Operating method of a reverse osmosis membrane apparatus

Abstract

This invention provides an operating method for a reverse osmosis membrane apparatus in which aromatic polyamide reverse osmosis membranes are less susceptible to compaction. [Solution] 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 membrane surface effective pressure of 2 MPa and a water temperature of 25°C, with a permeation flux of 0.9 m³ of pure water (RO permeate). 3 / (m 2 A method for operating a reverse osmosis membrane apparatus, wherein the apparatus has a silica removal rate of 99.7% or higher and / or an IPA removal rate of 96% or higher and / or a boron removal rate of 80% or higher at a membrane surface effective pressure of 1 MPa, a water temperature of 25°C, and a pH of 7.0, characterized in that the apparatus is operated so that the intermembrane differential pressure is 1.0 to 2.1 MPa.

Description

[Technical Field]

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

[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-supported 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. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 8-972 [Non-patent literature]

[0007] [Non-Patent Document 1] MEMBRANE, 36(2), 79-81(2011) [Non-Patent Document 2] Desalination and Water Treatment, 33, 283-288 (2011) [Non-Patent Document 3] Journal of Membrane Science, Vol. 654, 15, 120553 (2022) [Overview of the initiative] [Problems that the invention aims to solve]

[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. [Means for solving the problem]

[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 membrane surface effective pressure of 2 MPa and a water temperature of 25°C, with a permeation flux of pure water (RO permeate water) of 0.9 m³. 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 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 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 the operation method of the reverse osmosis membrane device according to one aspect of the present invention, at least one of the inverter of the high-pressure pump for feeding water 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.

[0012] In the operation method of the reverse osmosis membrane device according to one aspect of the present invention, the feed water to the reverse osmosis membrane device is sodium at 0.05 to 2500 mg / L, silica at 0.1 to 240 mg / L boron at 0.01 to 1 mg / L and has a water quality satisfying at least one of them.

Effects of the Invention

[0013] Regarding the reason why the water permeability of the reverse osmosis membrane with a large ridge structure (large protrusion of the ridge structure) and high water permeability decreases due to compaction, in order to increase the water permeability, the polyamide layer is thinned and the height of the protrusion is increased to increase the surface area. Therefore, it is推测 that the mechanical strength of the ridge structure has decreased.

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

Modes for Carrying Out the Invention

[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 pure water (RO permeate) permeation flux 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 effective pressure on the membrane surface means, in a pressure type module, 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 ). 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 pressure type module. Here, the average operating pressure (P o ) is the pressure obtained by averaging the feed water pressure (P[[ID=第十七条]] 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 permeated water (π p ) are used. Δπ = (π[[ID=第二十九条]] f + π[[ID=第三十一条]] c ) / 2 - π[[ID=第三十三条]] p

[0019] By setting the differential pressure between membranes to 1.0 to 2.1 MPa in this way, the compaction of the reverse osmosis membrane is suppressed. The reason why the compaction is suppressed in this way is considered to be that when the differential pressure between membranes is 2.1 MPa or less, the deformation of the fold structure of the polyamide layer is suppressed.

[0020] In addition, when the differential pressure between membranes is less than 1.0 MPa, the removal rate of the solutes contained in the feed water decreases.

[0021] In order to set the differential pressure between membranes to 1.0 to 2.1 MPa, in one aspect of the present invention, an inverter controls the high-pressure pump for feeding water to the reverse osmosis membrane device.

[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 have a lifespan of 1 MPa or more, and at an effective membrane pressure of 1 MPa, a water temperature of 25°C, and a pH of 7.0, 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, are commercially available, including 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 8040-440 (Aquaporin, Denmark), K-RO-A-20WM-FP00 (Kurita Water Industries Ltd.), etc.

[0024] The reverse osmosis membrane feedwater treated by the present invention is preferably water that satisfies at least one of the following conditions: 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 (wastewater) 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. [Examples]

[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 procedure using a high-pressure pump, and the permeate flow rate was measured.

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

[0027] The permeate flow rate was recorded after running water through the system for more than 3 hours and reaching a constant flow rate. 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 permeation flux of 1.05 m³ for pure water (RO permeate) at an effective membrane pressure of 2 MPa and a water temperature of 25°C. 3 / (m 2 (In Japan), with test water containing a Na concentration of 250 mg / L, an SiO2 concentration of 25 mg / L, and a B concentration of 0.5 mg / L, the silica removal rate was 99.9%, the IPA removal rate was 98% or higher, and the boron inhibition rate at pH 7.0 was 81% at an effective membrane pressure of 1 MPa, a water temperature of 25°C, and pH 7.0.

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

[0030] Furthermore, this reverse osmosis membrane K-RO-A-20ZQ-FX00 has a permeation flux of 0.79 m³ for pure water (RO permeate) at an effective membrane pressure of 2 MPa and a water temperature of 25°C. 3 / (m 2 In a test water solution containing Na concentration of 250 mg / L, SiO2 concentration of 25 mg / L, and B concentration of 0.5 mg / L, the silica removal rate at pH 7.0 was 99.8%, the IPA removal rate was 98.5% or higher, and the boron inhibition rate at pH 7.0 was 81%.

[0031] [Table 1]

[0032] [Table 2]

[0033] [Consideration] As shown in Table 1, in Example 1, the correction flux decreased with increasing intermembrane pressure. Comparing the correction flux of Example 1-1 with an intermembrane pressure of 1.0 MPa with that of Examples 1-2, 1-3, and Reference Example 1 with intermembrane pressures of 1.5, 2.0, and 2.3 MPa, the correction fluxes for Examples 1-2, 1-3, and Reference Example 1 decreased by 1.2%, 1.9%, and 3.5%, respectively, compared to Example 1-1. From these results, it was found that the effect of compaction becomes significant when the intermembrane pressure exceeds 2.1 MPa.

[0034] In other words, it was found that the reduction in corrective flux due to compaction was significant in the membranes of Example 1 and Reference Example 1, which used reverse osmosis membranes with high water permeability.

[0035] On the other hand, in Comparative Example 1, which used a low-permeability reverse osmosis membrane, the corrective flux was maintained up to a membrane differential pressure of 2.1 MPa (Comparative Examples 1-3). Comparing the corrective flux at membrane differential pressures of 1.0 MPa (Comparative Example 1-1) and 2.3 MPa (Comparative Example 1-4), the decrease in corrective flux was a small 0.7%.

Claims

1. A method for operating a reverse osmosis apparatus equipped with an aromatic polyamide reverse osmosis membrane, The aromatic polyamide reverse osmosis membrane has a permeation flux of 0.9 m³ for pure water (RO permeate) at an effective membrane pressure of 2 MPa and a water temperature of 25°C. ３ / (m ２ In a reverse osmosis membrane apparatus operating method that is 24 hours or more, and has 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 a membrane surface effective pressure of 1 MPa, water temperature of 25°C, and pH 7.0, A method for operating a reverse osmosis membrane apparatus, characterized by operating it so that the intermembrane pressure differential is 1.0 to 2.1 MPa.

2. The method for operating a reverse osmosis membrane apparatus according to claim 1, wherein the aromatic polyamide reverse osmosis membrane comprises a polyamide layer having a pleated structure.

3. A method for operating a reverse osmosis membrane apparatus according to claim 1, which controls 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 so that the intermembrane pressure difference does not exceed 2.1 MPa.

4. The water supply for the reverse osmosis membrane device is Sodium 0.05–2500 mg / L, Silica 0.1–240 mg / L Boron 0.01–1 mg / L A method for operating a reverse osmosis membrane apparatus according to any one of claims 1 to 3, having water quality that satisfies at least one of the following conditions.

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