Draw solute, draw solution and water treatment equipment

Abstract

This draw solute for a forward osmosis membrane method contains a random copolymer obtained by randomly adding a monomer containing ethylene oxide and butylene oxide to a compound having at least one hydroxyl group.

Description

[Technical field]

[0001] The present invention relates to a draw solute, and a draw solution and water treatment device using the 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) having 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 after that, the draw solution needs to have a property that allows the solvent to be easily separated, and various osmotic pressure inducers (draw solutes) 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] Incidentally, even if the amount of the draw solute in the draw solution is reduced, if the same amount of water can be drawn into the draw solution, the amount of water obtained per cycle (amount of water produced) increases, which is desirable from the viewpoints of energy efficiency, time reduction, etc. Such properties of the draw solute can be evaluated by the water transport capacity, which is an index showing the amount of water produced by the draw solute per unit weight.

[0006] Therefore, an object of the present invention is to provide a draw solute having improved water transporting 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 [5]. [1] A draw solute for forward osmosis, comprising a random copolymer obtained by randomly adding monomers including ethylene oxide and butylene oxide to a compound having one or more hydroxyl groups. [2] The draw solute according to [1], wherein the molar ratio of ethylene oxide to butylene oxide is 1:1 to 10:1. [3] The draw solute according to [1] or [2], wherein the random copolymer has a number average molecular weight of 500 to 10,000. [4] The draw solute according to any one of [1] to [3], wherein the cloud point of a 50% by mass draw solution prepared by dissolving the draw solute in water is 40 to 75°C. [5] A draw solution comprising the draw solute according to any one of [1] to [4]. [6] A water treatment device using the draw solution according to [5]. Effect of the Invention

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

[0009] Hereinafter, one embodiment of the present invention will be described in detail, but the present invention is not limited thereto.

[0010] <Draw solute> The draw solute of this embodiment includes a random copolymer obtained by randomly adding a monomer containing ethylene oxide and butylene oxide to a compound having one or more hydroxyl groups (hereinafter also referred to as a "hydroxyl group-containing compound"). The random copolymer has a structure in which at least an oxyethylene chain derived from ethylene oxide and an oxybutylene chain derived from butylene oxide are randomly bonded to the oxygen atoms of the hydroxyl groups of the hydroxyl group-containing compound. The random copolymer contained in the draw solute may be one type alone or two or more types. In addition, the draw solute may have a structure in which an oxybutylene group is bonded to the ends of the randomly bonded oxyethylene chains and oxybutylene chains to perform end capping.

[0011] Examples of the hydroxyl group-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-pentanol, Examples of the hydroxyl group-containing compound include 1,3-pentanediol, 1,4-pentanediol, 1,5-pentanediol, neopentyl glycol, allyl alcohol, methallyl alcohol, isoprenol, acrylic acid, methacrylic acid, acetic acid, propionic acid, butyric acid, phenol, glycerin, trimethylolpropane, erythritol, pentaerythritol, diglycerol, ditrimethylolpropane, phloroglucinol, sorbitol, sorbitan, glucose, fructose, xylitol, and methyl glucoside. The number of hydroxyl groups in the hydroxyl group-containing compound is preferably 2 or more, more preferably 3 or more, and even more preferably 3.

[0012] The molar ratio of ethylene oxide to butylene oxide is preferably 1:1 to 10:1, more preferably 2.5:1 to 7.5:1, and even more preferably 3:1 to 5:1. By setting the molar ratio of ethylene oxide to butylene oxide within the above range, both the osmotic pressure and phase separation properties can be improved.

[0013] The monomer may contain other monomers other than ethylene oxide and butylene oxide. Examples of other monomers include propylene oxide, butyl glycidyl ether, and phenyl glycidyl ether. The content of other monomers in the monomer is preferably 20 mol % or less, more preferably 10 mol % or less, and even more preferably 5 mol % or less.

[0014] In the random copolymer, the mass ratio of the structural units derived from a hydroxyl group-containing compound to the structural units derived from ethylene oxide and butylene oxide (mass of structural units derived from ethylene oxide and butylene oxide / mass of structural units derived from a hydroxyl group-containing compound) is preferably 1 or more and 110 or less, more preferably 5 or more and 50 or less, and even more preferably 10 or more and 30 or less.

[0015] The lower limit of the number average molecular weight of the random copolymer is preferably 500 or more, more preferably 1250 or more, and even 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 10000 or less, more preferably 5000 or less, and even more preferably 3000 or less, from the viewpoint of viscosity. The weight average molecular weight is preferably 500 to 10000, more preferably 1250 to 7000, and even more preferably 1500 to 5000. The number average molecular weight and weight average molecular weight can be measured by the method described in the Examples.

[0016] The content of the component having a number average molecular weight of 500 or less in the random copolymer 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 random copolymer 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.

[0017] The reaction conditions when ethylene oxide and butylene oxide are randomly added to a hydroxyl group-containing compound are not particularly limited except that ethylene oxide and butylene oxide are reacted simultaneously. For example, the hydroxyl group-containing compound and ethylene oxide and butylene oxide can be reacted as they are or diluted with a solvent as necessary at preferably 0 to 200°C, more preferably 120 to 180°C, and even more preferably 120 to 130°C. In this case, an alkali catalyst such as potassium hydroxide (KOH) or sodium hydroxide (NaOH) may be used as a catalyst. Examples of the solvent include benzene, toluene, xylene, diisopropyl ether, dibutyl ether, tetrahydrofuran, and dioxane. The reaction can be carried out, for example, by adding a catalyst to a hydroxyl group-containing compound and further feeding ethylene oxide and butylene oxide into the reaction system. Ethylene oxide and butylene oxide may be fed simultaneously using separate feed lines, or ethylene oxide and butylene oxide may be mixed in an intermediate tank and then fed as one liquid. The ethylene oxide and butylene oxide may each be fed in a plurality of times, and the feed time of butylene oxide may be shorter than that of ethylene oxide. After feeding of ethylene oxide and butylene oxide, the reaction rate can be further increased by aging for 1 to 3 hours until the reaction is sufficiently completed.

[0018] After the reaction, it is preferable to neutralize the 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 random copolymer under reduced pressure at 0 to 200°C, more preferably 120 to 180°C. It is also preferable to store the draw solute under a nitrogen atmosphere, and an antioxidant may be added to improve stability. Suitable antioxidants include dibutylhydroxytoluene, butylhydroxyanisole, ascorbic acid, tocopherol, and sodium erythorbate.

[0019] 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.

[0020] 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 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.

[0021] The water carrying capacity of the draw solute in this embodiment is preferably 52% or more, more preferably 54% or more, and even more preferably 56% or more. The upper limit of the water carrying capacity of the draw solute is not particularly limited, but can be, for example, 75% or less.

[0022] 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 35 to 80° C., more preferably 40 to 75° C. If the cloud point is within this range, it becomes easy to apply the forward osmosis membrane method 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.

[0023] 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.

[0024] 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.

[0025] <Drawing solution> The draw solution of the present embodiment contains the draw solute. The content of the draw solute is preferably 20 to 100% by mass, more preferably 50 to 100% by mass, and further preferably 75 to 100% by mass, based on the total amount of the draw solution.

[0026] 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, 80 to 0 mass% based on the total amount of the draw solution.

[0027] 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.

[0028] 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.

[0029] The cloud point of the draw solution can be appropriately adjusted by changing the composition of the addition polymer, for example, the molar ratio of ethylene oxide and butylene oxide added, the number of moles added, etc., and a draw solution with an appropriate cloud point can be selected depending on the application.

[0030] 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 a temperature around room temperature where the forward osmosis membrane treatment is performed, and that the draw solution undergoes phase separation at a temperature around the low-temperature waste heat temperature 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 35 to 80°C, and more preferably 40 to 75°C.

[0031] 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.

[0032] <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.

[0033] The draw solution having a cloud point allows for phase separation of the draw solute and the solvent upon heating.

[0034] 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.).

[0035] The temperature at which the forward osmosis membrane treatment is carried out is not particularly limited, but is usually around room temperature, for example, 5 to 40°C.

[0036] 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.

[0037] 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

[0038] The present invention will be described in more detail below by showing examples, but the scope of the present invention is not limited to these examples, and all modifications and variations that do not deviate from the gist of the present invention are included in the technical scope of the present invention. Unless otherwise specified, "%" means "% by mass".

[0039] <Polymer synthesis> Polymers of Examples 1 to 3 and Comparative Examples 1 to 3 were synthesized as shown below. For each polymer, the polymer core, sequence structure, mass ratio of ethylene oxide to propylene oxide or butylene oxide (EO / PO or EO / BO), weight average molecular weight, number average molecular weight, and viscosity are shown in Table 1. The weight average molecular weight and number average molecular weight were determined in terms of polystyrene using gel permeation chromatography (GPC). The apparatus and conditions used for the measurement are as follows: System: Tosoh GPC system HLC-8320 Measurement column configuration: Guard column (Tosoh, TSKguardcolumn SuperMP-M) - Two separation columns (Tosoh, TSKgel SuperMultipore HZ-M) connected in series Reference column configuration: Reference column (Tosoh, TSKgel SuperH2000) Developing solvent: Tetrahydrofuran (Fujifilm Wako Pure Chemical, special grade) Flow rate of developing solvent: 0.35mL / min Standard sample: TSK standard polystyrene (Tosoh, PS-oligomer kit) Column temperature: 40℃

[0040] Example 1 After 150.0 g of glycerin and 8.40 g of 50% KOH aqueous solution were charged into an autoclave at room temperature, the gas phase was replaced with nitrogen gas, and the pressure was reduced to -0.98 MPa 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, the bubbling was stopped, and 440.0 g of ethylene oxide and 160.0 g of butylene oxide were injected over 2 hours, followed by aging for 3 hours. 150.0 g of the intermediate thus obtained was charged into an autoclave at room temperature, and the gas phase was replaced with nitrogen gas to set the gauge pressure to 0.20 MPa. 497.6 g of ethylene oxide and 181.0 g of butylene oxide were injected over 2 hours while stirring, and aged for 3 hours. After lowering the temperature to 60°C, the pressure was released, and 1.16 g of 85% phosphoric acid was added. Nitrogen gas was bubbled at 20 mL / min while the pressure was reduced to -0.98 MPa, and stirring was performed at 125°C for 3 hours. This gave the polymer of Example 1.

[0041] Example 2 After 150.0 g of glycerin and 8.40 g of 50% KOH aqueous solution were charged into an autoclave at room temperature, the gas phase was replaced with nitrogen gas, and the pressure was reduced to -0.98 MPa 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, the bubbling was stopped, and 402.5 g of ethylene oxide and 188.2 g of butylene oxide were injected over 2 hours, followed by aging for 3 hours. 150.0 g of the intermediate thus obtained was charged into an autoclave at room temperature, and the gas phase was replaced with nitrogen gas to set the gauge pressure to 0.20 MPa. 345.3 g of ethylene oxide and 161.5 g of butylene oxide were injected over 2 hours while stirring, and then aged for 3 hours. After lowering the temperature to 60°C, the pressure was released, and 1.74 g of 85% phosphoric acid was added. Nitrogen gas was bubbled at 20 mL / min while the pressure was reduced to -0.98 MPa, and stirring was performed at 125°C for 3 hours. This resulted in the polymer of Example 2.

[0042] Example 3 After 150.0 g of glycerin and 8.40 g of 50% KOH aqueous solution were charged into an autoclave at room temperature, the gas phase was replaced with nitrogen gas, and the pressure was reduced to -0.98 MPa 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, the bubbling was stopped, and 402.5 g of ethylene oxide and 205.9 g of butylene oxide were injected over 2 hours, followed by aging for 3 hours. 150.0 g of the intermediate thus obtained was charged into an autoclave at room temperature, and the gas phase was replaced with nitrogen gas to set the gauge pressure to 0.20 MPa. 325.2 g of ethylene oxide and 166.3 g of butylene oxide were injected over 2 hours while stirring, and then aged for 3 hours. After lowering the temperature to 60°C, the pressure was released, and 1.70 g of 85% phosphoric acid was added. Nitrogen gas was bubbled at 20 mL / min while the gauge pressure was reduced to -0.98 MPa, and stirring was performed at 125°C for 3 hours. This resulted in the polymer of Example 3.

[0043] Example 4 After 150.0 g of glycerin and 8.40 g of 50% KOH aqueous solution were charged into an autoclave at room temperature, the gas phase was replaced with nitrogen gas, and the pressure was reduced to -0.98 MPa 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, the bubbling was stopped, and 502.3 g of ethylene oxide and 121.2 g of butylene oxide were injected over 2 hours, followed by aging for 3 hours. 150.0 g of the intermediate thus obtained was charged into an autoclave at room temperature, and the gas phase was replaced with nitrogen gas to set the gauge pressure to 0.20 MPa. 457.9 g of ethylene oxide and 110.4 g of butylene oxide were injected over 2 hours while stirring, and aged for 3 hours. Then, 68.0 g of butylene oxide was further injected over 1 hour, and aged for 3 hours. After lowering the temperature to 60°C, the pressure was released, and 1.16 g of 85% phosphoric acid was added. Nitrogen gas was bubbled at 20 mL / min while the gauge pressure was reduced to -0.98 MPa, and the mixture was stirred at 125°C for 3 hours. This gave a polymer of Example 4.

[0044] Example 5 After 150.0 g of glycerin and 8.40 g of 50% KOH aqueous solution were charged into an autoclave at room temperature, the gas phase was replaced with nitrogen gas, and the pressure was reduced to -0.98 MPa 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, the bubbling was stopped, and 402.5 g of ethylene oxide and 188.2 g of butylene oxide were injected over 2 hours, followed by aging for 3 hours. 150.0 g of the polymer thus obtained was charged into an autoclave at room temperature, and the gas phase was replaced with nitrogen gas to adjust the gauge pressure to 0.20 MPa. 345.3 g of ethylene oxide and 161.5 g of butylene oxide were injected into the autoclave over a period of 2 hours while stirring, and the mixture was then aged for 3 hours. Then, 150.0 g of the polymer obtained by the above process was charged into an autoclave at room temperature, and the gas phase was replaced with nitrogen gas to set the gauge pressure to 0.20 MPa. 62.1 g of ethylene oxide and 38.3 g of butylene oxide were injected over 2 hours while stirring, and then aged for 3 hours. After lowering the temperature to 60°C, the pressure was released, and 0.58 g of 50% lactic acid was added. While bubbling nitrogen gas at 20 mL / min, the pressure was reduced to -0.98 MPa, and stirring was performed at 125°C for 3 hours. This resulted in the polymer of Example 5.

[0045] Example 6 150.0g of ethylene glycol and 8.40g of 50% KOH aqueous solution were charged into the autoclave at room temperature, and the gas phase was replaced with nitrogen gas. The pressure was reduced to -0.98MPa 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, the bubbling was stopped, and 404.6g of ethylene oxide and 174.3g of butylene oxide were injected over 2 hours, followed by aging for 3 hours. 150.0 g of the polymer thus obtained was charged into an autoclave at room temperature, and the gas phase was replaced with nitrogen gas to set the gauge pressure to 0.20 MPa. 363.8 g of ethylene oxide and 224.7 g of butylene oxide were injected over 2 hours while stirring, and then aged for 3 hours. After lowering the temperature to 60°C, the pressure was released, and 2.87 g of 50% lactic acid was added. Nitrogen gas was bubbled at 20 mL / min to reduce the pressure until the gauge pressure was -0.98 MPa, and the mixture was stirred at 125°C for 3 hours. This gave the polymer of Example 6.

[0046] Comparative Example 1 After 150.0 g of trimethylolpropane was charged into an autoclave at room temperature, the gas phase was replaced with nitrogen gas, and the temperature was raised to 80°C to dissolve. Then, 8.40 g of 50% KOH aqueous solution was charged, and the gauge pressure was reduced to -0.98 MPa while bubbling nitrogen gas at 20 mL / min. Then, the temperature was raised to 125°C and stirred for 5 hours. After the pressure was raised to 0.20 MPa, bubbling was stopped, and 147.7 g of ethylene oxide and 177.1 g of propylene oxide were injected over 2 hours, and then aged for 3 hours. 150.0 g of the intermediate thus obtained was charged into an autoclave at room temperature, and the gas phase was replaced with nitrogen gas to set the gauge pressure to 0.20 MPa. 171.2 g of ethylene oxide and 205.2 g of propylene oxide were injected over 2 hours while stirring, and then aging was performed for 3 hours. After lowering the temperature to 60°C, the pressure was released, and 2.57 g of 85% phosphoric acid was added. Nitrogen gas was bubbled at 20 mL / min to reduce the pressure until the gauge pressure was -0.98 MPa, and stirring was performed at 125°C for 3 hours. This resulted in the polymer of Comparative Example 1.

[0047] Comparative Example 2 150.0 g of trimethylolpropane was charged into an autoclave at room temperature, and the gas phase was replaced with nitrogen gas and heated to 80°C to dissolve. Then, 8.40 g of 50% KOH aqueous solution was charged, and the gauge pressure was reduced to -0.98 MPa while bubbling nitrogen gas at 20 mL / min. Then, the temperature was raised to 125°C and stirred for 5 hours. After the pressure was raised to 0.20 MPa, bubbling was stopped, and 658.1 g of ethylene oxide was injected over 2 hours, and then aging was performed for 3 hours. 500.0 g of the intermediate thus obtained was charged into an autoclave at room temperature, and the gas phase was replaced with nitrogen gas to set the gauge pressure to 0.20 MPa. 175.4 g of butylene oxide was injected over 2 hours while stirring, and then aged for 3 hours. After lowering the temperature to 60°C, the pressure was released, and 5.19 g of 85% phosphoric acid was added. Nitrogen gas was bubbled at 20 mL / min while the pressure was reduced to -0.98 MPa, and stirring was performed at 125°C for 3 hours. This resulted in the polymer of Comparative Example 2.

[0048] Comparative Example 3 150.0 g of glycerin and 8.40 g of 50% KOH aqueous solution were charged into an autoclave at room temperature, and the gas phase was replaced with nitrogen gas. The pressure was reduced to -0.98 MPa 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, the bubbling was stopped and 502.3 g of ethylene oxide was injected over 2 hours, followed by aging for 3 hours. 150.0 g of the intermediate thus obtained was charged into an autoclave at room temperature, and the gas phase was replaced with nitrogen gas to set the gauge pressure to 0.20 MPa. 369.0 g of ethylene oxide was injected over 2 hours while stirring, and aged for 3 hours. Then, 226.3 g of butylene oxide was further injected over 2 hours, and aged for 3 hours. After lowering the temperature to 60°C, the pressure was released, and 1.97 g of 85% phosphoric acid was added. Nitrogen gas was bubbled at 20 mL / min to reduce the pressure until the gauge pressure was -0.98 MPa, and the mixture was stirred at 125°C for 3 hours. This gave a polymer of Comparative Example 3.

[0049] [Table 1]

[0050] <Evaluation 1> The polymers produced in the Examples and Comparative Examples were evaluated for osmotic pressure, phase separation, viscosity, cloud point, and water transport ability by the following methods. The results are shown in Table 2.

[0051] (Osmolarity evaluation) Aqueous solutions containing 40 mass%, 50 mass%, or 60 mass% of each polymer 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

[0052] (Phase separation evaluation) An aqueous solution containing 50% by mass of each polymer was prepared and sealed in a screw vial. This was left in a 97°C oven overnight to fully equilibrate, and then three samples of approximately 1 g of the upper layer (water-rich phase) and approximately 0.2 g of the lower layer (polymer-rich phase) were taken and placed in an aluminum cup. The aluminum cup was left in a 97°C oven for 2 hours to dry, and the polymer concentrations of the upper and lower layers were calculated from the weight difference before and after drying.

[0053] (Viscosity evaluation) The viscosity at 25°C was measured using a B-type viscometer (TVB-10, manufactured by Toki Sangyo Co., Ltd.).

[0054] (Cloud Point Rating) An aqueous solution containing 50% by mass of each polymer 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.

[0055] (Water transport capacity evaluation) The water transport capacity was calculated according to the following formula. Water carrying capacity=<Water passing weight> / <Polymer weight>×100 =(<Weight after water passage>-<Initial weight>) / <Polymer weight>×100 =(<Weight after passing water>-<Polymer concentration after passing water> / <Initial polymer concentration>×<Weight after passing water>) / (<Weight after passing water>×<Polymer concentration after passing water>)×100 =(<Initial polymer concentration>-<Polymer concentration after water passage>) / (<Initial polymer concentration>×<Polymer concentration after water passage>)×100 In the formula, "initial polymer concentration" refers to the concentration of the lower layer (polymer-rich phase) in the phase separation evaluation, and "polymer concentration after water passing" refers to the polymer concentration when the osmotic pressure becomes 48 bar, and was calculated by back-calculating from the correlation equation of osmotic pressure at polymer concentrations of 40 to 60 mass% measured in the osmotic pressure evaluation.

[0056] [Table 2]

[0057] <Evaluation 2> (Evaluation of membrane performance) The evaluation of the membrane flux in forward osmosis mode was carried out for the draw solution containing the polymer of Example 2 according to the following test procedure. The membrane flux was determined by a Membrane Testing Fixture (Model II) designed and manufactured by Trevi Systems, utilizing a Toyobo cellulose triacetate (CTA) hollow fiber FO module as the semipermeable membrane. Deionized water, 4.5% NaCl aqueous solution, and 7.5% NaCl aqueous solution were provided as the control solution, and a 75% aqueous solution of the driving compound (polymer of Example 2) was used as the draw solution. The liquid temperature of the draw solution was adjusted to five temperatures, namely 25°C, 33°C, 37°C, 41°C, and 45°C, and tests were carried out at each temperature. The volumetric flow rates of the control and draw solutions were selected to be close to the flow rates in commercial 5-inch and 10-inch hollow fiber membrane elements. The draw solution was directed toward the active layer of the hollow fiber (PRO mode). Both the control and draw solutions were circulated in a closed loop for at least 4 hours. Water flux and back solute diffusion were determined over a 4 hour run time and the results are summarized in Table 3.

[0058] [Table 3]

[0059] As is clear from Table 3, when the polymer of Example 2 was used as the driving compound, the movement of water from the target solution to the driving solution was observed under all conditions, confirming that high water permeability can be achieved.

Claims

1. A draw solute for a forward osmosis membrane process, comprising a random copolymer obtained by randomly adding a monomer including ethylene oxide and butylene oxide to a compound having two or three hydroxyl groups, the molar ratio of the ethylene oxide to the butylene oxide is 1:1 to 10:1; A draw solute for a forward osmosis membrane process, wherein the content of monomers other than the ethylene oxide and the butylene oxide in the monomers is 0 to 20 mol %.

2. 2. The draw solute according to claim 1, wherein the random copolymer has a number average molecular weight of 500 to 10,000.

3. The draw solute according to claim 1 or 2, wherein the cloud point of a 50% by mass draw solution prepared by dissolving the draw solute in water is 40 to 75° C.

4. A draw solute according to any one of claims 1 to 3, wherein the content of components in the random copolymer having a number average molecular weight of 500 or less is less than 10 mass%.

5. A draw solute according to any one of claims 1 to 4, wherein when the draw solute is dissolved in water to prepare a 5% by mass aqueous solution, the pH of the aqueous solution is 2 to 6.

6. A draw solution comprising the draw solute of any one of claims 1 to 5.

7. A water treatment device using the draw solution according to claim 6.

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