Draw solute, draw solution and water treatment apparatus

Abstract

To provide a draw solute having improved water conveyance ability, and a draw solution using the same and a water treatment apparatus.SOLUTION: A draw solute contains an addition compound to which one or more groups represented by the following general formula (1) are added to an active hydrogen-containing compound. In the general formula (1), EO represents an ethylene oxide group, and AO represents a propylene oxide group or a butylene oxide group. {(EO)n1(AO)n2} represents a structure that an ethylene oxide and a propylene oxide or a butylene oxide are randomly added. m, n1 and n2 represent the number of average addition moles of EO or AO, m is a number of 2.5 or more and 6 or less, n1 is a number of 6 or more and 15 or less, and n2 is a number of 2 or more and 18 or less. R2 represents a hydrogen atom, an alkyl group or an aryl group.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present disclosure relates to draw solutes, and draw solutions and water treatment devices using same. [Background technology]

[0002] The forward osmosis membrane method utilizes the phenomenon in which two solutions of different concentrations are brought into contact with each other through a semipermeable membrane, and the solvent moves from the side with lower osmotic pressure to the side with higher osmotic pressure, and can be used to separate the components of a solution. Compared to the reverse osmosis membrane method, in which pressure is applied to a solution against osmotic pressure to force the liquid through the membrane, the forward osmosis membrane method, which uses osmotic pressure to perform membrane filtration, is easier to use in energy conservation, and is expected to be applied to water treatment such as seawater desalination, wastewater treatment, and food concentration, as well as power generation.

[0003] When water treatment is performed using the forward osmosis membrane method, a solution (draw solution) with a higher osmotic pressure than the solution to be treated (treatment target solution) is used to move a solvent (water) from the treatment target solution side to the draw solution side through a semipermeable membrane. Since it is necessary to recover the solvent from the draw solution afterwards, the draw solution needs to have a property (phase separability) that allows the solvent to be easily separated, and various substances (draw solutes) having osmotic pressure induction properties for preparing such draw solutions have been studied. For example, Patent Document 1 proposes a draw solute made of a block copolymer containing ethylene oxide, propylene oxide, and butylene oxide. Patent Document 2 also proposes a draw solute made of a linear or branched random, sequential, or block copolymer containing ethylene oxide and propylene oxide. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2015 / 156404 [Patent Document 2] International Publication No. 2018 / 045393 Summary of the Invention [Problem to be solved by the invention]

[0005] A draw solute can increase the amount of water obtained per cycle (amount of water produced) by combining excellent osmotic pressure induction performance and excellent phase separation. Such properties of a draw solute can be evaluated by its water transport capacity, which is an index showing the amount of water produced by the draw solute per unit mass.

[0006] Therefore, an object of the present disclosure is to provide a draw solute having improved water transport ability, and a draw solution and a water treatment device using the same. [Means for solving the problem]

[0007] In view of the above circumstances, the present inventors conducted extensive research and completed the inventions described below in [1] to [9]. [1] A draw solute containing an adduct in which one or more groups represented by the following general formula (1) are added to an active hydrogen-containing compound: [ka] [In the general formula (1), EO represents an ethylene oxide group, and AO represents a propylene oxide group or a butylene oxide group. {(EO) n1 (AO) n2} represents a structure in which ethylene oxide and propylene oxide or butylene oxide are randomly added. m, n1, and n2 represent the average number of moles of EO or AO added, where m is a number of 2.5 or more and 6 or less, n1 is a number of 6 or more and 15 or less, and n2 is a number of 2 or more and 18 or less. R 2 represents a hydrogen atom, an alkyl group, or an aryl group. [2] The draw solute according to [1], wherein the adduct contains a compound having a structure represented by the following general formula (2): [ka] [In general formula (2), R 1represents a residue obtained by removing all active hydrogens from an x-valent active hydrogen-containing compound, where x is an integer of 1 or more. EO represents an ethylene oxide group, and AO represents a propylene oxide group or a butylene oxide group. {(EO) n1 (AO) n2} represents a structure in which ethylene oxide and propylene oxide or butylene oxide are randomly added. m, n1, and n2 represent the average number of moles of EO or AO added, where m is a number of 2.5 or more and 6 or less, n1 is a number of 6 or more and 15 or less, and n2 is a number of 2 or more and 18 or less. R 2 represents a hydrogen atom, an alkyl group, or an aryl group. [3] The draw solute according to [1] or [2], wherein the active hydrogen-containing compound is glycerin, polyglycerin, trimethylolpropane, ethylene glycol, triethylene glycol, 1-butanol, 2-butanol, 1-octanol, 2-octanol, 1-decanol, 2-decanol, 2-propyl-1-heptanol, 1-dodecanol, 2-dodecanol, allyl alcohol, isoprenol, phenol, polyethyleneimine, triethanolamine, ethylenediamine, or diethylenetriamine. [4] The draw solute according to any one of [1] to [3], wherein the ratio of m to n1 is 1:1 to 1:6. [5] The draw solute according to any one of [1] to [4], wherein the ratio of the sum of m and n1 to n2 is 1:0.1 to 1:2.0. [6] The draw solute according to any one of [1] to [5], wherein the number average molecular weight of the adduct is 500 or more and 10,000 or less. [7] The draw solute according to any one of [1] to [6], wherein the cloud point of a 50% by mass draw solution prepared by dissolving the draw solute in water is 30° C. or higher and 90° C. or lower. [8] A draw solution comprising the draw solute according to any one of [1] to [7]. [9] A water treatment device using the draw solution according to [8]. Effect of the Invention

[0008] According to the present disclosure, it is possible to provide a draw solute having improved water transport ability, as well as a draw solution and a water treatment device using the same. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] One embodiment of the present disclosure will be described in detail below, but the present disclosure is not limited thereto.

[0010] <Draw solute> The draw solute of the present embodiment contains an adduct compound in which one or more groups represented by the following general formula (1) are added to an active hydrogen-containing compound. [ka] [In the general formula (1), EO represents an ethylene oxide group, and AO represents a propylene oxide group or a butylene oxide group. {(EO) n1 (AO) n2} represents a structure in which ethylene oxide and propylene oxide or butylene oxide are randomly added. m, n1, and n2 represent the average number of moles of EO or AO added, where m is a number of 2.5 or more and 6 or less, n1 is a number of 6 or more and 15 or less, and n2 is a number of 2 or more and 18 or less. R 2 represents a hydrogen atom, an alkyl group, or an aryl group.

[0011] The active hydrogen-containing compound may contain one active hydrogen or may contain two or more active hydrogens. When the active hydrogen-containing compound contains one active hydrogen, the adduct compound has a structure in which the group represented by the general formula (1) is bonded to the residue of the active hydrogen-containing compound after removing the active hydrogen. When the active hydrogen-containing compound contains two or more active hydrogens, the adduct compound has a structure in which the group represented by the general formula (1) is bonded to the residue of the active hydrogen-containing compound after removing some or all of the active hydrogens.

[0012] Examples of the active hydrogen-containing functional group include a hydroxy group and an amino group.

[0013] Specific examples of the active hydrogen-containing compound include water; methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, 1-pentanol, 3-methyl-1-butanol, 2-methyl-1-butanol, 2,2-dimethyl-1-propanol, 2-pentanol, 3-methyl-2-butanol, 3-pentanol, 1,2-ethanediol, 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 1,2-pentanediol, 1,3-pentanediol, ethanol, 1,4-pentanediol, 1,5-pentanediol, neopentyl glycol, 1-octanol, 2-octanol, 1-decanol, 2-decanol, 2-propyl-1-heptanol, 1-dodecanol, 2-dodecanol, 1,4-cyclohexanedimethanol, allyl alcohol, methallyl alcohol, isoprenol, hydroxyacetone, tetrahydrofurfuryl alcohol, phenol, cresol, glycerin, polyglycerin, ethylene glycol, diethylene glycol, triethylene glycol, trimethylolpropane Compounds with hydroxyl groups such as bread, erythritol, pentaerythritol, diglycerol, ditrimethylolpropane, phloroglucinol, sorbitol, sorbitan, glucose, fructose, xylitol, and methyl glucoside; compounds with carboxyl groups such as acrylic acid, methacrylic acid, acetic acid, propionic acid, and butyric acid; polyethyleneimine, methylamine, ethylamine, propylamine, isopropylamine, butylamine, 2-pentylamine, 3-pentylamine, neopentylamine, hexylamine, octylamine, 2- Ethylhexylamine, nonylamine, decylamine, pentadecylamine, cetylamine, laurylamine, stearylamine, cyclopropylamine, cyclobutylamine, cyclopentylamine, cyclohexylamine, 1-adamantanamine, dimethylamine, ethylmethylamine, diethylamine, methylpropylamine, methylisopropylamine, ethylpropylamine, ethylisopropylamine, butylmethylamine, methyl t-butylamine, dipropylamine, diisopropylamine, ethyl t-butylamine, N-ethyl-1,2-Dimethylpropylamine, dibutylamine, diisobutylamine, di(t-butyl)amine, ethylhexylamine, dipentylamine, dihexylamine, di(2-ethylhexyl)amine, dioctylamine, didecylamine, dilaurylamine, dicetylamine, distearylamine, methylstearylamine, ethylstearylamine, butylstearylamine, methylcyclohexylamine, ethylcyclohexylamine, Nt-butylcyclohexylamine, dicyclohexylamine, di(2-methylcyclohexyl)amine, N,N '-Dimethyl-1,3-propanediamine, 1,3-pentanediamine, ethylenediamine, diethylenetriamine, triethylenetetramine (N,N'-di(2-aminoethyl)ethylenediamine), monoethanolamine, diethanolamine, dipropanolamine, benzylamine, phenylpropylamine, phenylbutylamine, 1,1-dimethyl-2-phenylethylamine, 3,4-dimethylbenzylamine, aniline, methylaniline, ethylaniline, propylaniline, isopropylaniline, butylaniline, laurylaniline , stearylaniline, dimethylaniline, diethylaniline, methylbenzylamine, 4,4'-methylenedianiline, naphthylamine, trimethylaniline, 4-methylphenethylamine, methylbenzylamine, ethylbenzylamine, t-butylbenzylamine, diphenylamine, dibenzylamine, N-benzyl-1,3-propanediamine, 2,4,6-trimethyl-1,3-phenylenediamine, 4-aminobenzylamine, aziridine, azetidine, pyrrolidine, 2-methylpyrrolidine, piperidine, 2-methylpiperidine, 3-methyl ethylpiperidine, 4-methylpiperidine, 2,4-dimethylpiperidine, 3,5-dimethylpiperidine, 2,6-dimethylpiperidine, 2,2,6,6-tetramethylpiperidine, piperazine, N-methylpiperazine, N-ethylpiperazine, N-isobutylpiperazine, N-cyclohexylpiperazine, N-cyclopentylpiperazine, N-phenylpiperazine, 1-(2-pyridyl)piperazine, 1-(4-pyridyl)piperazine, 1-(2-pyrimidyl)piperazine, morpholine, pyrrole, 2-methylpyrrole, 2,4-dimethylpyrrole, 3,Examples of the compounds having an amino group include 4-dimethylpyrrole, pyrazole, 3,5-dimethylpyrazole, imidazole, 3-methylindole, 2-phenylindole, triethanolamine, diethylenetriamine, and ethylene glycol. Among them, it is preferable to use glycerin, polyglycerin, trimethylolpropane, ethylene glycol, triethylene glycol, 1-butanol, 2-butanol, 1-octanol, 2-octanol, 1-decanol, 2-decanol, 2-propyl-1-heptanol, 1-dodecanol, 2-dodecanol, allyl alcohol, isoprenol, phenol, polyethyleneimine, triethanolamine, ethylenediamine, or diethylenetriamine.

[0014] Generally, when the hydrophilicity of the draw solute is improved, the phase separation of the draw solute tends to decrease, but the draw solute containing the above-mentioned adduct tends to maintain the phase separation while improving the hydrophilicity of the draw solute. The reason for this is unclear, but the inventors speculate that the above-mentioned adduct has a plurality of EOs introduced inside the compound, and a structure containing AO and a hydrogen atom, an alkyl group, or an aryl group introduced outside the compound, so that the hydrophilicity of the draw solute is improved while the decrease in the phase separation is suppressed.

[0015] In formula (1), m represents the average number of moles of EO directly bonded to the active hydrogen-containing compound, and is a number of 2.5 to 6. From the viewpoint of improving the hydrophilicity of the draw solute and improving the osmotic pressure induction performance, the lower limit of m is preferably 2.75 or more, and more preferably 3 or more. The upper limit of m is not particularly limited, but can be, for example, 5 or less, or 4 or less.

[0016] In formula (1), n1 is {(EO) n1 (AO) n2n1 represents the average number of moles of EO added in the formula {}, and is a number of 6 to 15. From the viewpoint of improving the hydrophilicity of the draw solute and improving the osmotic pressure induction performance, the lower limit of n1 is preferably 6.5 or more, and more preferably 7 or more. The upper limit of n1 is not particularly limited, and can be, for example, 13 or less, or 11 or less.

[0017] In formula (1), n2 is {(EO) n1 (AO) n2 n2 represents the average number of moles of AO added in the above formula {}, and is a number of 2 to 18. The lower limit of n2 is preferably 2.1 or more, and more preferably 2.2 or more, from the viewpoint of improving the phase separation property of the draw solute. The upper limit of n2 is preferably 10 or less, more preferably 8 or less, even more preferably 6 or less, particularly preferably 4 or less, and extremely preferably 3 or less, from the viewpoint of improving the osmotic pressure induction performance of the draw solute.

[0018] The ratio of m to n1 may be 1:1 to 1:6. From the viewpoint of controlling the balance between the effect of improving the osmotic pressure induction performance of the draw solute by introducing EO and the effect of reducing phase separation, and improving the water transport capacity, the ratio of m to n1 is preferably 1:1.5 to 1:5, and more preferably 1:1.75 to 1:4.

[0019] The ratio of the sum of m and n1 to n2 may be 1:0.1 to 1:2.0. From the viewpoint of controlling the balance between the osmotic pressure induction performance and phase separation property of the draw solute and improving the water transport ability, the ratio of the sum of m and n1 to n2 is preferably 1:0.1 to 1:1.2, more preferably 1:0.1 to 1:0.3, and even more preferably 1:0.2 to 1:0.28.

[0020] In formula (1), R 2represents a hydrogen atom, an alkyl group, or an aryl group. The alkyl group may be linear, branched, or cyclic. The alkyl group may specifically be a methyl group, an ethyl group, an n-propyl group, an i-propyl group, an n-butyl group, a t-butyl group, an n-pentyl group, an n-hexyl group, a cyclopentyl group, or a cyclohexyl group. The aryl group may specifically be a phenyl group, a naphthyl group, or the like.

[0021] The above-mentioned addition compound may contain a compound having a structure represented by the following general formula (2). [ka] [In general formula (2), R 1 represents a residue obtained by removing all active hydrogens from an x-valent active hydrogen-containing compound, where x is an integer of 1 or more. EO represents an ethylene oxide group, and AO represents a propylene oxide group or a butylene oxide group. {(EO) n1 (AO) n2} represents a structure in which ethylene oxide and propylene oxide or butylene oxide are randomly added. m, n1, and n2 represent the average number of moles of EO or AO added, where m is a number of 2.5 or more and 6 or less, n1 is a number of 6 or more and 15 or less, and n2 is a number of 2 or more and 18 or less. R 2 represents a hydrogen atom, an alkyl group, or an aryl group.

[0022] In formula (2), R 1 represents a residue obtained by removing all active hydrogens from an x-valent active hydrogen-containing compound. x is an integer of 1 or more, and may be an integer of 2 or more, or 3 or more. When an active hydrogen-containing compound has two or more active hydrogen-containing functional groups in the molecule, the active hydrogen-containing functional groups may be one type or two or more types.

[0023] The number average molecular weight of the addition compound may be 500 or more and 10000 or less. The lower limit of the number average molecular weight is preferably 1250 or more, more preferably 1500 or more, from the viewpoint of suppressing leakage of the polymer from the membrane. The upper limit of the number average molecular weight is preferably 5000 or less, more preferably 3000 or less, from the viewpoint of viscosity. In addition, the weight average molecular weight of the addition compound is preferably 500 or more and 10000 or less, more preferably 1250 or more and 7000 or less, and even more preferably 1500 or more and 5000 or less. The number average molecular weight and the weight average molecular weight can be measured, for example, using gel permeation chromatography (GPC).

[0024] The content of the component having a number average molecular weight of 500 or less in the adduct is preferably less than 10% by mass, more preferably less than 5% by mass. The content of the component having a number average molecular weight of 1000 or less in the adduct is preferably less than 25% by mass, more preferably less than 10% by mass. When the content of the above components is within these ranges, leakage of the draw solute from the forward osmosis membrane is easily suppressed.

[0025] The above-mentioned addition compound can be obtained, for example, by adding ethylene oxide to an active hydrogen-containing compound to obtain an intermediate, and then randomly adding ethylene oxide and propylene oxide or butylene oxide to the intermediate.

[0026] The reaction conditions for adding ethylene oxide to an active hydrogen-containing compound are not particularly limited. For example, the active hydrogen-containing compound and ethylene oxide can be reacted as they are or diluted with a solvent as necessary at a temperature of preferably 0°C to 200°C, more preferably 120°C to 180°C. In this case, an alkali catalyst such as potassium hydroxide (KOH) or sodium hydroxide (NaOH) may be used as a catalyst. The reaction can be carried out, for example, by adding a catalyst to the active hydrogen-containing compound and then feeding ethylene oxide into the reaction system. The ethylene oxide may be fed in multiple portions. After feeding the ethylene oxide, the reaction rate can be further increased by aging for 1 hour to 3 hours until the reaction is sufficient.

[0027] The reaction conditions when ethylene oxide and propylene oxide or butylene oxide are randomly added to a compound (intermediate) obtained by adding ethylene oxide to an active hydrogen-containing compound are not particularly limited except that ethylene oxide and propylene oxide or butylene oxide are simultaneously reacted. For example, the intermediate, ethylene oxide, and propylene oxide or butylene oxide can be reacted as they are or diluted with a solvent as necessary at preferably 0°C to 200°C, more preferably 120°C to 180°C. In this case, an alkali catalyst such as potassium hydroxide (KOH) or sodium hydroxide (NaOH) may be used as a catalyst. The reaction can be carried out, for example, by adding a catalyst to the intermediate and further feeding ethylene oxide and propylene oxide or butylene oxide into the reaction system. Ethylene oxide and propylene oxide or butylene oxide may be fed simultaneously using separate feed lines, or ethylene oxide and propylene oxide or butylene oxide may be mixed in an intermediate tank and then fed as one liquid. The feeding of ethylene oxide and propylene oxide or butylene oxide may be carried out in several separate times, and the feeding time of propylene oxide or butylene oxide may be shorter than the feeding time of ethylene oxide. After feeding of ethylene oxide and propylene oxide or butylene oxide, the reaction rate can be further increased by aging for 1 hour to 3 hours until the reaction is sufficient. 2 When an alkyl group or an aryl group is to be introduced as a substituent, it can be introduced, for example, by an addition reaction with an alkylene oxide, an alkyl glycidyl ether, or an aryl glycidyl ether, a substitution reaction with an alkyl halide, or an aryl alkyl halide such as benzyl chloride, or a transesterification reaction with an acid anhydride, an alkyl ester, or an aryl ester. In these reactions, an alkali catalyst or an acid catalyst may be used as a catalyst.

[0028] After the reaction, it is preferable to neutralize the reaction mixture by adding an acid such as acetic acid, phosphoric acid, or lactic acid, and remove light impurities such as ethylene glycol contained in the adduct under reduced pressure at a temperature of 0°C to 200°C, more preferably 120°C to 180°C. The draw solute is preferably stored under a nitrogen atmosphere, and an antioxidant may be added to improve stability. Suitable antioxidants include dibutylhydroxytoluene, butylhydroxyanisole, ascorbic acid, tocopherol, and sodium erythorbate.

[0029] When an antioxidant is added to the draw solute, the amount of the antioxidant added is preferably 50 ppm by mass or more, more preferably 200 ppm by mass or more, from the viewpoint of preventing deterioration of physical properties. The upper limit of the amount of the antioxidant is not particularly limited, but can be, for example, 1000 ppm by mass or less.

[0030] When the draw solute of the present embodiment is dissolved in water to prepare a 5 mass% aqueous solution, the pH of the aqueous solution is preferably from 2 to 6. When the pH is within this range, it is possible to suppress deterioration of the antioxidant, and the stability of the draw solute is improved.

[0031] The water carrying capacity of the draw solute in this embodiment is preferably 58% or more, more preferably 60% or more, and even more preferably 63% or more. The upper limit of the water carrying capacity of the draw solute is not particularly limited, but can be, for example, 80% or less.

[0032] When the draw solute of this embodiment is dissolved in water to prepare a 50% by mass draw solution, the cloud point of the draw solution is preferably 30° C. or more and 90° C. or less, more preferably 35° C. or more and 80° C. or less, and even more preferably 40° C. or more and 77° C. or less. When the cloud point is within these ranges, the forward osmosis membrane method can be easily applied to water treatment using low-temperature waste heat from factories, etc. The cloud point can be measured, for example, by the method described in the Examples.

[0033] The viscosity (25°C) of the draw solute of this embodiment is preferably 550 mPa·s (cPs) or less, more preferably 500 mPa·s or less. When the draw solute of this embodiment is dissolved in water to prepare a 50 mass% draw solution, the viscosity (25°C) of the draw solution is preferably 100 mPa·s or less, more preferably 50 mPa·s or less. When the viscosity is within these ranges, the energy required for transporting the draw solution in the forward osmosis membrane method is low, and costs can be reduced.

[0034] The purity of the draw solute of this embodiment is preferably 80% by mass or more, more preferably 99% by mass or more, from the viewpoint of reducing transportation costs. The water content of the draw solute of this embodiment is preferably less than 1% by mass, from the viewpoint of reducing transportation costs.

[0035] <Drawing solution> The draw solution of the present embodiment contains the draw solute. The content of the draw solute is preferably 20% by mass or more and 100% by mass or less, more preferably 50% by mass or more and 100% by mass or less, and even more preferably 75% by mass or more and 100% by mass or less, based on the total amount of the draw solution.

[0036] 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 solvents selected from water, methanol, ethanol, etc. may be used. It is more preferable that the draw solution contains the same solvent as the solvent to be treated. The content of the solvent may be, for example, 0% by mass or more and 80% by mass or less with respect to the total amount of the draw solution.

[0037] The draw solution may contain draw solutes other than the draw solutes, but the content of the draw solutes is preferably 20% by mass or less based on the total amount of the draw solutes. The draw solution is preferably composed of the draw solutes, any solvent, and any other draw solutes, and more preferably composed of the draw solutes and a solvent.

[0038] The draw solution preferably has a cloud point (lower critical solution temperature). The cloud point refers to the temperature at which a transparent or translucent liquid undergoes phase separation by changing its temperature, resulting in an opaque liquid. A draw solution having a cloud point can undergo phase separation between the draw solute and the solvent by heating.

[0039] The cloud point of the draw solution depends on the composition of the adduct, for example, the average number of moles of EO attached directly to the active hydrogen-containing compound, or {(EO) n1 (AO) n2 By changing the molar ratio of EO and AO added, the average number of moles added, etc. in}, it is possible to appropriately adjust the cloud point of the draw solution and select a draw solution with an appropriate cloud point according to the application.

[0040] For example, when applying the forward osmosis membrane method to water treatment using low-temperature waste heat from a factory, it is preferable that the draw solution does not undergo phase separation at temperatures around room temperature where the forward osmosis membrane treatment is performed, and that the draw solution undergoes phase separation at a temperature of about the low-temperature waste heat from the factory. The suitable cloud point of the draw solution used in such applications varies depending on the concentration of the draw solute in the draw solution, but is preferably, for example, 30°C to 90°C, more preferably 35°C to 80°C, and even more preferably 40°C to 77°C.

[0041] Conventionally, it has been difficult to utilize low-temperature waste heat from factories, and much of it has been discarded as waste heat. Therefore, water treatment using low-temperature waste heat is particularly favorable from the standpoint of energy efficiency.

[0042] <Forward osmosis membrane method> In the forward osmosis membrane process, 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 the forward osmosis membrane process, it is necessary to separate the draw solute and the solvent contained in the draw solution.

[0043] The draw solution having a cloud point allows for phase separation of the draw solute and the solvent upon heating.

[0044] In the forward osmosis membrane process using a draw solution having such a cloud point, for example, the forward osmosis membrane process can be continuously performed by repeating the following treatment. The feed solution is placed 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 the solvent is transferred from the feed solution side through the semipermeable membrane to the draw solution side. The reduced concentration draw solution is removed and heated to cause phase separation of the draw solute and the solvent. The phase-separated draw solute 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.).

[0045] The temperature at which the forward osmosis membrane treatment is carried out is not particularly limited, but is usually around room temperature, for example, from 5°C to 40°C.

[0046] As the semipermeable 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, it is preferable to use it in combination with a dense active layer that determines the selective permeability of the membrane and a porous support layer. Since the support layer is more likely to adsorb dirt than the active layer, from the viewpoint of reducing membrane dirt, it is generally preferable to provide the active layer of the semipermeable membrane on the feed liquid (water to be treated) side.

[0047] 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 can be suitably applied to these applications. EXAMPLES

[0048] The present disclosure will be described in more detail below by showing examples, but the scope of the present disclosure is not limited to these examples, and all modifications and implementations that do not deviate from the gist of the present disclosure are included in the technical scope of the present disclosure. In addition, unless otherwise specified, "%" means "% by mass".

[0049] <Synthesis of Compounds> The compounds of Examples 1 to 3 and Comparative Examples 1 and 2 were synthesized as shown below. For each compound, the core molecule before addition polymerization, {(EO) n1 (AO) n2 Table 1 shows the sequence structure of}, the average number of moles m, n1, and the average number of moles n2 of EO added to the core molecule corresponding to the above general formula (1) or (2), and the number average molecular weight.

[0050] Example 1 A 2L autoclave was charged with 150.0 g of glycerin and 8.75 g of 48% KOH aqueous solution at room temperature, and then the pressure was reduced to 10 kPa absolute pressure while bubbling nitrogen gas at 20 mL / min. The temperature was then raised to 125°C and the mixture was stirred for 5 hours. After the pressure was raised to 0.20 MPa absolute pressure, the bubbling was stopped, and 645.8 g of ethylene oxide was injected over 4 hours, followed by aging for 3 hours. 150.0 g of the intermediate thus obtained was charged into a 2 L autoclave, after which the gas phase was replaced with nitrogen gas, the pressure was increased to an absolute pressure of 0.20 MPa, and the temperature was increased to 125° C. Then, 323.4 g of ethylene oxide and 198.5 g of butylene oxide were injected over a period of 4 hours, and the mixture was aged for 3 hours. After the temperature was lowered to 60° C., 2.7 g of 50% lactic acid was added, and the pressure was reduced to an absolute pressure of 10 kPa while bubbling nitrogen gas at 20 mL / min, followed by stirring at 125° C. for 3 hours. This gave the compound of Example 1.

[0051] Example 2 A 2L autoclave was charged with 150.0 g of glycerin and 8.75 g of 48% KOH aqueous solution at room temperature, and then the pressure was reduced to 10 kPa absolute pressure while bubbling nitrogen gas at 20 mL / min. The temperature was then raised to 125°C and the mixture was stirred for 5 hours. After the pressure was raised to 0.20 MPa absolute pressure, the bubbling was stopped, and 645.8 g of ethylene oxide was injected over 4 hours, followed by aging for 3 hours. 150.0 g of the intermediate thus obtained was charged into a 2 L autoclave, the gas phase was replaced with nitrogen gas, the pressure was increased to an absolute pressure of 0.20 MPa, and the temperature was increased to 125° C. Then, 202.2 g of ethylene oxide and 198.5 g of butylene oxide were injected over a period of 4 hours, and the mixture was aged for 3 hours. After the temperature was lowered to 60° C., 2.7 g of 50% lactic acid was added, and the pressure was reduced to an absolute pressure of 10 kPa while bubbling nitrogen gas at 20 mL / min, followed by stirring for 3 hours at 125° C. This gave the compound of Example 2.

[0052] Example 3 A 2L autoclave was charged with 150.0 g of glycerin and 8.75 g of 48% KOH aqueous solution at room temperature, and then the pressure was reduced to 10 kPa absolute pressure while bubbling nitrogen gas at 20 mL / min. The temperature was then raised to 125°C and the mixture was stirred for 5 hours. After the pressure was raised to 0.20 MPa absolute pressure, the bubbling was stopped, and 861.0 g of ethylene oxide was injected over 4 hours, followed by aging for 3 hours. 150.0 g of the intermediate thus obtained was charged into a 2 L autoclave, the gas phase was replaced with nitrogen gas, the pressure was increased to an absolute pressure of 0.20 MPa, and the temperature was increased to 125° C. Then, 95.5 g of ethylene oxide and 156.4 g of butylene oxide were injected over a period of 4 hours, and the mixture was aged for 3 hours. After the temperature was lowered to 60° C., 2.1 g of 50% lactic acid was added, and the pressure was reduced to an absolute pressure of 10 kPa while bubbling nitrogen gas at 20 mL / min, followed by stirring for 3 hours at 125° C. This gave the compound of Example 3.

[0053] Comparative Example 1 A 2L autoclave was charged with 150.0 g of glycerin and 8.75 g of 48% KOH aqueous solution at room temperature, and then the pressure was reduced to 10 kPa absolute pressure while bubbling nitrogen gas at 20 mL / min. The temperature was then raised to 125°C and the mixture was stirred for 5 hours. After the pressure was raised to 0.20 MPa absolute pressure, bubbling was stopped, and 717.5 g of ethylene oxide was injected over 4 hours, followed by aging for 3 hours to obtain a first intermediate. After 150.0 g of the first intermediate was charged into a 2 L autoclave, the gas phase was replaced with nitrogen gas, the absolute pressure was increased to 0.20 MPa, and the temperature was increased to 125° C. Then, 284.4 g of ethylene oxide was injected over 4 hours, and the mixture was aged for 3 hours to obtain a second intermediate. After 150.0 g of the second intermediate was charged into a 2 L autoclave, the gas phase was replaced with nitrogen gas, the pressure was increased to an absolute pressure of 0.20 MPa, and the temperature was increased to 125° C. Then, 202.4 g of butylene oxide was injected over 4 hours, and the mixture was aged for 3 hours. After lowering the temperature to 60° C., 2.5 g of 50% lactic acid was added, and the pressure was reduced to an absolute pressure of 10 kPa while bubbling nitrogen gas at 20 mL / min, followed by stirring for 3 hours at 125° C. This gave the compound of Comparative Example 1.

[0054] Comparative Example 2 A 2L autoclave was charged with 150.0g of glycerin and 8.75g of 48% KOH aqueous solution at room temperature, and then the pressure was reduced to 10kPa absolute pressure while bubbling nitrogen gas at 20mL / min. The temperature was then raised to 125°C and the mixture was stirred for 5 hours. After the pressure was raised to 0.20MPa absolute pressure, the bubbling was stopped, and 430.5g of ethylene oxide and 130.6g of butylene oxide were injected over 4 hours, followed by aging for 3 hours. 150.0 g of the intermediate thus obtained was charged into a 2 L autoclave, after which the gas phase was replaced with nitrogen gas, the pressure was increased to an absolute pressure of 0.20 MPa, and the temperature was increased to 125° C. Then, 429.5 g of ethylene oxide and 130.6 g of butylene oxide were injected over a period of 4 hours, and the mixture was aged for 3 hours. After the temperature was lowered to 60° C., 2.1 g of 50% lactic acid was added, and the pressure was reduced to an absolute pressure of 10 kPa while bubbling nitrogen gas at 20 mL / min, followed by stirring for 3 hours at 125° C. This gave the compound of Comparative Example 2.

[0055] [Table 1]

[0056] <Evaluation> The compounds prepared in the Examples and Comparative Examples were evaluated for cloud point, phase separation, osmotic pressure, and water transport ability by the following methods. The results are shown in Table 2.

[0057] (Cloud Point Rating) An aqueous solution containing 50% by mass of each compound was prepared and sealed in a screw vial. This was left to stand in an oven at 97°C for 1 hour to separate into layers, and then cooled while measuring the internal temperature. The temperature at which a uniform layer was visually observed was taken as the cloud point.

[0058] (Phase separation evaluation) An aqueous solution containing 50% by mass of each compound was prepared and sealed in a screw vial. This was left in a 97°C oven overnight to allow for sufficient equilibrium, after which approximately 1g of the upper layer and approximately 1g of the lower layer were taken in three samples and placed in an aluminum cup. The aluminum cup was left in a 97°C oven for two hours to dry, and the compound concentrations in the upper and lower layers were calculated from the mass difference before and after drying, and the layer with the highest compound concentration was determined to be the compound-rich phase.

[0059] (Osmolarity evaluation) Aqueous solutions containing 40 mass%, 50 mass%, or 60 mass% of each compound were prepared, and the osmotic pressure was measured using a vapor pressure osmometer (5600, WESCOR). Each measurement was performed three times, and the average value was taken as the osmotic pressure (osmoles: Osm). The obtained osmotic pressure (osmoles) was converted to osmotic pressure (bars: bar) using the following formula. Osmolality (bar) = Osmolality (Osm) x 8.314 x 298.15 / 100000

[0060] (Water transport capacity evaluation) The water transport capacity was calculated according to the following formula. Water transport capacity = <Water passing mass> / <Compound substance amount> x 100 =(<mass after water flow>-<initial mass>) / <amount of compound>×100 =(<Mass after water flow>-<Compound concentration after water flow> / <Initial compound concentration>×<Weight after water flow>) / (<Weight after water flow>>×<Compound concentration after water flow>)×100 =(<Initial compound concentration>-<Compound concentration after water flow>) / (<Initial compound concentration>×<Compound concentration after water flow>)×100 In the formula, "initial polymer concentration" indicates the concentration of the compound-rich phase in the phase separation evaluation, and "compound concentration after water passing" is the compound concentration when the osmotic pressure becomes 48 bar, and was calculated by back-calculating from the correlation equation of the osmotic pressure at the compound concentration measured in the osmotic pressure evaluation (the osmotic pressure when the compound concentration is 0 mass% is set to 0 bar).

[0061] [Table 2]

Claims

1. A draw solute containing an adduct in which one or more groups represented by the following general formula (1) are added to an active hydrogen-containing compound: 【Chemistry 1】 [In the general formula (1), EO represents an ethylene oxide group, and AO represents a propylene oxide group or a butylene oxide group. {(EO) ｎ１ (A.O.) ｎ２ } represents a structure in which ethylene oxide and propylene oxide or butylene oxide are randomly added. m, n1, and n2 represent the average number of moles of EO or AO added, where m is a number of 2.5 to 6, n1 is a number of 6 to 15, and n2 is a number of 2 to 18. R ２ represents a hydrogen atom, an alkyl group, or an aryl group.

2. The draw solute according to claim 1 , wherein the adduct comprises a compound having a structure represented by the following general formula (2): 【Chemistry 2】 [In general formula (2), R １ represents a residue obtained by removing all active hydrogens from an x-valent active hydrogen-containing compound, where x is an integer of 1 or more. EO represents an ethylene oxide group, and AO represents a propylene oxide group or a butylene oxide group. {(EO) ｎ１ (A.O.) ｎ２ } represents a structure in which ethylene oxide and propylene oxide or butylene oxide are randomly added. m, n1, and n2 represent the average number of moles of EO or AO added, where m is a number of 2.5 to 6, n1 is a number of 6 to 15, and n2 is a number of 2 to 18. R ２ represents a hydrogen atom, an alkyl group, or an aryl group.

3. 2. The draw solute of claim 1, wherein the active hydrogen-containing compound is glycerin, polyglycerin, trimethylolpropane, ethylene glycol, triethylene glycol, 1-butanol, 2-butanol, 1-octanol, 2-octanol, 1-decanol, 2-decanol, 2-propyl-1-heptanol, 1-dodecanol, 2-dodecanol, allyl alcohol, isoprenol, phenol, polyethyleneimine, triethanolamine, ethylenediamine, or diethylenetriamine.

4. 2. The draw solute of claim 1, wherein the ratio of m to n1 is from 1:1 to 1:

6.

5. 2. The draw solute of claim 1, wherein the ratio of the sum of m and n1 to n2 is from 1:0.1 to 1:2.

0.

6. 2. The draw solute according to claim 1, wherein the number average molecular weight of the adduct is 500 or more and 10,000 or less.

7. The draw solute according to claim 1, wherein the cloud point of a 50% by mass draw solution prepared by dissolving the draw solute in water is 30° C. or more and 90° C. or less.

8. A draw solution comprising a draw solute according to any one of claims 1 to 7.

9. A water treatment device using the draw solution according to claim 8.

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