Cleaning agent, cleaning solution, and cleaning method for aromatic polyamide reverse osmosis membrane

Abstract

The cleaning agent for the aromatic polyamide-based reverse osmosis membrane comprises an aqueous solution containing a stabilized halogen and a silicic acid compound. The aromatic polyamide reverse osmosis membrane is cleaned using a cleaning solution containing a diluted aqueous solution of the cleaning agent. As the stabilizing halogen, it is preferable that a chloramine compound obtained by mixing a compound having a primary amino group with hypochlorous acid and / or hypochlorite.

Description

Technical Field

[0001] The present invention relates to a cleaning agent, cleaning solution, and cleaning method for aromatic polyamide reverse osmosis membranes used in the water treatment field. Specifically, the present invention relates to a cleaning agent for effectively restoring the performance of aromatic polyamide reverse osmosis membranes when they become contaminated, resulting in reduced membrane performance such as flux and rejection; a cleaning solution containing the cleaning agent; and a method for cleaning aromatic polyamide reverse osmosis membranes using the cleaning solution. Background Art

[0002] Currently, as a countermeasure to global water shortages, alkaline water desalination and wastewater recovery using permeable membranes such as reverse osmosis (RO) membranes are being implemented. In systems using these membranes, performance degradation due to membrane contamination is a problem, and there is a desire to develop a cleaning technology that effectively restores the performance of contaminated membranes.

[0003] In recent years, aromatic polyamide-based RO membranes have become widely used as RO membranes for water treatment, due to their ability to operate at low pressures and their excellent desalination performance. However, aromatic polyamide-based RO membranes have low resistance to chlorine and, unlike cellulose acetate-based RO membranes, cannot withstand exposure to chlorine under operating conditions. This leads to a greater tendency for contamination by microorganisms and organic matter than cellulose acetate-based RO membranes. On the other hand, aromatic polyamide-based RO membranes have higher resistance to alkali than cellulose acetate-based membranes and can be cleaned under alkaline conditions of pH 10 or higher.

[0004] Patent Document 1 describes a cleaning agent for an alkali-resistant aromatic polyamide RO membrane comprising an aqueous solution having a pH of 13 or higher containing a chloramine compound, a non-amine surfactant such as an alkylbenzene sulfonate, and an alkaline agent.

[0005] Paragraph 0051 of Patent Document 1 states that “in order to enhance the effect of removing membrane fouling substances, a chelating agent such as ethylenediaminetetraacetic acid (EDTA) may be further added.”

[0006] However, when an amine-based chelating agent such as EDTA is added to the cleaning agent of Patent Document 1, it reacts with chloramine compounds, resulting in a decrease in the concentration of chloramine compounds.

[0007] Patent Document 2 describes a cleaning agent for aromatic polyamide RO membranes comprising an aqueous solution having a pH of 13 or higher, the aqueous solution containing a chelating agent such as a chloramine compound, an aliphatic carboxylic acid having no amino group such as oxalic acid, a non-amine surfactant such as an alkylbenzene sulfonate, and an alkaline agent.

[0008] According to Patent Document 2, a decrease in the concentration of chloramine compounds is suppressed, and contaminants in the aromatic polyamide-based RO membrane are effectively removed.

[0009] [Prior art literature]

[0010] [Patent Document]

[0011] Patent Document 1: Japanese Patent Application Laid-Open No. 2015-97991.

[0012] Patent Document 2: Japanese Patent No. 7136385. Summary of the Invention

[0013] [Problems to be Solved by the Invention]

[0014] The present invention aims to provide a cleaning agent, cleaning solution, and cleaning method that can effectively remove contaminants by further suppressing the decrease in stabilized halogen concentration compared to Patent Document 2 when an aromatic polyamide-based RO membrane is contaminated, resulting in a decrease in performance such as permeation flux and salt rejection rate.

[0015] [Methods for solving the problem]

[0016] The gist of the present invention is as follows.

[0017] [1] A cleaning agent for an aromatic polyamide reverse osmosis membrane, wherein the cleaning agent comprises an aqueous solution containing a stabilized halogen and a silicic acid compound.

[0018] [2] The cleaning agent for an aromatic polyamide-based reverse osmosis membrane according to [1], wherein the concentration of the stabilized halogen in the cleaning agent is 0.1M to 2M, and the concentration of the silicic acid compound is 0.01M to 0.05M.

[0019] [3] The cleaning agent for an aromatic polyamide-based reverse osmosis membrane according to [1] or [2], wherein the stabilized halogen contains monochlorosulfamic acid.

[0020] [4] The cleaning agent for an aromatic polyamide-based reverse osmosis membrane according to any one of [1] to [3], wherein the silicic acid compound is at least one of sodium silicate and potassium silicate.

[0021] [5] The cleaning agent for an aromatic polyamide reverse osmosis membrane according to any one of [1] to [4], wherein the cleaning agent comprises a non-amine anionic surfactant having no amino group or amine oxide with a molecular weight of less than 1000 in its molecular structure.

[0022] [6] The cleaning agent for an aromatic polyamide-based reverse osmosis membrane according to [5], wherein the concentration of the non-amine anionic surfactant in the aqueous solution is 0.002M to 0.5M.

[0023] [7] The cleaning agent for an aromatic polyamide-based reverse osmosis membrane according to any one of [1] to [6], wherein the stabilized halogen is a reaction product of one or more selected from the group consisting of a compound having a primary amino group, ammonia, and an ammonium salt, with hypochlorous acid and / or a hypochlorite.

[0024] [8] A cleaning solution for an aromatic polyamide-based reverse osmosis membrane, comprising a diluted aqueous solution of the cleaning agent for an aromatic polyamide-based reverse osmosis membrane according to any one of [1] to [7].

[0025] [9] The cleaning solution for an aromatic polyamide-based reverse osmosis membrane according to [8], wherein the pH of the cleaning solution is 11 to 13.

[0026]

[10] The cleaning solution for an aromatic polyamide-based reverse osmosis membrane according to [8] or [9], wherein the concentration of the stabilized halogen in the cleaning solution is 0.001M to 0.02M, and the concentration of the silicate compound is 0.0001M to 0.0005M.

[0027]

[11] A method for cleaning an aromatic polyamide reverse osmosis membrane, comprising the step of contacting the aromatic polyamide reverse osmosis membrane with the cleaning solution described in any one of [8] to

[10] .

[0028] [Effects of the Invention]

[0029] According to the present invention, even aromatic polyamide RO membranes with low chlorine resistance can be treated with chlorine-based cleaning agents. Furthermore, the decrease in the concentration of stabilized halogen is significantly suppressed. Furthermore, alkaline conditions are maintained by the silicic acid compound. Therefore, in addition to the stripping and hydrolysis effects under alkaline conditions, the bactericidal and organic matter decomposition effects of the stabilized halogen also synergistically contribute to effectively restoring the performance of the aromatic polyamide reverse osmosis membrane. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is a graph showing the results of Examples and Comparative Examples.

[0031] Figure 2 It is a graph showing the results of Examples and Comparative Examples.

[0032] Figure 3 It is a graph showing the results of Examples and Comparative Examples. DETAILED DESCRIPTION

[0033] Hereinafter, embodiments of the present invention will be described in detail.

[0034] The cleaning agent for an aromatic polyamide reverse osmosis membrane of the present invention comprises an aqueous solution containing a stabilized halogen and a silicic acid compound. The cleaning liquid for an aromatic polyamide reverse osmosis membrane of the present invention comprises a diluted aqueous solution of the cleaning agent.

[0035] <Aromatic polyamide reverse osmosis membrane>

[0036] The present invention uses aromatic polyamide reverse osmosis membranes (including nanofiltration (NF) membranes) as cleaning objects.

[0037] Stabilized halogens

[0038] In the present invention, the stabilized halogen used as a component of a halogen-based cleaning agent can be produced by mixing any one of a compound having a primary amino group, ammonia, and an ammonium salt (hereinafter referred to as "NH2-based compound") with a halogen-based oxidant such as a chlorine-based oxidant or a bromine-based oxidant. As the chlorine-based oxidant, hypochlorous acid and / or hypochlorite are preferably used. In addition, as the bromine-based oxidant, bromine (liquid bromine), bromine chloride, bromic acid, bromate, hypobromous acid, etc. can be listed. As the stabilized halogen, a chloramine compound is preferably used, that is, a compound (XNHC1) in which the hydrogen atom of the amino group is replaced by a chlorine atom by reacting hypochlorous acid (HOCl) with a compound having a primary amino group (XNH2) in the reaction shown in the following reaction formula (1) and reaction formula (2). Since this compound has a weak oxidizing effect on the membrane, it can be used as a cleaning agent even for aromatic polyamide-based RO membranes with low chlorine resistance.

[0039]

[0040] Examples of the compound having a primary amino group include aliphatic amines, aromatic amines, sulfamic acid, sulfanilic acid, sulfamoylbenzoic acid, and amino acids.

[0041] Examples of the ammonium salt include ammonium chloride and ammonium sulfate, which may be used alone or in combination of two or more.

[0042] Among these NH2-based compounds, sulfamic acid (NH2SO2OH) is preferred. Using sulfamic acid to generate monochlorosulfamic acid results in a stable chloramine compound. Since sulfamic acid does not contain carbon, it does not increase the total organic carbon (TOC) value of the cleaning agent.

[0043] As the hypochlorite to be reacted with the NH2-based compound, alkali metal salts of hypochlorous acid such as sodium hypochlorite, alkaline earth metal salts of hypochlorous acid such as calcium hypochlorite, etc. can be used. These can be used alone or in combination of two or more.

[0044] When an NH2 compound is mixed with hypochlorous acid and / or hypochlorite to generate a chloramine compound, in terms of the efficiency and stability of chloramine generation, the NH2 compound and hypochlorous acid and / or hypochlorite are preferably used in such a manner that the molar ratio of available chlorine (Cl2) derived from hypochlorous acid and / or hypochlorite to nitrogen atoms N derived from the NH2 compound, i.e., the Cl2 / N molar ratio, is 0.1 to 1, preferably 0.2 to 0.85, and more preferably 0.3 to 0.7.

[0045] If the Cl2 / N molar ratio is greater than the upper limit, free chlorine may be generated. If it is less than the lower limit, the efficiency of chloramine generation relative to the NH2-based compound used is reduced.

[0046] In this case, the amount of hypochlorous acid and / or hypochlorite corresponds to the amount of chloramine compounds in the cleaning agent.

[0047] <Surfactants>

[0048] The cleaning agent of the present invention may also contain a non-amine anionic surfactant whose molecular structure does not contain amine groups or amine oxides. In terms of cleaning effectiveness, non-amine anionic surfactants with a molecular weight of 1000 or less are preferred. Non-amine surfactants with excessively high molecular weights not only fail to achieve a cleaning effect but may also contaminate the membrane.

[0049] As such non-amine anionic surfactants, one or more of alkylbenzene sulfonates such as sodium dodecylbenzenesulfonate, alkyl sulfates such as sodium lauryl sulfate, alkyl diphenyl ether disulfonates, alkylnaphthalene sulfonates, dialkyl sulfosuccinates, polyoxyethylene alkyl ether sulfates, α-sulfo fatty acid methyl ester salts, α-olefin sulfonates, etc. can be used.

[0050] <Silicic acid compounds>

[0051] As the silicic acid compound (silicate), preferred are one or more of metasilicates such as sodium metasilicate, potassium metasilicate, lithium metasilicate, calcium metasilicate, and magnesium metasilicate, orthosilicates such as sodium orthosilicate, and pyrosilicates such as sodium pyrosilicate, among which sodium metasilicate is preferred.

[0052] <Cleanser pH and Component Concentration>

[0053] The pH of the cleaning agent of the present invention is usually 13 or higher due to the presence of the silicic acid compound. Preferably, the concentration of the stabilized halogen in the cleaning agent is 0.1M to 2M, the concentration of the silicic acid compound is 0.01M to 0.05M, and the concentration of the non-amine surfactant is 0.5M or less, for example, 0.002M to 0.5M.

[0054] <Cleansing solution pH and component concentration>

[0055] The cleaning solution of the present invention comprises an aqueous solution obtained by diluting the cleaning agent with water. If the pH of the cleaning solution is less than 11, the permeate flux cannot be fully restored. Higher pH values improve cleaning effectiveness, but excessively high pH values impair handling as a cleaning solution, increasing the risk of degradation of permeable membranes such as RO membranes. The pH of the cleaning solution is preferably between 11 and 13.

[0056] The concentration of stabilized halogens such as chloramine compounds in the cleaning solution is preferably 0.001M to 0.02M, particularly preferably 0.005M to 0.02M. If the stabilized halogen concentration of the cleaning solution is too low, a sufficient cleaning effect cannot be obtained. If it is too high, permeable membranes such as RO membranes may be degraded. It should be noted that the so-called chloramine compound concentration of 0.1M is a concentration equivalent to 7100mg-Cl2 / L in terms of total chlorine concentration. The total chlorine concentration can be measured by the diethyl-p-phenylenediamine (DPD) method specified in Japanese Industrial Standards (JIS) K0400-33-10.1999.

[0057] Chloramine compounds have been used as slime control agents for membranes. These slime control agents are typically used at low concentrations, with total chlorine concentrations ranging from 0.05 mg-Cl2 / L to 50 mg-Cl2 / L. The pH at these concentrations is less than 10. In contrast, the cleaning solution of the present invention contains chloramine compounds at such high concentrations that it exhibits a high alkalinity of pH 11 or higher, resulting in a high cleaning effect.

[0058] The concentration of the silicate compound in the cleaning solution including the diluent is preferably 0.0001M to 0.0005M.

[0059] The concentration of the non-amine anionic surfactant in the cleaning solution is preferably 0.005M or less, and particularly preferably 0.0002M to 0.005M.

[0060] <Cleaning agent and cleaning liquid manufacturing method>

[0061] The stabilized halogen used in the cleaning agent of the present invention is monochloroaminosulfonic acid, etc., and can be prepared by adding hypochlorous acid and / or hypochlorite to an aqueous solution of an NH2-based compound such as sulfamic acid and mixing the mixture. The aqueous solution preferably contains 50% to 90% water by weight. The silicic acid compound and the non-amine anionic surfactant can be added during the preparation of the cleaning agent or to the aqueous stabilized halogen solution.

[0062] Compounds having a primary amino group such as sulfamic acid may be in the form of salts. Examples of such salts include salts that are soluble in an alkaline aqueous solution containing a chloramine compound / silicic acid compound, such as sodium sulfamate, potassium sulfamate, and ammonium sulfamate.

[0063] The cleaning liquid of the present invention is produced by diluting the cleaning agent of the present invention produced in this manner with water, preferably pure water. The cleaning liquid of the present invention can also be produced directly by the same method as described above without using the cleaning agent of the present invention.

[0064] <Other cleaning agent ingredients>

[0065] Other cleaning agent components may be added to the cleaning agent or cleaning solution used in the present invention, provided that their cleaning effect is not impaired. For example, the cleaning agent or cleaning solution of the present invention may also contain an alkaline agent. The alkaline agent may be an alkali metal hydroxide such as sodium hydroxide or potassium hydroxide. These may be used alone or in combination of two or more.

[0066] Cleaning method

[0067] The method for cleaning the aromatic polyamide reverse osmosis membrane using the cleaning solution of the present invention is not particularly limited as long as the aromatic polyamide reverse osmosis membrane is brought into contact with the cleaning solution. Immersion cleaning is typically performed by introducing the cleaning solution to the raw water side of the permeable membrane module and allowing the membrane to stand.

[0068] The immersion and cleaning time in the cleaning solution is not particularly limited as long as the target recovery rate of membrane performance can be obtained, and is generally about 2 to 24 hours.

[0069] After cleaning with the cleaning solution, high-purity water such as pure water is usually passed through for final cleaning.

[0070] Furthermore, the aromatic polyamide reverse osmosis membrane may be cleaned with another cleaning solution before or after cleaning using the cleaning solution of the present invention. The aromatic polyamide reverse osmosis membrane may also be cleaned with an alkaline aqueous solution free of chloramine compounds and silicic acid compounds before or after cleaning using the cleaning solution of the present invention. Furthermore, acid cleaning, which is effective for removing scale and metal colloids, may also be performed.

[0071] [Example]

[0072] [Examples 1 to 3 and Comparative Examples 1 to 3]

[0073] The present invention will be described in more detail below with reference to Examples and Comparative Examples.

[0074] In the following examples and comparative examples, an RO membrane (Filmtec SW30) contaminated with organic matter recovered from a wastewater treatment plant was placed in a container filled with a cleaning solution. The cleaning solution in the container was circulated at 35°C using a pump connected to the container. 2 0.9 L of cleaning solution was used. The pH and total chlorine content of the cleaning solution were measured (DPD method) at regular intervals, and the total chlorine consumption was calculated.

[0075] [Chlorine consumption] = [initial chlorine concentration] - [chlorine concentration after a certain period of time]

[0076] Cleaning fluid

[0077] As the cleaning liquid, a sodium hydroxide aqueous solution with a pH of 12 containing the components shown in Table 1 was used.

[0078] [Table 1]

[0079]

[0080] The changes in pH and chlorine consumption over time in Example 1 and Comparative Example 1 are shown in FIG. Figure 1 、 Figure 2 The time-dependent changes in chlorine consumption of Example 2, Example 3 and Comparative Example 2, Comparative Example 3 are shown in FIG. Figure 3 Compared to the comparative examples, the examples showed less reduction in pH and less increase in chlorine consumption. This demonstrates that, in the examples, the decrease in stabilized halogen concentration was sufficiently suppressed, maintaining alkaline conditions. Therefore, the cleaning solutions of the examples, in addition to the stripping and hydrolysis effects under alkaline conditions, also exhibit synergistic effects of the stabilized halogen in terms of sterilization and organic matter decomposition, effectively restoring the performance of aromatic polyamide reverse osmosis membranes.

[0081] Although the present invention has been described in detail using specific embodiments, it is obvious to those skilled in the art that various modifications can be made while still achieving the effects of the invention.

[0082] This application is based on Japanese patent application No. 2023-001215 filed on January 6, 2023, the entire contents of which are incorporated herein by reference.

Claims

1. A cleaning agent for aromatic polyamide reverse osmosis membrane, wherein: The cleaning agent includes an aqueous solution containing a stabilized halogen and a silicic acid compound.

2. The cleaning agent for aromatic polyamide reverse osmosis membrane according to claim 1, wherein The concentration of the stabilized halogen in the cleaning agent is 0.1M-2M, and the concentration of the silicic acid compound is 0.01M-0.05M.

3. The cleaning agent for aromatic polyamide reverse osmosis membrane according to claim 1, wherein The stabilizing halogen comprises monochlorosulfamic acid.

4. The cleaning agent for aromatic polyamide reverse osmosis membrane according to claim 1, wherein The silicic acid compound is at least one of sodium silicate and potassium silicate.

5. The cleaning agent for aromatic polyamide reverse osmosis membrane according to claim 1, wherein The cleaning agent includes a non-amine anionic surfactant having no amine group or amine oxide with a molecular weight less than 1000 in its molecular structure.

6. The cleaning agent for aromatic polyamide reverse osmosis membrane according to claim 5, wherein The concentration of the non-amine anionic surfactant in the aqueous solution is 0.002M to 0.5M.

7. The cleaning agent for aromatic polyamide reverse osmosis membrane according to claim 1, wherein The stabilized halogen is a reaction product of one or more selected from the group consisting of a compound having a primary amino group, ammonia, and an ammonium salt, and hypochlorous acid and / or hypochlorite.

8. A cleaning solution for an aromatic polyamide reverse osmosis membrane, wherein: The cleaning liquid comprises a diluted aqueous solution of the cleaning agent for the aromatic polyamide-based reverse osmosis membrane according to any one of claims 1 to 7.

9. The cleaning solution for an aromatic polyamide reverse osmosis membrane according to claim 8, wherein The pH of the cleaning solution is 11-13.

10. The cleaning solution for an aromatic polyamide reverse osmosis membrane according to claim 8, wherein The concentration of the stabilized halogen in the cleaning solution is 0.001M to 0.02M, and the concentration of the silicic acid compound is 0.0001M to 0.0005M.

11. A method for cleaning an aromatic polyamide reverse osmosis membrane, wherein: The cleaning method comprises the step of bringing the aromatic polyamide reverse osmosis membrane into contact with the cleaning solution according to claim 8 .

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