JP2021042330A - Copolymer, draw solute, draw solution and water treatment device - Google Patents

Abstract

To provide a copolymer that can be suitably used for a positive osmosis membrane method, a draw solute, and a draw solution and a water treatment device using the same.SOLUTION: A copolymer has a constitutional unit derived from a monomer having a nitrogen-containing heterocycle and an ethylenically unsaturated group of 35-75 mass% and a constitutional unit derived from (meth) acrylate of 25-65 mass% and has a molecular weight distribution of 1.5 or less.SELECTED DRAWING: None

Description

The present invention relates to copolymers, draw solutes, draw solutions and water treatment equipment.

The forward osmosis membrane method utilizes a phenomenon in which two solutions having different concentrations are brought into contact with each other via a semipermeable membrane, and the solvent moves from the side having a low osmotic pressure to the side having a high osmotic pressure. It can be used. Compared to the reverse osmosis membrane method, which applies pressure to the solution against the osmotic pressure to forcibly permeate the membrane, the forward osmosis membrane method, which uses osmotic pressure to perform membrane filtration, is easier to save energy and is freshwater in seawater. It is expected to be applied to water treatment such as chemical conversion and power generation.

When water treatment is performed using the forward osmosis membrane method, a draw solution is used from the treatment target solution side through a semipermeable membrane using a solution (draw solution) having a higher osmotic pressure than the treatment target solution (treatment target solution). Move the solvent (water) to the side. After that, since it is necessary to recover the solvent from the draw solution, the draw solution must have a property that the solvent can be easily separated, and an osmotic pressure inducer (draw solute) for preparing such a draw solution is used. Various studies have been conducted. For example, in Patent Document 1, "a block copolymer having a glycerin skeleton as a basic skeleton and containing an ethylene oxide group as a hydrophilic part and a group consisting of propylene oxide and / or butylene oxide as a hydrophobic part" is subjected to temperature-sensitive water absorption. It has been proposed to be used as an agent (draw solute).

Japanese Patent No. 6172385

By the way, from the viewpoint of expanding the range of application of the forward osmosis membrane method to various techniques in the future, it is preferable to increase the variation of the draw solute so that the optimum draw solution can be selected according to the process.

Therefore, an object of the present invention is to provide a copolymer, a draw solute, and a draw solution and a water treatment apparatus using the copolymer, which can be suitably used for the forward osmosis membrane method.

In view of the above circumstances, the present inventors have completed the inventions shown in the following [1] to [5] as a result of repeated diligent studies.
[1] Containing 35 to 75% by mass of a nitrogen-containing heterocycle and a structural unit derived from a monomer having an ethylenically unsaturated group, and 25 to 65% by mass of a structural unit derived from a (meth) acrylic acid ester. A copolymer having a molecular weight distribution of 1.5 or less.
[2] The copolymer according to [1], which has a weight average molecular weight of less than 100,000.
[3] A draw solute for a forward osmosis membrane containing the copolymer according to [1] or [2].
[4] A draw solution containing the draw solute for a forward osmosis membrane according to [3].
[5] A water treatment apparatus using the draw solution according to [4].

According to the present invention, it is possible to provide a copolymer, a draw solute, and a draw solution and a water treatment apparatus using the copolymer, which can be suitably used for the forward osmosis membrane method.

It is a phase diagram about the aqueous solution containing about 50% of polymer 1. It is a phase diagram about the aqueous solution containing about 50% of polymer 9. It is a figure which shows the result of having measured the osmotic pressure about the aqueous solution of the polymer 1 with the concentration of 5 to 95%. It is a figure which shows the result of having measured the osmotic pressure about the aqueous solution of the polymer 9 with the concentration of 5 to 95%.

Hereinafter, one embodiment of the present invention will be described in detail, but the present invention is not limited thereto. In the present specification, the (meth) acrylic acid ester means an acrylic acid ester and / or a methacrylic acid ester. The same applies to similar expressions such as (meth) acrylate.

<Copolymer>
The copolymer of the present embodiment is derived from a structural unit derived from a monomer having 35 to 75% by mass of a nitrogen-containing heterocycle and an ethylenically unsaturated group, and 25 to 65% by mass from a (meth) acrylic acid ester. It contains structural units and has a molecular weight distribution of 1.5 or less.

Such a copolymer may have a cloud point (lower limit critical solution temperature) when dissolved in a solvent (particularly water) to form a solution. The cloud point means the temperature at which phase separation occurs by changing the temperature of a transparent or translucent liquid, resulting in opacity. Therefore, since the copolymer and the solvent can be separated by heating the solution, the copolymer of the present embodiment can be suitably applied as a draw solute for a forward osmosis membrane.

The nitrogen-containing heterocycle in the nitrogen-containing heterocycle and the monomer having an ethylenically unsaturated group is not particularly limited, and for example, a lactam ring (pyrrolidone ring, piperidone ring, ε-caprolactam ring, etc.), imidazole ring, pyridine. Examples thereof include a ring, a pyrrol ring, a pyrimidine ring, a morpholin ring, a pyrrolidine ring, a piperidine ring, a piperazine ring, a pyrazine ring, a hexamethyleneimine ring, and a heptamethyleneimine ring. The nitrogen-containing heterocycle is preferably a non-aromatic nitrogen-containing heterocycle, more preferably a lactam ring, a pyrrolidine ring, a piperidine ring or a morpholin ring, and further preferably a lactam ring or a morpholin ring.

The ethylenically unsaturated group in the monomer having a nitrogen-containing heterocycle and an ethylenically unsaturated group is not particularly limited, but for example, a vinyl group, an allyl group, a (meth) acryloyl group, a (meth) acryloyloxy group and the like. Can be mentioned.

Specific examples of the monomer having a nitrogen-containing heterocycle and an ethylenically unsaturated group include lactam-based vinyl monomers such as N-vinylpyrrolidone, N-vinylpiperidone, N-vinyl-ε-caprolactam, and methylvinylpyrrolidone; Vinyl-based monomers having a nitrogen-containing heterocycle such as vinylpyridine, vinylpyrimidine, vinylpiperazin, vinylpyrazine, vinylpyrrole, vinylimidazole, vinyloxazole, vinylmorpholin, N- (meth) acryloylmorpholin, N- (meth) It has a nitrogen-containing heterocycle such as acryloyl piperidine, N- (meth) acryloyl piperidine, N- (meth) acryloyl pyrrolidine, N-acrylic oxysuccinimide, acrylate morpholine carbonyl, (meth) acrylate morpholine carbamate (meth). ) Acrylic monomer and the like can be mentioned. Among these, a lactam vinyl monomer or a (meth) acrylic monomer having a nitrogen-containing heterocycle is preferable, and N-vinylpyrrolidone or N- (meth) acryloylmorpholine is more preferable.

The content of the structural unit derived from the nitrogen-containing heterocycle and the monomer having an ethylenically unsaturated group is 35 to 75% by mass and 37.5 to 72.5% by mass with respect to the total amount of the copolymer. It is preferable, and it is more preferable that it is 40 to 70% by mass.

The (meth) acrylic acid ester is not particularly limited, but for example, an aliphatic (meth) acrylate [for example, (meth) acrylic acid alkyl ester (for example, methyl (meth) acrylic acid, ethyl (meth) acrylic acid, ( _{(Meta) acrylic acid C 1-18} alkyl such as butyl acrylate (meth)], alicyclic (meth) acrylate [eg, (meth) acrylic acid cycloalkyl ester (eg, (meth) acrylic acid cyclopropyl, _{C 3-20} cycloalkyl (meth) acrylate such as cyclobutyl (meth) acrylate), crosslinked (meth) acrylate (eg, isobornyl (meth) acrylate)], aromatic (meth) acrylate [eg. _{(Meta) acrylic acid aryl ester (eg, (meth) acrylic acid C 6-20} aryl such as (meth) acrylic acid phenyl, (meth) acrylic acid o-tolyl), (meth) acrylic acid aralkyl ester (eg, (meth) acrylic acid aralkyl ester (Meta) acrylate C such as benzyl (meth) acrylate _6-10aryl C _1-4 alkyl), phenoxyalkyl (meth) acrylate (eg, phenoxy C (meth) acrylate such as phenoxyethyl (meth) acrylate) _1-4 alkyl), etc.], (meth) acrylic acid ester having a hydroxyl group [for example, (meth) acrylic acid hydroxyalkyl ester (for example, (meth) acrylic acid hydroxyC, such as 2-hydroxyethyl (meth) acrylic acid) _1-12 Alkyl), etc.], (meth) acrylic acid ester having an alkoxy group [for example, (meth) acrylic acid alkoxyalkyl ester (for example, C _1-12 alkoxymethacrylate such as 2-methoxyethyl (meth) acrylic acid) C _1-12 alkyl, etc.)], (meth) acrylic acid ester having a glycidyl group (for example, glycidyl (meth) acrylate, etc.) and the like. These may be used individually by 1 type, and may be used in combination of 2 or more type.

Among these, the copolymer of the present embodiment preferably contains a structural unit derived from an aliphatic (meth) acrylate _{, more preferably contains C 1-18} alkyl (meth) acrylate, and (meth). It is more preferable to contain C _{1-10 alkyl acrylate, further preferably C 1-6} alkyl (meth) acrylate, and particularly preferably _{C 1-4 alkyl (meth) acrylate.}

The content of the structural unit derived from the (meth) acrylic acid ester is 25 to 65% by mass, preferably 27.5 to 62.5% by mass, preferably 30 to 60% by mass, based on the total amount of the copolymer. % Is more preferable.

The copolymer of the present embodiment may contain a structural unit derived from another polymerizable monomer (monomer), if necessary. Examples of such other monomers include acid group-containing monomers (methacrylic acid, acrylic acid, etc.), styrene-based monomers [for example, styrene, vinyltoluene, substituents (eg, halogen group, alkoxy group, alkyl group, hydroxy). Styrene having a group (eg, α-methylstyrene, chlorostyrene, etc.), styrene sulfonic acid or a salt thereof, etc.], vinyl ester (eg, vinyl acetate, etc.), unsaturated nitrile (eg, acrylonitrile, methacrylnitrile, etc.), etc. _{), Olefin-based monomers (eg, C 2-10} alkenes such as ethylene, propylene, 1-butene, isobutylene, 1-octene), amide group-containing vinyl-based monomers [eg, (meth) acrylamide, N-substituted (eg, (meth) acrylamide, N-substituted (. Meta) acrylamide (eg, N-alkyl (meth) acrylamide such as N-methyl (meth) acrylamide; N-cycloalkyl (meth) acrylamide such as N-cyclohexyl (meth) acrylamide; N-phenyl (meth) acrylamide and the like. N-aryl (meth) acrylamide; N-aralkyl (meth) acrylamide such as N-benzyl (meth) acrylamide), etc.], 2- (Hydroxymethyl) acrylic acid ester (for example, ethyl 2- (hydroxymethyl) acrylic acid) Alkyl ester) and the like. These may be used individually by 1 type, and may be used in combination of 2 or more type.

The content of the structural unit derived from the other polymerizable monomer is preferably 30% by mass or less, more preferably 20% by mass or less, and 10% by mass or less, based on the total amount of the copolymer. Is even more preferable.

The polymerization average molecular weight (Mw) of the copolymer of the present embodiment is preferably less than 100,000, more preferably less than 80,000, and even more preferably less than 60,000. When the weight average molecular weight is in the above range, cloud points are likely to occur when the solution is prepared. The lower limit of the weight average molecular weight is not particularly limited, but may be, for example, 10,000 or more.

The number average molecular weight (Mn) of the copolymer of the present embodiment is preferably less than 80,000, more preferably less than 70,000.

The molecular weight distribution (Mw / Mn) of the copolymer of the present embodiment is 1.5 or less, preferably 1.4 or less, and more preferably 1.3 or less. When the molecular weight distribution is in the above range, cloud points are likely to occur when the solution is prepared.

The molecular weight (and molecular weight distribution) may be measured by, for example, using GPC in terms of polystyrene, or may be measured by the method described in Examples.

The above-mentioned copolymer can be produced by appropriately selecting the above-mentioned monomer and carrying out a polymerization reaction. The preferable amount of the monomer used in the polymerization reaction is the same as the preferable content of the structural unit derived from these monomers in the above-mentioned copolymer.

The polymerization reaction is preferably carried out in the presence of a polymerization initiator. Examples of the polymerization initiator include hydrogen peroxide; persulfates such as sodium persulfate, potassium persulfate, and ammonium persulfate; dimethyl 2,2'-azobis (2-methylpropionate), 2,2'-azobis. (Isobutyronitrile), azo compounds such as 2,2'-azobis (2,4-dimethylvaleronitrile); organic peroxides such as benzoyl peroxide, peracetic acid, di-t-butyl peroxide, etc. Suitable. These polymerization initiators may be used alone or in the form of a mixture of two or more.
The amount of the polymerization initiator used is preferably 0.1 to 20 parts by mass, preferably 0.5 to 15 parts by mass, per 100 parts by mass of the amount of the monomer used in the polymerization reaction. More preferred.

The polymerization reaction is preferably carried out in the presence of a chain transfer agent. This makes it easier to make the molecular weight distribution smaller.

Examples of the chain transfer agent include alkali metal salts of thioacetate such as sodium thioacetate and potassium thioacetate, cysteine, cysteamine, 2-mercaptoethanol, thioglycerol, thioglycolic acid, mercaptopropionic acid, 2-mercaptopropionic acid, 3 -Hydrothiol chain transfer agents such as mercaptopropionic acid, thioacetic acid, thioannic acid, 2-mercaptoethanesulfonic acid, their sodium salts and potassium salts; primary alcohols such as 2-aminopropan-1-ol, isopropyl Secondary alcohols such as alcohols, phosphite, hypophosphoric acid and salts thereof (eg, sodium hypophosphite, potassium hypophosphite, etc.), sulfites, hydrogen sulfites, dithionic acids, metabisulfites and Non-thiol chains of their salts (eg, sodium sulfite, sodium hydrogen sulfite, sodium dithionate, sodium metabisulfite, potassium sulfite, potassium hydrogen sulfite, potassium dithioate, potassium metabisulfite, etc.) Transfer agents: butane thiol, octane thiol, decane thiol, dodecane thiol, hexadecane thiol, octadecane thiol, cyclohexyl mercaptan, thiophenol, octyl thioglycolate, octyl 2-mercaptopropionate, octyl 3-mercaptopropionate, mercaptopropionic acid 2 Hydrophobic thiol-based chain transfer agents such as −ethylhexyl ester, octanoic acid 2-mercaptoethyl ester, 1,8-dimercapto-3,6-dioxaoctane, decantrythiol, dodecyl mercaptan; 4-chloro-3,5- Dimethylpyrazole-1-carbodithioic acid 2'-cyanobutane-2'-yl, 3,5-dimethylpyrazole-1-carbodithioic acid 2'-cyanobutane-2'-yl, 3,5-dimethylpyrazole-1-carbodithioate cyanomethyl , 2-Cyanoprop-2-yl-dithiobenzoate, S- (2-cyanoprop-2-yl) -S-dodecyltrithiocarbonate, 4-[(2-carboxyethyl sulfanylthiocarbonyl) sulfanyl] -4- Reversible addition cleavage of cyanopentanoic acid, 4-cyano-4- (thiobenzoylthio) pentanoic acid, 4-cyano-4-[(dodecylsulfanylthiocarbonyl) sulfanyl] pentanoic acid, bis (dodecylsulfanylthiocarbonyl) disulfide, etc. Examples thereof include a chain transfer agent (RAFT agent) for a chain transfer polymerization method. These chain transfer agents may be used alone or in combination of two or more. Among these, it is preferable to use a RAFT agent from the viewpoint of making it easier to further reduce the molecular weight distribution.

The amount of the chain transfer agent may be appropriately set according to the target molecular weight, molecular weight distribution, etc. of the copolymer, and is not particularly limited, but is not particularly limited, but per 100 parts by mass of the amount of the monomer used in the polymerization reaction. It is preferably 0.1 to 20 parts by mass, and more preferably 0.5 to 15 parts by mass.

A solvent can be used in the polymerization reaction. As the solvent, for example, an aliphatic hydrocarbon compound such as n-hexane and n-heptane; an aromatic compound such as benzene, toluene and xylene; an alcohol such as methanol, ethanol, isopropyl alcohol, n-butyl alcohol and 1-hexanol; Ethers such as propylene glycol methyl ether, dipropylene glycol methyl ether, ethyl cellosolve, butyl cellosolve; esters such as ethyl acetate, butyl acetate, cellosolve acetate; ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, diacetone alcohol; Examples include organic solvents such as amides. Each of these solvents may be used alone, or two or more kinds may be used in combination. Among these, aliphatic hydrocarbon compounds, alcohols, ethers, esters, ketones and amides are preferable, aliphatic hydrocarbon compounds and esters are more preferable, and n-hexane and ethyl acetate are preferable from the viewpoint of reducing the influence on the human body. More preferred.

The polymerization reaction is usually preferably carried out at 0 to 150 ° C., more preferably 30 to 120 ° C., and even more preferably 50 to 90 ° C. The polymerization temperature does not have to be kept substantially constant in the polymerization reaction, and may be changed once or twice or more (heating or cooling). The polymerization reaction may be carried out under any conditions of normal pressure, pressure and reduced pressure.

In the above polymerization reaction, the monomer, the polymerization initiator and the like may be added to the reactor all at once, or may be added sequentially or continuously.

The method for producing the copolymer may include steps other than the above-mentioned polymerization reaction step. Examples of other steps include a aging step, a neutralizing step, a deactivating step of a polymerization initiator and a chain transfer agent, a diluting step, a drying step, a concentration step, and a purification step.

<Draw solution>
The draw solution of the present embodiment contains the above-mentioned copolymer as a draw solute. The content of the draw solute is preferably 20 to 100% by mass, more preferably 50 to 100% by mass, and even more preferably 75 to 100% by mass with respect to the total amount of the draw solution.

The draw solution may contain a solvent. The solvent may be appropriately selected depending on the conditions of the forward osmosis membrane method using a draw solution, etc., but one or more solvents selected from water, methanol, ethanol and the like can be used. It is more preferable to contain the same solvent as the solvent to be treated. The content of the solvent can be, for example, 80 to 0% by mass with respect to the total amount of the draw solution.

The draw solution may contain a draw solute other than the draw solute (other draw solutes), but the content thereof is preferably 20% by mass or less based on the total amount of the draw solute. The draw solution is preferably composed of the above draw solute, any solvent, any other draw solute, and more preferably composed of the above draw solute and solvent.

The draw solution preferably has a cloud point. The draw solution having a cloud point can be phase-separated from the draw solute and the solvent by heating.

The cloud point of the draw solution is the composition of the copolymer, for example, the type and content and weight average of structural units derived from a monomer having a nitrogen-containing heterocycle and an ethylenically unsaturated group and a (meth) acrylic acid ester. By changing the molecular weight, the molecular weight distribution, etc., it can be appropriately adjusted, and an appropriate cloud point draw solution can be selected according to the application.

For example, when the forward osmosis membrane method is applied to water treatment using low temperature exhaust heat of a factory, the draw solution does not phase-separate at a temperature around room temperature where the forward osmosis membrane treatment is performed, and the low temperature exhaust heat of the factory is about It is preferable that the draw solution is phase-separated at the temperature of. The suitable cloud point of the draw solution used in such an application varies depending on the concentration of the draw solute in the draw solution, but is preferably 35 to 80 ° C, more preferably 40 to 75 ° C, for example.

Since low-temperature waste heat from factories has been difficult to utilize in the past and most of it has been regarded as waste heat, water treatment using low-temperature waste heat is particularly preferable from the viewpoint of energy efficiency.

<Forward osmosis membrane method>
In the forward osmosis membrane method, the feed solution (solution to be treated) and the draw solution are brought into contact with each other via a semipermeable membrane, and the solvent moves from the feed solution side having a low osmotic pressure to the draw solution having a high osmotic pressure. As the solvent moves, the concentration of the draw solution gradually decreases. Therefore, in order to continue the forward osmosis membrane method, it is necessary to separate the draw solute and the solvent contained in the draw solution.

According to the above-mentioned draw solution having a cloud point, the draw solute and the solvent can be phase-separated by heating.

In the forward osmosis membrane method using a draw solution having such a cloud point, for example, the target processed product can be continuously produced by repeating the following treatment.
-Place the feed solution on one side of the semipermeable membrane and the draw solution on the other side so that they are in contact with the semipermeable membrane, and move the solvent from the feed solution side through the semipermeable membrane to the draw solution side.
-Take out the drawn solution with reduced concentration and heat it to separate the draw solute and the solvent from each other in phase.
-The phase-separated draw solute is circulated again to the other side.
-The phase-separated solvent is further purified using, for example, a nanofiltration membrane (NF membrane) to obtain a desired treated product (purified water, etc.).

As another method, a draw solution having improved compatibility with the solvent by allowing the draw solute to absorb the acid gas is used, the solvent is permeated from the supply solution side to the draw solution side, and then the draw solute to the acid gas. It is also possible to apply a method of phase-separating the draw solute and the solvent by removing the acid gas.
Examples of the acidic gas include carbon oxides such as carbon monoxide and carbon dioxide; sulfur oxides such as sulfur monoxide, sulfur dioxide and sulfur trioxide; nitric oxide, nitrogen dioxide, nitrous oxide and dinitrogen trioxide. Examples thereof include oxides of nitrogen such as dinitrogen tetroxide and dinitrogen pentoxide. Among these, the acid gas is preferably carbon dioxide.

The temperature at which the forward osmosis membrane treatment is performed is not particularly limited, but is usually around room temperature, and can be, for example, 5 to 40 ° C.

As the semipermeable membrane (Membrane) used in the forward osmosis membrane method, a conventionally known one can be used, but in order to maintain the strength of the membrane, a dense active layer (Active) that determines the selective permeability of the membrane is used. It is preferable to use it in combination with a layer) and a porous support layer. Since the support layer is more likely to adsorb dirt than the active layer, it is generally preferable to provide the active layer of the semipermeable membrane on the supply liquid (water to be treated) side from the viewpoint of reducing film dirt.

The draw solution can be applied to various applications utilizing the forward osmosis membrane method. Among them, water treatment equipment and power generation equipment are applications in which the forward osmosis membrane method is expected to be used, and the draw solution can be suitably applied to these applications.

Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples. Unless otherwise specified, "%" shall mean "mass%".

<Synthesis of polymer>
(Example 1)
18.92 g of ethyl acetate was added to a 100 mL test tube containing a stir bar to dissolve 8.0 g of N-vinylpyrrolidone (NVP) and 5.34 g of methyl acrylate (MA). Further, 0.26 g of azobisisobutyronitrile (AIBN) and 4-[(2-carboxyethyl sulfanylthiocarbonyl) sulfanyl] -4-cyanopentanoic acid (hereinafter, also referred to as "chain transfer agent A") 0. After adding 82 g, the inside of the test tube was replaced with nitrogen and sealed. Then, the reaction was carried out at 70 ° C. for 24 hours, the obtained composition was reprecipitated in hexane, and the mixture was dried under reduced pressure to obtain polymer 1.

(Example 2)
The same operation as in Example 1 except that the amount of ethyl acetate was changed to 9.91 g, the amount of NVP was changed to 3.5 g, the amount of MA was changed to 3.5 g, the amount of AIBN was changed to 0.14 g, and the amount of chain transfer agent A was changed to 0.44 g. The polymer 2 was obtained.

(Example 3)
The amount of AIBN was changed to 0.2 g, and the chain transfer agent A was changed to 0.31 g of 3,5-dimethylpyrazole-1-carbodithioic acid 2'-cyanobutane-2'-yl (hereinafter, also referred to as "chain transfer agent B"). The polymer 3 was obtained by performing the same operation as in Example 2 except for the above.

(Example 4)
The same operation as in Example 3 except that the amount of ethyl acetate was changed to 7.93 g, the amount of NVP was changed to 2.5 g, the amount of MA was changed to 3.06 g, the amount of AIBN was changed to 0.11 g, and the amount of chain transfer agent B was changed to 0.29 g. The polymer 4 was obtained.

(Example 5)
The same operation as in Example 1 except that the amount of ethyl acetate was changed to 8.78 g, the amount of NVP was 2.4 g, the amount of MA was 3.6 g, the amount of AIBN was 0.12 g, and the amount of chain transfer agent A was changed to 0.32 g. The polymer 5 was obtained.

(Example 6)
Examples except that the amount of ethyl acetate was changed to 9.56 g, the amount of NVP was changed to 4.0 g, MA was changed to ethyl acrylate (EA) 2.67 g, the amount of AIBN was changed to 0.12 g, and the amount of chain transfer agent B was changed to 0.32 g. The polymer 6 was obtained by performing the same operation as in 4.

(Example 7)
Examples except that the amount of ethyl acetate was changed to 8.63 g, the amount of NVP was changed to 4.2 g, the amount of MA was changed to 1.8 g of butyl acrylate (BA), the amount of AIBN was changed to 0.10 g, and the amount of chain transfer agent B was changed to 0.27 g. The polymer 7 was obtained by performing the same operation as in 4.

(Example 8)
Examples except that the amount of ethyl acetate was changed to 8.61 g, the amount of NVP was changed to 4.8 g, the amount of MA was changed to 1.2 g of methyl methacrylate (MMA), the amount of AIBN was changed to 0.11 g, and the amount of chain transfer agent B was changed to 0.28 g. The polymer 8 was obtained by performing the same operation as in 4.

(Example 9)
101.2 g of 2-propanol was added to a 300 mL separable flask equipped with a cooling tube and a thermometer, and the temperature was raised to 75 ° C. with stirring by flowing nitrogen. Then, a solution prepared by dissolving 2.1 g of AIBN in 31.5 g of NVP, 38.5 g of MA, and 60 g of ethyl acetate was separately added dropwise over 3 hours. After completion of the dropping, aging was carried out while maintaining 75 ° C. for 1 hour, and then the temperature was lowered. The obtained composition was reprecipitated in hexane and dried under reduced pressure to obtain a polymer.

(Example 10)
Example 1 except that the amount of ethyl acetate was changed to 9.61 g, the amount of NVP was changed to 4.0 g of acryloyl morpholine (ACMO), the amount of MA was 2.67 g, the amount of AIBN was 0.19 g, and the amount of chain transfer agent A was changed to 0.36 g. The polymer 10 was obtained by performing the same operation as in the above.

(Comparative Example 1)
The same operation as in Example 1 except that the amount of ethyl acetate was changed to 8.63 g, the amount of NVP was changed to 1.8 g, the amount of MA was changed to 4.2 g, the amount of AIBN was changed to 0.10 g, and the amount of chain transfer agent A was changed to 0.26 g. The comparative polymer 1 was obtained.

(Comparative Example 2)
The same operation as in Example 4 except that the amount of ethyl acetate was changed to 8.78 g, the amount of NVP was 2.4 g, the amount of MA was 3.6 g, the amount of AIBN was 0.12 g, and the amount of chain transfer agent B was changed to 0.32 g. The comparative polymer 2 was obtained.

(Comparative Example 3)
The same operation as in Example 1 except that the amount of ethyl acetate was changed to 8.61 g, the amount of NVP was changed to 4.8 g, the amount of MA was changed to 1.2 g, the amount of AIBN was changed to 0.11 g, and the amount of chain transfer agent A was changed to 0.27 g. The comparative polymer 3 was obtained.

<Evaluation of polymer 1>
The polymers obtained in Examples and Comparative Examples were evaluated by the following methods. The results are shown in Table 1.

(Weight average molecular weight, number average molecular weight and dispersity)
The weight average molecular weight (Mw), number average molecular weight (Mn) and dispersity (Mw / Mn) were determined by gel permeation chromatography (GPC) in terms of polystyrene. The equipment and measurement conditions used for the measurement are as follows.
System: Tosoh GPC system HLC-8220
Measurement side column configuration:
・ Guard column (manufactured by Tosoh, TSKguardcolum SuperHZ-L)
-Separation column (manufactured by Tosoh, TSKgel SuperHZM-M) 2 series connection Reference side column configuration:
・ Reference column (manufactured by Tosoh, TSKgel SuperH-RC)
Developing solvent: Dimethylformamide (manufactured by Wako Pure Chemical Industries, Ltd., special grade)
Flow rate of developing solvent: 0.6 mL / min Standard sample: TSK standard polystyrene (manufactured by Tosoh, PS-oligomer kit)
Column temperature: 40 ° C

(Cloud point)
The polymer was dissolved in water to prepare a 30% aqueous solution, and the cloud point (Cp) was evaluated. Specifically, when the temperature of the aqueous solution was raised, the temperature at which phase separation occurred and became opaque was evaluated as a cloud point (Cp).

As is clear from Table 1, the cloud point in the 30% aqueous solution of the polymers 1 to 10 obtained in Examples 1 to 10 is about 30 to 75 ° C., and it can be seen that the polymer is suitable as a draw solute. On the other hand, with respect to the comparative polymer 1 obtained in Comparative Example 1, the polymer did not dissolve in water at 5 ° C. For each of the 30% aqueous solutions of the comparative polymers 2 and 3 obtained in Comparative Examples 2 and 3, phase separation did not occur even when the temperature was raised to 100 ° C.

<Evaluation of polymer 2>
For the polymers 1 and 9 obtained in Examples 1 and 9, the phase diagram and the osmotic pressure measurement shown below were performed.

(Phase diagram creation)
An aqueous solution containing about 50% of the above polymer was prepared and sealed in a screw vial. This was allowed to stand in a constant temperature bath at a predetermined temperature to achieve sufficient equilibrium, and then the upper phase (organic rich phase) and the lower phase (water-rich phase) were taken out with a syringe. For the water content of the organic rich phase and the organic matter content of the water rich phase of each sample, use a hybrid Karl Fischer titer (MKH-700, manufactured by Kyoto Electronics Co., Ltd.) and a total organic carbon analyzer (TOC-VCSH, Shimadzu Corporation), respectively. It was measured. The measurement was performed 3 to 5 times, and the average value was used as the measured value. The weight percentage of the solute was calculated from the obtained water content or organic matter content and plotted against the equilibrium temperature.
The phase diagram for the polymer 1 is shown in FIG. 1, and the phase diagram for the polymer 9 is shown in FIG. 2, respectively.

(Osmotic pressure measurement)
An aqueous solution having a concentration of 5 to 95% of the above polymer was prepared. About 7 ml of the aqueous solution sample was transferred to a dedicated sample cup, and the water activity of each aqueous solution at 25 ° C. was measured using a water activity measuring device (AquaLab Series4 TDL). The measurement was performed 3 to 5 times, and the average value was taken as the water activity measurement value. The osmotic pressure (bar) was calculated from the obtained measured values of water activity by a calculation formula and unit conversion, and plotted against the charged concentration.
The evaluation results for the polymer 1 are shown in FIG. 3, and the evaluation results for the polymer 9 are shown in FIG. 4, respectively.

Claims (5)

It contains 35 to 75% by mass of a nitrogen-containing heterocycle and a structural unit derived from a monomer having an ethylenically unsaturated group, and 25 to 65% by mass of a structural unit derived from a (meth) acrylic acid ester, and has a molecular weight distribution. A copolymer having a value of 1.5 or less. The copolymer according to claim 1, wherein the weight average molecular weight is less than 100,000. A draw solute for a forward osmosis membrane containing the copolymer according to claim 1 or 2. A draw solution containing the draw solute for a forward osmosis membrane according to claim 3. A water treatment apparatus using the draw solution according to claim 4.

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