JP2011125856A - Method for manufacturing composite semipermeable membrane and polyamide composite semipermeable membrane - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semipermeable membrane having a practical water permeability amount, a salt rejection and also a high durability, and a manufacturing method of the same. <P>SOLUTION: A semipermeable membrane having a separation function layer including a primary amino group is reformed by being brought into contact with a reagent, which generates a diazonium salt or its derivative when reacting with a primary amino group, for the period of one second or longer and 60 minutes or shorter. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a modified semipermeable membrane imparted with high performance and high durability for selectively permeating and separating components of a liquid mixture, and a method for producing the same.

  Regarding the separation of a mixture, there are various techniques for removing substances (for example, salts) dissolved in a solvent (for example, water). In recent years, a membrane separation method has been used as a process for saving energy and resources. Yes. Examples of membranes used in the membrane separation method include microfiltration membranes, ultrafiltration membranes, and reverse osmosis membranes. Furthermore, in recent years, a membrane (loose RO membrane or NF “nanofiltration” membrane) located at the boundary between a reverse osmosis membrane and an ultrafiltration membrane has also appeared and is used. In the case of obtaining drinking water from water containing harmful substances, it has been used for the production of industrial ultrapure water, wastewater treatment, recovery of valuable resources, and the like.

  Most of the reverse osmosis membranes, loose RO membranes, and NF membranes currently on the market are composite semipermeable membranes, which have a gel layer and an active layer crosslinked with a polymer on a porous support membrane, and a porous support There are two types, one having an active layer in which monomers are polycondensed on the membrane. Among these, composite semipermeable membranes obtained by coating a porous support membrane with a separation functional layer made of a crosslinked polyamide obtained by polycondensation reaction between a polyfunctional amine and a polyfunctional acid halide have permeability and selective separation properties. Widely used as a high reverse osmosis membrane. However, it is known that the membrane performance deteriorates when an oxidant such as hydrogen peroxide, hypochlorous acid, ozone, etc. applied for oxidative removal and sterilization is contacted with a reverse osmosis membrane for a long time. Therefore, improvement in durability is desired.

  Patent Document 1 discloses, on average, at least one primary amino group or a salt thereof by reacting a primary amino group or a salt thereof with a diazonium salt precursor or a reactive group with a diazonium salt. It is disclosed that a reverse osmosis membrane having a high solute removal property and a high water permeability can be obtained by providing an identification layer derived from a polymer having a group reactive with at least one diazonium salt. However, according to the method specifically described in this document, the treatment time takes into account the dependence of nitrous acid concentration, membrane prewetting, the concentration of primary amine groups present, and the concentration at which contact occurs. However, in order to obtain an effect in a short time, pressurization is required for the diffusion of the reagent to the membrane. In addition, a nitrous acid aqueous solution, which is a diazotization reaction reagent, is chemically unstable, and generates toxic nitric oxide and nitric acid and decomposes rapidly particularly at high concentrations and heating conditions (Non-patent Document 1). For this reason, the treatment for a long time has a problem in productivity because the concentration of nitrous acid is not stable. Furthermore, it cannot be said that the solute removal property and the water permeability are improved simultaneously by the treatment, and a treatment method that satisfies this requirement is desired.

  As described above, the semipermeable membrane still has a more stable operation and simple operability in various water treatments, and a low cost pursuit by reducing the frequency of membrane exchange, and various oxidizing agents, particularly hypochlorous acid. Durability that can withstand washing and sterilization with acid is required.

JP-A-63-175604

Iwanami Encyclopedia 5th Edition (Iwanami Shoten, February 20, 1998, 96 pages)

  The present invention provides a semipermeable membrane having high solute removal properties, high water permeability, and high durability, and at the same time, providing a semipermeable membrane capable of realizing high productivity and a method for producing the same. It is the purpose.

  In order to achieve the above object, the present invention has the following configurations (1) to (5).

(1) A method for producing a composite semipermeable membrane in which a polyamide separation functional layer is formed on a porous support membrane by a polycondensation reaction between a polyfunctional amine and a polyfunctional acid halide, the composite semipermeable membrane In a wet state with a water content of 5% or more, and the amount of a primary aromatic amine having a molecular weight of 300 or less and 500 mg / m ² or less present in the separation functional layer, Production of a composite semipermeable membrane comprising a modification treatment step of contacting a solution containing a compound that reacts with a group to form a diazonium salt or a derivative thereof at 40 ° C. or lower for 1 second or longer and 2 minutes or shorter Method.

  (2) The EI value calculated from the pH of the solution containing the compound, the total molar concentration of nitrous acid and / or its salt (mol / L), and the reaction time (s) is in the range of 0.005 to 500. The manufacturing method of the composite semipermeable membrane as described in said (1).

  (3) The production of the composite semipermeable membrane according to (1) or (2) above, comprising a step of bringing the composite semipermeable membrane into contact with an acidic aqueous solution having a pH of 4 or less before and / or after the modification treatment step. Method.

  (4) The method for producing a composite semipermeable membrane according to any one of (1) to (3), wherein the primary aromatic amine is m-phenylenediamine.

(5) A polyamide composite semipermeable membrane in which a polyamide separation functional layer is formed on a porous support membrane by a polycondensation reaction between a polyfunctional amine and a polyfunctional acid halide, and has a moisture content of 5% or more. A diazonium salt which reacts with the primary aromatic amino group in the separation functional layer in the state and the amount of the primary aromatic amine having a molecular weight of 300 or less present in the separation functional layer is 500 mg / m ² or less. Obtained by a modification treatment in which a solution containing a compound that forms the derivative is contacted at 40 ° C. or less for 1 second or more and 2 minutes or less, and the light transmittance at a wavelength of 450 nm is in the range of 10 to 95%; A polyamide composite semipermeable membrane characterized by having a phenolic hydroxyl group.

  According to the present invention, it is possible to obtain a semipermeable membrane having both high water permeability and high solute removability and high durability with high productivity.

The relationship between the molar fraction of nitrous acid in a non-dissociated state and pH calculated using the dissociation equilibrium constant of nitrous acid is shown.

The present invention is a production method for improving the properties of a composite semipermeable membrane having a separation functional layer containing a primary aromatic amino group. Here, the separation functional layer containing a primary aromatic amino group means that an aromatic compound having at least one amino group (—NH ₂ ) and a salt thereof are present in the separation functional layer. The type of the compound is not particularly limited, and may be a constituent component of the separation functional layer or may not be accompanied by a chemical bond with the separation functional layer.

  In the present invention, the composite semipermeable membrane is formed by coating a separation functional layer having substantially separation performance on a porous support membrane having substantially no separation performance. It consists of a crosslinked polyamide obtained by reaction with a polyfunctional acid halide. Here, the polyfunctional amine comprises at least one component of an aliphatic polyfunctional amine and an aromatic polyfunctional amine.

  The aliphatic polyfunctional amine is an aliphatic amine having two or more amino groups in one molecule, and is preferably a piperazine-based amine and a derivative thereof. For example, piperazine, 2,5-dimethylpiperazine, 2-methylpiperazine, 2,6-dimethylpiperazine, 2,3,5-trimethylpiperazine, 2,5-diethylpiperazine, 2,3,5-triethylpiperazine, 2- Examples thereof include n-propylpiperazine and 2,5-di-n-butylpiperazine, and piperazine and 2,5-dimethylpiperazine are particularly preferable from the viewpoint of stability of performance.

  The aromatic polyfunctional amine is an aromatic amine having two or more amino groups in one molecule, and is not particularly limited, but includes metaphenylene diamine, paraphenylene diamine, 1, 3, 5 -Triaminobenzene and the like, and N-alkylated products thereof include N, N-dimethylmetaphenylenediamine, N, N-diethylmetaphenylenediamine, N, N-dimethylparaphenylenediamine, N, N-diethylparaphenylenediamine, etc. In view of the stability of performance, metaphenylenediamine and 1,3,5-triaminobenzene are particularly preferable.

  The polyfunctional acid halide is an acid halide having two or more carbonyl halide groups in one molecule, and is not particularly limited as long as it gives a polyamide by reaction with the amine. Examples of the polyfunctional acid halide include oxalic acid, malonic acid, maleic acid, fumaric acid, glutaric acid, 1,3,5-cyclohexanetricarboxylic acid, 1,3-cyclohexanedicarboxylic acid, and 1,4-cyclohexanedicarboxylic acid. 1,3,5-benzenetricarboxylic acid, 1,2,4-benzenetricarboxylic acid, 1,3-benzenedicarboxylic acid, and acid halides of 1,4-benzenedicarboxylic acid can be used. Among acid halides, acid chlorides are preferred, and are acid halides of 1,3,5-benzenetricarboxylic acid, particularly in terms of economy, availability, ease of handling, and ease of reactivity. Trimesic acid chloride is preferred. Although the said polyfunctional acid halide can also be used independently, you may use it as a mixture.

  The organic solvent that dissolves the polyfunctional acid halide is not miscible with water, and preferably does not destroy the porous support membrane, and may be any as long as it does not inhibit the formation reaction of the crosslinked polyamide. . Typical examples include halogenated hydrocarbons such as liquid hydrocarbons and trichlorotrifluoroethane, but they are substances that do not destroy the ozone layer, are easily available, are easy to handle, and are safe for handling. In consideration of the properties, octane, nonane, decane, undecane, dodecane, tridecane, tetradecane, heptadecane, hexadecane, etc., and simple substances such as cyclooctane, ethylcyclohexane, 1-octene, 1-decene, or a mixture thereof are preferably used.

  Next, the preferable manufacturing method of a semipermeable membrane is demonstrated. The separation functional layer having substantially separation performance in the semipermeable membrane is, for example, an aqueous solution containing the above-mentioned polyfunctional amine and an organic solvent immiscible with water containing the above-mentioned polyfunctional acid halide. It forms by making it react on the below-mentioned porous support membrane using a solution.

  Here, the concentration of the aqueous solution containing the polyfunctional amine is preferably 0.1 to 20% by weight, more preferably 0.5 to 15% by weight.

  In the case of an aqueous solution containing a polyfunctional amine or an organic solvent solution containing a polyfunctional acid halide, an acylation catalyst, a polar solvent, an acid scavenger may be used as long as it does not interfere with the reaction between the two components. In addition, compounds such as surfactants and antioxidants may be contained.

  In the present invention, the porous support membrane is used to support a separation functional layer such as a crosslinked polyamide. Although the structure of a porous support membrane is not specifically limited, As a preferable porous support membrane, the polysulfone support membrane reinforced with the cloth etc. can be illustrated. The pore diameter and the number of pores of the porous support membrane are not particularly limited, but it has uniform fine pores or gradually large pores from one side to the other side, and the size of the fine pores is the size of one side. A support film having a structure in which the surface of the film is 100 nm or less is preferable.

  The porous support membrane used in the present invention can be selected from various commercially available materials such as “Millipore Filter VSWP” (trade name) manufactured by Millipore and “Ultra Filter UK10” (trade name) manufactured by Toyo Roshi Kaisha. “Office of Saleen Water Research and Development Progress Report” No. 359 (1968).

  The material used for the porous support membrane is not particularly limited. For example, polysulfone, cellulose acetate, cellulose nitrate, polyvinyl chloride, or other homopolymers or blended materials can be used, but chemically, mechanically, and thermally. It is preferable to use polysulfone having high stability. Specifically, a solution of polysulfone in dimethylformamide (hereinafter referred to as DMF) is applied on a densely woven polyester cloth or non-woven fabric to a substantially constant thickness, and sodium dodecyl sulfate 0.5 wt% DMF 2 wt% By wet coagulation in an aqueous solution containing, a suitable porous support membrane having most of the surface with fine pores having a diameter of several tens of nm or less can be obtained.

  The surface of the porous support membrane may be coated with an aqueous solution containing a polyfunctional amine as long as the aqueous solution is uniformly and continuously coated on the surface. For example, the coating may be carried out by a method of coating a porous support membrane in the aqueous solution. Next, the excessively applied aqueous solution is removed by a liquid draining step. As a method for draining liquid, for example, there is a method in which the film surface is allowed to flow naturally while being held in a vertical direction. After draining, the membrane surface may be dried to remove all or part of the water in the aqueous solution. Then, the organic solvent solution containing the above-mentioned polyfunctional acid halide is applied to the porous support membrane coated with the aqueous solution containing the polyfunctional amine, and a separation functional layer of crosslinked polyamide is formed by reaction.

  The concentration of the polyfunctional acid halide is not particularly limited, but if it is too small, the formation of the separation functional layer, which is an active layer, may become a disadvantage, and if it is too large, it will be disadvantageous in terms of cost. Among these, about 0.01 to 1.0% by weight is preferable. The removal of the organic solvent after the reaction can be performed, for example, by the method described in JP-A-5-76740.

  In the present invention, the composite semipermeable membrane produced by the above-described method is wetted with a water content of 5% or more in a solution containing a compound that reacts with a primary aromatic amino group to produce a diazonium salt or a derivative thereof. The modified semipermeable membrane is obtained by contacting for 1 second to 2 minutes. The method of bringing the solution containing the above compound into contact with the composite semipermeable membrane is not particularly limited. For example, a method of immersing the entire composite semipermeable membrane in the solution containing the above compound, a spraying method, or a separation function may be used. The method is not limited as long as it comes into contact with the layer.

  Here, according to the above-mentioned Patent Document 1, the purpose is to sufficiently diffuse the nitrous acid in the membrane and to react the nitrous acid with the primary amine to mainly increase the water flow rate of the membrane. Therefore, it is specifically explained that a reaction time of 1 to 72 hours is required. However, as a result of examining the diazonium salt formation reaction in detail, the present inventors have been able to simultaneously exhibit practical improvements in membrane water permeability and salt rejection in a time range of 1 second or more and 2 minutes or less. It was found that decomposition and harmful substance diffusion are minimized. Specifically, the membrane water permeability increases with time immediately after the treatment with the reagent, whereas the salt rejection rate increases immediately after the treatment, but begins to decrease with the maximum value with time, and the salt rejection rate before the treatment in 60 minutes. It has been found that the salt rejection rate is lowered at the same level or higher. It should be noted that the contact with the reagent is sufficient as long as the contact can be made sufficiently, but in order to prevent contact unevenness, it is necessary to make contact for 1 second or more.

Examples of the solution containing a compound that reacts with a primary aromatic amino group to produce a diazonium salt or a derivative thereof according to the present invention include aqueous solutions of nitrous acid, a salt thereof, and a nitrosyl compound. Since an aqueous solution of nitrous acid or a nitrosyl compound easily generates gas and decomposes, it is preferable to sequentially generate nitrous acid by, for example, a reaction between nitrite and an acidic solution. In general, nitrite reacts with hydrogen ions to produce nitrous acid (HNO ₂ ), but it is efficiently produced at 20 ° C. when the pH of the aqueous solution is 7 or less, preferably 5 or less, more preferably 4 or less. Among these, an aqueous solution of sodium nitrite reacted with hydrochloric acid or sulfuric acid in an aqueous solution is particularly preferable because of easy handling.

  In the present invention, the concentration of nitrous acid or nitrite in the reagent brought into contact with the membrane is preferably in the range of 0.01 to 1% by weight at 20 ° C. If the concentration is lower than 0.01%, a sufficient effect cannot be obtained. If the concentration of nitrous acid and nitrite is higher than 1%, handling of the solution becomes difficult.

  In the present invention, when an aqueous solution having a nitrite concentration of 0.5% by weight or more is used as a reagent, “contact between the membrane and nitrite” and “sublimation caused by contact between the nitrite remaining on the membrane surface and the acidic solution”. Separating the “generation of nitric acid” is preferable because handling becomes simple. That is, before and / or after contact with the aqueous solution containing nitrite, the semipermeable membrane is contacted with an acidic solution having a pH of 4 or less.

  Furthermore, in the present invention, in order to obtain a higher effect, the value calculated by the reaction time between the reagent and the semipermeable membrane, the pH of the reagent, the total molar concentration of nitrous acid or a salt thereof, and the EI value are 0. It is preferable to process so that it may become in the range of 005-500. The EI value is defined as follows.

EI (mol · s / l)
= (Reaction time: s) · (Nitrite concentration: mol / l) / (10 ^pH-3.15 +1).

  Furthermore, the temperature of the reagent is preferably 95 ° C. or lower in order to suppress the denaturation of the semipermeable membrane due to heat, and more preferably 40 ° C. or lower that reduces the volatilization and decomposition of the reagent.

  In addition, when the composite semipermeable membrane to which the solution containing the above compound is brought into contact is not in a wet state, it is brought into a sufficiently wet state by contacting with water for a necessary time before the treatment. Here, the wet state means that the composite semipermeable membrane contains water and can be quantified by the moisture content (= water content in the membrane / total weight of the membrane). The water content of the composite semipermeable membrane with which the aqueous solution containing the above compound is brought into contact needs to be 5% or more, and more preferably 25% or more.

In performing such treatment, in the semipermeable membrane, the amount of unreacted primary amine having a molecular weight of 300 or less remaining during the formation reaction of the polyamide or separately added primary amine having a molecular weight of 300 or less is added to the membrane. It is preferable that only 500 mg or less per 1 m ^{2 of} area is present. If it exceeds this, sufficient water permeability cannot be obtained. The amount of primary amine is determined by chromatography and mass spectrometry of components extracted into ethanol by cutting out a semipermeable membrane 10 × 10 cm, immersing it in 50 g of ethanol for 8 hours.

  A characteristic of the modified semipermeable membrane obtained by the present invention is a colored separation functional layer. This is presumably because an azo compound is generated by the bond formation by the diazonium salt generated by the reaction of the primary amino group. The absorption band of the azo compound varies depending on the compound, but in the present invention, a characteristic absorption is observed at 450 nm. This can be quantified by the integrating sphere measurement method of the visible absorption spectrum method, and the light transmittance at 450 nm is 10% or more and 95% or less, preferably 50% or more and 80% or less.

  In addition, the modified semipermeable membrane obtained by the present invention contains a compound that generates a diazonium salt or a derivative thereof by reacting a part of the amino group present in the functional layer with a primary aromatic amino group depending on reaction conditions. It is converted into a phenolic hydroxyl group by the solution. This can be understood as a part of the produced diazonium salt reacting with water. In addition, the identification of a compound can be measured by NMR method. For example, a liquid separation membrane having a separation functional layer on a support in which a porous support membrane made of polysulfone is formed on a substrate is identified as follows when identifying a compound by the NMR method. First, a base material (taffeta or nonwoven fabric made of polyester fiber) which is a part of the support is peeled off to obtain a mixture of a microporous support membrane made of polysulfone and a separation functional layer of crosslinked polyamide. This is dissolved in methylene chloride and then filtered to obtain a separation functional layer. The separation functional layer is dried and collected in a sealed container. A 6N aqueous sodium hydroxide solution is added, and the mixture is heated to 120 ° C. for dissolution, followed by filtering insoluble matters. The obtained filtrate is put in an NMR tube and analyzed by an FT-NMR analyzer, and the compound is identified from the δ value of the obtained proton.

Then, according to the present invention, the semipermeable membrane once manufactured is modified to adjust the sodium chloride concentration to 0.15% by weight, with an aqueous solution having an operating pressure of 0.75 MPa, a temperature of 25 ° C., and a pH of 6.5. When evaluated, it is possible to easily obtain a semipermeable membrane having a sodium chloride removal rate of 98% or more and a permeated water amount of 1.0 m ³ / m ² · day or more.

Using the semipermeable membrane obtained by the production method of the present invention, for example, removal of harmful substances such as inorganic substances and organic substances and precursors thereof contained in raw water at an operating pressure of 0.1 to 3.0 MPa can be performed. Possible Here, if the operating pressure is lowered, the capacity of the pump to be used is reduced and the power cost is lowered, but the amount of permeate tends to be reduced. Conversely, if the operating pressure is increased, the power cost increases for the reasons described above, and the amount of permeated water tends to increase. On the other hand, if the amount of permeated water is too high, clogging due to fouling of the membrane surface may occur. And the cost is high. Therefore, in order to carry out stable operation at a reduced cost, the operating pressure is preferably in the range of 0.1 to 3.0 MPa, more preferably 0.1 to 2.0 MPa, and still more preferably 0.1 to 3.0 MPa. Within the range of 1.0 MPa. For the same reason, the permeated water amount is preferably in the range of 0.5 to 5.0 m ³ / m ² · d, more preferably 0.6 to 3.0 m ³ / m ² · d. More preferably, it is in the range of 0.8 to 2.0 m ³ / m ² · d.

  Further, in order to efficiently treat the supplied water and reduce the water production cost, the ratio of the permeated water amount to the raw water supply amount, that is, the recovery rate is preferably 80% or more, more preferably 85% or more, and more preferably 90% or more. good. However, if it exceeds 99.5%, clogging due to fouling of the film surface may occur, so it is preferable not to exceed 99.5%.

  And the modified semipermeable membrane of this invention can have the outstanding durability in addition to the above water permeability and sodium chloride inhibition. Specifically, when the raw water containing a sodium hypochlorite aqueous solution having a free chlorine concentration of 700 mg / L prepared at pH 7 was continuously operated at an operating pressure of 0.75 MPa for 8 hours, it was obtained by the above evaluation method. The change rate of the sodium chloride transmission rate is 0.5 or more and 5 or less.

  In the present invention, the form of the semipermeable membrane is not limited and may be a hollow fiber membrane or a flat membrane. The modified semipermeable membrane obtained by the present invention forms elements and modules when used for liquid separation, but the form thereof is not particularly limited, such as a module type or a spiral type.

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples.
In the examples, the removal rate and the transmittance were obtained by the following equations.
Removal rate (%) = {1- (solute concentration in permeate) / (solute concentration in feed solution)} × 100
Permeability (%) = {(solute concentration in permeate) / (solute concentration in feed)} × 100.

The amount of water permeated was determined by the amount of permeated water per unit area (m ² ) per unit area (m ² ) (m ³ / m ² · d). Furthermore, the moisture content was determined by drying a semipermeable membrane that had been well drained in advance with a hot air drier at a temperature of 120 ° C. for 3 hours and dividing the weight change by the weight before drying.

<Reference Examples A and B>
A fabric-reinforced polysulfone support membrane (ultrafiltration membrane), which is a porous support membrane, was produced by the following method. That is, a wet non-woven fabric of polyester fiber having a single yarn fineness of 0.5 and 1.5 dtex, an air permeability of 0.7 cm ³ / cm ² · sec, an average pore diameter of 7 μm or less, a length of 30 cm and a width of 20 cm Was fixed on a glass plate, and a solution of dimethylformamide (DMF) solvent in a polysulfone concentration of 15% by weight (2.5 poise: 20 ° C.) was cast to a total thickness of 200 μm, and immediately poured into water. A porous support membrane of polysulfone was obtained by immersion (this is referred to as a PS support membrane).

Next, this porous support membrane was immersed in an aqueous solution containing 2.0% by weight of m-phenylenediamine and 2.0% by weight of ε-caprolactam for 2 minutes, and then 0.1% by weight of trimesic acid chloride in decane. The solution so dissolved was applied at a rate of 160 cm ³ / m ² , and the excess solution was removed to obtain a composite reverse osmosis membrane. As a result of a reverse osmosis test under conditions of 0.75 MPa and 25 ° C., a 0.15 wt% sodium chloride aqueous solution prepared by adjusting the pH value of the composite semipermeable membrane thus obtained to pH 6.5 was used. The removal rate of 0.76 m ³ / m ² · d and sodium chloride was 99.0% (Reference Example A).

The obtained film was dried at 60 ° C. for 4 minutes. The moisture content of this dry reverse osmosis membrane was 2.8% by weight. As a result of the reverse osmosis test as described above, the water permeability was 0.40 m ³ / m ² · d, and the sodium chloride removal rate was 98.7% (Reference Example B).

<Examples 1 and 2-7, Comparative Examples 1 and 2>
The membrane obtained in Reference Example A was treated at room temperature with an aqueous solution containing 0.07 wt% sodium nitrite and 0.1 wt% concentrated sulfuric acid. Here, the concentration of nitrous acid produced by the reaction can be determined as the nitrite present being converted to nitrous acid. The treatment time was 2 minutes. After removing the membrane from the aqueous nitrous acid solution, the membrane was immediately washed with water and stored at room temperature. The membrane changed from white to yellow to brown. When a performance test was performed under the same conditions as in the reference example, the water permeability of this membrane was 0.97 m ³ / m ² · d, and the sodium chloride removal rate was 99.5% (Example 1). Further, Table 1 shows the membrane performance of the results (Examples 2 to 7, Comparative Examples 1 and 2) in which the treatment time, the concentration of sodium nitrite, the moisture content of the membrane, and the m-phenylenediamine concentration in the membrane were variously changed. .

  From the results of Examples 1 and 2 and Comparative Examples 1 and 2, when the treatment time exceeds 2 minutes, both the membrane water permeability and the desalination rate before treatment cannot be improved, and the treatment cannot be applied. Recognize.

Nitrous acid (HNO ₂ ) dissociates into hydrogen ions and nitrite ions in water. Using this dissociation equilibrium constant (Ka), the pH dependence of the concentration of nitrous acid in a non-dissociated state can be calculated, which is shown in FIG. 1, as shown in FIG. From the results of 6 and 6, it is clear that when the pH is higher than 4, nitrous acid is dissociated, and the concentration of nitrous acid becomes 10% or less of the total concentration of nitrous acid and nitrite ions, thereby reducing the performance improvement effect.

  Further, from the results of Examples 1, 3, 4 and 7, when the concentration of sodium nitrite is smaller than 0.01% by weight, the film performance can be improved, but the effect is lowered.

<Comparative Example 3>
The membrane obtained in Reference Example A was treated at room temperature with an aqueous solution containing 0.07 wt% sodium nitrite and 0.1 wt% concentrated sulfuric acid. Here, the concentration of nitrous acid produced by the reaction can be determined as the nitrite present being converted to nitrous acid. The treatment time was 2 minutes, and after removing the membrane from the nitrous acid aqueous solution, it was immediately washed with water and stored at room temperature. As a result, the membrane changed from yellow to brown. When a performance test was performed under the same conditions as in the Reference Example, the water permeability of this membrane was 0.65 m ³ / m ² · d, and the removal rate of sodium chloride was 98.7%.

<Comparative example 4>
The film obtained in Reference Example A was immersed in a 500 ppm aqueous sodium hypochlorite solution at pH 7 for 2 minutes. When a performance test was performed under the same conditions as in the reference example, the water permeability of this membrane was 1.01 m ³ / m ² · d, and the removal rate of sodium chloride was 99.7%.

<Example 8>
The membrane obtained in Example 1 and the membrane of Comparative Example 4 were immersed in a 700 ppm aqueous sodium hypochlorite solution at pH 7 for 8 hours. These membranes are washed with water and the results of performance tests under the same conditions as in the reference example are shown.
Example 1 Membrane treatment:
Water permeability 1.84m ³ / m ² · d, sodium chloride removal rate 98.4%
Comparative Example 4 Membrane treatment:
Water permeability 2.09m ³ / m ² · d, sodium chloride removal rate 97.1%
From this, it is clear that the film of Example 1 is excellent in durability.

<Reference Example>
The polyester nonwoven fabric was peeled off from the membrane obtained in Example 1 to obtain a mixture of a microporous support membrane made of polysulfone and a separation functional layer of crosslinked polyamide. This was dissolved in methylene chloride and then filtered to obtain a separation functional layer. The separation functional layer was dried and then collected in a sealed container. A 6N aqueous sodium hydroxide solution was added, and the mixture was heated to 120 ° C. for dissolution. The obtained filtrate was diluted with heavy water (D ₂ O), put into an NMR tube, and analyzed with an FT-NMR analyzer. When the compound was identified from the δ value of protons obtained here, δ = 8.1 (trimesic acid), 6.71-6.65 (m-phenylenediamine), 6.65-6.59 (3-amino Phenol), 5.98-5.88 (m-phenylenediamine), 5.81-5.70 (3-aminophenol). In the membranes obtained in Reference Example A and Comparative Example 4, no signal that could be attributed to 3-aminophenol was obtained.

  From this, it is clear that the amino group in the polyamide was converted to a phenol group by the reagent.

Claims (5)

A method for producing a composite semipermeable membrane by forming a separation functional layer of polyamide by polycondensation reaction between a polyfunctional amine and a polyfunctional acid halide on a porous support membrane, wherein the composite semipermeable membrane has a moisture content. Reacts with primary aromatic amino groups in the separation functional layer in a wet state of 5% or more and the amount of primary aromatic amine having a molecular weight of 300 or less present in the separation functional layer is 500 mg / m ² or less. And a modification treatment step of contacting a solution containing a compound that forms a diazonium salt or a derivative thereof at 40 ° C. or less for 1 second or more and 2 minutes or less, and a method for producing a composite semipermeable membrane. The EI value calculated by the pH of the solution containing the compound, the total molar concentration (mol / L) of nitrous acid and / or a salt thereof, and the reaction time (s) is in the range of 0.005 to 500. 2. A method for producing a composite semipermeable membrane according to 1. The method for producing a composite semipermeable membrane according to claim 1, further comprising a step of bringing the composite semipermeable membrane into contact with an acidic aqueous solution having a pH of 4 or less before and / or after the modification treatment step. The method for producing a composite semipermeable membrane according to any one of claims 1 to 3, wherein the primary aromatic amine is m-phenylenediamine. A polyamide composite semipermeable membrane in which a polyamide separation functional layer is formed on a porous support membrane by a polycondensation reaction of a polyfunctional amine and a polyfunctional acid halide, and the moisture content is 5% or more, and The diazonium salt or derivative thereof reacts with the primary aromatic amino group in the separation functional layer when the amount of the primary aromatic amine having a molecular weight of 300 or less present in the separation functional layer is 500 mg / m ² or less. It is obtained by a modification treatment in which a solution containing the compound to be produced is contacted at 40 ° C. or less for 1 second or more and 2 minutes or less, and the light transmittance at a wavelength of 450 nm is in the range of 10 to 95%, and phenolic A polyamide composite semipermeable membrane characterized by having a hydroxyl group.

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