Method for operating reverse osmosis membrane device

Abstract

Provided is a method for operating a reverse osmosis membrane device equipped with an aromatic polyamide reverse osmosis membrane, the aromatic polyamide reverse osmosis membrane having a permeation flux with respect to pure water (RO permeated water) is 0.9 m3 / (ｍ2·day) at a membrane surface effective pressure of 2 MPa and a water temperature of 25°C, and having a silica removal rate of 99.7% or greater and / or an IPA removal rate of 96% or greater and / or a boron removal rate of 80% or greater at a membrane surface effective pressure of 1 MPa, a water temperature of 25°C, and a pH of 7.0, wherein the method is characterized in that the reverse osmosis membrane device is operated so that the inter-membrane differential pressure is 1.0-2.1 MPa.

Description

Operating method of a reverse osmosis membrane apparatus

[0001] The present invention relates to a method for operating a reverse osmosis apparatus equipped with an aromatic polyamide reverse osmosis membrane.

[0002] Aromatic polyamide reverse osmosis membranes are widely used as reverse osmosis membranes in reverse osmosis membrane devices. Patent document 1, for example, describes forming an aromatic polyamide layer on a fiber-reinforced polysulfone support membrane, which is formed by an interfacial polymerization reaction on a polysulfone film formed on polyester fiber taffeta, as an aromatic polyamide reverse osmosis membrane.

[0003] The separation function of the aromatic polyamide reverse osmosis membrane is achieved by the aromatic polyamide layer formed on top of the polysulfone support layer, which is formed on top of the polyester base fabric.

[0004] Non-patent documents 1 and 2 show that the polyamide layer has a pleated structure, that the pleated structure increases the film surface area, that the inside of the polyamide layer is hollow, and that water permeability is increased by making the polyamide layer thinner.

[0005] One known operational problem with reverse osmosis membranes is compaction (a phenomenon in which the membrane's water permeability deteriorates due to mechanical pressure compression). Non-patent document 3 indicates that there are two reasons for the decrease in water permeability due to compaction: shrinkage of the polyamide layer or collapse of macrovoids in the support layer. Specifically, it is shown that the greater the ridges (larger protrusions) in the fold structure of the polyamide layer, the more susceptible it is to compaction. When compaction occurs, higher pressure is required to maintain the desired water permeability, increasing the energy required for the membrane separation process.

[0006] Japanese Patent Application Publication No. 8-972

[0007] Membrane (MEMBRANE), 36(2), 79-81(2011)Desalination and Water Treatment, 33, 283-288 (2011)Journal of Membrane Science, Vol. 654, 15, 120553 (2022)

[0008] The object of this invention is to provide a method for operating a reverse osmosis membrane apparatus in which aromatic polyamide reverse osmosis membranes are less susceptible to compaction.

[0009] A method for operating a reverse osmosis membrane apparatus according to one aspect of the present invention is a method for operating a reverse osmosis membrane apparatus equipped with an aromatic polyamide reverse osmosis membrane, wherein the aromatic polyamide reverse osmosis membrane has a permeation flux of 0.9 m³ of pure water (RO permeate) at an effective membrane pressure of 2 MPa and a water temperature of 25°C. ３ / (m ２ The method for operating a reverse osmosis membrane apparatus is characterized by operating it so that the intermembrane differential pressure is 1.0 to 2.1 MPa, and the silica removal rate is 99.7% or higher and / or the IPA (isopropyl alcohol) removal rate is 96% or higher and / or the boron removal rate is 80% or higher at a membrane surface effective pressure of 1 MPa, water temperature of 25°C, and pH of 7.0.

[0010] In one embodiment of the present invention, the method for operating a reverse osmosis membrane apparatus comprises an aromatic polyamide reverse osmosis membrane with a polyamide layer having a pleated structure.

[0011] In one embodiment of the present invention, in a method for operating a reverse osmosis membrane apparatus, at least one of the inverter of the high-pressure pump for supplying water to the reverse osmosis membrane apparatus and the opening degree of the back pressure valve of the reverse osmosis membrane apparatus are controlled so that the intermembrane pressure difference does not exceed 2.1 MPa.

[0012] In one embodiment of the present invention, the reverse osmosis membrane apparatus is operated by supplying water to the reverse osmosis membrane apparatus, which has a water quality that satisfies at least one of the following: sodium 0.05 to 2500 mg / L, silica 0.1 to 240 mg / L, and boron 0.01 to 1 mg / L.

[0013] The reason why the water permeability of highly permeable reverse osmosis membranes with large folds (large protrusions) decreases due to compaction is presumed to be because, in order to increase water permeability, the polyamide layer was made thinner and the height of the protrusions was increased to increase the surface area, which reduced the mechanical strength of the folds.

[0014] According to the present invention, by setting the differential pressure between membranes within a low range, it is possible to prevent a decrease in water permeability due to compaction in a reverse osmosis membrane device equipped with a highly water-permeable aromatic polyamide reverse osmosis membrane.

[0015] Hereinafter, the present invention will be described in more detail.

[0016] The reverse osmosis membrane of the reverse osmosis membrane device used in the operation method of the present invention has a permeation flux of pure water (RO permeate water) of 0.9 m ３ / (m ２ ·day) or more at a membrane surface effective pressure of 2 MPa and a water temperature of 25 °C, and has an aromatic polyamide reverse osmosis membrane with a silica removal rate of 99.7% or more and / or an IPA removal rate of 96% or more and / or a boron removal rate of 80% or more under the conditions of a membrane surface effective pressure of 1 MPa, a water temperature of 25 °C, and a pH of 7.0.

[0017] In the present invention, such a reverse osmosis membrane device is operated so that the differential pressure between membranes becomes 1.0 to 2.1 MPa.

[0018] In the present invention, the membrane surface effective pressure is the effective pressure acting on the membrane obtained by subtracting the osmotic differential pressure (Δπ) and the secondary side pressure (P ｏ ) from the average operating pressure (P ｐ ) in a pressurized module. Further, the differential pressure between membranes is the pressure obtained by subtracting the secondary side pressure (P ｏ ) from the average operating pressure (P ｐ ) in a pressurized module. Here, the average operating pressure (P ｏ ) is the pressure obtained by averaging the feed water pressure (P f ) and the concentrated water pressure (P ｃ ). The osmotic pressure difference (Δπ) is calculated by the following formula when the osmotic pressure of the supply water (π ｆ ), the osmotic pressure of the concentrated water (π ｃ ), and the osmotic pressure of the permeate water (π ｐ ) are used. Δπ = (π ｆ + π ｃ ) / 2 - π ｐ

[0019] By setting the intermembrane pressure differential to 1.0 to 2.1 MPa, compaction of the reverse osmosis membrane is suppressed. The reason for this suppression of compaction is thought to be that when the intermembrane pressure differential is 2.1 MPa or less, deformation of the fold structure of the polyamide layer is suppressed.

[0020] Furthermore, if the intermembrane pressure difference is less than 1.0 MPa, the removal rate of solutes contained in the feedwater decreases.

[0021] In order to achieve a differential pressure between membranes of 1.0 to 2.1 MPa, in one aspect of the present invention, the high-pressure pump for supplying water to the reverse osmosis membrane apparatus is controlled by an inverter.

[0022] In another aspect of the present invention, a back pressure valve is installed in the concentrated water line of a reverse osmosis membrane apparatus. The opening degree of the back pressure valve is then controlled so that the intermembrane pressure differential is 1.0 to 2.1 MPa. In this case, inverter control of the high-pressure pump may also be performed.

[0023] Furthermore, the permeation flux of pure water (RO permeate) at an effective membrane pressure of 2 MPa and a water temperature of 25°C is 0.9 m ３ / (m ２ Polyamide reverse osmosis membranes that are (1) or more in length, and have a silica removal rate of 99.7% or more and / or an IPA removal rate of 96% or more and / or a boron removal rate of 80% or more at an effective membrane pressure of 1 MPa, a water temperature of 25°C, and a pH of 7.0 include TBW-400XHR (Toray Industries, Inc.), TBW-440XHR (Toray Industries, Inc.), BW30XHR PRO-400 / 34 (Dupont), BW30XHR PRO-400 / 34(i) (Dupont), BW30XHR PRO-440 (Dupont), CLEAR Classic HR 8040-400 (Aquaporin, Denmark), CLEAR Classic HR Products such as the 8040-440 (Aquaporin, Denmark) and the K-RO-A-20WM-FP00 (Kurita Water Industries Ltd.) are commercially available.

[0024] The reverse osmosis membrane feedwater treated by the present invention is preferably water having a quality that satisfies at least one of the following: sodium 0.05 to 2500 mg / L, silica 0.1 to 240 mg / L, and boron 0.01 to 1 mg / L. Examples of water with such quality include surface water, well water, secondary treated water from dyeing wastewater, secondary treated water from sewage discharge, pollutant wastewater, and brine recovered from reverse osmosis membrane systems.

[0025] [Example 1, Reference Example 1] A reverse osmosis membrane apparatus equipped with a single-membrane vessel (8 inches) and an aromatic polyamide reverse osmosis membrane, TBW-440XHR (Toray Industries, Inc.), was subjected to the following flow of pure water (persistent water obtained by RO treatment of tap water) using a high-pressure pump, and the permeate flow rate was measured.

[0026] First, pure water was supplied to the reverse osmosis membrane apparatus, and circulation was performed using a high-pressure pump at the intermembrane pressure differential shown in Table 1. The water temperature was adjusted to a range of 25 ± 2°C using a chiller. The amount of concentrated water was 3.6 m³. ３ It was fixed to / h.

[0027] The permeate flow rate was recorded after water had been passed through for more than three hours and the flow rate reached a constant level. From this permeate flow rate, the corrected flux (permeate flux converted to a differential pressure of 2 MPa and a temperature of 25°C) was calculated. The results are shown in Table 1.

[0028] Furthermore, this reverse osmosis membrane TBW-440XHR has a membrane surface effective pressure of 2 MPa and a water temperature of 25°C, with a permeation flux of pure water (RO permeate) of 1.05 m³. ３ / (m ２ ・Na concentration 250mg / L, SiO ２ For test water containing a concentration of 25 mg / L and a B concentration of 0.5 mg / L, the silica removal rate was 99.9% at an effective membrane pressure of 1 MPa, a water temperature of 25°C, and a pH of 7.0, the IPA removal rate was 98% or higher, and the boron inhibition rate at pH 7.0 was 81%.

[0029] [Comparative Example 1] K-RO-A-20ZQ-FX00 (Kurita Water Industries Ltd.) was used as the reverse osmosis membrane. Other conditions were the same as in Example 1 and Reference Example 1. The results are shown in Table 2.

[0030] Incidentally, this reverse osmosis membrane K-RO-A-20ZQ-FX00 has a permeate flux of pure water (RO permeate water) of 0.79 m ３ / (m ２ ·day) at a membrane surface effective pressure of 2 MPa and a water temperature of 25°C. For test water containing a Na concentration of 250 mg / L, a SiO ２ concentration of 25 mg / L, and a B concentration of 0.5 mg / L, the silica removal rate at pH 7.0 is 99.8%, the IPA removal rate is 98.5% or more, and the boron rejection rate at pH 7.0 is 81%.

[0031]

[0032]

[0033] [Discussion] As shown in Table 1, in Example 1, the corrected flux decreased as the transmembrane differential pressure increased. Comparing the corrected flux between Example 1-1 with a transmembrane differential pressure of 1.0 MPa and Examples 1-2, 1-3, and Reference Example 1 with transmembrane differential pressures of 1.5, 2.0, and 2.3 MPa, the corrected fluxes of Examples 1-2, 1-3, and Reference Example 1 decreased by 1.2%, 1.9%, and 3.5% respectively from Example 1-1. From this result, it was found that when the transmembrane differential pressure exceeds 2.1 MPa, the influence of compaction is large.

[0034] That is, it was found that in the membranes of Example 1 and Reference Example 1 using reverse osmosis membranes with high water permeability, the decrease in the corrected flux due to compaction is significant.

[0035] On the other hand, in Comparative Example 1 using a reverse osmosis membrane with low water permeability, the corrected flux was maintained up to a transmembrane differential pressure of 2.0 MPa (Comparative Example 1-3). Comparing the corrected fluxes at a transmembrane differential pressure of 1.0 MPa (Comparative Example 1-1) and 2.3 MPa (Comparative Example 1-4), the decrease in the corrected flux was a small value of 0.7%.

[0036] Although the present invention has been described in detail using specific embodiments, it is obvious to those skilled in the art that various changes are possible within the scope where the effects of the invention are achieved. This application is based on Japanese Patent Application No. 2025-003035 filed on January 8, 2025, the entire contents of which are incorporated herein by reference.

Claims

1. A method for operating a reverse osmosis membrane apparatus equipped with an aromatic polyamide reverse osmosis membrane, wherein the aromatic polyamide reverse osmosis membrane has a permeation flux of pure water (RO permeate water) of 0.9 m ３ / (m ２ ·day) or more, and at a membrane surface effective pressure of 1 MPa, a water temperature of 25 °C, and a pH of 7.0, the silica removal rate is 99.7% or more and / or the IPA removal rate is 96% or more and / or the boron removal rate at pH 7.0 is 80% or more. In the method for operating a reverse osmosis membrane apparatus, the operation is carried out such that the intermembrane differential pressure is 1.0 to 2.1 MPa.

2. The operation method of the reverse osmosis membrane device according to claim 1, wherein the aromatic polyamide reverse osmosis membrane is provided with a polyamide layer having a pleated structure.

3. The operation method of the reverse osmosis membrane device according to claim 1, wherein at least one of the inverter of the high-pressure pump for water supply to the reverse osmosis membrane device and the opening degree of the back pressure valve of the reverse osmosis membrane device is controlled so that the differential pressure between the membranes does not exceed 2.1 MPa.

4. The operation method of the reverse osmosis membrane device according to any one of claims 1 to 3, wherein the water supply of the reverse osmosis membrane device has a water quality satisfying at least one of sodium of 0.05 to 2500 mg / L, silica of 0.1 to 240 mg / L, and boron of 0.01 to 1 mg / L.

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