Osmotic pressure assisted reverse osmosis membrane device, device for concentrating aqueous solution containing organic solvent, and method for concentrating aqueous solution

Abstract

To provide an osmotic pressure assisted reverse osmosis membrane device that can stably concentrate water to be treated that contains an organic solvent to a high concentration.SOLUTION: There is provided an osmotic pressure assisted reverse osmosis membrane device used for concentrating water to be treated that contains an organic solvent, the osmotic pressure assisted reverse osmosis membrane device including: an upstream osmotic pressure-assisted reverse osmosis membrane module located on a side where the water to be treated is supplied, and a downstream osmotic pressure-assisted reverse osmosis membrane module located on a side where concentrated liquid is discharged, in which pressure adjusting means is provided between the upstream osmotic pressure-assisted reverse osmosis membrane module and the downstream osmotic pressure-assisted reverse osmosis membrane module, and the pressure adjusting means allows the downstream osmotic pressure-assisted reverse osmosis membrane module to perform concentration under a lower pressure condition than the upstream osmotic pressure-assisted reverse osmosis membrane module.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present disclosure relates to an osmotic pressure-assisted reverse osmosis membrane device, an apparatus for concentrating an aqueous solution containing an organic solvent, and a method for concentrating an aqueous solution. [Background technology]

[0002] Conventionally, attempts have been made to concentrate wastewater containing organic solvents and recover valuable materials, or to reduce industrial waste disposal costs.

[0003] For example, distillation, pervaporation, and the like are used to concentrate aqueous solutions containing organic solvents. However, these concentration methods have the problem of high energy consumption due to the phase change involved. In particular, when concentrating an aqueous solution containing a high-boiling organic solvent, evaporation of water precedes evaporation. Therefore, the energy consumption required for concentration is particularly high.

[0004] Meanwhile, membrane filtration, which uses reverse osmosis (RO) membranes, is also known as a method for concentrating aqueous solutions. Membrane filtration allows for energy-saving concentration because there is no phase change in the aqueous solution. However, reverse osmosis (RO) membranes, for example, can only concentrate aqueous solutions to an osmotic pressure below the applied pressure, so there is a limit to how highly concentrated they can be.

[0005] Compared to the conventional RO method, the Osmotically Assisted Reverse Osmosis Method (OARO method) is known as a reverse osmosis membrane method that can concentrate aqueous solutions at lower pressures (see Patent Document 1, etc.). The OARO method is a method in which, when concentrating an aqueous solution with high osmotic pressure using an RO membrane, an aqueous solution with osmotic pressure is also passed through the permeate side, thereby reducing the osmotic pressure difference with the concentrated side (high-pressure side), and enabling concentration to a concentration with a higher osmotic pressure than the applied pressure. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Special Publication No. 2019-504763 Summary of the Invention [Problem to be solved by the invention]

[0007] As mentioned above, the OARO method can concentrate aqueous solutions to higher concentrations than the conventional RO method. Therefore, the present inventors investigated the use of the OARO method to highly concentrate aqueous solutions containing organic solvents.

[0008] As a result of the investigation, it was found that the OARO method could concentrate organic solvents to higher concentrations than the conventional RO method, i.e., to concentrations with a higher osmotic pressure than the applied pressure. However, when high concentration was carried out continuously for several days or more, the concentration of the resulting concentrated solution decreased, making stable concentration difficult. This presented a new problem.

[0009] A primary object of the present disclosure is to provide an osmotic pressure-assisted reverse osmosis membrane device capable of stably concentrating water containing an organic solvent to a high concentration. Another object of the present disclosure is to provide an apparatus for concentrating an aqueous solution containing an organic solvent and a method for concentrating an aqueous solution using the osmotic pressure-assisted reverse osmosis membrane device. [Means for solving the problem]

[0010] The inventors of the present disclosure conducted extensive research to solve the above-mentioned problems, and as a result, they found that an osmotic pressure-assisted reverse osmosis membrane device used for concentrating water to be treated containing an organic solvent can be provided with an upstream osmotic pressure-assisted reverse osmosis membrane module located on the side to which the water to be treated is supplied and a downstream osmotic pressure-assisted reverse osmosis membrane module located on the side to which the concentrated liquid is discharged, and further provided with a pressure adjustment means between the upstream osmotic pressure-assisted reverse osmosis membrane module and the downstream osmotic pressure-assisted reverse osmosis membrane module, and designed by the pressure adjustment means to perform concentration under lower pressure conditions for the downstream osmotic pressure-assisted reverse osmosis membrane module than for the upstream osmotic pressure-assisted reverse osmosis membrane module, thereby enabling the water to be treated containing an organic solvent to be stably concentrated at a high concentration.

[0011] The present disclosure has been completed based on these findings and further investigations. That is, the present disclosure provides the inventions of the following aspects. Item 1. An osmotic pressure-assisted reverse osmosis membrane device used to concentrate water to be treated that contains organic solvents, The osmotic pressure-assisted reverse osmosis membrane device includes an upstream osmotic pressure-assisted reverse osmosis membrane module located on the side where the water to be treated is supplied, and a downstream osmotic pressure-assisted reverse osmosis membrane module located on the side where the concentrated liquid is discharged, a pressure adjusting means is provided between the upstream osmotic pressure-assisted reverse osmosis membrane module and the downstream osmotic pressure-assisted reverse osmosis membrane module; The pressure adjustment means allows the downstream osmotic pressure-assisted reverse osmosis membrane module to concentrate under lower pressure conditions than the upstream osmotic pressure-assisted reverse osmosis membrane module. Item 2. The osmotic pressure-assisted reverse osmosis membrane device according to Item 1, wherein at least one of the upstream osmotic pressure-assisted reverse osmosis membrane module and the downstream osmotic pressure-assisted reverse osmosis membrane module includes a plurality of osmotic pressure-assisted reverse osmosis membrane modules. Item 3. The osmotically-assisted reverse osmosis membrane device according to Item 1 or 2, wherein the upstream osmotically-assisted reverse osmosis membrane module performs concentration under a pressure condition higher than 3 MPa. Item 4. The osmotically-assisted reverse osmosis membrane device according to Item 1 or 2, wherein the downstream osmotically-assisted reverse osmosis membrane module performs concentration under a pressure condition lower than 7 MPa. Item 5. The organic solvent concentration of the water to be treated supplied to the upstream osmotic pressure-assisted reverse osmosis membrane module is 0.1% by mass or more and less than 50% by mass; 5. The osmotic pressure-assisted reverse osmosis membrane device according to any one of items 1 to 4, wherein the concentration of the water to be treated supplied to the downstream reverse osmosis membrane module is 40% by mass or more and 50% by mass or less. Item 6. The osmotically-assisted reverse osmosis membrane device according to any one of Items 1 to 5, wherein the boiling point of the organic solvent at 1 atmospheric pressure is 105°C or higher. Item 7. The osmotic pressure-assisted reverse osmosis membrane apparatus according to any one of Items 1 to 6, which is used for continuous operation for 5 days or more. Item 8. The osmotic pressure-assisted reverse osmosis membrane device according to any one of Items 1 to 7, wherein the organic solvent concentration of the concentrated liquid discharged from the osmotic pressure-assisted reverse osmosis membrane device is 40% by mass or more. Item 9. An apparatus for concentrating an aqueous solution containing an organic solvent, comprising the osmotic pressure-assisted reverse osmosis membrane device according to any one of items 1 to 8. Item 10. The concentrating apparatus according to Item 9, further comprising a reverse osmosis membrane device different from the osmotic pressure-assisted reverse osmosis membrane device. Item 11. A method for concentrating an aqueous solution, comprising concentrating an aqueous solution containing an organic solvent using the osmotic pressure-assisted reverse osmosis membrane device according to any one of Items 1 to 10. Item 12. A method for concentrating water to be treated that contains an organic solvent, comprising: a first step of concentrating the water to be treated using a first osmotic pressure-assisted reverse osmosis membrane module; a second step of concentrating the water to be treated concentrated in the first step using a second osmotic pressure-assisted reverse osmosis membrane module under lower pressure conditions than in the first step; A method for concentrating an aqueous solution, comprising: Item 13. The organic solvent concentration of the water to be treated supplied to the osmotic pressure-assisted reverse osmosis membrane module is 40% by mass or more and less than 50% by mass; The method for concentrating an aqueous solution comprises concentrating the water to be treated using the osmotic pressure-assisted reverse osmosis membrane module under a pressure condition of 3.5 to 5 MPa. [Effects of the Invention]

[0012] The present disclosure provides an osmotic pressure-assisted reverse osmosis membrane device capable of stably concentrating water containing an organic solvent to a high concentration. The present disclosure also provides an apparatus for concentrating an aqueous solution containing an organic solvent and a method for concentrating an aqueous solution, both of which utilize the osmotic pressure-assisted reverse osmosis membrane device. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a schematic diagram illustrating an example of the configuration of an osmotic pressure-assisted reverse osmosis membrane device according to the present disclosure. FIG. [Figure 2]1 is a graph showing the relationship between the concentration (mass %) of the concentrate and the operation time (days) when NMP (N-methylpyrrolidone) is concentrated using the osmotic pressure-assisted reverse osmosis membrane device of Example 1. [Figure 3] 1 is a graph showing the relationship between the concentration (mass %) of the concentrate and the operation time (days) when NMP is concentrated using the osmotic pressure-assisted reverse osmosis membrane device of Comparative Example 1. [Figure 4] 1 is a graph showing the relationship between the concentration (mass %) of the concentrate and the operation time (days) when NMP is concentrated using the osmotic pressure-assisted reverse osmosis membrane device of Comparative Example 2. [Figure 5] FIG. 1 is a schematic diagram of an apparatus used to verify the performance of a reverse osmosis membrane (BC membrane (cellulose acetate hollow fiber membrane)) in a highly concentrated aqueous organic solvent solution in Test Example 2, simulating the state of the fifth membrane module in FIG. 1. [Figure 6] 6 is a graph verifying the performance of a reverse osmosis membrane (BC membrane (cellulose acetate hollow fiber membrane)) in a high-concentration aqueous organic solvent solution in Test Example 2. The graph on the left side of FIG. 6 is a graph showing the relationship between the concentrated NMP concentration (mass%) and the flow rate (mL / min), and the graph on the right side is a graph showing the relationship between the concentrated NMP concentration (mass%) and the applied pressure (MPa). [Figure 7] FIG. 1 is a schematic diagram of a membrane module used in Test Example 3 to evaluate the performance of a reverse osmosis membrane (BC membrane (cellulose acetate hollow fiber membrane)) in a highly concentrated aqueous organic solvent solution. [Figure 8] 1 is a graph showing the relationship between NMP rejection (%) and NMP concentration (mass %) in Test Example 3, which verified the performance of a reverse osmosis membrane (BC membrane (cellulose acetate hollow fiber membrane)) in a highly concentrated aqueous organic solvent solution. [Figure 9] 1 is a graph showing the relationship between the concentration (mass%) of the concentrate and the operation time (days) when DMAc (N,N-dimethylacetamide) is concentrated using the osmotic pressure-assisted reverse osmosis membrane device of Example 2. [Figure 10] 1 is a graph showing the relationship between the concentration (mass %) of the concentrate and the operation time (days) when DMAc is concentrated using the osmotic pressure-assisted reverse osmosis membrane device of Comparative Example 3. [Figure 11]In one example of the configuration of the osmotic pressure-assisted reverse osmosis membrane device of the present disclosure, the dilute liquid is mixed with the feed liquid after the concentration thereof is adjusted using an RO membrane. [Figure 12] This is an example of the configuration of an osmotic pressure-assisted reverse osmosis membrane device of the present disclosure, in which an RO membrane that adjusts the concentration after mixing the feed liquid with the diluent is installed. DETAILED DESCRIPTION OF THE INVENTION

[0014] The osmotic pressure-assisted reverse osmosis membrane device of the present disclosure is an osmotic pressure-assisted reverse osmosis membrane device used to concentrate water to be treated containing an organic solvent (sometimes referred to as an aqueous solution containing an organic solvent). The osmotic pressure-assisted reverse osmosis membrane device according to the first invention of the present disclosure includes an upstream osmotic pressure-assisted reverse osmosis membrane module located on the side where the water to be treated is supplied, and a downstream osmotic pressure-assisted reverse osmosis membrane module located on the side where the concentrated liquid is discharged. The osmotic pressure-assisted reverse osmosis membrane of the present disclosure includes a pressure adjustment means between the upstream osmotic pressure-assisted reverse osmosis membrane module and the downstream osmotic pressure-assisted reverse osmosis membrane module. The pressure adjustment means allows the downstream osmotic pressure-assisted reverse osmosis membrane module to concentrate the water under lower pressure conditions than the upstream osmotic pressure-assisted reverse osmosis membrane module. The osmotic pressure-assisted reverse osmosis membrane device according to the first invention of the present disclosure, having such a configuration, can stably concentrate water to be treated containing an organic solvent to a high concentration.

[0015] The present disclosure also provides a method for concentrating water to be treated containing an organic solvent using an osmotic pressure-assisted reverse osmosis membrane module, in which the organic solvent concentration in the water to be treated supplied to the osmotic pressure-assisted reverse osmosis membrane module is 40% by mass or more but less than 50% by mass, and the water to be treated is concentrated by the osmotic pressure-assisted reverse osmosis membrane module under a pressure condition of 3.5 to 5 MPa. The aqueous solution concentration method according to the second invention, as described below, differs from the first invention in that it does not require separate osmotic pressure-assisted reverse osmosis membrane modules for the upstream and downstream stages, and is characterized by controlling the concentration of the water to be treated supplied to the osmotic pressure-assisted reverse osmosis membrane module and the pressure conditions during concentration by the osmotic pressure-assisted reverse osmosis membrane module. The aqueous solution concentration method according to the second invention also enables water to be treated containing an organic solvent to be stably concentrated to a high concentration.

[0016] Hereinafter, the osmotic pressure-assisted reverse osmosis membrane device of the present disclosure, an apparatus for concentrating an aqueous solution containing an organic solvent using the osmotic pressure-assisted reverse osmosis membrane device, and a method for concentrating an aqueous solution will be described in detail with reference to the drawings.

[0017] In this specification, numerical values ​​connected with "~" mean a numerical range that includes the numerical values ​​before and after "~" as the lower and upper limits. When multiple lower limits and multiple upper limits are listed separately, any lower limit and upper limit can be selected and connected with "~".

[0018] FIG. 1 is a schematic diagram of an osmotic pressure-assisted reverse osmosis membrane device according to a first aspect of the present invention. The osmotic pressure-assisted reverse osmosis membrane device includes multiple osmotic pressure-assisted reverse osmosis membrane modules. In FIG. 1, a feed liquid (water to be treated containing an organic solvent) is sent to the osmotic pressure-assisted reverse osmosis membrane modules using a liquid feed pump 10. The osmotic pressure-assisted reverse osmosis membrane device is composed of multiple osmotic pressure-assisted reverse osmosis membrane modules, and the feed liquid is pressurized and sent to one side (the high-pressure side, the concentrated water chamber) of the upstream osmotic pressure-assisted reverse osmosis membrane module.

[0019] The feed liquid is concentrated in the osmotic pressure-assisted reverse osmosis membrane modules, and the feed liquid that has passed through the final osmotic pressure-assisted reverse osmosis membrane module is discharged as a concentrate from the high-pressure side outlet of the osmotic pressure-assisted reverse osmosis membrane module. As shown in Figure 1, the high-pressure sides of the osmotic pressure-assisted reverse osmosis membrane modules included in the osmotic pressure-assisted reverse osmosis membrane device are connected by piping. The high-pressure sides of the osmotic pressure-assisted reverse osmosis membrane modules may be connected by piping in series or in parallel.

[0020] In addition, a portion of the concentrated liquid can be supplied as a reflux liquid to the opposite side of the osmotic pressure-assisted reverse osmosis membrane (hereinafter referred to as the low-pressure side) at a pressure lower than that of the high-pressure side via a branch pipe. The liquid flowing through the low-pressure side (permeate chamber) of the osmotic pressure-assisted reverse osmosis membrane device is diluted with permeate and discharged as a diluted liquid. As shown in FIG. 1, the low-pressure sides of each osmotic pressure-assisted reverse osmosis membrane module included in the osmotic pressure-assisted reverse osmosis membrane device are also connected by pipes. The low-pressure sides of each osmotic pressure-assisted reverse osmosis membrane module may also be connected by pipes in series or in parallel.

[0021] Although not shown, at least a portion of the diluted solution discharged from the osmotically assisted reverse osmosis membrane module can be mixed with the feed liquid and resupplied to the upstream side of the osmotically assisted reverse osmosis membrane module for concentration. Also, as shown in Figure 1, at least a portion of the concentrated solution discharged from the osmotically assisted reverse osmosis membrane module can be supplied as reflux to the low-pressure side of the osmotically assisted reverse osmosis membrane module. The pressure value of pressure gauge 23 and the flow rate ratio of the reflux solution to the concentrated solution can be adjusted by adjusting flow control valve 31 and flow control valve 32 in Figure 1.

[0022] The disclosed osmotic pressure-assisted reverse osmosis membrane device can also be used in combination with, for example, a reverse osmosis membrane device (RO membrane) other than the osmotic pressure-assisted reverse osmosis membrane device to form a concentration device for an aqueous solution containing an organic solvent. For example, if the diluted solution discharged from the osmotic pressure-assisted reverse osmosis membrane module is mixed with the feed solution and the resulting mixture is supplied to the upstream side of the osmotic pressure-assisted reverse osmosis membrane module for concentration, the concentration of the diluted solution can be adjusted using a separately installed reverse osmosis membrane device (RO membrane) before mixing the diluted solution with the feed solution (see FIG. 11). Alternatively, the concentration of the mixture can be adjusted using a separately installed reverse osmosis membrane device (RO membrane) after mixing the diluted solution with the feed solution (see FIG. 15).

[0023] In the osmotic pressure-assisted reverse osmosis membrane device according to the first aspect of the present disclosure, the pressure adjustment means can be placed at any position in the high-pressure piping between the connected osmotic pressure-assisted reverse osmosis membrane modules. In FIG. 1, a pressure adjustment valve 11 (back pressure valve) is placed between the third and fourth osmotic pressure-assisted reverse osmosis membrane modules, counting from the feed liquid inlet side of the osmotic pressure-assisted reverse osmosis membrane module. A pressure adjustment valve 12 (back pressure valve) is also placed at the high-pressure outlet of the fifth (final) reverse osmosis membrane module. This allows the first to third (front stage) osmotic pressure-assisted reverse osmosis membrane modules and the fourth to fifth (rear stage) osmotic pressure-assisted reverse osmosis membrane modules in the osmotic pressure-assisted reverse osmosis membrane device to be controlled at different operating pressures. In the osmotic pressure-assisted reverse osmosis membrane device of FIG. 1, each osmotic pressure-assisted reverse osmosis membrane module is divided into an upstream and a downstream section, separated by pressure adjustment valve 11 (back pressure valve) as the pressure adjustment means.

[0024] In Figure 1, five osmotic pressure-assisted reverse osmosis membrane modules are connected in series within the osmotic pressure-assisted reverse osmosis membrane device, but there is no limit to the number of osmotic pressure-assisted reverse osmosis membrane modules and it can be adjusted, for example, in the range of about 2 to 50. There is also no particular limit to the number of upstream osmotic pressure-assisted reverse osmosis membrane modules and the number of downstream osmotic pressure-assisted reverse osmosis membrane modules and they can be adjusted, for example, in the range of about 1 to 25. It is preferable to provide multiple upstream osmotic pressure-assisted reverse osmosis membrane modules or upstream / downstream osmotic pressure-assisted reverse osmosis membrane modules in order to achieve a high concentration of the concentrate.

[0025] In order to more effectively achieve the effects of the present invention, the flow rate of the feed liquid when it is fed to the osmotic pressure-assisted reverse osmosis membrane module is set to 1 / m2 / m2. 2 The flow rate is, for example, 5 mL / min or more, preferably 10 mL / min or more, more preferably 15 mL / min or more, and is, for example, 100 mL / min or less, preferably 80 mL / min or less, more preferably 70 mL / min or less, and preferred ranges include 5 to 100 mL / min, 5 to 80 mL / min, 5 to 70 mL / min, 10 to 100 mL / min, 10 to 80 mL / min, 10 to 70 mL / min, 15 to 100 mL / min, 15 to 80 mL / min, and 15 to 70 mL / min.

[0026] From the viewpoint of more suitably exerting the effects of the present invention, the concentration of organic solvent in the feed liquid supplied to the osmotic pressure-assisted reverse osmosis membrane device of the present disclosure (i.e., the water to be treated supplied to the upstream osmotic pressure-assisted reverse osmosis membrane module) is preferably less than 50% by mass, more preferably 40% by mass or less, even more preferably 30% by mass or less, and may be 20% by mass or less, 15% by mass or less, 10% by mass or less, or 5% by mass or less, and is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, even more preferably 1% by mass or more, with a preferred range being 0. 1 mass% or more and less than 50 mass%, 0.1-40 mass% or less, 0.1-30 mass% or less, 0.1-20 mass% or less, 0.1-15 mass% or less, 0.1-10 mass% or less, 0.1-5 mass% or less, 0.5 mass% or more and less than 50 mass%, 0.5-40 mass% or less, 0.5-30 mass% or less , 0.5-20 mass% or less, 0.5-15 mass% or less, 0.5-10 mass% or less, 0.5-5 mass% or less, 1 mass% or more and less than 50 mass%, 1-40 mass% or less, 1-30 mass%, 1-20 mass% or less, 1-15 mass% or less, 1-10 mass% or less, 1-5 mass% or less.

[0027] Furthermore, in the osmotic pressure-assisted reverse osmosis membrane device of the present disclosure, the pressure conditions when the upstream osmotic pressure-assisted reverse osmosis membrane module concentrates may be higher than the pressure conditions of the downstream osmotic pressure-assisted reverse osmosis membrane module. From the viewpoint of more suitably exerting the effects of the present disclosure, the pressure is preferably 3 MPa or higher, more preferably 3.5 MPa or higher, even more preferably 4 MPa or higher, and is preferably 9 MPa or lower, more preferably 8 MPa or lower, even more preferably 7 MPa or lower. Preferred ranges include 3 to 9 MPa, 3 to 8 MPa, 3 to 7 MPa, 3.5 to 9 MPa, 3.5 to 8 MPa, 3.5 to 7 MPa, 4 to 9 MPa, 4 to 8 MPa, and 4 to 7 MPa.

[0028] From the viewpoint of more suitably exerting the effects of the present invention, the concentration of the organic solvent in the water to be treated supplied to the downstream osmotic pressure-assisted reverse osmosis membrane module is preferably 40% by mass or more, and a preferred range is 40 to 50% by mass.

[0029] Furthermore, the pressure conditions when the subsequent osmotic pressure-assisted reverse osmosis membrane module concentrates may be lower than those of the preceding osmotic pressure-assisted reverse osmosis membrane module, but from the viewpoint of more suitably exerting the effects of the present disclosure, the pressure is preferably 7 MPa or less, more preferably 6 MPa or less, and even more preferably 5 MPa or less, and is also preferably 2 MPa or more, more preferably 3 MPa or more, and even more preferably 3.5 MPa or more, and preferred ranges include 2 to 7 MPa, 2 to 6 MPa, 2 to 5 MPa, 3 to 7 MPa, 3 to 6 MPa, 3 to 5 MPa, 3.5 to 7 MPa, 3.5 to 6 MPa, and 3.5 to 5 MPa.

[0030] As described above, in the osmotic pressure-assisted reverse osmosis membrane device according to the first aspect of the present disclosure, by using a pressure adjustment means, concentration is performed under lower pressure conditions in the downstream osmotic pressure-assisted reverse osmosis membrane module compared to the upstream osmotic pressure-assisted reverse osmosis membrane module. That is, in the downstream osmotic pressure-assisted reverse osmosis membrane module, the water to be treated, which has been concentrated under high pressure conditions by the upstream osmotic pressure-assisted reverse osmosis membrane module, is concentrated to a high concentration under relatively low pressure conditions. As a result, in the present disclosure, water to be treated containing an organic solvent can be stably concentrated to a high concentration.

[0031] This mechanism can be explained as follows. Specifically, when the organic solvent concentrated by the osmosis-assisted reverse osmosis membrane becomes highly concentrated, the polymer that constitutes the osmosis-assisted reverse osmosis membrane softens. This likely leads to deformation of the osmosis-assisted reverse osmosis membrane under high-pressure conditions, causing the lumen of the osmosis-assisted reverse osmosis membrane to collapse, making it difficult for the liquid to pass through. This likely results in a deterioration in the performance of the osmosis-assisted reverse osmosis membrane. In contrast, in the osmosis-assisted reverse osmosis membrane device of the present disclosure, in the upstream osmosis-assisted reverse osmosis membrane module to which low-concentration water to be treated is supplied, the reverse osmosis membrane is less likely to deform even when the water to be treated is concentrated under high-pressure conditions. Furthermore, in the downstream osmosis-assisted reverse osmosis membrane module that concentrates the highly concentrated water to be treated, the concentration is performed under lower pressure than in the upstream module, thereby suppressing deformation of the osmosis-assisted reverse osmosis membrane. As a result, in the osmotic pressure-assisted reverse osmosis membrane device of the present disclosure, deformation of all osmotic pressure-assisted reverse osmosis membranes in the osmotic pressure-assisted reverse osmosis membrane module is suppressed, and it is believed that the treated water containing organic solvents is concentrated to a high concentration and in a stable manner.

[0032] In the present disclosure, the organic solvent contained in the feed liquid (water to be treated that contains an organic solvent) is not particularly limited as long as it can be concentrated by an osmotic pressure-assisted reverse osmosis membrane device. The osmotic pressure-assisted reverse osmosis membrane device of the present disclosure is particularly suitable for concentrating, for example, an aqueous solution of an organic solvent that has a boiling point higher than that of water. The boiling point of the organic solvent contained in the water to be treated at 1 atmosphere is preferably 105°C or higher, more preferably 110°C or higher, and even more preferably 115°C or higher, and is preferably 300°C or lower, more preferably 250°C or lower, and even more preferably 230°C or lower. Preferred ranges include approximately 105 to 300°C, 105 to 250°C, 105 to 230°C, 110 to 300°C, 110 to 250°C, 110 to 230°C, 115 to 300°C, 115 to 250°C, and 115 to 230°C.

[0033] Specific examples of organic solvents contained in the water to be treated include water-soluble organic solvents such as ethanol, isopropanol, ethylene glycol, and glycerol; carbon-containing alcohols such as acetic acid and propionic acid; and acetonitrile, dioxane, tetrahydrofuran, and acetone. Other particularly suitable examples include high-boiling water-soluble organic solvents such as N-methylpyrrolidone (NMP), N,N-dimethylacetamide (DMAc), N,N-dimethylformamide (DMF), and dimethyl sulfoxide (DMSO). Other examples of organic solvents include water-soluble organic ionic liquids that are liquid at room temperature, such as choline glycolate; nonionic surfactants such as Pluronic®, a copolymer of ethylene oxide and propylene oxide; and water-soluble polymers such as polyethylene glycol. The organic solvent contained in the feed solution (water to be treated containing an organic solvent) may be one type or two or more types.

[0034] The osmotic pressure-assisted reverse osmosis membrane used in each osmotic pressure-assisted reverse osmosis membrane module is not particularly limited as long as it is an osmotic pressure-assisted reverse osmosis membrane that can be used to concentrate organic solvents. The osmotic pressure-assisted reverse osmosis membrane is preferably a hollow fiber membrane. The osmotic pressure-assisted reverse osmosis membrane is made of a polymer such as cellulose acetate or polyamide. An example of a commercially available osmotic pressure-assisted reverse osmosis membrane is the BC (Brine Concentration) membrane manufactured by Toyobo MC Co., Ltd. For example, the BC membrane is made of cellulose triacetate.

[0035] In the present disclosure, a pressure adjustment means is provided at least between a front-stage osmotic pressure-assisted reverse osmosis membrane module and a rear-stage osmotic pressure-assisted reverse osmosis membrane module. The pressure adjustment means allows the front-stage osmotic pressure-assisted reverse osmosis membrane module to perform concentration under higher pressure conditions than the rear-stage osmotic pressure-assisted reverse osmosis membrane module. A pressure adjustment means may also be provided downstream of the rear-stage osmotic pressure-assisted reverse osmosis membrane module. For example, in the configuration diagram of FIG. 1 , a pressure adjustment valve 11 (back pressure valve) is provided as pressure adjustment means between the front-stage osmotic pressure-assisted reverse osmosis membrane module and the rear-stage osmotic pressure-assisted reverse osmosis membrane module, thereby causing the front-stage osmotic pressure-assisted reverse osmosis membrane module to be under higher pressure conditions than the rear-stage osmotic pressure-assisted reverse osmosis membrane module (i.e., the pressure of the rear-stage osmotic pressure-assisted reverse osmosis membrane module is under lower pressure conditions than the front-stage osmotic pressure-assisted reverse osmosis membrane module). Furthermore, a pressure regulating valve 12 (back pressure valve) is provided as a pressure adjusting means after the downstream osmotic pressure-assisted reverse osmosis membrane module, thereby adjusting the pressure of the downstream osmotic pressure-assisted reverse osmosis membrane module.

[0036] In the present disclosure, the type of pressure adjustment means is not particularly limited as long as it can adjust the pressure so that the upstream osmotically-assisted reverse osmosis membrane module can concentrate at a higher pressure than the downstream osmotically-assisted reverse osmosis membrane module, and a known pressure adjustment valve such as a back pressure valve can be used. It is also preferable to use multiple pressure adjustment valves to adjust the pressure conditions of the upstream and downstream osmotically-assisted reverse osmosis membrane modules, as described above.

[0037] The concentration of the organic solvent in the concentrated liquid discharged from the osmotic pressure-assisted reverse osmosis membrane module is not particularly limited, and is, for example, 40% by mass or more, preferably 45% by mass or more, and more preferably 50% by mass or more, and is, for example, 70% by mass or less, preferably 65% ​​by mass or less, and more preferably 60% by mass or less. Preferred ranges include 40 to 70% by mass, 40 to 65% by mass, 40 to 60% by mass, 45 to 70% by mass, 45 to 65% by mass, 45 to 60% by mass, 50 to 70% by mass, 50 to 65% by mass, and 50 to 60% by mass.

[0038] Although the organic solvent concentration of the concentrate tends to be low in the early stages of operation (e.g., on the first day) of the osmotic pressure-assisted reverse osmosis membrane apparatus of the present disclosure, if operation is continued for, for example, one day or more, preferably two days or more, and more preferably three days or more, the organic solvent concentration of the discharged concentrate can be stably maintained at the above-mentioned high concentration for an extended period of time. That is, the osmotic pressure-assisted reverse osmosis membrane apparatus of the present disclosure can be continuously operated for, for example, five days or more, preferably seven days or more, and more preferably ten days or more while discharging a concentrate of such a high concentration (e.g., 40% by mass or more, preferably 45% by mass or more, and more preferably 50% by mass or more).

[0039] For example, by using the osmotic pressure-assisted reverse osmosis membrane device according to the first invention of the present disclosure, the aqueous solution concentrating method of the present disclosure shown below can be realized. A method for concentrating water to be treated containing an organic solvent, comprising: a first step of concentrating the water to be treated using a first osmotic pressure-assisted reverse osmosis membrane module; a second step of concentrating the water to be treated concentrated in the first step using a second osmotic pressure-assisted reverse osmosis membrane module under lower pressure conditions than in the first step; A method for concentrating an aqueous solution, comprising:

[0040] In the aqueous solution concentrating method of the present disclosure, the first step can be carried out using the aforementioned front-stage osmotic pressure-assisted reverse osmosis membrane module, and the second step can be carried out using the aforementioned rear-stage osmotic pressure-assisted reverse osmosis membrane module and pressure adjustment means.

[0041] The aqueous solution concentrating method according to the second invention of the present disclosure is also an aqueous solution concentrating method used to concentrate water to be treated that contains an organic solvent. The aqueous solution concentrating method according to the second invention of the present disclosure is characterized in that it uses an osmotic pressure-assisted reverse osmosis membrane module, sets the concentration of the water to be treated that is supplied to the osmotic pressure-assisted reverse osmosis membrane module to 40 mass% or more and less than 50 mass%, and concentrates the water to be treated using the osmotic pressure-assisted reverse osmosis membrane module under a pressure condition of 3.5 to 5 MPa. The aqueous solution concentrating method according to the second invention of the present disclosure also makes it possible to stably concentrate water to be treated that contains an organic solvent to a high concentration. When water to be treated with an organic solvent concentration of 40 mass% or more and less than 50 mass% can be prepared in advance, the aqueous solution concentrating method according to the second invention is effective.

[0042] The method for concentrating an aqueous solution according to the second aspect of the present disclosure can be said to be an invention that focuses on the osmotically-assisted reverse osmosis membrane module in the latter stage of the first aspect of the present disclosure. That is, in the method for concentrating an aqueous solution according to the second aspect of the present disclosure, the concentration of the water to be treated supplied to the osmotically-assisted reverse osmosis membrane module is set to a high concentration of 40 mass % or more but less than 50 mass %, and the pressure condition of the osmotically-assisted reverse osmosis membrane module is set to a low pressure condition of 3.5 to 5 MPa, thereby suppressing deformation of the osmotically-assisted reverse osmosis membrane under high pressure conditions caused by a high concentration of organic solvent, and enabling the water to be treated containing the organic solvent to be stably concentrated at a high concentration.

[0043] In the aqueous solution concentration method according to the second invention of the present disclosure, it is not necessary to separate the osmotic pressure-assisted reverse osmosis membrane module into an upstream and downstream stages, as in the first invention. The configuration of the aqueous solution concentration method according to the second invention is similar to that of the configuration diagram of Figure 1, for example, except that there is no upstream stage, and the feed solution is supplied to the downstream osmotic pressure-assisted reverse osmosis membrane module. Other than this, the configuration of the aqueous solution concentration method according to the second invention of the present disclosure is similar to the configuration of the osmotic pressure-assisted reverse osmosis membrane device according to the first invention of the present disclosure. Therefore, the description of the first invention will be cited, and a detailed description of the second invention will be omitted.

[0044] From the viewpoint of more suitably exerting the effects of the present invention, in the second invention, the concentration of the organic solvent in the water to be treated supplied to the osmotic pressure-assisted reverse osmosis membrane module may be in the range of 40% by mass or more and less than 50% by mass, preferably 41% by mass or more and 49% by mass or less, and preferred ranges include 40% by mass or more and 49% by mass or less, 41% by mass or more and less than 50% by mass, and 41 to 49% by mass.

[0045] In addition, in the second invention, the pressure conditions under which the osmotic pressure-assisted reverse osmosis membrane module performs concentration are preferably 7 MPa or less, more preferably 6 MPa or less, and even more preferably 5 MPa or less, from the viewpoint of more suitably exhibiting the effects of the invention of the present disclosure. Preferred ranges include 3.5 to 7 MPa, 3.5 to 6 MPa, and 3.5 to 5 MPa. [Example]

[0046] The present disclosure will be explained in more detail below by showing examples, but the present disclosure is not limited to these examples.

[0047] [Example 1] An aqueous organic solvent solution was concentrated using an osmotic pressure-assisted reverse osmosis apparatus having the configuration shown in the schematic diagram of Figure 1. The osmotic pressure-assisted reverse osmosis membrane module was a cellulose triacetate hollow fiber membrane module (HOLLOSEP Mini (registered trademark) BC membrane module manufactured by Toyobo MC Co., Ltd., membrane area 1.1 m). 2) was used. This membrane can withstand a pressure of 7 MPa in aqueous liquids such as saline. Five of these were connected in series, and the feed liquid (water to be treated containing an organic solvent) was pressurized and sent to one side (hereinafter referred to as the high-pressure side) of the hollow fiber membranes using a liquid feed pump 10. This concentrated the feed liquid and discharged it as a concentrated liquid from the high-pressure side outlet of the final membrane module. In addition, a portion of the concentrated liquid discharged from the final membrane module was passed through a branch pipe as a reflux liquid to the other side (hereinafter referred to as the low-pressure side) of the hollow fiber membranes at a pressure lower than that of the high-pressure side. As a result, the liquid flowing through the low-pressure side was diluted with permeate water and discharged (diluted liquid). A pressure regulating valve 11 (back pressure valve) as a pressure regulating means could be placed at any position on the high-pressure side pipe of the connected membrane modules. In Figure 1, a pressure regulating valve 11 (back pressure valve) is placed between the third and fourth membrane modules counting from the inlet side of the feed liquid, and a pressure regulating valve 12 (back pressure valve) is placed at the high-pressure outlet of the final membrane module. This allows the first to third membrane modules (front stage) and the fourth to fifth membrane modules (rear stage) to be controlled with different operating pressures.

[0048] In Figure 1, a 5% by mass N-methylpyrrolidone (NMP) aqueous solution was used as the feed liquid (water to be treated containing an organic solvent). The feed liquid was pumped to the outside of the hollow fiber membrane at a flow rate of 50 mL / min using a feed pump 10. The feed pressure of the first to third membrane modules (previous stage) was adjusted to 6 MPa (pressure gauge 21) by adjusting the pressure regulator valve 11. The pressure on the high-pressure side (outside the hollow fiber membrane) of the fourth and fifth modules was adjusted to 4 MPa (pressure gauge 22) by adjusting the pressure regulator valve 12. The flow rate regulator valves 31 and 32 were adjusted so that the pressure on the pressure gauge 23 was 1.5 MPa and the flow rate ratio of the reflux liquid to the concentrated liquid was 2. After 24 hours of operation at room temperature under these conditions, the flow rate of the feed pump was increased to 40 mL / min, and operation was continued. Periodic sampling of the concentrated liquid and diluted liquid was performed, and the flow rate and NMP concentration were measured. The flow rate of the concentrated liquid was measured by the change in mass of the concentrated liquid, and the NMP concentration was measured by refractive index measurement. Figure 2 shows a graph showing the relationship between the concentration (mass%) of the concentrated liquid and the operating time (days) when concentrating NMP using the osmotic pressure-assisted reverse osmosis membrane device of Example 1. The NMP concentration of the concentrated liquid reached 55 mass% on the second day of operation and remained at approximately 55 mass% thereafter. The NMP concentration in the dilute liquid was approximately constant at 4 mass%. These results demonstrate that when the upstream stage of a connected membrane module is pumped at a high pressure of 6 MPa and the downstream stage is pumped at a low pressure of 4 MPa, the membrane module as a whole can stably concentrate an NMP aqueous solution to a concentration of 50 mass% or more for a long period of time.

[0049] [Comparative Example 1] The NMP aqueous solution was concentrated in the same manner as in Example 1, except that the pressure applied to the high-pressure side of all five membrane modules was set to 6 MPa by fully opening the pressure regulating valve 11 and adjusting the pressure regulating valve 12. Figure 3 shows a graph illustrating the relationship between the concentration (mass%) of the concentrate and the operating time (days) when NMP was concentrated using the osmotic pressure-assisted reverse osmosis membrane device of Comparative Example 1. The NMP concentration of the concentrate reached 51-52 mass% on the second or third day, but gradually decreased thereafter, reaching 47 mass% on the seventh day and 45 mass% on the eleventh day. These results demonstrate that when all five membrane modules are operated at an operating pressure of 6 MPa, the NMP concentration can be initially concentrated to 50 mass% or more, but the concentration subsequently decreases, and it is not possible to stably maintain a high concentration of 50 mass% or more for a long period of time, as in Example 1.

[0050] Comparative Example 2 The NMP aqueous solution was concentrated in the same manner as in Example 1, except that the pressure on the high-pressure side of all five membrane modules was set to 4 MPa by adjusting the pressure regulating valve 12 after fully opening the pressure regulating valve 11. Fig. 4 shows a graph showing the relationship between the concentration (mass%) of the concentrate and the operating time (days) when NMP was concentrated using the osmotic pressure-assisted reverse osmosis membrane apparatus of Comparative Example 2. The NMP concentration of the concentrate was 43-44 mass% on the second or third day, and remained approximately constant at 46 mass% from the fifth day onwards. These results indicate that when all five membrane modules were operated at an operating pressure of 4 MPa, the NMP concentration could only be concentrated to approximately 45 mass%.

[0051] The results of Example 1 and Comparative Examples 1 and 2 revealed that when concentrating an aqueous solution of a water-soluble organic solvent such as NMP using an osmotic pressure-assisted reverse osmosis device, operating the front-stage membrane modules at high pressure (e.g., 6 MPa) and the rear-stage modules at relatively low pressure (e.g., 4 MPa) is more effective than operating all of the membrane modules at high pressure (e.g., 6 MPa or higher) or low pressure (e.g., 4 MPa or lower). This enables the entire membrane module to stably concentrate the aqueous solution of the water-soluble organic solvent to a high concentration of 50 mass% or higher for a long period of time.

[0052] [Test Example 1] Hollow fiber membranes were removed from an unused osmotic pressure-assisted reverse osmosis membrane module (an unused reverse osmosis membrane (BC membrane (cellulose acetate hollow fiber membrane)) used in stages 1 to 5 of each Example and Comparative Example), a membrane module (stage 5 for high concentration) used in Example 1 (after 11 days of operation), and a membrane module (stage 5 for high concentration) used in Comparative Example 1 (after 11 days of operation). They were cut into lengths of approximately 6 cm and fixed in place with carbon tape at two points near the center to prevent the bundle from falling apart. These were frozen in liquid nitrogen, cut midway between the two carbon tape wrappings, and freeze-dried. The cut surfaces were aligned, further cut into approximately 8 mm pieces, and fixed to an electron microscope sample stage. They were coated with osmium acid vapor using an osmium coater (Neoc / HSM51, manufactured by Meiwafosis Co., Ltd.) and observed at 750x magnification using a tabletop electron microscope (Phenom ProX, manufactured by Jasco International Co., Ltd.). As a result, compared to the hollow fiber membranes in an unused osmotic pressure-assisted reverse osmosis membrane module, the hollow fiber membranes in the membrane module used in Example 1 were slightly deformed but maintained their hollow fiber shape. On the other hand, the hollow fiber membranes in the membrane module used in Comparative Example 1 were significantly deformed, with their lumens crushed and liquid permeability reduced. From this, it is believed that the cellulose triacetate hollow fiber membranes exposed to a pressure of 6 MPa and an NMP concentration of around 50% by mass lost strength due to softening by NMP, and were deformed by the high pressure. On the other hand, at a pressure of 4 MPa, extreme deformation is unlikely to occur, even when the NMP concentration is around 50% by mass.

[0053] [Test Example 2] To verify the performance of osmotically assisted hollow-fiber reverse osmosis membranes in high-concentration NMP aqueous solutions, we conducted concentration tests on a 45% NMP aqueous solution using the apparatus shown in Figure 5, which mimics the fifth membrane module shown in Figure 1. Figure 6 shows the results of tests conducted at varying operating pressures and feed flow rates. The graph on the left side of Figure 6 shows the relationship between the concentrated NMP concentration (mass%) and flow rate (mL / min), while the graph on the right side shows the relationship between the concentrated NMP concentration (mass%) and applied pressure (MPa). These results indicate that when the NMP concentration of the feed solution is 45% by mass, an applied pressure of 4 MPa results in the most efficient concentration, and this trend remains unchanged regardless of the flow rate. Therefore, it was revealed that in the high-concentration range (>45% by mass) of NMP, operating pressures above 4 MPa actually result in a decrease in concentration due to a decrease in membrane performance.

[0054] [Test Example 3] The degradation of performance of osmotic pressure-assisted hollow-fiber reverse osmosis membranes in highly concentrated organic solvent aqueous solutions was verified by varying the organic solvent concentration using the apparatus shown in Figure 7. Figure 8 shows a graph showing the relationship between NMP rejection (%) and NMP concentration (mass%). As is clear from the graph in Figure 8, when the NMP concentration was varied between 5 and 60 mass%, the rejection performance of the reverse osmosis membrane was only slightly degraded at feed NMP concentrations of 40 mass% or less, both at pressures of 4 MPa and 6 MPa. When the NMP concentration exceeded 40 mass%, the decline in rejection was more pronounced at a pressure of 6 MPa. It was found that almost no rejection was observed at an NMP concentration of 50 mass%, while at a pressure of 4 MPa, the NMP concentration at which almost no rejection was observed increased to 60 mass%. This confirms that high pressures significantly degrade the performance of reverse osmosis membranes under high organic solvent concentrations. This is thought to be because the polymer that constitutes the reverse osmosis membrane becomes soft due to the organic solvent, making the reverse osmosis membrane more susceptible to deformation, causing the lumen to collapse and making it difficult for the liquid to pass through.

[0055] [Example 2] A 5% by mass aqueous solution of DMAc was concentrated in the same manner as in Example 1, except that the type of organic solvent was changed to N,N-dimethylacetamide (DMAc). Figure 9 is a graph showing the relationship between the concentration (% by mass) of the concentrate and the operating time (days) when DMAc was concentrated using the osmotic pressure-assisted reverse osmosis membrane apparatus of Example 2. By concentrating the first one to three membrane modules at 6 MPa and the second four to five membrane modules at 4 MPa, the DMAc concentration was able to be maintained at 51 to 52% by mass over a long period of time.

[0056] Comparative Example 3 A DMAc aqueous solution was concentrated in the same manner as in Example 2, except that the pressure applied to all five membrane modules was 6 MPa. Fig. 10 is a graph showing the relationship between the concentration (mass%) of the concentrate and the operation time (days) when DMAc was concentrated using the osmotic pressure-assisted reverse osmosis membrane device of Comparative Example 3. When all five membrane modules were operated at 6 MPa, a concentrate of 52-53 mass% was obtained on the second or third day, but the concentrate concentration gradually decreased thereafter, reaching 45 mass% by the tenth day. This demonstrates that even when the organic solvent is DMAc, a decrease in the concentrate concentration occurs when all membrane modules are operated at a high pressure of 6 MPa. [Explanation of symbols]

[0057] 10 Liquid transfer pump 11 Pressure regulating valve 12 Pressure Regulating Valve 21 Pressure gauge 22 Pressure gauge 23 Pressure gauge 31 Flow control valve 32 Flow control valve

Claims

1. An osmotic pressure-assisted reverse osmosis membrane device used for concentrating water to be treated that contains an organic solvent, The osmotic pressure-assisted reverse osmosis membrane device includes an upstream osmotic pressure-assisted reverse osmosis membrane module located on the side where the water to be treated is supplied, and a downstream osmotic pressure-assisted reverse osmosis membrane module located on the side where the concentrated liquid is discharged, a pressure adjusting means is provided between the upstream osmotic pressure-assisted reverse osmosis membrane module and the downstream osmotic pressure-assisted reverse osmosis membrane module; The pressure adjustment means allows the downstream osmotic pressure-assisted reverse osmosis membrane module to concentrate under lower pressure conditions than the upstream osmotic pressure-assisted reverse osmosis membrane module.

2. 2. The osmotic pressure-assisted reverse osmosis membrane device of claim 1, wherein at least one of the upstream osmotic pressure-assisted reverse osmosis membrane module and the downstream osmotic pressure-assisted reverse osmosis membrane module includes a plurality of osmotic pressure-assisted reverse osmosis membrane modules.

3. 3. The osmotically-assisted reverse osmosis membrane device according to claim 1, wherein the upstream osmotically-assisted reverse osmosis membrane module performs concentration under a pressure condition higher than 3 MPa.

4. The osmotically-assisted reverse osmosis membrane device according to claim 1 or 2, wherein the downstream osmotically-assisted reverse osmosis membrane module performs concentration under a pressure condition lower than 7 MPa.

5. the organic solvent concentration of the water to be treated supplied to the upstream osmotic pressure-assisted reverse osmosis membrane module is 0.1% by mass or more and less than 50% by mass; 3. The osmotic pressure-assisted reverse osmosis membrane device according to claim 1, wherein the concentration of the water to be treated supplied to the downstream reverse osmosis membrane module is 40% by mass or more and 50% by mass or less.

6. 3. The osmotically-assisted reverse osmosis membrane device according to claim 1, wherein the organic solvent has a boiling point of 105°C or higher at 1 atmospheric pressure.

7. 3. The osmotic pressure-assisted reverse osmosis membrane device according to claim 1, which is operated continuously for five days or more.

8. 3. The osmotic pressure-assisted reverse osmosis membrane device according to claim 1, wherein the organic solvent concentration of the concentrated liquid discharged from the osmotic pressure-assisted reverse osmosis membrane device is 40% by mass or more.

9. An apparatus for concentrating an aqueous solution containing an organic solvent, comprising the osmotic pressure-assisted reverse osmosis membrane device according to claim 1 or 2.

10. 10. The concentrator of claim 9, further comprising a reverse osmosis membrane device different from the osmotically assisted reverse osmosis membrane device.

11. A method for concentrating an aqueous solution, comprising concentrating an aqueous solution containing an organic solvent using the osmotic pressure-assisted reverse osmosis membrane device according to claim 1 or 2.

12. A method for concentrating water to be treated containing an organic solvent, comprising: a first step of concentrating the water to be treated using a first osmotic pressure-assisted reverse osmosis membrane module; a second step of concentrating the water to be treated concentrated in the first step using a second osmotic pressure-assisted reverse osmosis membrane module under a lower pressure condition than in the first step; A method for concentrating an aqueous solution, comprising:

13. A method for concentrating water to be treated containing an organic solvent using an osmotic pressure-assisted reverse osmosis membrane module, comprising: the organic solvent concentration of the water to be treated supplied to the osmotic pressure-assisted reverse osmosis membrane module is 40% by mass or more and less than 50% by mass; The method for concentrating an aqueous solution comprises concentrating the water to be treated using the osmotic pressure-assisted reverse osmosis membrane module under a pressure condition of 3.5 to 5 MPa.

Images