic acid polymer contained in the reaction solution is about 20 to 60% by mass. In addition, since the monomer is usually polymerized so that the temperature of the reaction liquid is kept constant, the reaction apparatus 100 includes a temperature adjusting means for adjusting the temperature of the raw material or the reaction liquid, and reflux heat. It is often equipped with an exchanger. The temperature adjusting means preferably has a structure that covers the bottom wall and the side wall of the reaction vessel 11.

  A circulation pipe 20 serving as an external circulation line for circulating a reaction liquid containing a polymer generated in the tank is disposed outside the reaction tank 11. The circulation pipe 20 communicates the discharge port 15 formed on the bottom wall of the reaction tank 11 and the introduction port 17 formed on the upper side of the side wall. The circulation pipe 20 includes a heat exchanger 25 that lowers the temperature of the reaction liquid supplied from the reaction tank 11, and the cooled reaction liquid is discharged from the inlet 17 into the reaction tank 11 and returned. Is done. As the heat exchanger 25, various heat exchangers such as a multi-tube heat exchanger, a plate heat exchanger, a double tube heat exchanger, and a spiral heat exchanger can be used.

  Furthermore, the reaction liquid is circulated in the circulation pipe 20 by the liquid feed pump 27, but the position of the liquid feed pump 27 is not particularly limited. The liquid feed pump 27 may be disposed at an appropriate position of the pipe 21 from the outlet 15 of the reaction tank 11 to the heat exchanger 25 or the pipe 23 from the heat exchanger 25 to the inlet 17 of the reaction tank 11. Although it is possible, as shown in the drawing, it is preferable that the pipe 21 is disposed. Further, the pipes 21 and 23 constituting the circulation pipe 20 may be provided with temperature holding means for holding the temperature of the reaction liquid flowing in the pipe on the outer periphery thereof.

  In FIG. 1, the position of the discharge port 15 for discharging the reaction liquid is the bottom wall of the reaction tank 11, but is not limited thereto. For example, the position of the discharge port 15 may be the side wall of the reaction tank 11, and in this case, it is preferably on the lower side of the reaction tank 11. Furthermore, the position of the introduction port 17 for discharging the reaction liquid cooled by the heat exchanger 25 into the reaction tank 11 is the upper part of the side wall of the reaction tank 11, but is not limited to this. Also good. Moreover, in FIG. 1, although the inlet 17 is opened in the position higher than the liquid level in the reaction tank 11, it is not limited to this, You may open in the liquid. Note that the number of circulation pipes 20 provided in the reaction apparatus 100 may be one, or two or more (usually one).

Hereinafter, the manufacturing method of an acrylic acid polymer using the manufacturing apparatus 100 which comprises the reaction tank 11 and the piping 20 for circulation provided with the heat exchanger 25 (external circulation line provided with a heat exchanger) is demonstrated.
A monomer, a polymerization initiator, a chain transfer agent, water and the like are usually supplied to the reaction tank 11 from the raw material supply means 13 separately, continuously or intermittently. The monomer is polymerized while being driven and stirred. Further, it is preferable to perform polymerization of the monomers and circulation of the reaction liquid while maintaining the amounts of the raw materials and the reaction liquid in the reaction tank 11 almost constant.

  Furthermore, the linear velocity of the reaction liquid in the heat exchanger 25 is 0.1 to 1.0 m / s, preferably 0.2 to 0.9 m / s, more preferably 0.3 to 0.8 m / s. s. By setting this linear velocity to 0.1 or more, the production of a high molecular weight polymer, for example, a polymer having Mw of 70000 or more can be suppressed, and an acrylic acid polymer having a narrow molecular weight distribution can be produced. Further, by setting the linear velocity to 1.0 m / s or less, the reaction solution is sufficiently removed of heat without using a heat exchanger having a larger heat transfer area, and a desired acrylic polymer is produced. be able to.

  When the linear velocity of the reaction liquid in the heat exchanger 25 is less than 0.1 m / s, the reaction liquid is sufficiently removed from the heat, but the polymerization at the boundary film proceeds and a high molecular weight polymer is easily generated. Thus, an acrylic acid polymer having a wide molecular weight distribution is obtained. On the other hand, when the linear velocity exceeds 1.0 m / s, the heat removal of the reaction solution becomes insufficient, and the polymerization cannot be performed at the target temperature. Thus, when the linear velocity of the reaction liquid in the heat exchanger 25 is less than 0.1 m / s or exceeds 1.0 m / s, it is useful as an inorganic pigment dispersant, a scale control agent, etc. in any case. It cannot be made an acrylic acid polymer.

  The polymerization temperature of the monomer is appropriately set depending on the types of the monomer and the polymerization initiator, but is preferably 50 ° C to 100 ° C, more preferably 60 ° C to 90 ° C. Further, since the production of a high molecular weight polymer is suppressed and a reaction liquid containing an acrylic acid polymer having a narrow molecular weight distribution is continuously produced, the temperature of the reaction liquid at the outlet 15 and the cooling at the inlet 17 are reduced. The difference from the temperature of the reaction solution is 20 ° C. or less, preferably 15 ° C. or less, more preferably 1 to 15 ° C., and still more preferably 2 to 10 ° C. The temperature of the reaction liquid in the reaction tank 11 is easily changed with the polymerization of the supplied monomer, and the temperature of the reaction liquid in the reaction tank 11 is returned by cooling and returning the reaction liquid flowing through the circulation pipe 20. Change can be suppressed. The reaction tank 11 is usually equipped with a cooling jacket, and a known temperature adjusting means such as an internal coil can be used in combination.

  In the method for producing an acrylic acid polymer of the present invention, a monomer containing at least acrylic acid is polymerized in an aqueous medium containing water. This medium may be composed of only water or a mixture of water and an organic solvent. Preferred organic solvents include alcohols such as isopropyl alcohol and ketones such as acetone, with isopropyl alcohol being particularly preferred.

In the polymerization, a known polymerization initiator can be used, and a radical polymerization initiator is particularly preferably used.
Examples of the radical polymerization initiator include persulfates such as sodium persulfate, potassium persulfate and ammonium persulfate, hydroperoxides such as t-butyl hydroperoxide, water-soluble peroxides such as hydrogen peroxide, and methyl ethyl ketone. Oil-soluble peroxides such as peroxides, ketone peroxides such as cyclohexanone peroxide, dialkyl peroxides such as di-t-butyl peroxide and t-butylcumyl peroxide, 2,2′-azobis (2- And azo compounds such as methylpropionamidine) dihydrochloride. As the radical polymerization initiator, persulfates and azo compounds are preferable from the viewpoint of easy control of the polymerization reaction, and persulfates are particularly preferable. Moreover, only one type of radical polymerization initiator may be used, or two or more types may be used in combination.
The radical polymerization initiator is diluted with, for example, an aqueous medium and supplied to the reactor from a supply port different from that of the monomer.

  The use ratio of the radical polymerization initiator is not particularly limited, but is 0.1 to 15% by weight, particularly 0.5 to 10% by weight, based on the total weight of all monomers constituting the acrylic acid polymer. Is preferably used. By making this proportion 0.1% by weight or more, the (co) polymerization rate can be improved, and by making it 15% by weight or less, the stability of the resulting polymer is improved and used for a dispersant or the like. When it is done, it will have excellent performance.

  Furthermore, in this invention, a well-known chain transfer agent can be used as needed for the purpose of adjusting the molecular weight of the acrylic acid polymer obtained. Examples of the chain transfer agent include bisulfite, hypophosphorous acid and its salt, phosphorous acid and its salt, mercaptoacetic acid, mercaptopropionic acid, 2-propanethiol, 2-mercaptoethanol, thiophenol and the like. . Isopropyl alcohol also acts as a chain transfer agent. Therefore, when isopropyl alcohol is contained in the medium, this isopropyl alcohol aqueous solution is used as a reaction solvent and a chain transfer agent. Moreover, only one type of chain transfer agent may be used, or two or more types may be used in combination.

When bisulfite, hypophosphorous acid or a salt thereof is used as the chain transfer agent, the reaction rate usually increases, and the amount of polymer produced in the boundary film portion where the reaction solution stays tends to increase. However, even in such a case, according to the production method of the present invention, it is easy to control the molecular weight distribution and the like, and the effects of the invention tend to be manifested.
Examples of the bisulfite include sodium bisulfite, potassium bisulfite, and ammonium bisulfite. Examples of hypophosphites include sodium hypophosphite, potassium hypophosphite, lithium hypophosphite, calcium hypophosphite, magnesium hypophosphite, and barium hypophosphite. Among these salts, a sodium salt that can efficiently produce an acrylic acid polymer having a small content of a high molecular weight polymer and a narrow molecular weight distribution is preferable.

  The chain transfer agent may be supplied to the reactor from a supply port different from each of the monomer and the polymerization initiator, but may be supplied after being mixed with the monomer immediately before being supplied to the reactor. . The preferable usage-amount is 0.3-50 mol% with respect to the quantity (mol number) of a monomer, More preferably, it is 1.0-25 mol%.

  The monomer may be only acrylic acid or may contain a compound having a polymerizable unsaturated bond copolymerizable with acrylic acid (hereinafter referred to as “other monomer”). Other monomers include acrylic acid salts, unsaturated monocarboxylic acids having 4 or more carbon atoms or salts thereof, unsaturated dicarboxylic acids or anhydrides or salts thereof, sulfonic acid group-containing vinyl compounds, (meth) Examples include alkyl acrylates, hydroxyalkyl esters of (meth) acrylic acid, amino group-containing vinyl compounds, amide group-containing vinyl compounds, polyoxyalkylene group-containing vinyl compounds, and alkoxyl group-containing vinyl compounds. These other monomers may be used alone or in combination of two or more.

Examples of the salt include alkali metal salts such as sodium salt and potassium salt, alkaline earth metal salts such as calcium salt and magnesium salt, and organic amine salts such as ammonium salt, monoethanolamine salt and triethanolamine salt. In addition, as other monomers, among the exemplified monomers, since they are excellent in scale inhibiting ability and have good solubility in water, salts of acrylic acid, unsaturated monocarboxylic acids having 4 or more carbon atoms Acids or salts thereof, unsaturated dicarboxylic acids or anhydrides or salts thereof, and sulfonic acid group-containing vinyl compounds are preferred.
When the total amount of monomers is 100% by mass, acrylic acid is preferably 50% by mass or more, more preferably 80% by mass or more, still more preferably 90% by mass or more, and particularly preferably 100% by mass. %.

  Examples of the unsaturated monocarboxylic acid having 4 or more carbon atoms include methacrylic acid, crotonic acid, isocrotonic acid, α-hydroxyacrylic acid and the like. Examples of the unsaturated dicarboxylic acid or its anhydride include maleic acid, maleic anhydride, itaconic acid, mesaconic acid, fumaric acid, and citraconic acid. Furthermore, examples of the sulfonic acid group-containing vinyl compound include methallylsulfonic acid, acrylamide-2-methyl-2-propanesulfonic acid, and the like.

  Examples of the (meth) acrylic acid alkyl ester include methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, and butyl (meth) acrylate. Furthermore, examples of the (meth) acrylic acid hydroxyalkyl ester include 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, and the like.

  Examples of the amino group-containing vinyl compound include dimethylaminomethyl (meth) acrylate, diethylaminomethyl (meth) acrylate, 2-dimethylaminoethyl (meth) acrylate, 2-diethylaminoethyl (meth) acrylate, (meth ) 2- (di-n-propylamino) ethyl acrylate, 2-dimethylaminopropyl (meth) acrylate, 2-diethylaminopropyl (meth) acrylate, 2- (di-n-propylamino) (meth) acrylate ) Propyl, (meth) acrylic acid 3-dimethylaminopropyl, (meth) acrylic acid 3-diethylaminopropyl, (meth) acrylic acid 3- (di-n-propylamino) propyl, and the like.

  Furthermore, examples of the amide group-containing vinyl compound include (meth) acrylamide, N, N-dimethyl (meth) acrylamide, N, N-dimethylaminopropyl (meth) acrylamide, N-methylol (meth) acrylamide and the like. Examples of the polyoxyalkylene group-containing vinyl compound include (meth) acrylic acid esters of alcohols having a polyoxyethylene group and / or a polyoxypropylene group. Furthermore, as the alkoxyl group-containing vinyl compound, 2-methoxyethyl (meth) acrylate, 2-ethoxyethyl (meth) acrylate, 2- (n-propoxy) ethyl (meth) acrylate, (meth) acrylic acid 2 -(N-butoxy) ethyl, 3-methoxypropyl (meth) acrylate, 3-ethoxypropyl (meth) acrylate, 2- (n-propoxy) propyl (meth) acrylate, 2- (meth) acrylic acid 2- ( n-butoxy) propyl and the like.

  In addition to the monomer, the reaction system for polymerizing the monomer containing acrylic acid to produce the acrylic acid polymer contains a polymerization initiator, a chain transfer agent, and an aqueous medium as a reaction solvent. In this production method, the monomers, polymerization initiator, chain transfer agent, and aqueous medium are added to the reaction system separately or collectively, or continuously or intermittently. It can be polymerized. In addition, monomers can be polymerized by introducing raw materials such as monomers separately or collectively, or continuously or intermittently into a reaction tank in which an aqueous medium has been previously charged. In this case, the monomer other than acrylic acid can be added to the reaction tank in advance together with the aqueous medium. Among these production methods, at least a total amount of each of the monomer, the polymerization initiator and the chain transfer agent may be separately and continuously charged into a reaction vessel in which an aqueous medium has been previously charged, and polymerized. preferable.

  Although superposition | polymerization temperature can be suitably set according to the kind of polymerization initiator, Usually, it is 40 degreeC or more, 50 degreeC or more is preferable and 60 degreeC or more is more preferable. On the other hand, the upper limit of the polymerization temperature is a temperature slightly exceeding the boiling point of water as a reaction solvent, and when pressurized, it can be up to about 110 ° C., but is usually 90 ° C. or less, preferably 85 ° C. or less. .

  Further, after the polymerization reaction is completed, post-treatment is usually performed. In this post-treatment, after the reaction is completed, the reaction solution is kept at the reaction temperature for aging for a predetermined time, for example, 15 to 120 minutes, particularly 20 to 60 minutes, and then sodium hydroxide, potassium hydroxide and the like are put into water. This is done by introducing a dissolved alkali aqueous solution having a concentration of 30 to 70% by mass, particularly 40 to 60% by mass, and water. By this post-treatment, an aqueous polymer solution having a hydrogen ion index in the neutral region of about 7 is obtained. The solid content contained in the aqueous polymer solution, that is, the acrylic acid polymer, can be about 20 to 60% by mass, particularly about 30 to 50% by mass when the aqueous solution is 100% by mass.

  Further, the polymer contained in the polymer aqueous solution, that is, the Mw, number average molecular weight (Mn) and molecular weight distribution (Mw / Mn) of the acrylic acid polymer are not particularly limited, but the inorganic pigment dispersant and the scale control agent Mw is preferably 2000 to 15000, more preferably 3000 to 10000, and particularly preferably 4000 to 9000 in order to obtain a polymer useful as an equivalent. Further, Mw / Mn is preferably 1.8 to 3.0, more preferably 1.8 to 2.7, and particularly preferably 1.8 to 2.5. Furthermore, in applications such as inorganic pigment dispersants and scale control agents, it is particularly preferable that the content of the polymer is small. For example, when the total amount of the polymer is 100% by mass, the content of the high molecular weight polymer having an Mw of 70000 or more is preferably 0.15% by mass or less, more preferably 0.10% by mass or less, and particularly preferably 0.00. 05% by mass or less.

  The acrylic acid polymer produced by the method of the present invention is useful as an inorganic pigment dispersant, a scale control agent and the like. When used as an inorganic pigment dispersant, usually a large amount of ion exchange water or the like is mixed with the reaction solution, but other components such as an antifoaming agent and preservative may be blended as necessary. As the inorganic pigment, fine particles made of calcium carbonate, kaolin, titanium dioxide, zinc oxide, zinc sulfide, chromium oxide or the like can be used. In addition, when used as a scale control agent, the reaction solution can be used as it is, but other scale inhibitors such as polymaleic acid or salts thereof, styrene / maleic acid copolymers, bactericides, anticorrosives, and slime inhibitors. Other components such as an antifoaming agent may be blended. By using such a scale inhibitor, for example, problems such as a decrease in heat exchange efficiency and blockage of piping in a cooling water system, a boiler water system, a seawater desalination apparatus, and the like can be suppressed.

Hereinafter, the present invention will be specifically described with reference to the drawings. However, the present invention is not limited to this embodiment.
In the following,% is based on mass unless otherwise specified.

Example 1
(1) Reactor A reaction vessel 11 made of SUS having a capacity of 3 m ³ withdraws a stirrer 12, a condenser (not shown) and a reaction solution from a reaction solution outlet 15 at the bottom of the reaction vessel 11, and a reaction solution introduction port 17 at the top. An external circulation line for discharging to the reaction tank 11 was disposed. The external circulation line includes a multi-tube heat exchanger 25 having an outer diameter of 4 inches, a length of 2 m, and a total cross-sectional area of the reaction liquid flow path portion of 0.0031 m ² .
(2) Polymerization conditions and post-treatment The reaction tank 11 was charged with 600 kg of water and maintained at 70 ° C. Thereafter, 1130 kg of an 80% strength aqueous solution of acrylic acid, 60 kg of a 15% strength aqueous solution of sodium persulfate and 270 kg of a 30% strength aqueous solution of sodium hydrogen sulfite were each supplied over 2.5 hours. While these were being supplied, the reaction solution was fed to the external circulation line by the solution feed pump 27 so that the flow rate was 6.0 m ³ / Hr. The average linear velocity of the reaction liquid in the multi-tubular heat exchanger 25 is 0.55 m / s [flow rate (6.0 m ³ / Hr) / reaction liquid channel section (0.0031 m ² )]. . Furthermore, the temperature of the reaction liquid cooled by the multi-tube heat exchanger 25 and discharged from the reaction liquid inlet 17 to the reaction tank 11 was 64 ° C., which was 6 ° C. lower than the temperature of the reaction liquid in the reaction tank 11. . In addition, the temperature of the cooling water discharged | emitted from the multitubular heat exchanger 25 was 37 degreeC. Next, aging was performed for 30 minutes while maintaining the temperature of the reaction solution in the reaction tank 11 at 70 ° C., and then 990 kg of a 48% sodium hydroxide aqueous solution and 80 kg of water were added, and the solid content concentration was 40%, pH 7, specific gravity. A polymer aqueous solution of 1.3 was obtained.

[1] Measurement of weight average molecular weight, molecular weight distribution and content of polymer having molecular weight of 70,000 or more Mw and Mw / Mn of solid content (acrylic acid polymer) were measured by gel permeation chromatography (GPC). For measurement of GPC, an HLC8020 system (manufactured by Tosoh Corporation) was used, and detection was performed by RI. In addition, G4000PWxl, G3000PWxl, and G2500PWxl (all manufactured by Tosoh Corporation) are connected and used as the column, and the eluent is 0.1M NaCl + phosphate buffer (pH 7). It was made using the company. As a result of the measurement, the Mw of the acrylic acid polymer is 7000, the Mw / Mn is 2.3, and the content of the polymer having Mw of 70000 or more obtained by molecular weight fractionation calculation is as follows when the total amount of the polymer is 100%. 0.02%.

[2] Performance evaluation (1) Wet grinding test of heavy calcium carbonate 7.5 g of polymer aqueous solution, 340 g of ion exchange water and 1000 g of heavy calcium carbonate (manufactured by Maruo Calcium Co., Ltd., trade name “No. A heavy coal”) The mixture was put into a cylindrical container equipped with a stirrer and lightly stirred to be evenly blended. Thereafter, 2800 g of media (φ1 mm ceramic beads) was put into a cylindrical container and stirred at 1000 rpm for 50 minutes to perform wet grinding. Next, the slurry was recovered by passing through a 150 mesh filter cloth, and then ion-exchanged water was added to prepare a slurry having a solid content concentration of 75%. Further, the viscosity after 1 hour from the preparation of the slurry and the viscosity after standing for 7 days at 25 ° C. were measured using a B-type viscometer under the conditions of 25 ° C. and 60 rpm. As a result, the viscosity after 1 hour from the adjustment was 280 mPa · s, and the viscosity after standing for 7 days was 1700 mPa · s. Furthermore, as a result of measuring the 2.0 μm under integrated value of the slurry using a particle size distribution measuring apparatus (manufactured by Micromeritics, model “Sedigraph 5120”), a value of 90% was obtained.

(2) Stirring dispersion test of heavy calcium carbonate A cylindrical container equipped with a stirrer of 6.0 g of an aqueous polymer solution, 330 g of ion-exchanged water and 1000 g of heavy calcium carbonate (trade name “Super # 2000” manufactured by Maruo Calcium Co., Ltd.) And a slurry was prepared by stirring at 4000 rpm for 10 minutes. Immediately after the preparation of this slurry and after standing at 25 ° C. for 7 days, the respective viscosities were measured using a B-type viscometer under the conditions of 25 ° C. and 60 rpm. As a result, the viscosity immediately after slurry preparation was 160 mPa · s, and the viscosity after standing for 7 days was 710 mPa · s.

(3) Mud dispersion test 13 mg of an aqueous polymer solution, 1 g of clay (manufactured by Mitsubishi Corporation, trade name “Amazon 88 Non-Predispers”), and 100 g of ion-exchanged water are put into a 100 mL measuring cylinder and a magnetic stirrer is used. And stirred for 10 minutes. Then, it left still at 25 degreeC for 18 hours. Next, the supernatant was collected and the absorbance at a wavelength of 380 nm was measured. As a result, the absorbance of the supernatant was 1.0.

(4) Calcium carbonate scale inhibition test For 100 mL of calcium carbonate aqueous solution in which 200 mg of CaCO ₃ was dissolved in 1 L of water, the polymer aqueous solution was adjusted so that the content of the acrylic acid polymer (solid content) was 10 mg. Added. Thereafter, 10 g of 0.2% aqueous sodium hydrogen carbonate solution was added, and then sodium hydroxide was added to adjust the pH of the aqueous solution to 8.5. Then, this liquid mixture was left to stand at 60 degreeC for 24 hours, the deposit was filtered, the calcium concentration in a filtrate was measured by EDTA titration, and the scale inhibition rate was computed. As a result, the calcium carbonate scale inhibition rate of the acrylic acid polymer was 94%.

Examples 2 to 6 and Comparative Example 1
A polymer solution containing an acrylic acid polymer described in Table 2 was obtained in the same manner as in Example 1 except that the initial input raw material, continuous feed raw material, polymerization conditions and post-treatment were as shown in Table 1. Further, the Mw of the acrylic acid polymer and the content of the polymer having Mw of 70000 or more were measured by the same method as in Example 1. The results are listed in Table 2. Further, the performance of each acrylic acid polymer was evaluated by the wet pulverization test, the stirring dispersion test, the mud dispersion test, and the scale inhibition test according to the method described in Example 1. The results are listed in Table 2.

  According to Table 1 and Table 2, in Example 1 where the linear velocity of the reaction liquid in the heat exchanger is 0.55 m / s, the temperature difference between the reaction liquid in the reaction tank and the reaction liquid discharged into the reaction tank. Is as small as 6 ° C. Moreover, Mw was as small as 7000, the polymer content of Mw 70000 or more was as small as 0.02%, and Mw / Mn was as narrow as 2.3. As a result, it has extremely excellent performance in all evaluation items of wet calcium carbonate wet grinding test, heavy calcium carbonate stirring dispersion test, mud dispersion test and calcium carbonate scale inhibition test, and inorganic pigment dispersion It can be seen that an acrylic acid polymer having practically excellent performance is obtained in applications such as an agent and a scale control agent.

  Further, in Examples 2 and 3, the acrylic solution was treated in the same manner as in Example 1 except that the flow rate of the reaction solution in the external circulation line was reduced and the linear velocity of the reaction solution in the heat exchanger was reduced to 0.36 m / s. An acid polymer was produced. Further, in Example 4, an acrylic acid polymer was produced in the same manner as in Examples 2 and 3, except that maleic anhydride was used in combination as a monomer. As a result, in Examples 2 to 4, the temperature difference between the reaction solution in the reaction vessel and the reaction solution discharged to the reaction vessel was slightly increased. In Examples 2 and 3, and particularly in Example 4 in which anhydrous malein was used in combination, Mw was slightly increased, and the content of the polymer having Mw of 70000 or more was increased. However, when performance evaluation was performed in the same manner as in Example 1 using an aqueous polymer solution, although there was a slight decrease in performance in any of the evaluation items, an acrylic acid-based polymer having sufficiently excellent performance in practical use. Coalescence was obtained.

  Furthermore, in Example 5, acrylic acid was used in the same manner as in Example 1 except that the flow rate of the reaction solution in the external circulation line was further reduced and the linear velocity of the reaction solution in the heat exchanger was reduced to 0.27 m / s. A polymer was produced. In Example 6, the acrylic acid polymer was prepared in the same manner as in Example 1 except that the flow rate of the reaction solution in the external circulation line was further reduced and the linear velocity of the reaction solution was reduced to 0.18 m / s. Manufactured. As a result, as the linear velocity of the reaction liquid decreases, the temperature difference between the reaction liquid in the reaction tank and the reaction liquid discharged to the reaction tank becomes larger, Mw tends to be slightly larger, and Mw / Mn is a little. It became wider and the content of polymers with Mw of 70000 or more also increased. However, when performance evaluation was performed in the same manner as in Example 1 using an aqueous polymer solution, although the performance was lower than in Examples 2 to 4 in any evaluation item, the performance was sufficiently excellent in practical use. An acrylic acid-based polymer having

  On the other hand, Comparative Example 1 was the same as Example 1 except that the flow rate of the reaction solution in the external circulation line was greatly reduced and the linear velocity of the reaction solution in the heat exchanger was set to 0.07 m / s, which was less than the lower limit. Thus, an acrylic acid polymer was produced. As a result, the temperature difference between the reaction liquid in the reaction tank and the reaction liquid discharged into the reaction tank was 30 ° C. That is, since the circulating reaction liquid was excessively cooled, Mw was considerably increased, Mw / Mn was also increased, and the content of the polymer having Mw of 70000 or more was greatly increased. And when performance evaluation was carried out similarly to Example 1, in any evaluation item, performance will fall further from Example 6, and it will be evaluated that it is an acrylic acid type polymer which cannot be put to practical use.

  The acrylic acid polymer produced by the method of the present invention is useful as an inorganic pigment dispersant, a scale control agent and the like because it has a low content of high molecular weight polymer and a narrow molecular weight distribution.

100: reactor, 11: reaction tank, 12: stirrer, 13: raw material supply pipe, 15: reaction liquid outlet, 17: reaction liquid inlet, 20: circulation pipe, 21: heat from reaction liquid outlet Piping to the exchanger, 23: piping from the heat exchanger to the reaction liquid inlet, 25: heat exchanger, 27: liquid feed pump.

Claims (4)

Using a reaction apparatus comprising a reaction tank and an external circulation line equipped with a heat exchanger, a method for producing an acrylic acid polymer that performs polymerization while circulating a reaction liquid from the reaction tank to the external circulation line There,
A method for producing an acrylic acid polymer, wherein a linear velocity of a reaction liquid in the heat exchanger is 0.1 to 1.0 m / s.   The method for producing an acrylic acid polymer according to claim 1, wherein the polymerization is carried out batchwise.   The acrylic acid system according to claim 1 or 2, wherein the temperature of the reaction solution discharged from the external circulation line to the reaction vessel is lower than the temperature of the reaction solution in the reaction vessel, and the temperature difference is 15 ° C or less. A method for producing a polymer.   The method for producing an acrylic acid polymer according to any one of claims 1 to 3, wherein at least one chain transfer agent selected from bisulfite, hypophosphorous acid and salts thereof is used.

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