Draw solute, draw solution and water treatment equipment for forward osmosis membrane process

Abstract

To provide a draw solute for a forward osmosis membrane method suitably applicable to a UCST type draw solution, a draw solution containing the draw solute, and a water treatment device based on the draw solution.SOLUTION: A draw solute for a forward osmosis membrane method comprises a polymer having a structural unit represented by a general formula (1) in the figure. [In the formula (1), R1 represents a hydrogen atom or a methyl group, R2 represents a linear or branched alkylene group, and R3 represents an amino group or a salt thereof.]SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a draw solute, a draw solution, and a water treatment device for forward osmosis membrane processing, and more particularly to a draw solute that has high-temperature solubility (upper critical solution temperature: UCST) temperature sensitivity in solution and exhibits liquid-liquid phase separation behavior. [Background technology]

[0002] The forward osmosis membrane method uses the phenomenon of solvent migration from the side with lower osmotic pressure to the side with higher osmotic pressure when two solutions of different concentrations are brought into contact via a semipermeable membrane, and can be used to separate the components of a solution. Compared to the reverse osmosis membrane method, which applies pressure to a solution against osmotic pressure to force the liquid through a membrane, the forward osmosis membrane method, which uses osmotic pressure to perform membrane filtration, is more energy-efficient and is expected to be applied to water treatment such as seawater desalination and power generation.

[0003] When water is treated using a forward osmosis membrane process, a solution (draw solution) with a higher osmotic pressure than the solution to be treated (the solution to be treated) is used to move a solvent (water) from the solution to be treated to the draw solution through a semipermeable membrane. Since the solvent must then be recovered from the draw solution, the draw solution must have properties that allow for easy solvent separation. Various osmotic pressure inducers (draw solutes) for preparing such draw solutions have been investigated. For example, Patent Document 1 below proposes the use of a "block copolymer having a glycerin skeleton and containing ethylene oxide groups as the hydrophilic portion and groups consisting of propylene oxide and / or butylene oxide as the hydrophobic portion" as a temperature-sensitive water absorbent (draw solute) that aggregates and separates the solvent when heated. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2015 / 156404 Summary of the Invention [Problem to be solved by the invention]

[0005] In order to broaden the scope of application of the forward osmosis membrane method to various technologies in the future, it is desirable to increase the variety of draw solutes so that the optimum draw solution can be selected according to the process. For example, the draw solute in Patent Document 1 has the property of flocculating when heated (lower critical solution temperature: LCST type), but there is also a need to develop a draw solute that is soluble at high temperatures in solution (upper critical solution temperature: UCST type) and has temperature sensitivity.

[0006] The present invention has been made in view of the above circumstances, and aims to provide a draw solute for a forward osmosis membrane process that can be suitably used in a UCST-type draw solution, a draw solution containing the draw solute, and a water treatment device using the draw solution. [Means for solving the problem]

[0007] The present invention provides a draw solute for a forward osmosis membrane process, which comprises a polymer having a structural unit represented by the following general formula (1):

[0008] [ka] [In formula (1), R 1 represents a hydrogen atom or a methyl group, and R 2 represents a linear or branched alkylene group, and R 3 represents an amino group or a salt thereof.]

[0009] The polymer may further have a structural unit represented by the following general formula (2).

[0010] [ka] [In formula (2), R 4 represents a hydrogen atom or a methyl group, and R 5represents a single bond or a linear or branched alkylene group, and R 6 represents an alkylene group which may be substituted with a hydroxyl group, and M represents a hydrogen atom or an alkali metal element.

[0011] The polymer may further have a structural unit represented by the following general formula (3).

[0012] [ka] [In formula (3), R 7 represents a hydrogen atom or a methyl group.

[0013] The present invention also provides a draw solution containing the aforementioned draw solute for forward osmosis membrane processing according to the present invention.

[0014] The present invention further provides a water treatment device using the draw solution according to the present invention. [Effects of the Invention]

[0015] According to the present invention, it is possible to provide a draw solute for a forward osmosis membrane process that can be suitably used in a UCST-type draw solution, a draw solution containing the draw solute, and a water treatment device using the draw solution. DETAILED DESCRIPTION OF THE INVENTION

[0016] An embodiment of the present invention will be described in detail below, but the present invention is not limited thereto.

[0017] The draw solute for the forward osmosis membrane method according to this embodiment contains a polymer having a structural unit represented by the following general formula (1): The polymer contained in the draw solute may be one type alone or two or more types.

[0018] [ka] [In formula (1), R 1represents a hydrogen atom or a methyl group, and R 2 represents a linear or branched alkylene group, and R 3 represents an amino group or a salt thereof.]

[0019] In formula (1), R 2 represents a linear or branched alkylene group. The number of carbon atoms in the alkylene group may be, for example, 1 or more, 2 or more, 5 or less, or 3 or less. 2 Examples of the alkyl group include a methylene group, an ethylene group, and a propylene group, and among these, an ethylene group is preferred.

[0020] R in Equation (1) 3 represents an amino group or a salt thereof. The salt of the amino group can be appropriately determined depending on the use of the polymer, and is not particularly limited, but examples thereof include chloride salts, bromide salts, iodide salts, carbonate salts, sulfate salts, etc.

[0021] The polymer may be a polymer consisting only of the structural unit represented by the general formula (1), or may further contain other structural units. In this case, the content of the structural unit represented by the general formula (1) may be, for example, 10 mol% or more, 20 mol% or more, or 40 mol% or more, in terms of molar ratio based on the total amount of the polymer. The upper limit of the content of the structural unit represented by the general formula (1) may be, for example, 95 mol% or less, or 90 mol% or less, in terms of molar ratio based on the total amount of the polymer.

[0022] The other structural units mentioned above may include, for example, a structural unit represented by the following general formula (2) or a structural unit represented by the following general formula (3).

[0023] [ka] [In formula (2), R 4 represents a hydrogen atom or a methyl group, and R 5 represents a single bond or a linear or branched alkylene group, and R 6represents an alkylene group which may be substituted with a hydroxyl group, and M represents a hydrogen atom or an alkali metal element.

[0024] [ka] [In formula (3), R 7 represents a hydrogen atom or a methyl group.

[0025] In equation (2), R 5 represents a single bond or a linear or branched alkylene group. The number of carbon atoms in the alkylene group may be, for example, 1 or more, 5 or less, or 3 or less. 5 Examples of the alkyl group include a methylene group, an ethylene group, and a propylene group, and among these, a methylene group is preferred.

[0026] R in Equation (2) 6 R represents an alkylene group which may be substituted with a hydroxyl group. Such an alkylene group may be linear or branched. 6 The number of carbon atoms in the alkylene group of R may be, for example, 1 or more, 3 or more, 10 or less, or 5 or less. 6 Examples of the hydroxyl group include a methylene group, an ethylene group, a propylene group, a butylene group, a pentylene group, a methylene group substituted with a hydroxyl group, an ethylene group substituted with a hydroxyl group, a propylene group substituted with a hydroxyl group, a butylene group substituted with a hydroxyl group, and a pentylene group substituted with a hydroxyl group, and among these, a propylene group substituted with a hydroxyl group is preferred.

[0027] In formula (2), M represents a hydrogen atom or an alkali metal element, such as Li, Na, or K, with Na being preferred.

[0028] When the polymer has a structural unit represented by general formula (2), the content thereof may be, for example, 5 mol% or more, or 10 mol% or more, in terms of molar ratio based on the total amount of the polymer. The upper limit of the content of the structural unit represented by general formula (2), in terms of molar ratio based on the total amount of the polymer, may be 50 mol% or less, or 30 mol% or less.

[0029] When the polymer has a structural unit represented by general formula (3), the content thereof may be, for example, 10 mol% or more, 15 mol% or more, or 20 mol% or more, in terms of molar ratio based on the total amount of the polymer. The upper limit of the content of the structural unit represented by general formula (3), in terms of molar ratio based on the total amount of the polymer, may be, for example, 70 mol% or less, 60 mol% or less, or 50 mol% or less.

[0030] Such a polymer is more preferably a polymer having structural units represented by the following formula (4A), and optionally formula (4B) and / or formula (4C).

[0031] [ka]

[0032] [ka]

[0033] [ka]

[0034] The polymer may contain the structural unit represented by the general formula (1) above, and optionally the structural unit represented by the general formula (2) and the structural unit represented by the general formula (3) in a predetermined ratio, and each structural unit may be present in either a block form or a random form.

[0035] The weight-average molecular weight of the polymer is not particularly limited and may be, for example, 20,000 or more, 30,000 or more, or 35,000 or more. The upper limit of the weight-average molecular weight of the polymer is also not particularly limited and may be, for example, 200,000 or less, 100,000 or less, or 50,000 or less. In this specification, the weight-average molecular weight is a value measured by GPC (gel permeation chromatography).

[0036] The aminoalkylation ratio of the polymer according to this embodiment is not particularly limited, but may be, for example, 30% or more, or 50% or more. The upper limit of the aminoalkylation ratio is also not particularly limited, and may be, for example, 100% or less, or 80% or less. In this specification, the aminoalkylation ratio of a polymer refers to the proportion of aminoalkylated carboxyl groups in the polymer, and more specifically, refers to the number of structural units represented by general formula (1) relative to the total number of structural units represented by general formula (1) and general formula (3). For example, an aminoalkylation ratio of 100% refers to a polymer that has structural units represented by general formula (1) but does not have structural units represented by general formula (3). The aminoalkylation ratio of a polymer can be determined by the acid value titration method described in the Examples below.

[0037] The polymer according to this embodiment can be produced, for example, by randomly or block copolymerizing a compound represented by the following general formula (1'), a compound represented by the following general formula (2'), and, if necessary, a compound represented by the following general formula (3') as monomers in a predetermined ratio.

[0038] [ka] [In formula (1'), R 1 , R 2 and R 3 are R in the above general formula (1), 1 , R 2 and R 3 is equivalent to.]

[0039] [ka] [In formula (2'), R 4 , R 5 , R 6 and M are R in the above general formula (2), 4 , R 5 , R 6 and M.]

[0040] [ka] [In formula (3'), R 7 is R in the above general formula (3). 7 is equivalent to.]

[0041] A preferred example of the compound represented by the general formula (1') above is 2-aminoethyl (meth)acrylate, etc. A preferred example of the compound represented by the general formula (2') above is sodium 3-allyloxy-2-hydroxypropanesulfonate, etc.

[0042] In the copolymerization reaction, the preferred amount of each of the above compounds used in the polymerization can be appropriately set, for example, as follows, depending on the structure of the resulting polymer.

[0043] The amount of the compound represented by the general formula (1') used may be, for example, 20 mol% or more, or 40 mol% or more, in terms of a molar ratio based on the total amount of monomers used in polymerization. There is no particular upper limit to the amount of the compound represented by the general formula (1') used, and it may be 90 mol% or less, or 85 mol% or less, in terms of a molar ratio based on the total amount of monomers.

[0044] The amount of the compound represented by the general formula (2') used may be, for example, 5 mol% or more, or 10 mol% or more, in terms of a molar ratio based on the total amount of monomers used in polymerization. There is no particular upper limit to the amount of the compound represented by the general formula (2') used, and it may be 50 mol% or less, or 30 mol% or less, in terms of a molar ratio based on the total amount of monomers.

[0045] The amount of the compound represented by the general formula (3') used may be, for example, 10 mol% or more, 15 mol% or more, or 20 mol% or more, in terms of a molar ratio based on the total amount of monomers used in polymerization. The upper limit of the amount of the compound represented by the general formula (3') used may be, for example, 70 mol% or less, 60 mol% or less, or 50 mol% or less, in terms of a molar ratio based on the total amount of monomers.

[0046] In addition to the above, the polymer according to this embodiment can also be produced by a method in which a carboxyl group-containing monomer such as (meth)acrylic acid, maleic acid, or itaconic acid is randomly or block copolymerized as monomers with a compound represented by the general formula (2') in a predetermined ratio to obtain a base polymer, and then some or all of the carboxyl groups in the obtained base polymer are aminoalkylated. Here, when all of the carboxyl groups in the base polymer are aminoalkylated, the resulting polymer has only the structural units represented by the general formula (1) and the structural units represented by the general formula (2), while when some of the carboxyl groups are aminoalkylated, the resulting polymer has the structural units represented by the general formula (3) in addition to the structural units represented by the general formula (1) and the structural units represented by the general formula (2).

[0047] The compound for aminoalkylating a part or all of the carboxyl groups of the base polymer is not particularly limited, and examples thereof include ethyleneimine, propyleneimine, and the like.

[0048] The method of random or block copolymerization is not particularly limited, and a commonly used polymerization method or a modified method thereof can be used. Examples of the polymerization method include radical polymerization, and specific examples of the polymerization method that can be used include oil-in-water emulsion polymerization, water-in-oil emulsion polymerization, suspension polymerization, dispersion polymerization, precipitation polymerization, solution polymerization, aqueous solution polymerization, and bulk polymerization. Among these, it is preferable to use solution polymerization because it is highly safe and can reduce production costs (polymerization costs).

[0049] In the solution polymerization method, the monomer components may be polymerized in a solvent. The solvent may be an organic solvent alone, but preferably contains water. It is more preferable to use 50% by mass or more of water, even more preferable to use 80% by mass or more of water, and particularly preferable to use 100% by mass of water, based on 100% by mass of the total amount of solvent used. Suitable examples of organic solvents that can be used alone or together with water include aqueous organic solvents such as lower alcohols such as ethanol and isopropanol; amides such as N,N-dimethylformamide; ethers such as diethyl ether and dioxane; glycol, glycerin, and polyethylene glycols. One of these solvents may be used alone, or two or more may be used in combination.

[0050] The amount of the solvent used is preferably 40 to 300 parts by mass, more preferably 45 to 200 parts by mass, and even more preferably 50 to 150 parts by mass, relative to 100 parts by mass of the total amount of all monomers. Although a part or all of the solvent may be charged into the reaction vessel at the beginning of the polymerization, a part of the solvent may be added (dropped) into the reaction system during the polymerization reaction, or the monomer components and the like may be dissolved in the solvent in advance and added (dropped) together with these components into the reaction system during the polymerization reaction.

[0051] The reaction form of the solution polymerization is not particularly limited and can be carried out in a commonly used form, but a typical example is a form in which the monomers and the like are added dropwise to a solvent that has been previously charged into a reaction system to carry out the reaction. In such a reaction form, the concentrations of the solutions to be added dropwise are not particularly limited and any appropriate concentrations can be used.

[0052] In the method for producing the polymer, agents that are usually used in polymerization reactions, such as a polymerization initiator, a chain transfer agent, and a reaction accelerator, may be used as appropriate.

[0053] Specific examples of suitable polymerization initiators include hydrogen peroxide, persulfates such as sodium persulfate, potassium persulfate, and ammonium persulfate, azo compounds such as 2,2'-azobis(2-amidinopropane) hydrochloride, 4,4'-azobis-4-cyanovaleric acid, azobisisobutyronitrile, and 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile), and organic peroxides such as benzoyl peroxide, lauroyl peroxide, peracetic acid, di-t-butyl peroxide, and cumene hydroperoxide. These polymerization initiators may be used alone or in combination of two or more.

[0054] Specifically, the chain transfer agent is preferably a bisulfite and / or a compound capable of generating a bisulfite. In this case, it is more preferable to use a polymerization initiator in addition to the bisulfite and the compound capable of generating a bisulfite. Furthermore, a heavy metal ion may be used in combination as a reaction accelerator, as described below.

[0055] Furthermore, when hydrogen sulfite and / or a compound capable of generating hydrogen sulfite is used as a chain transfer agent, a polymer having a sulfonic acid (salt) group at least at one end of the main chain can be obtained.

[0056] Examples of compounds capable of generating the above-mentioned bisulfite salt include pyrosulfite (salt), dithionous acid (salt), sulfurous acid (salt), etc., with pyrosulfite (salt) being preferred. The above-mentioned salts are preferably salts with metal atoms, ammonium, or organic amines. Examples of the above-mentioned metal atoms include monovalent metal atoms of alkali metals such as lithium, sodium, and potassium; divalent metal atoms of alkaline earth metals such as calcium and magnesium; and trivalent metal atoms such as aluminum and iron. Examples of organic amines include alkanolamines such as monoethanolamine, diethanolamine, and triethanolamine; and triethylamine. Of the above-mentioned bisulfite salts and compounds capable of generating bisulfite salts, bisulfite salts are preferred.

[0057] Preferred examples of the bisulfite salt include sodium bisulfite, potassium bisulfite, and ammonium bisulfite, with sodium bisulfite being more preferred. Preferred examples of the compound capable of generating the bisulfite salt include sodium pyrosulfite, potassium pyrosulfite, sodium dithionite, potassium dithionite, sodium sulfite, potassium sulfite, and ammonium sulfite, with sodium pyrosulfite being more preferred.

[0058] The above-mentioned hydrogen sulfites and compounds capable of generating hydrogen sulfites may be used alone or in combination of two or more kinds.

[0059] In addition to the above-mentioned bisulfites and compounds capable of generating bisulfites, the following chain transfer agents can also be used. Examples of such chain transfer agents include thiol-based chain transfer agents such as mercaptoethanol, thioglycolic acid, 2-mercaptopropionic acid, 3-mercaptopropionic acid, octyl 3-mercaptopropionate, 2-mercaptoethanesulfonic acid, and n-dodecyl mercaptan; halides such as carbon tetrachloride, methylene chloride, bromoform, and bromotrichloroethane; secondary alcohols such as isopropanol and glycerin; and lower oxides and salts thereof such as phosphorous acid, hypophosphorous acid, and salts thereof (e.g., sodium hypophosphite, potassium hypophosphite, etc.). The above chain transfer agents can be used alone or in combination.

[0060] Specific examples of the reaction accelerator include heavy metal ions. Preferred examples of the heavy metal ions include iron, cobalt, manganese, chromium, molybdenum, tungsten, copper, silver, gold, lead, platinum, iridium, osmium, palladium, rhodium, and ruthenium. These heavy metals may be used alone or in combination. Among these, iron is more preferred.

[0061] In the above-mentioned production method, during polymerization, in addition to the above-mentioned compounds, a decomposition catalyst for the polymerization initiator or a reducing compound may be added to the reaction system. Examples of decomposition catalysts for the polymerization initiator include metal halides such as lithium chloride and lithium bromide; metal oxides such as titanium oxide and silicon dioxide; metal salts of inorganic acids such as hydrochloric acid, hydrobromic acid, perchloric acid, sulfuric acid, and nitric acid; carboxylic acids such as formic acid, acetic acid, propionic acid, butyric acid, isobutyric acid, and benzoic acid, esters thereof, and metal salts thereof; heterocyclic amines such as pyridine, indole, imidazole, and carbazole, and derivatives thereof. These decomposition catalysts may be used alone or in combination of two or more.

[0062] Examples of reducing compounds include organometallic compounds such as ferrocene; inorganic compounds capable of generating metal ions such as iron, copper, nickel, cobalt, and manganese ions, such as iron naphthenate, copper naphthenate, nickel naphthenate, cobalt naphthenate, and manganese naphthenate; inorganic compounds such as boron trifluoride etherate, potassium permanganate, and perchloric acid; sulfur-containing compounds such as sulfur dioxide, sulfates, thiosulfates, sulfoxylates, benzenesulfinic acid and its substituted derivatives, and homologues of cyclic sulfinic acids such as paratoluenesulfinic acid; nitrogen-containing compounds such as hydrazine, β-hydroxyethylhydrazine, and hydroxylamine; aldehydes such as formaldehyde, propionaldehyde, n-butylaldehyde, isobutyraldehyde, and isovaleric aldehyde; and ascorbic acid. These reducing compounds may also be used alone or in combination.

[0063] The draw solution according to this embodiment contains the draw solute for the forward osmosis membrane process described above. The content of the draw solute in the draw solution is not particularly limited as long as it is a concentration that can exhibit UCST properties, and may be 1% by mass or more, 5% by mass or more, or 8% by mass or more relative to the total amount of the draw solution. The upper limit of the content of the draw solute is also not particularly limited, and may be 50% by mass or less, 40% by mass or less, or 30% by mass or less relative to the total amount of the draw solution.

[0064] The draw solution may contain a solvent. The solvent may be appropriately selected depending on the conditions of the forward osmosis membrane method using the draw solution, and one or more types of solvents selected from water, methanol, ethanol, etc. may be used. It is preferable that the draw solution contains the same solvent as the solvent to be treated. The content of the solvent may be, for example, 80 to 9% by mass based on the total amount of the draw solution.

[0065] The draw solution may contain draw solutes other than the draw solutes, but the content of other draw solutes is preferably 20 mass % or less relative to the total amount of the draw solutes. The draw solution may be composed of the draw solutes, any solvent, and any other draw solutes, and is preferably composed of the draw solutes and solvents.

[0066] The draw solution preferably has an upper critical solution temperature (cloud point). The cloud point is the temperature at which a transparent or translucent liquid becomes opaque as its temperature is lowered, causing phase separation. The draw solution according to this embodiment can undergo phase separation between the draw solute and the solvent by lowering the temperature below the cloud point.

[0067] The cloud point of the draw solution can be adjusted as appropriate by changing the constitution of the polymer, for example, the amino alkylation rate, and a draw solution with an appropriate cloud point can be selected depending on the intended use.

[0068] For example, when the forward osmosis membrane process is applied to a site where wastewater treatment at high temperatures is required, such as produced water from oil drilling, it is preferable that the draw solution does not undergo phase separation at the high temperatures used in the forward osmosis membrane process, but rather undergoes phase separation at temperatures around room temperature. The cloud point of the draw solution used in such applications is preferably, for example, 0°C to 100°C, more preferably 30°C to 80°C, and even more preferably 40°C to 60°C.

[0069] In forward osmosis, the feed solution (the solution to be treated) and the draw solution are brought into contact with each other through a semipermeable membrane, and the solvent moves from the feed solution, which has a low osmotic pressure, to the draw solution, which has a high osmotic pressure. As the solvent moves, the concentration of the draw solution gradually decreases. Therefore, in order to continue forward osmosis, it is necessary to separate the draw solute and the solvent contained in the draw solution.

[0070] The draw solution has a cloud point, and a decrease in temperature can cause phase separation between the draw solute and the solvent.

[0071] In the forward osmosis membrane method using a draw solution having such a cloud point, the forward osmosis membrane method can be continuously carried out by repeating the following treatment, for example. The feed solution is placed on one side of the semipermeable membrane and the draw solution on the other side so that they come into contact with the semipermeable membrane, and the solvent is transferred from the feed solution side to the draw solution side through the semipermeable membrane. The reduced concentration draw solution is removed and its temperature is lowered to cause phase separation between the draw solute and the solvent. The phase-separated draw solution is circulated again to the other side. The phase-separated solvent is further purified, for example, using a nanofiltration membrane (NF membrane), to obtain the desired processed product (purified water, etc.).

[0072] As another method, a method can be applied in which a draw solution in which the compatibility with the solvent has been increased by making the draw solute absorb an acidic gas, the solvent is made to permeate through a membrane from the supply liquid side to the draw solution side, and then the acidic gas is removed from the draw solute to cause phase separation between the draw solute and the solvent.

[0073] 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, and nitrogen oxides such as nitrogen monoxide, nitrogen dioxide, nitrous oxide, dinitrogen trioxide, dinitrogen tetroxide and dinitrogen pentoxide. Of these, carbon dioxide is preferred as the acidic gas.

[0074] The temperature at which the forward osmosis membrane treatment is carried out is not particularly limited as long as the draw solution does not undergo phase separation during the membrane treatment, but it can be set to, for example, about 60°C to 100°C.

[0075] Although conventional semipermeable membranes can be used in the forward osmosis membrane method, it is preferable to use a combination of a dense active layer, which determines the selective permeability of the membrane, and a porous support layer in order to maintain the strength of the membrane. Since the support layer is more likely to adsorb contaminants than the active layer, it is generally preferable to provide the active layer of the semipermeable membrane on the feed liquid (water to be treated) side from the viewpoint of reducing membrane fouling.

[0076] The draw solution can be applied to various applications that utilize the forward osmosis membrane method. Among them, water treatment devices and power generation devices are applications where the forward osmosis membrane method is expected to be used, and the draw solution containing the polymer is particularly suitable for these applications because it has phase separation properties at a high concentration. [Example]

[0077] The present invention will be explained in more detail below by way of examples, but the present invention is not limited to these examples in any way.

[0078] <Synthesis of base polymer> (Production Example 1: AA / HAPS polymer) A 2.5 L SUS316 separable flask equipped with a reflux condenser and a stirrer was charged with 150.0 g of purified water and 0.020 g of Mohr's salt, and the mixture was heated to 85°C with stirring to form a polymerization reaction system. Next, 270.2 g of an 80% aqueous acrylic acid solution (hereinafter also referred to as "80% AA"), 409.1 g of a 40% aqueous solution of sodium 3-allyloxy-2-hydroxypropanesulfonate (hereinafter also referred to as "40% HAPS"), 65.0 g of a 15% aqueous solution of sodium persulfate (hereinafter also referred to as "15% NaPS"), and 34.6 g of a 35% aqueous solution of sodium hydrogen sulfite (hereinafter also referred to as "35% SBS") were each added dropwise from separate nozzles to the polymerization reaction system maintained at 85°C with stirring. The dropwise addition times for each solution were 180 minutes for 80% AA, 120 minutes for 40% HAPS, 190 minutes for 15% NaPS, and 175 minutes for 35% SBS. The dropwise addition rates for each solution were constant and continuous.

[0079] After the dropwise addition of 80% AA was completed, the reaction solution was maintained (aged) at 85° C. for an additional 30 minutes to complete the polymerization.

[0080] In this way, a polymer aqueous solution containing a base polymer (AA / HAPS polymer) with structural units derived from acrylic acid and sodium 3-allyloxy-2-hydroxypropanesulfonate (AA / HAPS polymer) with a solids concentration of 45% was obtained. The weight-average molecular weight of the resulting base polymer was 10,000, and the molar ratio of AA to HAPS was AA:HAPS=80:20.

[0081] (Production Example 2: AA / MA polymer) A 2.5 L SUS316 separable flask equipped with a reflux condenser and stirrer was charged with 250.0 g of pure water, 127.5 g of maleic anhydride (MA), and 54.2 g of 48% aqueous sodium hydroxide (48% NaOH). The mixture was heated to 100°C with stirring and refluxed. Next, 468.4 g of 80% AA, 104.0 g of 15% NaPS, 37.1 g of 35% aqueous hydrogen peroxide (35% HO), and 250.0 g of pure water were added dropwise from separate nozzles to the refluxing polymerization system under stirring. The addition times for each solution were 180 min for 80% AA, 180 min for 15% NaPS, and 120 min for 35% HO. The addition of each solution began simultaneously. After the dropwise addition was completed, the reaction solution was maintained in a reflux state (aged) for an additional 30 minutes to complete the polymerization.

[0082] In this way, a polymer aqueous solution containing a base polymer (AA / MA polymer) with a solids concentration of 43% was obtained. The weight-average molecular weight of the resulting base polymer was 10,000, and the molar ratio of AA to MA was AA:MA=80:20.

[0083] (Production Example 3: AA / MA / HAPS polymer) A 2.5 L SUS316 separable flask equipped with a reflux condenser and stirrer was charged with 250.0 g of pure water, 294.1 g of MA, 125.0 g of 48% NaOH, and 208.9 g of 40% HAPS. The mixture was heated to 100°C with stirring and refluxed. Next, 270.3 g of 80% AA, 102.1 g of 15% NaPS, 36.5 g of 35% HO, and 250.0 g of pure water were added dropwise from separate nozzles to the refluxing polymerization system. The addition times for each solution were 180 min for 80% AA, 180 min for 15% NaPS, and 120 min for 35% HO. All additions were initiated simultaneously. After the addition, the reaction solution was maintained at reflux (aging) for an additional 30 min to complete the polymerization.

[0084] In this way, a polymer aqueous solution containing a base polymer (AA / MA / HAPS polymer) with structural units derived from AA, MA, and HAPS was obtained with a solids concentration of 45%. The weight-average molecular weight of the resulting base polymer was 10,000, and the molar ratio of AA:MA:HAPS was 47:47:6.

[0085] <Addition of ethyleneimine to the base polymer> Example 1 A separable flask equipped with a reflux condenser and a thermometer was charged with 50 parts by mass of the base polymer obtained in Production Example 1 above and 71 parts by mass of pure water. The mixture was cooled in a water bath, and 11 parts by mass of ethyleneimine was added with stirring, followed by heating to 60°C. This temperature was maintained for 240 minutes to complete the addition reaction, yielding an aqueous solution of an aminoethylated polymer.

[0086] Example 2 An aqueous solution of an aminoethylated polymer was obtained by the same procedure as in Example 1, except that the amount of base polymer charged was 70 parts by mass, the amount of pure water charged was 82.5 parts by mass, and the amount of ethyleneimine added was 8 parts by mass.

[0087] Example 3 An aqueous solution of an aminoethylated polymer was obtained by the same procedure as in Example 1, except that the base polymer obtained in Production Example 2 was used instead of the base polymer obtained in Production Example 1, the amount of base polymer charged was 30 parts by mass, the amount of pure water charged was 46 parts by mass, and the amount of ethyleneimine added was 4 parts by mass.

[0088] Example 4 An aqueous solution of an aminoethylated polymer was obtained by the same procedure as in Example 1, except that the base polymer obtained in Production Example 3 was used instead of the base polymer obtained in Production Example 1, the amount of base polymer charged was 40 parts by mass, the amount of pure water charged was 70 parts by mass, and the amount of ethyleneimine added was 8 parts by mass.

[0089] Example 5 An aqueous solution of an aminoethylated polymer was obtained by the same procedure as in Example 4, except that the amount of base polymer charged was 40 parts by mass, the amount of pure water charged was 61 parts by mass, and the amount of ethyleneimine added was 4.4 parts by mass.

[0090] (Comparative Examples 1 to 3) In Comparative Examples 1 to 3, the aqueous polymer solutions containing the base polymer obtained in Production Examples 1 to 3 were used.

[0091] <Measurement of aminoethylation rate (acid value titration method)> 100 mL of the aminoethylated polymer aqueous solution obtained in Examples 1 to 5 above was prepared at a concentration of 0.2% by mass and set in an automatic titrator (Kyoto Electronics Manufacturing Co., Ltd., product name "CHA-600"). 1 mL of 1.0 M sodium hydroxide aqueous solution was added to make the aqueous solution alkaline, and titration was performed with 0.1 M hydrochloric acid. The acid value was calculated using the following formula from the titer A at the second inflection point and the titer B at the third inflection point.

[0092]

number

[0093] The aminoethylation rate (AE rate (%)) of the polymer was calculated from the obtained acid value using the following formula. The results are shown in Table 1.

[0094]

Number

[0095] <Evaluation of UCST property> 3 g of the aminoethylated polymer obtained in Examples 1 to 5 above and 3 g of the polymer obtained in Comparative Examples 1 to 3 were each collected in a glass vial, and concentrated sulfuric acid (95%) was added to adjust the pH to 4. While stirring, pure water was added, and the addition of pure water was stopped when the clear aqueous solution became turbid. From the concentration of the polymer at this point and the amount of pure water added, the solid content concentration of the suspension was calculated (UCST expression concentration). The obtained suspension was placed in a dryer at 80 °C, and it was visually confirmed whether it became a uniform aqueous solution. The uniform aqueous solution was taken out of the dryer and cooled in a water bath, and it was confirmed whether it became turbid and separated into two layers after standing (UCST property). The results are shown in Table 1.

[0096]

Table 1

Claims

1. A polymer having a structural unit represented by the following general formula (1a) and a structural unit represented by the following general formula (2a), The content of the structural unit represented by the following general formula (1) in the polymer is 10 mol % or more in terms of molar ratio based on the total amount of the polymer, The draw solute for a forward osmosis membrane process, wherein the content of the structural unit represented by the following general formula (2) in the polymer is 5 mol % or more in terms of molar ratio based on the total amount of the polymer: 【Chemical 1】 [In formula (1a), R 1 represents a hydrogen atom or a methyl group, R 2 represents a linear or branched alkylene group, and R 3 represents an amino group or a salt thereof.] 【Chemistry 2】 [In formula (2a), R 4 represents a hydrogen atom or a methyl group, R 5 represents a single bond or a linear or branched alkylene group, R 6 represents an alkylene group optionally substituted with a hydroxyl group, and M represents a hydrogen atom or an alkali metal element.] 【Chemistry 3】 [In formula (1), R 1 , R 2 and R 3 have the same meanings as R 1 , R 2 and R 3 in general formula (1a), respectively.] 【Chemistry 4】 [In formula (2), R 1 , R 2 , R 3 and M have the same meanings as R 1 , R 2 , R 3 and M in formula (2a), respectively.]

2. The polymer further has a structural unit represented by the following general formula (3a):

2. The draw solute for a forward osmosis membrane process according to claim 1, wherein the content of the structural unit represented by the following general formula (3) in the polymer is 10 mol % or more in terms of molar ratio based on the total amount of the polymer: 【Chemistry 5】 [In formula (3a), R 7 represents a hydrogen atom or a methyl group.] 【Chemistry 6】 [In formula (3), R 7 has the same meaning as R 7 in general formula (3a)]

3. A polymer having a structural unit represented by the following general formula (1a) and a structural unit represented by the following general formula (3a), The content of the structural unit represented by the following general formula (1) in the polymer is 10 mol % or more in terms of molar ratio based on the total amount of the polymer, The draw solute for a forward osmosis membrane process, wherein the content of the structural unit represented by the following general formula (3) in the polymer is 10 mol % or more in terms of molar ratio based on the total amount of the polymer: 【Chemistry 7】 [In formula (1a), R 1 represents a hydrogen atom or a methyl group, R 2 represents a linear or branched alkylene group, and R 3 represents an amino group or a salt thereof.] 【Chemistry 8】 [In formula (3a), R 7 represents a hydrogen atom or a methyl group.] 【Chemistry 9】 [In formula (1), R 1 , R 2 and R 3 have the same meanings as R 1 , R 2 and R 3 in general formula (1a), respectively.] 【Chemistry 10】 [In formula (3), R 7 has the same meaning as R 7 in general formula (3a)]

4. A draw solution comprising the draw solute for forward osmosis membrane processing according to any one of claims 1 to 3.

5. A water treatment device using the draw solution of claim 4.

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