WO2006061953A1

WO2006061953A1 - Detergent for selectively permeable membranes and method for washing the membranes

Info

Publication number: WO2006061953A1
Application number: PCT/JP2005/019190
Authority: WO
Inventors: Shuhei Izawa; Takahiro Kawakatsu
Original assignee: Kurita Water Industries Ltd.
Priority date: 2004-12-06
Filing date: 2005-10-19
Publication date: 2006-06-15
Also published as: JP4691970B2; JP2006159062A

Abstract

A method for washing a selectively permeable membrane, in which the detergency against strong complex pollutants formed by combination of organic substances such as surfactant with inorganic pollutants such as scale is enhanced by enhancing the detergency against TOC components having molecular weights exceeding 400 such as polyalkylene glycol, nonionic surfactants, proteins, polysaccharides, glycoproteins, or humins and imparting the ability to remove inorganic substances such as scales, whereby effective recovery of the membrane performance can be attained in a short time via simple steps. This method comprises bringing a selectively permeable membrane into contact with a detergent for selectively permeable membranes which contains a polyol having a molecular weight of 400 or below and an acid or an alkali to dissolve and remove the pollutants adhering to the membrane.

Description

Selective permeable membrane cleaning agent and cleaning method

Technical field

[0001] The present invention relates to a cleaning agent for cleaning a selective permeable membrane such as a reverse osmosis membrane or a nanofiltration membrane, and a cleaning method using the cleaning agent. A cleaning agent for cleaning the permeation flux and other selectively permeable membranes that have been degraded by water treatment such as desalination, pure water production, etc. It is related with the washing | cleaning method which uses.

Background art

[0002] When selective permeable membranes such as reverse osmosis membranes and ultrafiltration membranes are used to concentrate liquids, desalinate, produce pure water, and other water treatments, the selective permeable membranes are contaminated with various pollutants. As a result, the permeation flux decreases and the selective permeability decreases. For this reason, the selective permeation membrane with reduced performance is washed with a cleaning agent to restore the performance.

[0003] Conventionally, in selective permeation membrane cleaning methods with reduced performance such as permeation flux, acids, alkalis, organic solvents or surfactants are often used as cleaning agents. For example, Patent Document 1 (Japanese Patent Publication No. 54-99783) discloses a cleaning method using an alkali as a cleaning agent. In this method, the permeation flux is recovered in a short time when the degree of contamination is high. The permeation flux recovery rate is less than 100%. When a selective permeable membrane is used for treatment of wastewater containing inorganic and organic substances, contaminants including inorganic and organic substances will adhere, but such deposits cannot be removed by using the above cleaning agent alone. For this reason, for example, after washing with an acid, washing with an alkali is performed in combination with the front and back. However, even in this case, although the washing process is complicated and the washing time becomes long, the improvement of the washing effect is small and the recovery rate of the permeation flux is not sufficient.

[0004] On the other hand, wastewater containing TOC (total organic carbon) components exceeding 400 molecular weight such as high molecular weight polyalkylene glycol, non-ionic surfactant, protein, polysaccharide, glycoprotein, humin, etc. By treating with a selective permeable membrane, the selective permeable component with these TOC components attached is obtained. The film cannot recover its performance with the above-mentioned conventional cleaning agents. As a method for cleaning the selective permeable membrane to which the above polyalkylene glycol or nonionic surfactant is attached, Patent Document 2 (WO 2004-076040) is a cleaning agent containing a positive molecular weight having a molecular weight of 400 or less, Alternatively, a cleaning method is shown in which the selective permeable membrane is cleaned with a cleaning agent containing an organic solvent. This method is a method in which a permselective membrane having a reduced permeation performance such as a permeation flux is brought into contact with the above-mentioned cleaning agent for cleaning, and the polyalkylene glycol or the non-ionic surfactant adheres thereto. It has been shown that the selective permeable membrane can be effectively washed.

[0005] In Patent Document 2, in order to further enhance the cleaning effect of cleaning with a cleaning agent containing a polyol having a molecular weight of 400 or less, cleaning with a cleaning agent containing an acid as a pre-cleaning or post-cleaning, or a cleaning agent containing alkali Or other cleanings have been shown. This method is a combination of cleaning with a cleaning agent containing a polyol having a molecular weight of 400 or less and cleaning with an acid-containing cleaning agent or cleaning with an alkali-containing cleaning agent by shifting them back and forth. It is a method to do. However, such a cleaning method has problems such as a complicated cleaning process, a long cleaning time, and insufficient cleaning recovery. Patent Document 1: Japanese Patent Publication No. 54-99783

Patent Document 2: WO 2004-076040

Disclosure of the invention

Problems to be solved by the invention

[0006] An object of the present invention is to increase the cleaning effect on organic substances that are difficult to remove, such as TOC components having a molecular weight of more than 400, and to add the ability to remove inorganic substances such as scales. To propose a cleaning method for selective permeation membranes that can improve the cleaning performance against strong complex contamination with contamination by inorganic substances and can effectively restore membrane performance in a short time with a simple process. It is.

Means for solving the problem

The present invention provides the following selective permeable membrane cleaning method.

(1) A cleaning agent for a selective permeable membrane containing a polyol having a molecular weight of 400 or less and an acid or an alkali. (2) The cleaning agent according to the above (1), wherein the polyol is at least one selected from the group power of ethylene glycol, diethylene glycol, propylene glycol, glycerin, polydalicol and sugar alcohol.

(3) The cleaning agent according to (1) or (2) above, wherein the acid is at least one selected from the group power of nitric acid, hydrochloric acid, sulfuric acid, oxalic acid, and succinic acid.

(4) The washing according to any one of (1) and (3) above, wherein the alkali is at least one selected from the group consisting of sodium hydroxide, potassium hydroxide and lithium hydroxide. Agent.

(5) The cleaning agent according to any one of (1) and (4) above, wherein the selective permeable membrane to be cleaned is a TOC component having a molecular weight of more than 400 attached.

(6) A method for cleaning a selective permeable membrane, in which the selective permeable membrane having a reduced permeation flux is washed with a selective permeable membrane cleaner containing a polyol having a molecular weight of 400 or less and an acid or an alkali.

[0008] In the present invention, the selective permeable membrane to be cleaned is a selective permeable membrane with reduced permeation flux, selective permeability, and other performance. Here, the selective permeable membrane is a semipermeable membrane that selectively permeates a specific substance, component, etc., such as a reverse osmosis membrane or a nanofiltration membrane. Things are the target. The material of the selective permeable membrane is not particularly limited, and examples thereof include polyamide permeable membranes, polysulfone permeable membranes, polyimide permeable membranes, and cellulose permeable membranes. The membrane to be cleaned may be a selective permeable membrane itself or a membrane module. The membrane module to be cleaned is not particularly limited, and examples thereof include a tubular membrane module, a planar membrane module, a spiral membrane module, and a hollow fiber membrane module.

[0009] Although the cause of the performance degradation of the selective permeable membrane is not limited, it can be contaminated by the use of a reverse osmosis membrane such as water treatment such as liquid concentration, desalting, pure water production, or other treatments. Is common. All contaminants such as organic substances such as surfactants and inorganic substances such as scales, which are not limited as contaminants, are targeted, but the selective permeation has deteriorated due to the strong combined contamination of organic and inorganic contamination. Membrane is suitable for cleaning. In particular, TOC components with a molecular weight of more than 400, specifically high molecular weight polyalkylene glycols, nonionic surfactants (especially alkyl ether type Detergents), proteins, polysaccharides, glycoproteins, humins (e.g. humic acid), etc., and selective permeable membranes with inorganic substances such as calcium salts attached. Even a selective permeable membrane can be washed.

[0010] Polyalkylene glycols such as polyethylene glycol and polypropylene glycol, particularly polyethylene glycol, are selected as nonionic surfactants, particularly alkyl ether type nonionic surfactants. Since it has a high affinity with the permeable membrane, it adheres to the surface and pores of the selective permeable membrane and causes a decrease in performance. Of these, those with a molecular weight of 400 or less have high affinity water, so they are easily washed and removed by washing with water, etc., but are selected with a high molecular weight polyalkylene glycol or nonionic surfactant that exceeds 400 in molecular weight. The permeable permeable membrane is not removed by permeation of water, causing performance degradation, and is difficult to remove by washing with water. The same applies to other TOC components having a molecular weight exceeding 400 such as proteins, polysaccharides, glycoproteins, and humins. The above polyalkylene glycols with a molecular weight exceeding 400, non-ionic surfactants, and other TOC components with a molecular weight exceeding 400, even when only these adhere to the selective permeable membrane as contaminants. Forces that are difficult to remove by washing In addition to these, it is difficult to wash and remove composite contaminants when inorganic scale components such as calcium adhere to the selective permeable membrane as composite contaminants.

[0011] The selective permeable membrane cleaning agent of the present invention is a cleaning agent including both a polyol having a molecular weight of 400 or less and an acid or alkali. In addition to these components, an organic solvent or other solvent is also included. Ingredients may be included. The selective permeable membrane cleaning agent of the present invention is often used as an aqueous solution at the time of use, but as a product form, it may or may not contain water. The selective permeable membrane cleaning agent of the present invention only needs to contain both a polyol having a molecular weight of 400 or less and an acid or alkali at the time of use. It may be prepared and used.

[0012] Polyol is a compound having a plurality of OH groups, such as ethylene glycol, propylene glycol, trimethylene glycol and other alkylene glycols; glycerin; diethylene glycol and other polyalkylene glycols such as polyglycols; and erythritol Sugar alcohols and the like. These polyols are preferably those having 2 to 6 carbon atoms and an OHZC ratio of 0.5 to 1 which are preferably hydrophilic. These poly Although oar can be used alone, it is preferred because it can improve the cleaning effect by using it as a mixture of two or more. In order to increase the cleaning effect by increasing the solubility of the non-ionic surfactant, the polyalkylene glycol such as diethylene glycol and other substances may be used. It is preferable to use a polyol in combination.

[0013] Examples of the acid used for the cleaning agent in the present invention include inorganic acids such as nitric acid, hydrochloric acid and sulfuric acid, and organic acids such as oxalic acid and citrate, and nitric acid is particularly preferred. Detergents that combine polyols and acids with a molecular weight of 400 or less are suitable for cleaning membranes that adhere to inorganic scale components such as calcium carbonate and calcium phosphate, and contaminants such as metals such as iron and manganese. Among these, nitric acid is suitable for cleaning a selectively permeable membrane to which contaminants such as proteins are attached by simply removing the inorganic components described above.

[0014] Examples of the alkali include sodium hydroxide, potassium hydroxide, lithium hydroxide, and the like, and sodium hydroxide is particularly preferable. A cleaning agent combining a polyol with a molecular weight of 400 or less and an alkali is suitable for cleaning a selective permeable membrane to which inorganic components such as silica and aluminum hydroxide and contaminants such as high molecular organic substances such as protein and humin are attached. Yes.

[0015] As the organic solvent blended in the cleaning agent of the present invention as necessary, organic solvents that have been used conventionally such as monohydric alcohols, ethers, ketones and amides can be used. These organic solvents are preferably those having 1 to 3 carbon atoms, which polar solvents are preferred. Examples of the monovalent alcohol include methanol and ethanol, examples of the ether include ethers of the above monohydric alcohol or polyol, examples of the ketone include acetone and acetyl acetate, and examples of the amide include formamide. These organic solvents may also be included alone or in a mixture of two or more.

[0016] For the selective permeable membrane whose permeation flux is reduced due to organic contamination, an anionic surfactant can be further blended as another component if necessary. Examples of the anionic surfactant include alkyl sulfate esters such as sodium alkyl sulfate, linear alkyl benzene sulfonate such as sodium dodecyl benzene sulfonate, and alkyl sulfate such as sodium dodecyl sulfate (SDS). It is done.

[0017] For a film to which an inorganic component such as a scale adheres, if necessary, as another component, A chelating agent can be blended with. Chelating agents include aliphatic carboxylic acids such as oxalic acid, citrate or their salts: ethylenepolyamine tetraacetic acid (EDTA) or aminopolycarboxylic acids such as their salts: darconic acid, phosphonic acid, polyphosphoric acid (pyrophosphoric acid, And other acids such as hexametaphosphoric acid) or salts thereof.

[0018] A reducing agent can be further blended as another component if necessary to the film contaminated by the adhesion of slime (microorganisms). Examples of the reducing agent include sodium sulfite, sodium sulfite, sodium thionite, sodium erythorbate, sodium ascorbate, cysteine, and hydrazine.

[0019] The cleaning agent containing a polyol having a molecular weight of 400 or less and an acid or alkali used as a cleaning agent for the selective permeable membrane of the present invention may be used without containing water, or may be used as an aqueous solution. Good. The concentration of the aqueous solution during use of these components as a cleaning agent is not particularly limited, but the concentration of a polyol having a molecular weight of 400 or less is usually 1 to 50% by weight, and preferably 20 to 50% by weight. When an acid is used, it can be added in such an amount that the aqueous solution strength during use is H3 or less, preferably pH2 or less. In the case of nitric acid, it can usually be 0.01 to 30% by weight, preferably 1 to 20% by weight. When an alkali is used, it can be added in such an amount that the aqueous solution strength during use is H10 or more, preferably pH 12 or more, more preferably pH 12-13. The concentration of other components to be blended if necessary is usually 1% by weight or less, preferably 0.2% by weight or less for each component, but the total amount of each component is preferably 1% by weight or less, preferably 0.2% by weight or less is preferable. The above concentration is the concentration at the time of use. Depending on the product, it may be used at this concentration, or it may be diluted at a higher concentration than this. Also good.

[0020] The selective permeable membrane cleaning method of the present invention is a method of cleaning a selective permeable membrane with reduced performance such as permeation flux with a cleaning agent containing the above polyol and an acid or an alkali. As a specific method of cleaning, there is a method in which the selective permeable membrane is brought into contact with a cleaning agent, and immersion in a cleaning agent solution, cleaning by a parallel flow or a stirring flow is preferable, but the cleaning agent permeates the selective permeable membrane. It can also be washed. The pressure at the time of washing is not particularly limited in the case of immersion, but it may not be pressurized, but in the case of washing by parallel flow, stirring flow or permeation, the treatment Pressurization can be performed at a pressure equal to or lower than the pressure during liquid permeation. The cleaning time, that is, the time of contact with the cleaning agent varies depending on the degree of contamination, the concentration of the cleaning agent, etc., but can generally be 1 to 8 hours.

[0021] By cleaning with the above-described cleaning agent, the contaminants adhering to the selective permeable membrane dissolve and flow out in the cleaning agent, and the permeation flux and the selective permeation rate of the selective permeable membrane are reduced. Etc. can be recovered. The cleaning agent of the present invention has a high cleaning effect on the selective permeable membrane and is safe and safe for people and the environment without degrading the selective permeable membrane. A selective permeable membrane with reduced performance can be efficiently washed in a short time to restore performance. In this case, in addition to the contaminants attached due to the use of the selective permeable membrane, the contaminants that had been attached to the pre-use force may also be removed, and the removal rate and performance recovery rate may exceed 100%.

[0022] In the above-described cleaning, pre-processing cleaning, post-processing cleaning, and the like by other cleaning methods may be performed before and after cleaning with a cleaning agent. If necessary, after washing, operations such as washing with pure water and solvent replacement with the liquid to be treated can be performed.

The invention's effect

[0023] According to the present invention, the selective permeable membrane is washed with a detergent containing a polyol having a molecular weight of 400 or less and an acid or an alkali. Therefore, an organic substance that is difficult to remove such as a TOC component having a molecular weight of more than 400 is used. In addition to improving the cleaning effect against scales, it is possible to add the ability to remove inorganic substances such as scales. The membrane performance can be effectively recovered in a short time.

Brief Description of Drawings

FIG. 1 is a graph showing the results of Example 1.

BEST MODE FOR CARRYING OUT THE INVENTION

[0025] Examples and comparative examples of the present invention will be described below. In each example, unless otherwise specified,% is% by weight.

[Comparative Examples 1 to 3]:

Alkyl ether type nonionic surfactant (polyoxyethylene (20) lauryl ether NTR '759H R manufactured by Nitto Denko Co., Ltd. (the pure water permeation flux of the new membrane is 1.2MPa with operating pressure of 1.2MPa and 1.0 to 1.2mZd) As a result, the permeation flux decreased to 0.20 mZd, and in Comparative Example 1, this contaminated membrane (CMe) was immersed in an aqueous solution of sodium hydroxide (pH 12) for 24 hours. Pure water was passed through (indicated as NaOH (pH 12)) In Comparative Example 2, pure water was passed through after being immersed in a 20% nitric acid aqueous solution for 24 hours (indicated as 20% HNO). In 3, the contamination film is 50

Three

o / o ethylene glycol (EG), 20% nitric acid aqueous solution (HNO) in this order, 24 hours each

Three

After that, pure water was passed through (displayed as 50% EG → 20% HNO). Pure water permeability after each cleaning operation

Three

Table 1 shows the overflux. In Comparative Examples 1 and 2, the permeation flux hardly recovered. On the other hand, in Comparative Example 3, the force at which the permeation flux was recovered as compared with Comparative Examples 1 and 2 due to the use of the polyol was satisfactory in comparison with the following examples.

[Example 1]:

The contaminated membrane (CMe) used in Comparative Examples 1 to 3 was immersed in an aqueous solution of 50% ethylene glycol (EG) and 0.06 to 20% nitric acid (HNO) for 24 hours, and then purified water was passed through (50% EG + 0.

Three

06-20% HNO is displayed). Figure 1 shows the pure water permeation flux (Flux) after cleaning of each cleaning solution.

Three

. The pure water permeation flux of 50% ethylene glycol (EG) and 20% nitric acid (HNO) is shown in Table 1.

Three

Show. From the results shown in Fig. 1 and Table 1, the higher the concentration of nitric acid, the higher the detergency. Therefore, nitric acid swells the membrane and the polyol easily comes into contact with the non-ionic surfactant that is a membrane contaminant. It is thought that the cleaning effect has improved. The effect was particularly remarkable at nitric acid concentrations of 1% or higher. It is clear that the performance of a reverse osmosis membrane with a significantly reduced permeation flux with a nonionic surfactant can be effectively recovered in a short time by washing with a mixture of polyol and acid, particularly nitric acid. is there.

[0028] [Table 1] table 1

[Comparative Examples 4 to 5]:

TOC component exceeding 400 molecular weight: 0.3 mgZL, Ca: 0.7 mg / L, A1: 0. Olmg / L, Fe: 0.05 mgZL Reverse Osmosis Membrane SU · 720 Co., Ltd. (The pure water permeation flux of the new membrane was filtered using 1.2 to 1.3 mZd at an operating pressure of 1.2 MPa and an operating pressure of 1.2 MPa. As a result, the permeation flux was As a result of observing the film surface with fluorescent X-rays, inorganic substances such as Al, Ca, and Fe were attached.

In Comparative Example 4, this contaminated membrane (CMe) was immersed in a sodium hydroxide aqueous solution (pH 12) for 24 hours, and then purified water was passed through (labeled NaOH (pH 12)). In Comparative Example 5, pure water was passed through after being immersed in a 5% nitric acid aqueous solution for 24 hours (indicated as 5% HNO). Pure after each cleaning operation

Three

Table 2 shows the water flux. These cleaning methods were unable to recover to the same extent as the new membrane.

[Comparative Example 6]:

After immersing the contaminated film (CMe) used in Comparative Examples 4 and 5 in the order of sodium hydroxide aqueous solution (pH 12), 5% aqueous nitric acid solution, and aqueous sodium hydroxide solution (PH12) for 24 hours, respectively, pure water Water was passed through (NaOH (pH12) → 20% HNO → NaOH (pH12)). Pure water permeation after washing

Three

Table 2 shows the flux. This contaminated film was a composite contamination of organic contamination and scale, so it is considered that the performance could be recovered by alternately performing alkaline cleaning and acid cleaning. However, this cleaning method required more than 3 days for cleaning. [Comparative Examples 7 to 8]:

The contamination film (CMe) used in Comparative Examples 4 and 5 was washed using a 5% nitric acid aqueous solution and a mixed aqueous solution of 50% propylene glycol (PG) and 20% methanol (MeOH) as a washing solution. In Comparative Example 7, the acid and polyol were soaked in the order of 24 hours, respectively, and then pure water was passed (indicated as 5% HN 2 O → 50% PG + 20% MeOH). In Comparative Example 8, the order of polyol and acid was followed. 24 each

Three

After soaking for a while, pure water was passed (50% PG + 20% MeOH → 20% HNO)

Three

). Table 2 shows the pure water permeation flux after washing. In Comparative Example 7, since the polyol was washed in the presence of scale, the removal of organic contaminants by the polyol was hindered, and the permeation flux could not be restored to the level of the unused membrane. In Comparative Example 8, it was possible to recover the permeation flux by performing the polyol washing after the scale removal, and it took more than 2 days for the force washing.

[Example 2]:

The contaminated membrane (CMe) used in Comparative Examples 4 and 5 was immersed in an aqueous solution of 50% propylene glycol (PG) and 5% nitric acid for 24 hours and then passed with pure water (50% PG + 5% HNO and display). Wash

3 Table 2 shows the pure water permeation flux after purification. The permeation flux was recovered even when the combination of alkali cleaning and acid cleaning in Comparative Example 6 and the combination of polyol cleaning and acid cleaning in Comparative Example 8 were restored, but in Example 2, organic contaminant removal by polyol and acid cleaning were performed. Due to the combined effect of scale removal by, higher permeation flux was obtained with cleaning times from 1Z3 min to 1Z2.

[0033] [Table 2]

Table 2

[Comparative Examples 9 to 10]:

Nitto Denko Co., Ltd. reverse osmosis membrane ES · Treatment liquid of material processing plant wastewater treatment equipment (TOC component exceeding 400 molecular weight: 0.25mg ZL, A1: 0. Olmg / L, Si: 3mgZL) 20 (The water-saving permeation flux of the new membrane was filtered at an operating pressure of 0.75 MPa and 1.0-1.2 mZd at an operating pressure of 0.75 MPa. As a result, the permeation flux decreased to 0.56 mZd. As a result of observing the film surface, inorganic substances such as Al and Si were adhered.

In Comparative Example 9, the contaminated membrane (CMe) was immersed in a sodium hydroxide aqueous solution (pH 12) for 4 hours, and then pure water was passed through (displayed as NaOH (pH 12)). In Comparative Example 10, the contaminated film (C Me) was immersed in a 1% aqueous propylene glycol (PG) solution for 4 hours, and then pure water was passed through (denoted as 1% PG). Table 3 shows the pure water permeation flux after each washing operation. These cleaning methods have been unable to recover to the same extent as the new membrane.

[Comparative Example 11]

The contaminated (CMe) membranes used in Comparative Examples 9 and 10 were soaked in the order of 1% propylene glycol (PG) and aqueous sodium hydroxide solution (PH12) for 4 hours, respectively, and then passed with pure water (1 % PG → NaOH (pH12)). Table 3 shows the pure water permeation flux after washing. Since the polyol was washed in the presence of scale, removal of organic pollutants by the polyol was hindered, and it was considered impossible to restore the permeation flux to the level of the unused membrane. [Example 3]:

The contaminated membrane (CMe) used in Comparative Examples 9 and 10 was immersed in a mixed aqueous solution (pH 12) of 1% propylene glycol (PG) and sodium hydroxide for 4 hours, and then purified water was passed through (1% PG + Na OH (pH12)). Table 3 shows the pure water permeation flux after washing. At the same time that inorganic substances such as A1 and some organic substances are removed by alkali, organic substances that cannot be removed by alkali can be removed by polyol, so that the permeation flux can be restored to the same level as the new membrane. It is thought that it was able to wash effectively in a shorter time than Comparative Example 11.

[0037] [Table 3]

Table 3

[Comparative Examples 12 to 14]:

NTR-759HRC, a reverse osmosis membrane manufactured by Nitto Denko Co., Ltd. Filtration was performed at 1.2 MPa with an operating pressure of 1.2 MPa at 1.2 MPa, and as a result, the permeation flux decreased to 0.56 mZd. After being immersed in an aqueous sodium solution (PH12) for 24 hours, pure water was passed through (indicated as NaOH (pH 12)) In Comparative Example 13, after being immersed in a 20% nitric acid aqueous solution for 24 hours, pure water was passed through In Comparative Example 14, 50% ethylene glycol (EG), 20%

Three

After immersing in a mixed aqueous solution of ethanol for 24 hours, pure water was passed through (displayed as 50% PG + 20% Me OH). Table 4 shows the pure water permeation flux after each washing operation. Comparative Examples 12-14 However, it was not possible to restore the performance to the level of the unused membrane.

[Comparative Example 15]

The contaminated soot (CMe) used in Comparative Examples 12 to 14 was immersed in a 20% nitric acid aqueous solution, 50% ethylene glycol (EG) and 20% methanol mixed aqueous solution in this order for 24 hours, respectively, followed by pure water flow. (Displayed as 20% HNO → 50% PG + 20% MeOH). Permeation of pure water after washing operation

Three

Table 4 shows the flux. By combining a high concentration of nitric acid with a polyol wash, the performance could be fully restored. It is thought that protein was decomposed by the oxidizing power of nitric acid and removed from the membrane surface by polyol.

[Example 4]:

The contaminated membrane (CMe) used in Comparative Examples 12 to 14 was immersed in a mixed aqueous solution of 50% ethylene glycol (EG) and 20% nitric acid for 24 hours and then passed with pure water (50% PG + 20% HNO

3). Table 4 shows the pure water permeation flux after washing. By the cleaning method of the present invention, the permeation flux was recovered to the same level as that of the new membrane. It has been clarified that the performance of the reverse osmosis membrane having a reduced permeation flux can be recovered by a polymer organic material such as protein by a mixture of polyol and acid. The permeation flux recovers even with the cleaning method of Comparative Example 15. With this cleaning method, an even higher permeation flux was obtained in half the cleaning time.

[0041] [Table 4]

Table 4 Comparative Example 12 Comparative Example 13 Comparative Example 14 Comparative Example 15 Example 4

20% HN0 ₃ →

Contaminated membrane NaOH 50 EG + 50% EG + Cleaning solution 20% 隱₃ 50% EG +

(CMe) (pH12) 20 MeOH 20% HN0 ₃

20% eOH

Cleaning time

_ 2 4 2 4 2 4 4 8 2 4

[hour]

Pure water permeation flux

0. 56 0. 62 0. 75 0. 77 1. 00 1.05 [m / d] Industrial applicability

Selective permeable membranes such as reverse osmosis membranes and nanofiltration membranes that have been contaminated by water treatment such as liquid concentration, desalination, pure water production, etc. Can be used for cleaning to restore performance.

Claims

The scope of the claims

[1] A selective permeable membrane cleaning agent comprising a polyol having a molecular weight of 400 or less and an acid or an alkali.

[2] The cleaning agent according to claim 1, wherein the polyol is at least one selected from ethylene glycol, diethylene glycol, propylene glycol, glycerin, polydaricol, and a group power that also has sugar alcohol power.

[3] The cleaning agent according to claim 1 or 2, wherein the acid is at least one selected from the group power of nitric acid, hydrochloric acid, sulfuric acid, oxalic acid, and succinic acid.

[4] The cleaning agent according to any one of [1] to [3], wherein the alkali is at least one selected from the group strength including sodium hydroxide, potassium hydroxide and lithium hydroxide.

[5] The cleaning agent according to any one of claims 1 and 4, wherein the selective permeable membrane to be cleaned is attached with a TOC component having a molecular weight exceeding 400.

[6] A method for cleaning a selective permeable membrane, in which a selective permeable membrane having a reduced permeation flux is washed with a selective permeable membrane cleaner containing a polyol having a molecular weight of 400 or less and an acid or alkali.