JP5772083B2 - Reverse osmosis membrane rejection rate improving method, rejection rate improving treatment agent, and reverse osmosis membrane - Google Patents

Description

  The present invention relates to a method for improving a rejection rate (desalting rate) of a reverse osmosis membrane, and more particularly to a method for repairing a deteriorated reverse osmosis (RO) membrane and effectively improving the rejection rate.

  The present invention also relates to a reverse osmosis membrane that has been subjected to a treatment for improving the rejection rate by the method for improving the rejection rate of the reverse osmosis membrane, and a treatment for improving the rejection rate used in this method.

  In recent years, in order to effectively use water resources, introduction of a process for recovering, reclaiming, and reusing wastewater and a process for desalinating seawater and brine has been promoted. Under these circumstances, in order to obtain treated water with high water quality, it is essential to use selective permeation membranes such as nanofiltration membranes and reverse osmosis membranes (RO membranes) that can remove electrolytes and medium and small molecules. It is.

  However, the blocking rate of permeable membranes such as RO membranes against separation targets such as inorganic electrolytes and water-soluble organic substances is due to the effects of oxidizing substances and reducing substances present in water, and deterioration of polymer materials due to other causes. The required quality of treated water cannot be obtained. This deterioration may occur little by little during long-term use, or it may occur suddenly due to an accident. In some cases, the rejection rate of the permeable membrane as a product does not reach the required level.

  In particular, in permeable membrane systems such as RO membranes, raw water is treated with chlorine (sodium hypochlorite, etc.) in the pretreatment process to prevent biofouling due to slime on the membrane surface. Since chlorine has a strong oxidizing action, it is known that when the residual chlorine is supplied to the permeable membrane without being sufficiently treated, the permeable membrane deteriorates.

  In order to decompose residual chlorine, a reducing agent such as sodium bisulfite is also added, but even in a reducing environment where sodium bisulfite is excessively added, metals such as Cu and Co are used. It is also known that the film deteriorates when coexisting (Patent Document 1, Non-Patent Document 1). When the membrane deteriorates, the blocking rate of the permeable membrane is greatly impaired.

  Conventionally, the following methods have been proposed as methods for improving the blocking rate of reverse osmosis membranes such as RO membranes.

(1) A method of improving the blocking rate of a permeable membrane by attaching an anionic or cationic ionic polymer compound to the membrane surface (Patent Document 2).

  Although this method shows a certain rejection rate improvement effect, the suppression rate improvement effect for the deteriorated film is not sufficient.

(2) A method for improving the rejection of nanofiltration membranes and RO membranes by attaching a compound having a polyalkylene glycol chain to the membrane surface (Patent Document 3).

  Although this method can also achieve the effect of improving the rejection rate, it is not fully satisfactory in the demand for improving the rejection rate without greatly reducing the permeation flux with respect to the deteriorated membrane.

(3) Treating nanofiltration membranes and RO membranes with anion charge with increased permeation flux with nonionic surfactants to reduce the permeation flux to an appropriate range, resulting in membrane contamination And a method for preventing deterioration of permeated water quality (Patent Document 4). In this method, the nonionic surfactant is brought into contact with and adhered to the membrane surface so that the permeation flux is in the range of +20 to −20% at the start of use.

The effectiveness of this method in improving the rejection rate can also be confirmed by comparing the Examples and Comparative Examples described in Patent Document 4, but in a membrane (95% or less in the desalination rate) in which deterioration has occurred significantly, A considerable amount of surfactant needs to be deposited on the membrane surface, which is thought to be accompanied by a dramatic decrease in permeation flux. Moreover, in the Example of this patent document 4, the initial performance at the time of manufacture is 1.20 m ³ / m ² · day in terms of permeation flux, the NaCl rejection is 99.7%, and the silica rejection is 99.5%. It is intended to use a membrane that has been oxidized and deteriorated for 2 years using an aromatic polyamide RO membrane, but has not yet been greatly degraded, with a NaCl rejection of 99.5% and a silica rejection of 98.0%. It is unclear whether this method can sufficiently improve the rejection of a deteriorated permeable membrane.

(4) A method of improving the desalination rate by attaching tannic acid or the like to a deteriorated film (Non-patent Document 2).

It cannot be said that the improvement effect of the rejection rate by this method is large. For example, the permeated water conductivity of ES20 (manufactured by Nitto Denko) and SUL-G20F (manufactured by Toray Industries), which are deteriorated RO membranes, are measured before and after the treatment. They are 82% → 88% and 92% → 94%, respectively, and the rejection rate cannot be increased until the solute concentration of the permeated water is halved.
(5) Polyvinyl methyl ether (PVME) is added to tannic acid to improve the RO membrane rejection (Non-patent Document 5). The drug use concentration is as high as 10 ppm or more. The desalination rate is recovered from 65% to 90%, but the decrease in permeation flux is 35%, and the decrease in permeation flux is 4% when 84% is recovered to 95%. Sustainability is low, 98.5% of new film → 99.2% immediately after repair → 98.7% after 190 hours.

  As for the deterioration of the permeable membrane, for example, it is known that the CN bond of the polyamide bond of the membrane material is broken due to the deterioration of the polyamide membrane by the oxidizing agent, and the original sieve structure of the membrane is collapsed ( Non-patent documents 3 and 4).

JP-A-7-308671 JP 2006-110520 A JP 2007-289922 A JP 2008-86945 A

Fujiwara et al., Desalination, Vol.96 (1994), 431-439 Sato, Tamura, Chemical Engineering, Vol.34 (2008), 493-498 Uemura et al., Bulletin of the Society of Sea Water Science, Japan, 57, 498-507 (2003) Yoshiyasu Kamiyama, Surface, vol.31, No.5 (1993), 408-418 S.T.Mitrouli, A.J.Karabelas, N.P.Isaias, D.C.Sioutopoulos, and A.S.Al Rammah, Reverse Osmosis Membrane Treatment Improves Salt-Rejection Performance, IDA Journal I Second Quarter 2010, p22-34

  As described above, various methods have conventionally been proposed as methods for improving the rejection rate of reverse osmosis membranes. However, the conventional method for improving the rejection rate is that a new substance adheres to the surface of the permeable membrane. A drop occurs. For example, in order to recover the rejection rate and reduce the solute concentration of the permeated water to ½, the permeation flux may be reduced by 20% or more compared to before the treatment.

  In addition, it is difficult to recover the rejection rate with the existing technology for a film that has undergone very large deterioration (for example, an electrical conductivity rejection rate of 95% or less).

  In addition, the addition of high-concentration chemicals causes operational problems such as increasing the concentrated water TOC, and it is not easy to restore the water to be treated by passing water to be treated. There was also a problem.

  The present invention solves the above-mentioned conventional problems, and a method for improving the rejection rate of a reverse osmosis membrane, which can effectively improve the rejection rate even if it is a significantly deteriorated membrane without greatly reducing the permeation flux, It aims at providing the processing agent.

  Another object of the present invention is to provide a reverse osmosis membrane that has been subjected to a rejection improvement process by such a reverse osmosis membrane rejection improvement method.

  In order to solve the above-mentioned problems, the present inventors have made extensive studies by repeatedly investigating and analyzing a deteriorated film with an actual machine, and obtained the following knowledge.

(1) As in the conventional method, in the method of closing the hole in the film due to the deterioration of the film by attaching a new substance (for example, a compound such as a nonionic surfactant or a cationic surfactant) to the film In addition, membrane permeabilization and membrane permeation flux decrease significantly due to adhesion of polymer substances, and it is difficult to ensure the amount of water.

(2) A reverse osmosis membrane, for example, a polyamide membrane, is degraded by an oxidant, so that the CN bond of the polyamide is broken and the original sieving structure of the membrane is broken. Although the amide group disappears, a part of the carboxyl group remains.

(3) By efficiently attaching and bonding an amino compound to the carboxyl group of the deteriorated film, the deteriorated film can be repaired and the blocking rate can be recovered. In this case, by using a low molecular weight compound having an amino group as the amino compound to be bonded to the carboxyl group, it is possible to suppress the membrane surface from being hydrophobized or a significant decrease in the permeation flux due to the attachment of a polymer substance. it can.

  The present invention has been completed based on such knowledge, and the gist thereof is as follows.

The method for improving the rejection of a reverse osmosis membrane according to claim 1 includes a first organic compound having a molecular weight of less than 200, a second organic compound having a molecular weight of 200 or more and less than 500, and a third organic compound having a molecular weight of 500 or more. A method for improving the rejection of a reverse osmosis membrane comprising a step of passing an aqueous solution through a reverse osmosis membrane, wherein the reverse osmosis membrane is a polyamide membrane, and the first organic compound and the second organic compound are low molecular weight amino acids. It is a compound, and the third organic compound is a compound having a carboxyl group, an amino group, or a hydroxyl group .
The method for improving the rejection of a reverse osmosis membrane according to claim 2 is the method according to claim 1, wherein the first organic compound is an aromatic amino compound having a benzene skeleton and an amino group, a benzene skeleton, two or more amino groups, and an amino group. Aromatic aminocarboxylic acid compounds having less than the number of carboxyl groups, linear or branched hydrocarbon groups having 1 to 20 carbon atoms and aliphatic amino compounds having one or more amino groups, linear or branched An organic compound selected from an aliphatic amino alcohol having an amino group and a hydroxyl group in a hydrocarbon group having 1 to 20 carbon atoms, a heterocyclic amino compound having a heterocyclic ring and an amino group, and an amino acid compound, wherein the second organic compound is , Aromatic amino compounds having a benzene skeleton and an amino group, aromatics having a benzene skeleton and two or more amino groups and a carboxyl group less than the number of amino groups A minocarboxylic acid compound, an aliphatic amino compound having a linear or branched hydrocarbon group having 1 to 20 carbon atoms and one or more amino groups, an amino group in a linear or branched hydrocarbon group having 1 to 20 carbon atoms And an aliphatic amino alcohol having a hydroxyl group, a heterocyclic amino compound having a heterocyclic ring and an amino group, an amino acid compound, a peptide or a derivative thereof.

According to a third aspect of the present invention, there is provided the reverse osmosis membrane blocking rate improving method according to the second aspect , wherein the first organic compound is an amino acid or an amino acid derivative.

According to a fourth aspect of the present invention, there is provided the reverse osmosis membrane blocking rate improving method according to any one of the first to third aspects, wherein the third organic compound has a cyclic structure.

The method for improving the rejection rate of a reverse osmosis membrane according to claim 5 is the method according to any one of claims 1 to 4 , wherein the desalination rate of the reverse osmosis membrane before passing the aqueous solution is 90% or less. It is a feature.

The method for improving the rejection of a reverse osmosis membrane according to claim 6 is the method according to any one of claims 1 to 5 , wherein the total concentration of the first organic compound and the second organic compound is 1 to 500 mg / L. And the concentration of the third organic compound is 1 to 500 mg / L.

A reverse osmosis membrane according to a seventh aspect is characterized in that a rejection rate improving process is performed by the method for improving the rejection rate of the reverse osmosis membrane according to any one of the first to sixth aspects.

The blocking ratio improver for a reverse osmosis membrane according to claim 8 includes a first organic compound having a molecular weight of less than 200, a second organic compound having a molecular weight of 200 or more and less than 500, and a third organic compound having a molecular weight of 500 or more. A reverse osmosis membrane rejection rate improver, wherein the reverse osmosis membrane is a polyamide membrane, the first organic compound and the second organic compound are low molecular weight amino compounds, and the third organic compound is: It is a compound having a carboxyl group, an amino group, or a hydroxyl group .
The reverse osmosis membrane rejection rate improver according to claim 9 is the reverse osmosis membrane rejection rate improver according to claim 8, wherein the first organic compound is an aromatic amino compound having a benzene skeleton and an amino group, a benzene skeleton, two or more amino groups, and an amino group. Aromatic aminocarboxylic acid compounds having less than the number of carboxyl groups, linear or branched hydrocarbon groups having 1 to 20 carbon atoms and aliphatic amino compounds having one or more amino groups, linear or branched An organic compound selected from an aliphatic amino alcohol having an amino group and a hydroxyl group in a hydrocarbon group having 1 to 20 carbon atoms, a heterocyclic amino compound having a heterocyclic ring and an amino group, and an amino acid compound, wherein the second organic compound is , An aromatic amino compound having a benzene skeleton and an amino group, an aromatic amine having a benzene skeleton and two or more amino groups and a carboxyl group less than the number of amino groups A nocarboxylic acid compound, an aliphatic amino compound having a linear or branched hydrocarbon group having 1 to 20 carbon atoms and one or more amino groups, an amino group in a linear or branched hydrocarbon group having 1 to 20 carbon atoms And an aliphatic amino alcohol having a hydroxyl group, a heterocyclic amino compound having a heterocyclic ring and an amino group, an amino acid compound, a peptide or a derivative thereof.

  According to the present invention, a reverse osmosis membrane deteriorated by an oxidizing agent or the like, a first organic compound having a molecular weight of less than 200, a second organic compound having a molecular weight of 200 or more and less than 500, and a third organic compound having a molecular weight of 500 or more. By passing the aqueous solution containing, the deteriorated portion of the membrane can be repaired and the rejection rate can be effectively improved without greatly reducing the permeation flux of the reverse osmosis membrane.

  Hereinafter, a mechanism for repairing a deteriorated film according to the present invention will be described with reference to FIG.

  A normal amide bond of a reverse osmosis membrane such as a polyamide membrane has a structure as shown in FIG. When this film is deteriorated by an oxidizing agent such as chlorine, the amide bond CN bond is broken, and finally the structure shown in FIG. 1B is obtained.

  As shown in FIG. 1B, the amino group may disappear due to the breakage of the amide bond, but a carboxyl group is formed at this breakage portion.

  As the deterioration progresses, the gap becomes larger, and various sizes of gaps are formed. By fixing the first to third organic compounds according to the size of the gap, various sizes of the deteriorated film are formed. Each hole is repaired and the blocking rate is restored.

  When permeating an organic compound through a membrane, a plurality of amino compounds having different molecular weights or skeletons (structures) are used in combination, and these are allowed to permeate at the same time. By prolonging the residence time in the degradation portion, the probability of contact between the carboxyl group of the film and the amino group of the low molecular weight amino compound is increased, and the repair efficiency of the film is increased.

  In addition, by using a third organic compound having a molecular weight of 500 or more in combination, it is possible to block a greatly deteriorated portion of the film and improve the repair efficiency. As this third organic compound, a functional group that acts with the carboxyl group of the film (cation group: 1 to 4 quaternary amino group), a compound that has an added amino group (anion group: carboxyl group, (Sulfone group), or a functional group (hydroxyl group) that acts on the polyamide membrane, or a cyclic structure.

It is explanatory drawing of a chemical structural formula which shows the mechanism of the rejection improvement process by this invention. It is a schematic diagram which shows the flat film test apparatus used in the Example.

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

[Reverse osmosis membrane rejection improvement method]
The method for improving the rejection of a reverse osmosis membrane according to the present invention includes an aqueous solution containing a first organic compound having a molecular weight of less than 200, a second organic compound having a molecular weight of 200 or more and less than 500, and a third organic compound having a molecular weight of 500 or more. A step of passing water through the permeable membrane.

<Inhibition rate improving treatment agent>
In the present invention, examples of the first organic compound having a molecular weight of less than 200 and the second organic compound having a molecular weight of 200 or more and less than 500 include the following.

Aromatic amino compounds: For example, those having a benzene skeleton and an amino group such as aniline and diaminobenzene. Aromatic aminocarboxylic acid compounds: For example, 3,5-diaminobenzoic acid, 3,4-diaminobenzoic acid, 2, Those having a benzene skeleton such as 4-diaminobenzoic acid, 2,5-diaminobenzoic acid, 2,4,6-triaminobenzoic acid, two or more amino groups, and a carboxyl group less than the number of amino groups.

Aliphatic amino compounds: for example, methylamine, ethylamine, octylamine, 1,9-diaminononane (may be abbreviated as “NMDA” in this specification) (C ₉ H ₁₈ (NH ₂ ) ₂ ), etc. And those having a straight-chain hydrocarbon group of about 1 to 20 carbon atoms and one or more amino groups, and aminopentane (in this specification, sometimes abbreviated as “IAAM”) (NH ₂ ( _{CH 2) 2 CH (CH 3} ) 2), a 2-methyl-octa-diamine (herein sometimes abbreviated as _{"MODA".) (NH 2 CH 3 CH} (CH 3) (CH 2) 6 NH ₂ ) A compound having a branched hydrocarbon group having about 1 to 20 carbon atoms and one or more amino groups.

Aliphatic amino alcohol: Monoaminoisopentanol (in this specification, sometimes abbreviated as “AMB”) (NH ₂ (CH ₂ ) ₂ CH (CH ₃ ) CH ₂ OH) or the like A branched hydrocarbon group having 1 to 20 carbon atoms and having an amino group and a hydroxyl group.

  Heterocyclic amino compound: A compound having a heterocyclic ring and an amino group such as tetrahydrofurfurylamine (may be abbreviated as “FAM” in the present specification) (the following structural formula).

・ アミノ酸化合物：例えば、アルギニンやリシン等の塩基性アミノ酸化合物、アスパラギンやグルタミン等のアミド基を有するアミノ酸化合物、グリシンやフェニルアラニン等のその他アミノ酸化合物。

Amino acid compounds: For example, basic amino acid compounds such as arginine and lysine, amino acid compounds having an amide group such as asparagine and glutamine, and other amino acid compounds such as glycine and phenylalanine.

  Of these, amino acids or amino acid compounds (amino acid derivatives) are preferred as the first organic compound (with a molecular weight of less than 200).

  For example, arginine (molecular weight 174), lysine (molecular weight 146), and histidine (molecular weight 155), which are basic amino acids, can be effectively used as the first organic compound. Further, as a peptide or a derivative thereof, for example, aspartame (molecular weight 294) which is a methyl ester of a dipeptide of phenylalanine and aspartic acid can be effectively used as the second organic compound.

  These low molecular weight amino compounds are highly soluble in water and can be passed through the reverse osmosis membrane as a stable aqueous solution. As described above, they react with the carboxyl group of the membrane and bind to the reverse osmosis membrane, making it insoluble. The salt is formed to close the hole caused by the deterioration of the film, thereby increasing the blocking rate of the film.

  These low molecular weight amino compounds may be used individually by 1 type, and 2 or more types may be mixed and used for them. In particular, in the present invention, two or more kinds of low molecular weight amino compounds having different molecular weights and skeleton structures are used in combination, and these are simultaneously permeated through the permeable membrane. It is preferable that the residence time at the deteriorated portion is increased because the contact probability between the carboxyl group of the film and the amino group of the low molecular weight amino compound is increased and the repair effect of the film is enhanced.

  The contents of the first and second organic compounds in the rejection improvement treatment water differ depending on the degree of deterioration of the membrane. However, if the amount is excessively large, the permeation flux may be greatly reduced. Therefore, it is preferable that the total concentration of the first and second organic compounds in the rejection-improving treatment water is about 0.2 to 500 mg / L, particularly about 1 to 200 mg / L.

  Moreover, as an organic compound having a molecular weight of 500 or more (preferably 500 to 500,000, particularly preferably 500 to 50,000), those having a carboxyl group, an amino group, or a hydroxyl group are suitable. Examples include tannic acid and peptides. Examples of tannic acid include hydrolyzable pentaploid, gallic, condensed kebracho and mimosa. Examples of the peptide include polyglycine, polylysine, polytryptophan, polyalanine and the like having a molecular weight of 500 or more.

  The concentration of the third organic compound in the rejection improvement treatment water is preferably about 0.1 to 500 mg / L, particularly about 0.5 to 100 mg / L.

  The treated water with improved rejection rate may contain, as a tracer, inorganic electrolytes such as sodium chloride (NaCl), neutral organic substances such as isopropyl alcohol and glucose, and low molecular weight polymers such as polymaleic acid. By analyzing the degree of permeation of salt and glucose into the permeated water of the membrane, the degree of membrane repair can be confirmed.

  In addition, when the water supply pressure when passing the treated water with improved rejection rate through the reverse osmosis membrane is excessively high, there is a problem that the adsorption to the undegraded portion proceeds, and when it is excessively low, the adsorption to the deteriorating portion is also caused. Since it does not advance, it is preferable to set it as 30 to 150%, especially 50 to 130% of the normal operating pressure of the reverse osmosis membrane.

  This blocking rate improving treatment step can be performed at room temperature, for example, a temperature of about 10 to 35 ° C., and the treatment time is such that each organic compound is sufficiently permeated through the reverse osmosis membrane and the permeated water side. It is sufficient that the organic compound is detected for a long time, and there is no particular upper limit. However, it is usually preferably 0.5 to 100 hours, particularly preferably about 1 to 50 hours.

  The rejection improvement process may be performed by adding a rejection improvement agent to the water to be treated during the steady operation of the reverse osmosis membrane device. The time for adding the drug is about 1 to 500 hours, but the addition is always possible.

  When the operation is performed for a long time, when the permeation flux is decreased due to membrane contamination, it is desirable to perform the operation after cleaning, but this is not restrictive.

  As a cleaning agent, acid cleaning can increase mineral acids such as hydrochloric acid, nitric acid and sulfuric acid, and organic acids such as citric acid and oxalic acid. In alkali cleaning, sodium hydroxide, potassium hydroxide, etc. can be raised. In general, the pH is about 2 for acid cleaning and about 12 for alkali cleaning.

[Reverse osmosis membrane]
A reverse osmosis membrane (RO membrane) is a liquid separation membrane that applies a pressure higher than the osmotic pressure difference between solutions through the membrane to the high concentration side to block solutes and permeate the solvent. Examples of the membrane structure of the RO membrane include polymer membranes such as asymmetric membranes and composite membranes. Examples of the RO membrane material include aromatic polyamides, aliphatic polyamides, polyamide materials such as composite materials thereof, and cellulose materials such as cellulose acetate. Among these, the reverse osmosis membrane inhibition rate improving method of the present invention is particularly suitable for a membrane made of an aromatic polyamide material and having many carboxyl groups due to degradation of CN bonds due to deterioration. Can be applied to.

  In addition, when the desalination rate of the RO membrane before the rejection improvement process is 90% or less, it is suitable for applying the method of the present invention.

  Moreover, there is no restriction | limiting in particular in the module format of a reverse osmosis membrane, For example, a tubular membrane module, a plane membrane module, a spiral membrane module, a hollow fiber membrane module etc. can be mentioned.

  The reverse osmosis membrane treated by the method of the present invention is a water treatment for recovery and reuse of wastewater containing high or low concentration TOC discharged in the electronic device manufacturing field, semiconductor manufacturing field, and other various industrial fields. Alternatively, it is effectively applied to the production of ultrapure water from industrial water and city water, and water treatment in other fields. The water to be treated is not particularly limited, but can be suitably used for organic substance-containing water. For example, TOC = 0.01 to 100 mg / L, preferably about 0.1 to 30 mg / L. It is suitably used for the treatment of organic substance-containing water. Examples of such organic substance-containing water include, but are not limited to, wastewater from electronic device manufacturing factories, transportation machinery manufacturing factories, organic synthesis factories, printing plate making / painting factories, or the primary treatment water thereof. .

  Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples.

First, Comparative Examples 1-6 and Examples 1-6 will be described.
[Comparative Example 1]
The treated water was passed through the flat membrane test apparatus shown in FIG. 2 under the following conditions.

  This flat membrane test apparatus is provided with a flat membrane cell 2 at an intermediate position in the height direction of a cylindrical container 1 having a bottom and a lid, and the inside of the container is divided into a raw water chamber 1A and a permeated water chamber 1B, and the container 1 is divided into a stirrer. 3, water to be treated is supplied to the raw water chamber 1 </ b> A via the pipe 11 by the pump 4, and the stirrer 5 in the container 1 is rotated to stir the raw water chamber 1 </ b> A so that the permeated water passes through the permeated water. While taking out from the chamber 1B through the pipe 12, the concentrated water is taken out from the raw water chamber 1A through the pipe 13. The concentrated water outlet pipe 13 is provided with a pressure gauge 6 and an opening / closing valve 7.

Deteriorated membrane: Ultra-low pressure reverse osmosis membrane ES20 manufactured by Nitto Denko Corporation, sodium hypochlorite (free chlorine 1
mg / L) for 24 hours soaking in a solution. Original membrane
Permeation flux, desalination rate, and IPA removal rate of 0.81 m ³ / (m ² · d), respectively
0.972 and 0.875.
Water to be treated: Dechlorinated Nogicho water with activated charcoal, NaCl 500 mg / L, IPA 10
0 mg / L added Operating pressure: 0.75 MPa
Temperature: 24 ° C ± 2 ° C

[Comparative Example 2]
Comparative Example, except that after passing water under the conditions of Comparative Example 1 and confirming the deterioration state, the water to be treated was added with 1 mg / L of tannic acid (403040-50G manufactured by Sigma-Aldrich) to the water to be treated. Water was passed under the condition of 1.

[Comparative Example 3]
After passing water under the conditions of Comparative Example 1 and confirming the deterioration state, water to be treated was added with 1 mg / L of polyethylene glycol (molecular weight 4000, manufactured by Wako Pure Chemical Industries, Ltd.) for 2 hours as treated water. Conducted water under the conditions of Comparative Example 1.

[Comparative Example 4]
After passing water under the conditions of Comparative Example 1 and confirming the deterioration state, water treated with polyoxyethylene (10) oleyl ether (molecular weight 708, manufactured by Wako Pure Chemical Industries) 1 mg / L was added to the water to be treated. Water was passed under the conditions of Comparative Example 1 except that water was passed for hours.

[Comparative Example 5]
After passing water under the conditions of Comparative Example 1 and confirming the deterioration state, water treated with aspartame (Ajinomoto Co., Inc., food additive grade, molecular weight 294) 1 mg / L was added to the water to be treated for 2 hours. Except for this, water was passed under the conditions of Comparative Example 1.

[Comparative Example 6]
After passing water under the conditions of Comparative Example 1 and confirming the deterioration state, comparison was made except that 1 mg / L of arginine (made by Ajinomoto Co., Inc., food additive grade, molecular weight 174) was added to the water to be treated. Water was passed under the conditions of Example 1.

[Comparative Example 7]
After passing water under the conditions of Comparative Example 1 and confirming the deterioration state, water was passed under the conditions of Comparative Example 1 except that arginine added at 2 mg / L and aspartame at 1 mg / L was used as the water to be treated. Went water.

[Example 1]
After passing water under the conditions of Comparative Example 1 and confirming the deterioration state, 2 mg / L of arginine and 1 mg / L of aspartame were added to the water to be treated, polyglycine (P8791-500MG, molecular weight 500-5000, manufactured by Sigma-Aldrich) Water was passed under the conditions of Comparative Example 1 except that 1 mg / L added was passed as treated water for 24 hours.

[Example 2]
After confirming the deterioration state by passing water under the conditions of Comparative Example 1, 2 mg / L of arginine and 1 mg / L of aspartame were added to the water to be treated, and 1 mg of dietary tannic acid AL (manufactured by Fuji Chemical Industry Co., Ltd., molecular weight of 500 or more) Water was passed under the conditions of Comparative Example 1 except that water added with / L was passed as treated water for 24 hours.

The permeation flux, desalting rate, and IPA removal rate were calculated from the following equations.
Permeation flux [m ³ / (m ² d)] = permeated water amount [m ³ / d] / membrane area [m ² ] × temperature conversion coefficient [−]
Desalination rate [%] = (1-permeate conductivity [mS / m] / concentrate conductivity [mS / m]) × 100
IPA removal rate [%] = (1—TOC [mg / L] of permeate / TOC [mg / L] of concentrate) × 100

  Table 1 shows the results. In this invention, it turns out that the desalination rate improvement efficiency and the improvement efficiency of an IPA removal rate are high, and the value beyond the original or the original is obtained.

  Next, Comparative Examples 8 and 9 and Example 3 will be described.

[Comparative Example 8]
The treated water was passed through the flat membrane test apparatus shown in FIG. 2 for 2 hours under the following conditions.
Deteriorated membrane: Low-pressure reverse osmosis membrane NTR759HR manufactured by Nitto Denko Corporation used for wastewater recovery was immersed in a pH12 NaOH aqueous solution for 15 hours, rinsed with pure water, then immersed in 2% citric acid for 2 hours and rinsed with pure water.
Water to be treated: NaCl dissolved in pure water at 500 mg / L and IPA at 100 mg / L.
Operating pressure: 1.4 MPa
Temperature: 24 ° C ± 2 ° C

[Comparative Example 9]
After passing water under the conditions of Comparative Example 8 and confirming the deterioration state, PEG (polyethylene glycol) 4000 (molecular weight 4000, manufactured by Wako Pure Chemical Industries) 5 mg / L was added to the water to be treated for 2 hours. Water was passed under the conditions of Comparative Example 8 except that water was used.

[Example 3]
After passing water under the conditions of Comparative Example 8 and confirming the deterioration state, 20 mg / L of arginine, 20 mg / L of aspartame were added to the water to be treated, and 10 mg of dietary tannic acid AL (manufactured by Fuji Chemical Industry Co., Ltd., molecular weight of 500 or more) 10 mg Water was passed under the conditions of Test Method 2 except that water added with / L was passed as treated water for 2 hours.

  Table 2 shows the results. As shown in Table 2, according to the present invention, the decrease in the permeation flux can be stopped within 10%, and the desalination rate and the IPA removal rate can be greatly improved.

  As is clear from the above examples and comparative examples, according to the present invention, the chemical is added to the water to be treated and the water is passed through at a normal operating pressure, so that the deteriorated membrane can be largely permeated while collecting water. The desalination rate can be recovered without reducing the amount of water. The present invention can also be applied to a significantly deteriorated film having a desalination rate of 90% or less.

1 container 1A raw water chamber 1B permeate water chamber 2 flat membrane cell 3 stirrer

Claims (9)

Reverse osmosis having a molecular weight first organic compound of less than 200, a second organic compound having a molecular weight of less than 200 or 500, the step of passing water an aqueous solution containing a third organic compound having a molecular weight of at least 500 in the reverse osmosis membrane A method for improving the rejection rate of a membrane,
The reverse osmosis membrane is a polyamide membrane;
The first organic compound and the second organic compound are low molecular weight amino compounds;
A method for improving the rejection of a reverse osmosis membrane, wherein the third organic compound is a compound having a carboxyl group, an amino group, or a hydroxyl group . 2. The aromatic aminocarboxylic acid according to claim 1, wherein the first organic compound is an aromatic amino compound having a benzene skeleton and an amino group, a benzene skeleton, two or more amino groups, and a carboxyl group less than the number of amino groups. Compound, aliphatic amino compound having a linear or branched hydrocarbon group having 1 to 20 carbon atoms and one or more amino groups, amino group and hydroxyl group in a linear or branched hydrocarbon group having 1 to 20 carbon atoms An organic compound selected from an aliphatic amino alcohol having a heterocyclic amino compound having a heterocyclic ring and an amino group, and an amino acid compound,
The second organic compound is an aromatic amino compound having a benzene skeleton and an amino group, an aromatic aminocarboxylic acid compound having a benzene skeleton, two or more amino groups, and a carboxyl group less than the number of amino groups, and one carbon atom Aliphatic amino compounds having -20 linear or branched hydrocarbon groups and one or more amino groups, aliphatic amino compounds having amino groups and hydroxyl groups on linear or branched hydrocarbon groups having 1 to 20 carbon atoms A method for improving the rejection of a reverse osmosis membrane, which is an organic compound selected from alcohols, heterocyclic amino compounds having a heterocyclic ring and an amino group, amino acid compounds, peptides or derivatives thereof. 3. The method for improving the rejection of a reverse osmosis membrane according to claim 2 , wherein the first organic compound is an amino acid or an amino acid derivative. 4. The method for improving the rejection of a reverse osmosis membrane according to any one of claims 1 to 3 , wherein the third organic compound has a cyclic structure. In any one of claims 1 to 4, rejection enhancing method of the reverse osmosis membrane, wherein the salt rejection before passed through the aqueous solution of said reverse osmosis membrane is 90% or less. In any one of claims 1 to 5, wherein the first organic compound is the sum of the concentration of 1-500 mg / L of the second organic compound, the concentration of the third organic compound is 1-500 mg / A method for improving the rejection rate of a reverse osmosis membrane, which is L. A reverse osmosis membrane, which has been subjected to a rejection improvement process by the method for improving the rejection of a reverse osmosis membrane according to any one of claims 1 to 6 . A reverse osmosis membrane rejection rate improver comprising a first organic compound having a molecular weight of less than 200, a second organic compound having a molecular weight of 200 or more and less than 500, and a third organic compound having a molecular weight of 500 or more ,
The reverse osmosis membrane is a polyamide membrane;
The first organic compound and the second organic compound are low molecular weight amino compounds;
A reverse osmosis membrane rejection improvement agent, wherein the third organic compound is a compound having a carboxyl group, an amino group, or a hydroxyl group . 9. The aromatic aminocarboxylic acid according to claim 8, wherein the first organic compound is an aromatic amino compound having a benzene skeleton and an amino group, a benzene skeleton, two or more amino groups, and a carboxyl group less than the number of amino groups. Compound, aliphatic amino compound having a linear or branched hydrocarbon group having 1 to 20 carbon atoms and one or more amino groups, amino group and hydroxyl group in a linear or branched hydrocarbon group having 1 to 20 carbon atoms An organic compound selected from an aliphatic amino alcohol having a heterocyclic amino compound having a heterocyclic ring and an amino group, and an amino acid compound,
The second organic compound is an aromatic amino compound having a benzene skeleton and an amino group, an aromatic aminocarboxylic acid compound having a benzene skeleton, two or more amino groups, and a carboxyl group less than the number of amino groups, and one carbon atom Aliphatic amino compounds having -20 linear or branched hydrocarbon groups and one or more amino groups, aliphatic amino compounds having amino groups and hydroxyl groups on linear or branched hydrocarbon groups having 1 to 20 carbon atoms A reverse osmosis membrane blocking rate improver, which is an organic compound selected from alcohols, heterocyclic amino compounds having a heterocyclic ring and an amino group, amino acid compounds, peptides or derivatives thereof.

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