JP2003117360A - Method for manufacturing semipermeable membrane - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a semipermeable membrane having high desalting property and high water permeability and effective to desalt brine or sea water. SOLUTION: The method for manufacturing the semipermeable membrane features that a semipermeable membrane is brought into contact with an aqueous solution containing an organic acid.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a semipermeable membrane which is useful for the selective separation of an aqueous solution, and particularly for the desalination of brackish water or seawater which has both high desalination property and high water permeability.

[0002]

2. Description of the Related Art Semipermeable membranes selectively separate the components of a liquid mixture, and are produced by the production of ultrapure water, desalination of seawater or brackish water, dyeing and removal / separation recovery of electrodeposition paint wastewater. It is used to build a closed system of industrial water and to concentrate active ingredients in the food industry.

Specifically, a semipermeable membrane obtained by bringing a thin film layer made of a crosslinked polyamide obtained by an interfacial polycondensation reaction of a polyfunctional aromatic amine and a polyfunctional acid derivative (eg chloride) into contact with a porous support membrane. The permeable membrane has been attracting attention as a reverse osmosis membrane having high permeability and selective separation (for example, JP-A-55-55).
14706, JP-A-5-76740, etc.).

In order to exhibit high water permeability, a reverse osmosis membrane produced by using an additive in an interfacial polycondensation reaction has also been developed. Examples of the additive include compounds such as potassium hydroxide and trisodium phosphate for removing an acidic substance generated by an interfacial reaction to the outside of the system, an acylation catalyst, and a solubility parameter of 8 to 14 (cal / cm ² ). ^0.5 compounds and the like have been proposed (for example, JP-A-63-12310, JP-A-6-47260 and JP-A-9-8506).
No. 8, JP-A No. 13-179061, etc.).

As a means for improving the desalination performance, a method of treating a semipermeable membrane with hot water has been proposed (Japanese Patent Publication No. 7-114941). Further, there has been proposed a method of suppressing a decrease in the amount of permeated water by immersing in an aqueous solution containing a mixture of a polyhydric alcohol, a trialkylamine and an organic acid and performing hot water treatment (JP-A-10-165790, etc.).

[0006]

However, the membrane prepared by the conventional technique is not sufficient in salt removal performance, and higher desalination performance is required. The present invention is intended to solve the drawbacks of the prior art, and an object thereof is to provide a method for producing a semipermeable membrane having high desalination performance and high water permeability.

[0007]

The present invention for achieving the above object is a method of producing a semipermeable membrane, which comprises subjecting the semipermeable membrane to contact treatment with an aqueous solution containing an organic acid.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The semipermeable membrane of the present invention is preferably one in which a separation functional layer is provided on at least one surface of a porous support membrane. The separation functional layer may be provided on both sides of the porous support membrane, or a plurality of separation functional layers may be provided, but usually,
It is sufficient to have one separating functional layer on one side.

Here, the porous support membrane is used to give strength to the semipermeable membrane of the present invention as a support membrane for the separation functional layer. Therefore, it is not particularly limited as long as it is a film having a plurality of pores, but preferably, it has a substantially uniform pore or a pore in which the pore diameter gradually increases from one surface to the other surface, and the size of the pore is equal to that of the one surface. A film having a structure whose surface is 100 nm or less is preferable. Further, the pore size is more preferably within the range of 1 to 100 nm. If the pore size is less than 1 nm, the permeation flux tends to decrease, and if it exceeds 100 nm, the strength of the porous support membrane tends to decrease. The thickness of the porous support membrane is 1
It is preferably in the range of μm to 5 mm, and is 10 to 100.
More preferably, it is in the range of μm. If the thickness is less than 1 μm, the strength of the porous support membrane is likely to decrease, and if it exceeds 5 mm, it becomes difficult to handle.

The material used for the porous support membrane is not particularly limited, but examples thereof include homopolymers or copolymers of polysulfone, polyamide, polyester, cellulosic polymer, vinyl polymer, polyphenylene sulfide, polyphenylene sulfide sulfone, polyphenylene sulfone, polyphenylene oxide and the like. Can be used alone or as a blend. Among the above, it is preferable to use cellulose acetate, cellulose nitrate or the like as the cellulose-based polymer, and polyethylene, polypropylene, polyvinyl chloride, polyacrylonitrile or the like as the vinyl-based polymer. Of these, homopolymers and copolymers such as polysulfone, polyamide, polyester, cellulose acetate, cellulose nitrate, polyvinyl chloride, polyacrylonitrile, polyphenylene sulfide, and polyphenylene sulfide sulfone are preferable. Furthermore, among these materials, it is particularly preferable to use polysulfone, which has high chemical, mechanical and thermal stability and is easy to mold.

In the present invention, the porous support membrane is preferably lined with cloth, non-woven fabric, paper or the like to increase its mechanical strength.

The method for obtaining the porous support membrane used in the present invention is not particularly limited, but for example, "Office of
Saylene Water Research and Development Progress Report, "No. 359
As described in (1968), a solution of polysulfone in dimethylformamide (DMF) is cast on a densely woven polyester cloth or non-woven cloth so as to have a constant thickness, and the surface of the surface is kept in air for a predetermined time. After removing the solvent, a product obtained by coagulating in a coagulating liquid such as water can be used.

The material of the separation functional layer in the present invention is not particularly limited, but it is preferably a material having high water permeability such as permeation flux and easily enhancing the selective separation performance represented by the rejection rate, For example, polyamide, polyester, cellulose, polyacrylic acid, polymethylmethacrylate, etc. can be used. In particular, polyamide can increase both the permeation flux and the rejection, and aromatic polyamide can further improve the performance thereof, and can also improve the mechanical strength and chemical resistance. It is possible and more preferable.

Among them, the separation functional layer comprises an aromatic amine having at least two amino groups in the aromatic ring and an aromatic carboxylic acid derivative having two or more functional groups capable of acylating the amine in the aromatic ring. It is particularly preferred that it consists of an aromatic polyamide obtained by the reaction. Here, the aromatic amine only needs to have an average of two or more amino groups in the aromatic ring, and a part of the aromatic amine may have an aromatic ring of one or less amino groups. Similarly, the aromatic carboxylic acid derivative may have a functional group capable of acylating two or more amines on average in the aromatic ring.

The aromatic amine preferably used as a raw material of the aromatic polyamide is represented by the formula [I] or [II] shown below as the chemical formula 1, and R of the formula [I] is used.
Two or more of _{1 to} R ₆ and R _{1 to} R ₁₀ of the formula [II] are amino groups.

[0016]

[Chemical 1]

Among the R _{1 to} R _{6 of} the above formula [I] and the R _{1 to} R ₁₀ of the above formula [II], the substituent other than the amino group is an aromatic polyamide such as the following chemical formula. It may be any as long as it does not inhibit the formation,
Preferably, in order to increase the permeability of water, -H, -OC
H _3, etc. -OH, substituents having a hydrophilic employed.

[0018]

[Chemical 2]

Further, in the formula [II], X may be any as long as it can bond two aromatic rings, such as the chemical formula shown below as the chemical formula 3.

[0020]

[Chemical 3]

X is preferably a group having oxygen, such as the chemical formula shown below as Chemical Formula 4, from the viewpoint of interaction with water, and more preferably either -O- or -NHCO-.

[0022]

[Chemical 4]

Considering the separation characteristics and durability in the present invention, a particularly preferred aromatic amine is metaphenylenediamine.

The aromatic carboxylic acid derivative preferably used as a raw material for the aromatic polyamide is one represented by the following formula [III] or formula [IV] as the chemical formula 5.

[0025]

[Chemical 5]

In the formula [III], two or more of R _{1 to} R ₆ are functional groups capable of acylating an amine. It is preferably a chloroformyl group, but the number thereof is preferably 2 to 6, and more preferably 2 to 6 from the viewpoint of easy handling of the compound.
It is 3. As the substituent other than the functional group capable of acylating an amine among R _{1 to} R _{6 in} the formula [III], any substituent can be used as long as it does not inhibit the formation of an aromatic polyamide, such as the following chemical formula. It may be present, and more preferably, a substituent having hydrophilicity such as —H or —OCH ₃ is used in order to increase water permeability.

[0027]

[Chemical 6]

In the above formula [IV], R _{1 to} R ₁₀
Of these, two or more are functional groups capable of acylating amines, preferably chloroformyl groups, but the number of functional groups is preferably 2 to 7 because a film having salt concentration dependence is obtained. And more preferably 2 to 4 from the viewpoint of easy availability of raw materials and easy handling.

In the above formula [IV], R _{1 to} R ₁₀
Among Examples of the substituent group other than acylation functional groups of _{amine, -H, -OCH 3, -CH 3} , -C 2 H 5, -C
Any of ₃ H ₇ , —COCH ₃ , —F, —Cl, —Br, and —I may be used as long as it does not inhibit the formation of the aromatic polyamide. Considering the water permeability, a hydrophilic substituent such as —H or —OCH ₃ is preferably used.

In the formula [IV], X is the chemical formula 7
As long as two aromatic rings can be bonded to each other, such as the following chemical formula,

[0031]

[Chemical 7]

X is preferably an oxygen-containing bond represented by the following chemical formula as Chemical Formula 8 from the viewpoint of interaction with water, and more preferably —O— or —NHCO—.

[0033]

[Chemical 8]

The aromatic carboxylic acid derivative particularly suitable in the present invention can be selected from the compounds represented by the following chemical formulas.

[0035]

[Chemical 9]

In the semipermeable membrane of the present invention, the method of providing the separation functional layer on one surface of the porous support membrane is not particularly limited, but for example, a polymer constituting the separation functional layer is applied onto the porous support membrane. It is possible to use a method, or a method in which the polymer is further subjected to a crosslinking reaction after coating to form a separation functional layer. By carrying out the crosslinking reaction, durability such as chemical resistance and scratch resistance, exclusion rate, etc. can be improved. Further, an aromatic amine and an aromatic carboxylic acid derivative may be subjected to interfacial polycondensation on the porous support membrane to form a separation functional layer. The method using interfacial polycondensation is preferable because the film thickness of the separation functional layer can be easily controlled and a thin film can be formed if desired.

In the present invention, it is necessary to subject the semipermeable membrane to contact treatment with an aqueous solution containing an organic acid. The method of contact treatment is not particularly limited, and for example, a method of immersing the whole composite membrane in an aqueous solution or a method of spraying an aqueous solution may be used, and the method is not limited as long as the semipermeable membrane and the aqueous solution come into contact with each other. .

The organic acid referred to here is a proton donor at the time of hydrogen bond formation and is acidic (pH less than 7) in an aqueous solution.
Any acid containing an organic substance having the formula (1) may be used, and examples thereof include at least one of carboxylic acid, sulfonic acid, and phenols, or a mixture containing these. Specific examples include formic acid, acetic acid, oxalic acid, citric acid, p-toluenesulfonic acid, camphorsulfonic acid, 4-aminobenzoic acid hydrochloride, polyacrylic acid, 4-nitrophenol, pyrogallol, gallic acid and the like. Such as Depside. Preferably, at least one selected from citric acid, oxalic acid, ascorbic acid and tannic acid.

As a result of studying various factors, it was found that the thermal phase change of the molecules constituting the semipermeable membrane, the removal of unreacted compounds that do not contribute to the development of the semipermeable membrane performance, and the optimization of the intermolecular / internal hydrogen bonding network. It has become clear that it is extremely important and has reached the present invention. In particular, focusing on the hydrogen-bonding interaction between the polymer constituting the semipermeable membrane and the organic acid in the aqueous solution, there was a high correlation with the improvement of the exclusion rate of the semipermeable membrane.

Regarding the hydrogen-bonding interaction between the organic acid and the semipermeable membrane, in addition to various spectroscopic methods for evaluating the hydrogen-bonding energy, aramid fiber and benzanilide (adhesion model substance) were simply used. It can be quantified using a relative complexation evaluation (detergency evaluation) and the like. That is, having a hydrogen-bonding interaction means, for example, that the hydrogen-bonding energy is in the range of 8 to 30 kJ / mol, and is calculated by the method described in “New Experimental Chemistry Course” (Vol. 16, Maruzen). The stability constant of the complex formed by-(4-aminobenzoyl) aminobenzoic acid and the organic acid is greater than 0, and benzanilide adhering to the aramid fiber can be removed by 5% or more by the contact treatment using the aqueous organic acid solution. Is either.

Here, as the functional group exhibiting hydrogen-bonding interaction, in addition to an amino group, a carboxyl group, an amide group, a substituent on the polymer side chain, for example, a hydroxyl group, an alkoxyl group, an alkylamino group, a pyridyl group. , Imidazolyl group and the like.

The aqueous solution containing an organic acid used for the contact treatment is preferably an aqueous solution having a pH of 4 or more and 10 or less, which has a small effect on the membrane performance. Further, the water temperature of the aqueous solution is preferably 50 ° C. or higher and 100 ° C. or lower because the treatment effect by itself is small when the temperature is lower than 50 ° C. Furthermore, the effect of the contact treatment is maximized in a short period of time at 80 ° C or higher, 9
It is preferably 5 ° C or lower. However, even when it is subjected to contact treatment with an aqueous solution containing an organic acid at a temperature lower than 50 ° C., the object of the present invention can be achieved by subsequent further immersion in hot water at a temperature of 50 ° C. or higher. Here, the hot water is preferably 80 ° C. or higher and 95 ° C. or lower. Moreover, it is preferable to use purified water as the hot water.

The processing time is preferably 1 second or more and 2 hours or less. When it exceeds 2 hours, the effect reaches the equilibrium, and the productivity is reduced.

If chlorine treatment is added before the contact treatment, the organic substance removal performance as the permeation performance may be improved, so that it can be appropriately used.

[0045]

EXAMPLES Examples will be described below.

(Example 1) m-phenylenediamine 2.
The porous polysulfone support membrane was immersed in an aqueous solution containing 5% by weight for 2 minutes. After removing the excess aqueous solution from the surface of the support membrane, a saturated hydrocarbon solution containing 0.06% by weight of trimesic acid chloride and 0.08% by weight of terephthalic acid chloride was coated so that the surface was completely wetted. Let stand for 1 minute. After the membrane was made vertical and the excess solution was drained and removed, the membrane was immersed in an aqueous solution containing 0.2% by weight of sodium carbonate for 5 minutes and then washed with water. The obtained semipermeable membrane was immersed in an aqueous solution containing 100 ppm of tannic acid at pH 6.5, 90 to 95 ° C. for 1 hour, and the membrane was treated with NaCl 1500 ppm, pH 6.5, 15 kg /
cm ^2, 25 ℃ in was tested 24 hours, NaCl
The removal rate was 99.7%, and the amount of water produced was 0.95 m ³ / m ² · d.

Comparative Example 1 A semipermeable membrane was manufactured under the same conditions as in Example 1 except that the dipping was not performed, and the membrane performance was evaluated. The NaCl removal rate was 99.5%, and the amount of water produced. Was 0.96 m ³ / m ² · d.

Comparative Example 2 A semipermeable membrane was manufactured under the same conditions as in Example 1 except that it was immersed in hot water using distilled water as an aqueous solution, and the membrane performance was evaluated. Was 99.4% and the amount of water produced was 0.98 m ³ / m ² · d.

Example 2 A semipermeable membrane was produced in the same manner as in Example 1 except that the composition of the aqueous solution used for dipping was 1000 ppm ascorbic acid, and the membrane performance was evaluated. Is 99.6% and the amount of water produced is 0.
It was 96 m ³ / m ² · d.

(Example 3) The composition of the aqueous solution used for dipping was the same as in Example 1, the treatment temperature was room temperature (25 ° C) for 5 minutes, and then purified water (distilled at pH 6.5, 90 to 95 ° C) was added. Water). Other conditions were the same as in Example 1 except that a semipermeable membrane was produced and the membrane performance was evaluated.
The NaCl removal rate is 99.7%, and the amount of water produced is 0.96 m ³ /
It was m ² · d.

[0051]

According to the present invention, a semipermeable membrane having both high desalination and high permeability can be provided, and its practicality is great.

   ─────────────────────────────────────────────────── ─── Continued front page    F-term (reference) 4D006 GA02 MA06 MB06 MC11 MC22                       MC27 MC39 MC48 MC54X                       MC62 NA46 NA54 NA63 PB03

Claims (6)

[Claims] 1. A method for producing a semipermeable membrane, which comprises subjecting the semipermeable membrane to contact treatment with an aqueous solution containing an organic acid. 2. The method for producing a semipermeable membrane according to claim 1, wherein the semipermeable membrane is made of at least an aromatic polyamide. 3. The method for producing a semipermeable membrane according to claim 1, wherein an acid having a hydrogen-bonding interaction with the semipermeable membrane is used as the organic acid. 4. The semipermeable membrane according to claim 1, wherein at least one selected from citric acid, oxalic acid, ascorbic acid and tannic acid is used as the organic acid. Production method. 5. The method for producing a semipermeable membrane according to claim 1, wherein the liquid temperature of the aqueous solution containing an organic acid is 50 ° C. or higher and 100 ° C. or lower. 6. The semipermeable membrane according to claim 1, wherein the aqueous solution containing the organic acid has a liquid temperature of less than 50 ° C. and is subsequently immersed in hot water of 50 ° C. or more. Manufacturing method.