JP2003154238A - Composite semipermeable membrane and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a composite semipermeable membrane which has chemical resistance against a detergent, a disinfectant or the like and which realizes a high removing rate of salts and high permeation flux and to provide a method for manufacturing the membrane. SOLUTION: The composite semipermeable membrane has a semipermeable membrane layer formed on a microporous supporting membrane. The surface of the semipermeable membrane layer shows >=+10 mV zeta potential under the condition of pH=9.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a composite semipermeable membrane and a method for producing the same, which are useful for selective separation of a liquid mixture, particularly for removing an electrolyte in an aqueous solution having a low salt concentration, and high-purity water obtained by a multistage reverse osmosis membrane treatment. It relates to a manufacturing method.

[0002]

2. Description of the Related Art A composite semipermeable membrane obtained by coating a semipermeable membrane layer on a microporous support membrane is generally well known. When the semipermeable membrane layer is formed from a crosslinked aromatic polyamide,
Since it contains a benzene ring, it is highly rigid and has the advantage of being able to easily form a film by interfacial polycondensation of an aromatic polyfunctional amine and an aromatic polyfunctional acid halide, and also with a high salt exclusion rate and high permeation flux. Known to be (for example,
JP-A-1-180208, JP-A-2-11502
No. 7, JP-A-2-229538, JP-A-4-
90835, JP-A-4-104825, JP-A-4-161234).

However, the performance of the composite semipermeable membrane obtained by coating the semipermeable membrane layer made of the above crosslinked aromatic polyamide on the microporous support membrane depends on the electrolyte concentration in the aqueous solution,
There is a drawback that the electrolyte removal performance is deteriorated in a low concentration region where the electrolyte concentration is several ppm or less. In particular, it is known that the cation removal performance is greatly reduced. For this reason, for example, in a normal ultrapure water production process, a regenerable ion exchange resin tower is generally installed after the reverse osmosis membrane device.

In recent years, TO from a regenerative ion exchange resin tower
C elution has begun to be regarded as a problem, and from the viewpoint of omitting the regeneration step, development of a process that does not require the use of such a regenerated ion exchange resin tower is desired. Patent No. 25056
Since the quaternary ammonium group is introduced into the membrane by a covalent bond in the composite membrane described in JP-A No. 31, the quaternary ammonium group does not come off even after long-term operation,
It is a composite membrane that can maintain high performance of low concentration cation removal, and does not reduce the amount of water produced. On the contrary, it is a composite membrane that enables high amount of water produced by introducing quaternary ammonium groups. Has a drawback that when it is brought into contact with a sterilizing agent or a cleaning agent, the cationic property of the membrane is lowered and the water quality of the permeate is lowered.

[0005]

As described above, the conventional composite membrane has problems such as selectivity of ionic species that can be removed with high efficiency and chemical resistance, and a composite membrane satisfying these at the same time can be obtained. That was not the case.

Therefore, the present invention provides a composite semipermeable membrane obtained by coating a semipermeable membrane layer on a microporous support membrane, which has chemical resistance to detergents and bactericides and has a high salt removal rate, An object of the present invention is to provide a composite semipermeable membrane that can achieve a high permeation flux and a method for producing the same.

[0007]

[Means for Solving the Problems] The present invention for achieving the above object has the following constitution. That is, the present invention is (1) a composite semipermeable membrane in which a semipermeable membrane layer is formed on a microporous support membrane, wherein the surface of the semipermeable membrane layer is +
A composite semipermeable membrane having a zeta potential of 10 mV or higher. (2) The composite semipermeable membrane as described in (1), wherein the semipermeable membrane layer is made of crosslinked polyamide. (3) The composite semipermeable membrane according to (2), wherein the crosslinked polyamide is a crosslinked aromatic polyamide. (4) The compound containing a cationic group on the surface of the semipermeable membrane is
The composite semipermeable membrane according to any one of (1) to (3), which is bound by at least two covalent bonds. (5) The composite semipermeable membrane according to (4), wherein the cationic group is a quaternary ammonium group. (6) The composite semipermeable membrane according to any one of (1) to (5), which has a deterioration rate constant of 0.01 or less due to contact with a sodium bisulfite solution at a temperature of 25 ° C. adjusted to 100 ppm. . (7) After forming a semipermeable membrane layer on the microporous support membrane, a compound containing at least two reactive functional groups and cationic groups is reacted with the semipermeable membrane layer to form a covalent bond. And a method for producing a composite semipermeable membrane. (8) The method for producing a composite semipermeable membrane according to (7), wherein the reactive functional group is an epoxy group. (9) The method for producing a composite semipermeable membrane according to (7) or (8), wherein the cationic group is a quaternary ammonium group. (10) By X-ray photoelectron spectroscopy (ESCA) measurement,
The composite semipermeable membrane according to any one of (7) to (9), wherein the amino group concentration on the surface of the semipermeable membrane layer before reacting with the compound containing a cationic group is 0.002 or more. Membrane manufacturing method. (11) A composite semipermeable membrane element having the composite semipermeable membrane according to any one of (1) to (6). (12) A fluid separation device comprising the composite semipermeable membrane element according to (11). (13) A fluid separation device having a composite semipermeable membrane element arranged in multiple stages, wherein the composite semipermeable membrane element according to (11) is arranged at least in the final stage. (14) A liquid characterized by using the composite semipermeable membrane element according to (11), adjusting the pH of the liquid to be treated to a range of 8 or more and 12 or less, and then supplying the liquid to the composite semipermeable membrane element. Processing method. Is.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION In the composite semipermeable membrane of the present invention, a semipermeable membrane layer having substantially the ability to separate ions and the like is provided on a microporous support membrane having substantially no separation ability. The surface of the semipermeable membrane layer is +10 mV at pH 9
It is necessary to have the above zeta potential. As a material forming the semipermeable membrane layer, any material that can have a zeta potential of +10 mV or more can be used without limitation, but a crosslinked polyamide or a material containing a crosslinked polyamide as a main component is preferable.

The crosslinked polyamide is formed by interfacial polycondensation of a polyfunctional amine and a polyfunctional acid halide, and at least one amine or acid halide component contains a trifunctional or higher functional compound.

Here, the polyfunctional amine means an amine having at least two amino groups in one molecule. For example, the two amino groups are in the ortho position, the meta position, or the para position. Aromatic polyfunctional amines such as phenylenediamine, xylylenediamine, 1,3,5-triaminobenzene, 1,2,4-triaminobenzene, 3,5-diaminobenzoic acid bonded to benzene, ethylenediamine, propylene Aliphatic amines such as diamines, 1,2
Examples thereof include alicyclic polyfunctional amines such as diaminocyclohexane, 1,4-diaminocyclohexane, piperazine, 1,3-bispiperidylpropane, and 4-aminomethylpiperazine. Of these, aromatic polyfunctional amines are preferable in consideration of the selective separation property, permeability, and heat resistance of the membrane. Examples of such polyfunctional aromatic amines include m-phenylenediamine, p-phenylenediamine, 1, Although 3,5-triaminobenzene is preferably used, it is more preferable to use m-phenylenediamine (hereinafter referred to as m-PDA) from the viewpoint of easy availability and easy handling. These polyfunctional amines may be used alone or in combination.

The polyfunctional acid halide means an acid halide having at least two carbonyl halide groups in one molecule. For example, a trifunctional acid halide is trimesic acid chloride, 1,3,5-cyclohexane. Examples thereof include tricarboxylic acid trichloride and 1,2,4-cyclobutane tricarboxylic acid trichloride. Among the bifunctional acid halides, biphenyl dicarboxylic acid dichloride, biphenylene carboxylic acid dichloride, azobenzene dicarboxylic acid dichloride, terephthalic acid chloride and isophthalic acid chloride. Aromatic bifunctional acid halides such as acid chloride and naphthalene dicarboxylic acid chloride, aliphatic bifunctional acid halides such as adipoyl chloride and sebacyl chloride, cyclopentanedicarboxylic acid dichlora De, cyclohexanedicarboxylic acid dichloride, can be mentioned alicyclic bifunctional acid halides, such as tetrahydrofuran dicarboxylic acid dichloride. Considering the reactivity with the polyfunctional amine, the polyfunctional acid halide is preferably a polyfunctional acid chloride, and in view of the selective separation property and heat resistance of the membrane, the polyfunctional acid halide is an aromatic polyfunctional acid chloride. Preferably there is. Among them, it is more preferable to use trimesic acid chloride from the viewpoint of easy availability and easy handling. These polyfunctional acid halides may be used alone or in combination.

It is preferable that the compound having a cationic group is bound to the surface of the semipermeable membrane layer by at least two covalent bonds. The method of introducing a cationic group is not particularly limited, and examples thereof include a method of reacting a polyfunctional amine having a cationic group with a polyfunctional acid halide to form a crosslinked polyamide, or a polyfunctional amine and a polyfunctional acid halogen. A method of quaternizing an amine terminal remaining in a crosslinked polyamide formed by a reaction with a compound with an alkyl halide, or having a cationic group and a functional group reactive with the crosslinked polyamide A method of reacting a compound with a crosslinked polyamide can be used.

Among them, as a method for simply introducing a quaternary ammonium group without significantly deteriorating the membrane performance, 4
It is more preferable to use a method in which a compound having a primary ammonium group and having at least two reactive functional groups with respect to the crosslinked polyamide is reacted with the crosslinked polyamide. Examples of such reactive functional groups include epoxy groups, aziridine groups, episulfide groups, halogenated alkyl groups, amino groups, carboxylic acid groups, halogenated carbonyl groups, hydroxyl groups, etc. Can be used. Among them, the epoxy group is more preferable because it is easily available.

Since the skeleton of the crosslinked polyamide is formed by interfacial polycondensation of a polyfunctional amine and a polyfunctional acid halide, unreacted amine terminals and unreacted acid terminals are inevitably present. The epoxy group, aziridine group, and episulfide group are subjected to nucleophilic attack by the terminal amino group or the like of the crosslinked polyamide to open the ring and bond to the crosslinked polyamide. The halogenated alkyl group gives a secondary amine by reaction with the terminal primary amino group of the crosslinked polyamide, and the carboxylic acid group dehydrates and condenses with the terminal amino group of the crosslinked polyamide to form an amide bond. The group acylates the terminal amino group of the crosslinked polyamide to form an amide bond, and the amino group or the hydroxyl group dehydrates and condenses with the terminal carboxylic acid group of the crosslinked polyamide to form an amide bond or an ester bond. Therefore, by using a compound having these functional groups and having a cationic group, the cationic group can be introduced into the composite semipermeable membrane via a covalent bond.

The term "cationic group" used herein means, for example, 4
Primary ammonium group, sulfonium group, phosphonium group,
Examples thereof include an oxonium group, an arsonium group, and a selenonium group. Among these, a quaternary ammonium group is more preferable because it is easily available and easy to handle.

The term "quaternary ammonium group" as used herein means a nitrogen atom contained in the group represented by the following chemical formula 1.

[0017]

[Chemical 1]

(However, R1, R2, and R3 each independently represent a substituted or unsubstituted aliphatic group or aromatic group, and X is a halide ion, hydroxide ion, sulfate ion, nitrate ion, or phosphate ion. Represents anions such as.).

After that, the quaternary ammonium group is replaced by
Let us denote it by N ⁺ .

A compound having a quaternary ammonium group and having two or more epoxy groups is represented by the following chemical formula 2.
There is an epoxy compound represented by.

[0021]

[Chemical 2]

(However, R4, R5, and R6 each independently represent a hydrogen atom, or a substituted or unsubstituted aliphatic group or aromatic group, and n and m each represent an integer of 0 or more.).

Considering the reactivity with respect to crosslinked polyamide, the performance of the obtained film, and the availability, preferred epoxy compounds are hexamethylene bis (glycidyl dimethyl ammonium) dichloride, ethylene bis (glycidyl dimethyl ammonium) dichloride, octamethylene. Examples thereof include bis (glycidyldimethylammonium) dichloride.

As a compound having a quaternary ammonium group and two or more aziridine groups, there is an aziridine compound represented by the following chemical formula 3.

[0025]

[Chemical 3]

(However, R4, R5, R6, and R7 each independently represent a hydrogen atom, or a substituted or unsubstituted aliphatic group or aromatic group, and n and m each represent an integer of 0 or more).

The compound having a quaternary ammonium group and having two or more episulfide groups includes an episulfide compound represented by the following chemical formula 4.

[0028]

[Chemical 4]

(However, R4, R5, and R6 each independently represent a hydrogen atom, or a substituted or unsubstituted aliphatic group or aromatic group, and n and m each represent an integer of 0 or more).

The compound having a quaternary ammonium group and having at least two reactive functional groups with respect to the crosslinked polyamide preferably has a molecular weight of 100 to 500. This is because when the molecular weight exceeds 500, the amount of permeated water tends to decrease.

The semipermeable membrane layer made of crosslinked polyamide has an amine terminal or a carboxylic acid terminal, but the amine terminal has a low p
The H-region dissociates ionically to give the membrane cation chargeability, and the carboxylic acid terminal ionically dissociates in the high pH region to give the membrane anion chargeability. Therefore, the chargeability of the semipermeable membrane layer changes with pH, the anion chargeability becomes relatively high in the high pH region, and the exclusion rate of the oppositely charged cations of the membrane decreases. For example, since the quaternary ammonium group is a strongly basic functional group, it is ionically dissociated in all pH regions and imparts cation chargeability to the crosslinked polyamide film having a relatively high anion chargeability in a high pH range. Have the effect of Therefore, the cation removal performance, which is the cause of the electrolyte removal performance degradation in the low concentration region and the high pH region, is improved as the cation chargeability of the semipermeable membrane layer is increased.

As a method of increasing the cationic chargeability of the surface of the semipermeable membrane layer, a method of adhering a cationic compound to the surface of the semipermeable membrane layer by electrostatic force, or a method of adhering the cationic compound and the semipermeable membrane to each other The method of improving the reactivity with and increasing the amount of binding to the membrane, the method of reacting with the semipermeable membrane using a polymer having many cationic groups introduced, the unreacted acid terminal on the surface of the semipermeable membrane There is a method in which the anionic chargeability of the semipermeable membrane is reduced and the cation chargeability is relatively increased by esterification or amidation. The cationic chargeability of the surface of the semipermeable membrane can be increased by using these methods alone or in combination.

In the present invention, the microporous support membrane is used to give strength to the semipermeable membrane layer having substantially no separation performance for ions and the like, and having substantially separation performance. The size and distribution of the pores are not particularly limited, but for example, uniform and fine pores, or gradually larger micropores from one surface to the other surface, the size of the micropores on the surface of the support film is 100 nm or less. A support membrane of some structure is preferred.

The material used for the microporous support membrane and its shape are not particularly limited, but for example, polysulfone, cellulose acetate, or polyvinyl chloride reinforced by a cloth containing at least one selected from polyester or aromatic polyamide as a main component. , Or a mixture thereof is preferably used. As the material used for the matrix, it is particularly preferable to use polysulfone having high chemical, mechanical and thermal stability.

Specifically, it is preferable to use polysulfone composed of a repeating unit represented by the following chemical formula 5 because the pore diameter can be easily controlled and the dimensional stability is high.

[0036]

[Chemical 5]

As a method for producing polysulfone, for example, an N, N-dimethylformamide (DMF) solution of the above polysulfone is cast on a densely woven polyester cloth or non-woven cloth to a certain thickness, and the resulting solution is submerged in water. Most of the surface is several 10 nm in diameter by wet coagulation with
The microporous support membrane having the following fine pores can be obtained.

Next, a method for manufacturing the composite semipermeable membrane of the present invention will be described.

The semipermeable membrane layer constituting the composite semipermeable membrane uses, for example, an aqueous solution containing the above-mentioned polyfunctional amine and an organic solvent solution immiscible with water containing the polyfunctional acid halide, The skeleton can be formed by performing interfacial polycondensation on the surface of the microporous support film.

The concentration of the polyfunctional amine in the polyfunctional amine aqueous solution is preferably in the range of 0.1 to 10% by weight, more preferably 0.5 to 5.0% by weight.
Within the range of. If the concentration is less than 0.1% by weight, the progress of the reaction tends to be slow, while if it exceeds 10% by weight, the ultrathin film layer becomes thick and water permeability tends to be insufficient. The polyfunctional amine aqueous solution may contain a surfactant, an organic solvent, an alkaline compound, an antioxidant and the like as long as they do not interfere with the reaction between the polyfunctional amine and the polyfunctional acid halide. The surfactant has the effect of improving the wettability of the surface of the porous support film and reducing the interfacial tension between the amine aqueous solution and the non-polar solvent, and the organic solvent may act as a catalyst for the interfacial polycondensation reaction. In some cases, the interfacial interlocking reaction can be efficiently carried out by adding.

In order to carry out the interfacial polycondensation on the porous support membrane, it is advisable to first bring the above-mentioned polyfunctional amine aqueous solution into contact with the porous support membrane. The contact is preferably performed uniformly and continuously on the surface of the porous support membrane. Specifically, for example, a method of coating the polyfunctional amine aqueous solution on the porous support membrane and a method of immersing the porous support membrane in the polyfunctional amine aqueous solution can be mentioned. The contact time between the porous support membrane and the polyfunctional amine aqueous solution is preferably in the range of 1 to 10 minutes, more preferably in the range of 1 to 3 minutes.

After the polyfunctional amine aqueous solution is brought into contact with the porous support membrane, it is sufficiently drained so that no droplets remain on the membrane. When the liquid droplets remain, the portion where the liquid droplets remain after the film formation becomes a film defect, and the film performance is likely to deteriorate. As a method of draining, for example, as described in Japanese Patent Application Laid-Open No. 2-78428, a method of vertically holding the porous support membrane after contact with the aqueous solution of a polyfunctional amine to allow an excessive aqueous solution to flow down naturally. Furthermore, a method in which air such as nitrogen is then blown from the air nozzle to forcibly drain the liquid can be used. Further, after draining, the membrane surface may be dried to remove a part of the water of the aqueous solution.

Then, an organic solvent solution containing a polyfunctional acid halide is brought into contact with the support membrane thus obtained after contact with the polyfunctional amine aqueous solution to form a skeleton of a crosslinked polyamide ultrathin film layer by interfacial polycondensation.

The concentration of the polyfunctional acid halide in the organic solvent solution is preferably in the range of 0.01 to 10% by weight,
More preferably, it is in the range of 0.02 to 2.0% by weight. If it is less than 0.01% by weight, the progress of the reaction tends to be slow, and if it exceeds 10% by weight, side reactions are likely to occur. Furthermore, when an acylation catalyst such as N, N-dimethylformamide is contained in this organic solvent solution, interfacial polycondensation is promoted, which is more preferable.

The above organic solvents are immiscible with water,
In addition, it is desirable that the acid halide is dissolved and the microporous support film is not destroyed, and any material that is inert to the amino compound and the acid halide may be used. Preferred examples include, for example, n-hexane, n-octane, n-
Hydrocarbon compounds such as decane are mentioned.

The method for contacting the aqueous solution of the amino compound with the solution of the polyfunctional acid halide in the organic solvent may be the same as the method for coating the aqueous solution of the polyfunctional amine on the microporous support membrane.

As described above, after the solution of an acid halide in an organic solvent is contacted to perform interfacial polycondensation to form a separation functional layer containing a crosslinked polyamide on the porous support membrane,
It is advisable to drain off the excess solvent. As a method of draining, for example, a method of holding the film in the vertical direction and allowing the excess organic solvent to flow down naturally can be used. in this case,
The vertical gripping time is preferably 1 to 5 minutes, and more preferably 1 to 3 minutes.

The composite semipermeable membrane obtained by the above method is
Although it has sufficiently good exclusion performance and water permeability alone, it further improves the exclusion performance of the composite semipermeable membrane by contacting it with an aqueous polyfunctional amine solution and polycondensing it with the remaining acid halide to reduce the acid terminals. It can be further improved.

The method of contacting the composite semipermeable membrane with the polyfunctional amine aqueous solution phase may be carried out in the same manner as the above-mentioned coating method of the amine aqueous solution with the microporous support membrane.

The composite semipermeable membrane obtained by the above method is
In the range of 50 to 150 ° C., preferably in the range of 70 to 130 ° C., for 1 to 10 minutes, more preferably 2 to 8 minutes, a step of hot water treatment is added to remove the composite semipermeable membrane. The water permeability can be further improved.

A compound having a cationic group and having at least two reactive functional groups (hereinafter referred to as a cationization-reactive compound) is brought into contact with the semipermeable membrane layer of the crosslinked polyamide thus produced. . Examples of the cationization-reactive compound include two functional groups selected from the group consisting of an epoxy group, an aziridine group, an episulfide group, a halogenated alkyl group, an amino group, a carboxylic acid group, a carbonyl halide group, and a hydroxyl group. Have more than
Moreover, the compound containing a quaternary ammonium group can be mentioned. These compounds may be used alone or in combination of two or more. Considering the reactivity to the crosslinked polyamide, the performance of the obtained membrane and the availability, the cationization-reactive compound is 4
Compounds containing quaternary ammonium groups are preferred. A particularly preferred compound is hexamethylenebis (glycidyldimethylammonium) dichloride.

As the method for bringing the cationization-reactive compound into contact, the above-mentioned cationization-reactive compound is dissolved in a solvent that does not attack the composite semipermeable membrane, and this solution is applied to the composite semipermeable membrane, or this solution is used. A method of immersing the composite semipermeable membrane in can be used. A solvent that does not attack the composite semipermeable membrane is a solvent that does not dissolve or significantly swell the semipermeable membrane skeleton or the microporous support membrane layer of the composite semipermeable membrane and does not significantly impair the membrane performance, and a preferred example Examples of the water can include water, alcohol and hydrocarbons. Of these, water is preferably used in consideration of the solubility of the cationization-reactive compound, ease of handling, and economy.

The charge amount of the semipermeable membrane can be controlled by the concentration of the cationization-reactive compound to be contacted. That is, when the concentration is low, the amount of quaternary ammonium groups introduced into the film is small and the charge amount is small, and when the concentration is high, the amount of cationic groups introduced into the film is large and the charge amount is large. The concentration of the cationization-reactive compound is 0.1 to 2 with respect to the solvent.
It is preferably in the range of 0% by weight, more preferably 1 to 1
It is within the range of 0% by weight.

A zeta potential can be mentioned as a means for measuring the charge amount. The zeta potential is a measure of the net fixed charge on the surface of the ultrathin film layer, and the zeta potential on the surface of the thin film layer of the present invention can be calculated from the electric mobility by the Helmholtz.
It can be determined by the Helmholtz-Smoluchowski formula.

[0055]

[Equation 1]

(Where U is the electric mobility, ε is the dielectric constant of the solution, and η is the viscosity of the solution). Here, the values of literature values at the measurement temperature were used as the dielectric constant and viscosity of the solution.

The principle of measuring the zeta potential will be described.
In the (water) solution in contact with the material, there is a non-flowable stationary layer in the vicinity of the surface due to the influence of the charge on the material surface. The zeta potential is the boundary surface (sliding surface) between the stationary and fluidized beds of the material.
Is the potential for the solution at.

Considering the aqueous solution in the quartz glass cell, the quartz surface is usually negatively charged.
Positively charged ions and particles gather near the cell surface. On the other hand, negatively charged ions and particles are increased in the central portion of the cell, and an ion distribution is generated in the cell. When an electric field is applied in this state, the ion distribution is reflected in the cell, and the ions move at different migration velocities at the position in the cell (called electroosmotic flow). Since the migration velocity reflects the charge on the cell surface, the charge (surface potential) on the cell surface can be evaluated by obtaining this migration velocity distribution.

The size of the zeta potential is 20 mm × 3.
Using a 0 mm membrane sample, the standard particles for electrophoresis were 10 mmo polystyrene particles (particle size 520 nm) coated with hydroxypropylcellulose on the surface.
What was dispersed in a 1 / l NaCl aqueous solution was used. The measuring device is ELS-80, an electrophoretic light scattering photometer manufactured by Otsuka Electronics.
0 was used and the light source was a He-Ne laser.

In the composite semipermeable membrane of the present invention, the surface of the semipermeable membrane layer needs to have a zeta potential of +10 mV or more at pH 9. The zeta potential is preferably +11 mV or higher.

In order to give such a zeta potential, it is preferable that the amino group which reacts with the cationization-reactive compound is present uniformly and at a high concentration on the surface of the membrane. A semipermeable membrane can be obtained.

The amino group concentration on the surface of the semipermeable membrane layer before reacting with the cationization-reactive compound is determined by X-ray photoelectron spectroscopy (E
SCA) can be used for analysis, and the value is preferably 0.002 or more. When the amino group concentration is less than 0.002, the reaction amount of the cationization-reactive compound decreases, and the cationic property of the film tends to decrease.

Here, the amino group concentration is the ratio of the amount of amino groups (the number of moles) to the total amount of carbon (the number of moles) near the surface of the semipermeable membrane layer, and is the value calculated by the following formula. Say. Amino group concentration = amino group amount (mol) / total carbon amount (mol) The amino group concentration can be determined by a gas phase chemical modification method using a labeling reagent, and pentafluorobenzaldehyde or the like is used as the labeling reagent.

In obtaining the composite semipermeable membrane of the present invention, the reaction between the cationization-reactive compound and the semipermeable membrane is 50 to 150.
If the reaction is carried out at ℃, the reaction speed will increase and the time required for production will be reduced to 1
It can be shortened to 30 minutes, which is preferable. In addition, when the excess cationization-reactive compound is brought into contact with the semipermeable membrane before the heat treatment step, the solution of the cationization-reaction compound is adjusted to 50%.
The time required for production can also be shortened to 1 to 30 minutes by heating to -100 ° C and immersing the film in this.

The composite semipermeable membrane of the present invention preferably has a deterioration rate constant of 0.01 or less due to contact with a sodium bisulfite solution at a temperature of 25 ° C. adjusted to 100 ppm.

Here, the deterioration rate constant is obtained as follows. Temperature of composite semipermeable membrane adjusted to 100ppm 2
After immersing in a sodium bisulfite aqueous solution at 5 ° C. for 40 hours, and then supplying a 1 ppm aqueous sodium chloride solution having a pH adjusted to 9 to the composite semipermeable membrane under the conditions of an operating pressure of 10 kg / cm ² and a temperature of 25 ° C. In, the sodium ion permeability of the permeated water and the sodium ion permeability of the permeated water when the aqueous sodium chloride solution is permeated through the composite semipermeable membrane before being immersed in the sodium hydrogen sulfite solution, Calculate the degradation rate constant.

[0067]

[Equation 2]

The composite semipermeable membrane of the present invention is usually stored in a desired container and used as a composite semipermeable membrane element. Such an element can be suitably used for desalting an aqueous solution having a low salt concentration, and particularly in a fluid separation device in which a composite semipermeable membrane element is arranged in multiple stages, the water to be treated supplied to the subsequent stage does not generate carbonic acid. It can be suitably used for the semi-permeable membrane element in the latter stage when the content of sodium ion is 1 ppm or less.

When the raw water containing carbonic acid is treated as the water to be treated by using the fluid separation device, in order to remove the carbonic acid efficiently, at least the pH of the water to be treated to the reverse osmosis membrane to the final stage should be 8 -12, preferably 8-10, more preferably 8.5-9.5 is preferably adjusted for operation.

When the conventional composite semipermeable membrane is used, when the pH of the feed water is 8 or more, the carbonic acid can be removed efficiently, but the cation concentration in the permeate increases and the electrolyte concentration in the permeate increases. Is not practical because it increases. Also, the pH
If it is 12 or more, hydrolysis of the amide bond occurs and the performance of the film deteriorates. Therefore, when such a conventional composite semipermeable membrane is used, it is necessary to operate at a pH of less than 8 in order to minimize the total electrolyte concentration in the permeate, but carbon dioxide cannot be efficiently removed at a pH of less than 8. . When the composite semipermeable membrane of the present invention is used, low concentration cations are satisfactorily removed in the fluid separator at least when the pH of the water to be treated to the final stage reverse osmosis membrane is in the range of 8 to 12. As a result, carbonic acid is efficiently removed, the total electrolyte concentration in the permeated water can be reduced, and it is also effective in preventing deterioration of the membrane.

Considering the economical efficiency of using the composite semipermeable membrane,
The operating pressure for permeating the water to be treated through the composite semipermeable membrane is 30
It is preferably not more than kg / cm ² .

Next, a method of producing water by the fluid separation device using the composite semipermeable membrane element of the present invention will be described.

The water produced by the fluid separation device according to the present invention is
Alkali is added to the raw water containing carbonic acid, and then this alkali-added water is treated with the composite semipermeable membrane element in the previous stage to obtain primary permeate, and this primary permeated water is then treated with the reverse osmosis membrane element in the latter stage to obtain high It is carried out by obtaining secondary permeated water which is pure water. The alkali may be added to the primary permeated water.

Here, the composite semipermeable membrane element of the present invention is preferably used in the reverse osmosis membrane device in the subsequent stage.
The reverse osmosis membrane element having excellent low-concentration electrolyte removal performance as in the present invention can be used in any of the reverse osmosis membrane device in the preceding stage or the latter stage, but the former stage treats raw water having a relatively high electrolyte concentration. Therefore, the effect may not be so remarkable as compared with the conventional membrane, and the effect is large when used in the reverse osmosis membrane device in the subsequent stage.

When water having a hardness component is used as raw water, a step of providing a decarboxylation device or adding a scale inhibitor or an acid is added to prevent scale deposition on the reverse osmosis membrane surface. May be. Furthermore, it includes other water treatment steps used in known multi-stage reverse osmosis membrane treatment methods, such as the steps of degassing dissolved gas, injecting a germicide, and removing the germicide. May be. In addition, in order to efficiently remove carbonic acid and minimize the total electrolyte concentration in the obtained high-purity water by this multi-stage reverse osmosis membrane treatment method, the amount of alkali to be added is adjusted and the primary permeation is performed. It is preferable to adjust the pH of water to 8 to 12, preferably 8 to 10, and more preferably 8.5 to 9.5.

[0076]

EXAMPLES Examples and comparative examples are described below. First, the preparation method and evaluation method of the composite semipermeable membrane used will be described.

(Reference Example 1: Preparation method for composite semipermeable membrane) Taffeta made of polyester fiber (both warp and weft are 166)
Decitex multifilament yarn was used. Weave density 90 lengths / inch, 67 widths / inch, thickness 160
a 15.7 wt% solution of polysulfone in dimethylformamide (DMF) at a thickness of 200μ at room temperature (25 μm).
C.), immediately immersed in pure water and left for 5 minutes to prepare a fiber-reinforced polysulfone support membrane (hereinafter abbreviated as FR-PS support membrane). The FR-PS supporting film (thickness 210 to 215 μm) thus obtained
Was immersed in an aqueous solution of amine containing 1.5% by weight of m-phenylenediamine for 2 minutes, the support film was slowly pulled up in the vertical direction, and nitrogen was blown from an air nozzle to remove excess solution from the surface of the support film. An n-decane solution containing 0.06% by weight of trimesic acid chloride was applied so that the surface was completely wet, and the solution was allowed to stand for 1 minute. Next, the film is held vertically for 1 minute, the excess solution is drained and removed, then an amine aqueous solution containing 3% ethylenediamine is applied on the film by the FF method, and nitrogen is blown by an air nozzle to spray the film surface. To remove excess water from it and then at 90 ° C for 2
It was washed with hot water for a minute. The obtained composite membrane will be referred to as a pre-composite semipermeable membrane. The amino group concentration on the surface of the semipermeable membrane layer of the pre-composite semipermeable membrane was 0.170 as measured by X-ray photoelectron spectroscopy (ESCA). The pre-composite semipermeable membrane was used in Examples and Comparative Examples.

(Sodium Ion Exclusion Rate) A 1 ppm sodium chloride aqueous solution having a pH adjusted to 9 was supplied to a composite semipermeable membrane at a temperature of 25 ° C. and an operating pressure of 10 kg / cm ² ,
The contained sodium ion concentration was measured from the ion chromatograph and the sodium ion exclusion rate was calculated. The sodium exclusion rate was calculated by the following formula. Sodium ion exclusion rate = {(sodium ion concentration of treated liquid-sodium ion concentration of permeate) / sodium ion concentration of treated liquid} x 100 (membrane permeation flux) Used as a treated liquid for sodium ion elimination ratio Liquid is supplied, and per 1 square meter of the membrane surface, the permeation rate per day (cubic meter) to the membrane permeation flux (m ³ / m ² ·
Sought).

Example 1 A 5% by weight aqueous solution of hexamethylenebis (glycidyldimethylammonium) dichloride was applied to the semipermeable membrane layer of the pre-composite semipermeable membrane obtained in Reference Example 1 and allowed to stand for 2 minutes. After that, the membrane was made vertical and the excess solution was drained and removed, and heat-treated in a dryer at 120 ° C. for 2 minutes and washed with water. Then, it was immersed in a 10% isopropyl alcohol aqueous solution for 10 minutes for hydrophilic treatment to obtain a composite semipermeable membrane. The sodium ion exclusion rate of the composite semipermeable membrane is 98.3%, the membrane permeation flux is 0.9 m ³ / m ² · day, the degradation rate constant is 0.0046, and the zeta potential of the membrane surface is 12 m.
It was V.

Example 2 A composite semipermeable membrane was prepared in the same manner as in Example 1 except that the hexamethylenebis (glycidyldimethylammonium) dichloride used in Example 1 was changed to octamethylenebis (glycidyldimethylammonium) dichloride. Was produced. At this time, the sodium ion exclusion rate was 98.9%, and the membrane permeation flux was 1.0 m ³ / m ^2.
-The day, the deterioration rate constant was 0.0072, and the zeta potential of the film surface was 11 mV.

Comparative Example 1 A composite semipermeable membrane was prepared in the same manner as in Example 1 except that the hexamethylenebis (glycidyldimethylammonium) dichloride used in Example 1 was changed to glycidyltrimethylammonium chloride. At this time, the sodium ion exclusion rate is 98.9%,
The membrane permeation flux was 1.2 m ³ / m ² · day, and the deterioration rate constant was 0.
0345, the zeta potential of the film surface was 8 mV, and the deterioration rate constant was large.

Example 3 Except that the concentration of the aqueous solution of hexamethylenebis (glycidyldimethylammonium) dichloride used in Example 1 was changed to 2, 10% by weight,
A composite semipermeable membrane was prepared in the same manner as in Example 1. The evaluation results at this time are shown in Table 1.

Example 4 A composite semipermeable membrane was produced in the same manner as in Example 1 except that the heat treatment temperature in Example 1 was changed to 80 and 100 ° C. The evaluation results at this time are shown in Table 2.

(Example 5) A composite semipermeable membrane was prepared in the same manner as in Example 1 except that the heat treatment time in Example 1 was changed to 1 and 5 minutes. Table 3 shows the evaluation results at this time.

Comparative Example 2 A composite semipermeable membrane before being treated with an aqueous solution of hexamethylenebis (dimethylammonium) dichloride was evaluated in the same manner. At this time, the sodium ion exclusion rate was 70.3%, and the membrane permeation flux was 1.4 m.
³ / m ² · day, deterioration rate constant was 0.0002, zeta potential on the membrane surface was −1.2 mV, and the sodium ion exclusion rate was low.

Table 1 is a table in which the concentration of the aqueous solution of hexamethylenebis (glycidyldimethylammonium) dichloride is used as a parameter, Table 2 is a table in which the heat treatment temperature is used as a parameter, and Table 3 is used in which the heat treatment time is used as a parameter. It is a table.

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[Table 1]

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[Table 2]

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[Table 3]

[0090]

According to the present invention, it is possible to provide a composite semipermeable membrane which has a high cation exclusion rate even in a low concentration region and which is excellent in chemical resistance to detergents and bactericides, and a method for producing the same. In particular, it is possible to provide a composite semipermeable membrane having a high low concentration cation exclusion rate even under alkaline conditions and a method for producing the same.

Continued front page    F-term (reference) 4D006 GA03 KA53 KA55 KA56 MA06                       MA11 MB02 MB07 MB09 MB11                       MC51 MC55 MC62X MC78                       NA05 NA10 NA41 NA44 NA46                       NA49 NA59 NA63 NA64 PA01                       PB03 PB12 PB25 PB26 PC02

Claims (14)

[Claims] 1. A composite semipermeable membrane in which a semipermeable membrane layer is formed on a microporous support membrane, wherein the surface of the semipermeable membrane layer has a zeta potential of +10 mV or more at pH 9. Composite semi-permeable membrane to. 2. The composite semipermeable membrane according to claim 1, wherein the semipermeable membrane layer is made of crosslinked polyamide. 3. The composite semipermeable membrane according to claim 2, wherein the crosslinked polyamide is a crosslinked aromatic polyamide. 4. The compound semipermeable membrane according to claim 1, wherein a compound containing a cationic group is bound to the surface of the semipermeable membrane layer by at least two covalent bonds. film. 5. The composite semipermeable membrane according to claim 4, wherein the cationic group is a quaternary ammonium group. 6. A deterioration rate constant by contact with a sodium bisulfite solution at a temperature of 25 ° C. adjusted to 100 ppm is 0.
It is 01 or less, The composite semipermeable membrane in any one of Claims 1-5 characterized by the above-mentioned. 7. Forming a semipermeable membrane layer on a microporous support membrane, and then reacting a compound containing at least two reactive functional groups and cationic groups with the semipermeable membrane layer to form a covalent bond. A method for producing a composite semipermeable membrane, comprising: 8. The method for producing a composite semipermeable membrane according to claim 7, wherein the reactive functional group is an epoxy group. 9. The method for producing a composite semipermeable membrane according to claim 7, wherein the cationic group is a quaternary ammonium group. 10. The concentration of amino groups on the surface of the semipermeable membrane layer before reacting with the compound containing a cationic group is 0.002 or more as measured by X-ray photoelectron spectroscopy (ESCA). The method for producing a composite semipermeable membrane according to any one of claims 7 to 9. 11. A composite semipermeable membrane element comprising the composite semipermeable membrane according to any one of claims 1 to 6. 12. A fluid separation device provided with the composite semipermeable membrane element according to claim 11. 13. A fluid separation device in which composite semipermeable membrane elements are arranged in multiple stages, wherein the composite semipermeable membrane element according to claim 11 is arranged at least in the final stage. 14. The composite semipermeable membrane element according to claim 11, wherein the pH of the liquid to be treated is adjusted to be in the range of 8 or more and 12 or less and then supplied to the composite semipermeable membrane element. Liquid treatment method.