JPH07114942B2 - Permselective membrane - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention relates to a permselective polymer membrane made of a specific copolyamide, which is particularly suitable for desalination of seawater or brackish water to obtain fresh water. The present invention relates to a permeable polymer membrane.

(Prior Art) Selective permeation in which a solution of one or more substances dissolved in a common solvent is pumped to a permselective membrane at a pressure higher than the osmotic pressure of this solution to selectively separate the components in the solution. The law,
Reverse osmosis methods that allow water to permeate but not salts dissolved therein have been known for a long time.In these methods, a substantially permeable semi-permeable membrane called a selective permeable membrane or a reverse osmosis membrane is used. The permselective polymer membrane used (hereinafter, both are collectively referred to as permselective polymer membrane) is made of a polymer substance and is either in the form of an ultrathin layer with a support or in the form of a hollow fiber. Which has a dense and homogeneous structure, or is composed of a dense surface polymer layer generally having a thickness of 0.1 to 0.2 μm or less and a porous substructure serving as a support for this thin layer. Some have the heterogeneous structure of a "gel" film. The high permeability and desalination ability of this heterogeneous membrane for water flow depend on the above-mentioned thin and dense surface polymer layer adhered only on one side. Is also called an asymmetric membrane.

Conventionally, cellulose acetate acetate was industrially used as a polymer for forming a permselective polymer membrane, but this cellulose acetate acetate membrane has problems in hydrolysis resistance, microbial resistance, membrane life, etc. It was

In order to solve these problems, a permselective polymer membrane made of aromatic polyamide is known as a new membrane material to replace cellulose acetate (see Japanese Patent Publication No. Sho 50-8781). The polymer film has a problem that it lacks durability against oxidative chlorine used as a sterilizing agent for water, that is, chlorine resistance.

(Problems to be Solved by the Invention) The present invention has excellent water permeability, salt removability, and film-forming property, and chlorine sterilization that has not been satisfied by the prior art, and particularly water permeability which is not changed from the initial stage even after repeated chlorine sterilization treatment. Another object of the present invention is to provide an excellent chlorine resistant reverse osmosis membrane which retains salt removal property.

(Means for Solving Problems) That is, the present invention provides an aromatic diamine compound (A) having at least one diphenylsulfone unit having the following general formula (provided that the 3,3′-diaminodiphenylsulfone compound is And an aromatic amine compound (B) having at least one carboxyl group substituted with hydrogen on the benzene ring or a derivative thereof and the ratio of the diamine compounds (A) and (B) is a molar ratio. A selectively permeable membrane comprising an aromatic copolyamide obtained by reacting an aromatic polycarboxylic acid component with a mixed diamine component of 95/5 to 40/60.

It has been found that the selectively permeable membrane of the present invention has excellent chlorine resistance, film-forming property and reverse osmosis performance (water permeability, salt removal rate).

As the aromatic diamine compound (A), 3,4'-diaminodiphenyl sulfone, 4,4'-diaminodiphenyl sulfone, bis- [4- (3-aminophenoxy) phenyl] sulfone, bis [4- (4-amino) Phenoxy) phenyl] sulfone, 3,3 ', 4,4'-tetraaminodiphenyl sulfone, and the like. From the viewpoint of salt removal rate, 4,4'-diaminodiphenyl sulfone and 3,4'-diaminodiphenyl sulfone are particularly preferable. Further, two or more kinds of the above diamine compounds may be mixed and used, or may be mixed with another diamine compound and used. In particular, the combined use with 3,3'-diaminodiphenyl sulfone is preferable from the viewpoint of chlorine resistance.

Examples of the carboxyl group-containing aromatic diamine compound (B) substituted with hydrogen on the benzene ring include 3,5-diaminobenzoic acid, 3,5-diaminobenzoic acid methyl ester, 3,5-diaminobenzoic acid ethyl ester, 3 Lithium 5,5-diaminobenzoate, sodium 3,5-diaminobenzoate, 3,5-
Diaminobenzoic acid potassium, N, N'-dimethyl-3,5-diaminobenzoic acid, 3,4-diaminobenzoic acid, 3,4-diaminobenzoic acid methyl ester, 3,4-diaminobenzoic acid ethyl ester, 3, Lithium 4-diaminobenzoate, 3,4-
Sodium diaminobenzoate, potassium 3,4-diaminobenzoate, N, N′-dimethyl-3,4-diaminobenzoic acid,
2,5-diaminobenzoic acid, 2,5-diaminobenzoic acid methyl ester, 2,5-diaminobenzoic acid ethyl ester, 2,5
-Lithium diaminobenzoate, sodium 2,5-diaminobenzoate, potassium 2,5-diaminobenzoate, N, N'-
Dimethyl-2,5-diaminobenzoic acid, 2,5-diaminoterephthalic acid, 2,5-diaminoterephthalic acid dimethyl ester, 2,5-diaminoterephthalic acid diethyl ester, 2,5
-Lithium diaminoterephthalate, potassium 2,5-diaminoterephthalate, sodium 2,5-diaminoterephthalate, bis (3-carboxy-4-aminophenyl) methane, bis (3-carbomethoxy-4-aminophenyl) methane , Bis (3-carboethoxy-4-aminophenyl) methane, and the like.

The aromatic polycarboxylic acid as the acid component of the polyamide copolymer in the present invention is phthalic acid, isophthalic acid, terephthalic acid, 4,4'-diphenyldicarboxylic acid, 1,2-naphthalene dicarboxylic acid, 1,3-naphthalene dicarboxylic acid. Acid, 1,4
-Naphthalene dicarboxylic acid, 1,5-naphthalene dicarboxylic acid, 1,6-naphthalene dicarboxylic acid, 1,7-naphthalene dicarboxylic acid, 1,8-naphthalene dicarboxylic acid, 2,3-naphthalene dicarboxylic acid, 2,6-naphthalene Examples thereof include dicarboxylic acid, 2,7-naphthalene dicarboxylic acid, trimesic acid and trimellitic acid.

The copolymerization ratio of the compound represented by the general formula (A) and the compound represented by the general formula (B) is 95/5 to 40/60, preferably 90/10 to 70/30 in terms of molar ratio. If the amount of compound (A) is more than 95% or less than 40%, good reverse osmosis performance cannot be obtained. If it is less than 40%, the chlorine resistance of the film becomes poor. Considering the reverse osmosis performance, the diamine compound used is preferably 40 mol% or more, and more preferably 70 mol% or more, of primary diamine. When the amount of the secondary diamine used is large, the film forming ability is deteriorated and the reverse osmosis performance is also reduced.

The aromatic polyamide copolymer of the present invention is a polymerization method used for producing a usual polyamide, for example, a melt polymerization method,
It can be synthesized by a solid phase polymerization method, an interfacial polymerization method or a solution polymerization method. Of these, the interfacial polymerization method and the solution polymerization method are preferable.

As the solvent used in the solution polymerization method, various organic solvents can be used, but an amide solvent is preferably used.
Preferred solvents include N-methyl-2-pyrrolidone,
Hexamethylphosphoramide, N, N'-dimethylacetamide and mixtures thereof can be mentioned.

The general polymerization method of solution polymerization is as follows: After the mixture of diamine compounds is dissolved in the amide solvent, dicarboxylic acid halide is added to this solution with stirring, and stirring is continued for an appropriate time. . The reaction temperature is preferably -20 to 100 ° C, more preferably -5 to 70 ° C. Upon polymerization, an additive may be added to the mixture solution before, during, and after the polymerization. Such additives include various inorganic compounds and organic compounds,
Some are added to neutralize the hydrogen chloride produced by the polymerization and / or to facilitate dissolution of the polymer. Preferred examples of such inorganic compounds include lithium chloride, calcium chloride, potassium chloride, lithium carbonate, lithium oxide, lithium hydroxide, calcium hydroxide and calcium carbonate. Further, as an organic compound having such an effect, pyridine, triethylenediamine, triethylamine, N-methylmorpholine, N, N-dimethylaniline, N, N-diethylaniline, N, N-dimethylpiperazine and the like are preferable examples. As.

If necessary, a terminal terminating agent can be used as the other additive, and as the terminal terminating agent, a compound having only one group that reacts with an amino group and an acid halide group is suitable. In such a solution polymerization reaction, the charged concentration of monomers is generally preferably 5 to 20% by weight. After the polymerization reaction, the obtained solution is mixed with methanol, syrup, etc. as a solid matter, and the solid matter is repeatedly filtered, washed with water and methanol, and then dried to obtain the aromatic polyamide of the present invention. it can.

Next, a general method of interfacial polymerization will be described. Examples of the organic solvent for the organic phase used in the interfacial polymerization include chlorine-based hydrocarbon solvents such as methylene chloride, chloroform, carbon tetrachloride and chlorobenzene, aliphatic hydrocarbons such as n-hexane, n-octane and cyclohexanone, xylene and benzene. Examples thereof include aromatic hydrocarbons such as toluene. The most preferred solvent is cyclohexanone. As a substance that traps hydrogen chloride generated during interfacial polymerization, sodium hydroxide, sodium carbonate, lithium hydroxide, lithium carbonate, potassium hydroxide and the like are used, and sodium hydroxide and sodium carbonate are particularly preferable.

If a general polymerization operation is shown, a solution of a diamine compound and a hydrogen chloride trapping agent dissolved in water and a solution of a dicarboxylic acid halide compound dissolved in the above organic solvent are mechanically mixed to obtain a polymer of the present invention. . At this time, a part of the organic phase containing no dicarboxylic acid halide was mechanically mixed with the aqueous phase containing the diamine compound in advance, while stirring the solution of the organic solvent containing the dicarboxylic acid halide therein. It is preferable to add.

In order to promote the dispersion of the diamine compound in the water phase, it is possible to add a surfactant to the water phase. In general, the concentration of the dicarboxylic acid halide and the diamine compound in the organic phase and the aqueous phase is preferably 3-10% by weight. The solution obtained after the polymerization reaction was mixed with methanol, water, etc. to form a precipitate, which was repeatedly filtered and washed with water several times, and then dried at a predetermined temperature for about 24 hours to obtain the aroma of the present invention. Group polyamide copolymers can be obtained.

It is also possible to use the aromatic polyamide copolymer by copolymerizing it with another polyamide or blending it with another polymer.

The aromatic polyamide copolymer obtained by the present invention is dissolved in a suitable organic solvent, the solution is applied on a suitable plate, and then immersed in a poor solvent for the aromatic copolyamide copolymer to form an asymmetric membrane. Obtainable.

It is also possible to obtain a homogeneous film by evaporating the organic solvent from the plate. Further, a hollow fiber form is formed by spinning the solution, and the solution of the aromatic polyamide copolymer obtained in the present invention is applied onto a suitable porous membrane to form a composite membrane. It can also take the form. As the porous film to be used, a porous film obtained from a polymer compound, for example, a porous film made of polyethylene, polysulfone, polypropylene, polyimide or the like is suitable.

This coating method may be any method such as a dipping method, a roll coating method, a quick coating method and the like. The thickness of the applied polymer is 0.05-1.0 micron,
The coating conditions should be controlled so that it is preferably 0.1-0.5 micron.

Besides coating the polymer, it is also possible to form a film on the support as follows. That is, by applying a solution of a diamine compound on the porous film, by dipping in a dicarboxylic acid chloride dissolved organic solvent,
It is also possible to form the aromatic polyamide copolymer of the present invention on the porous film. Examples of the porous material used include polyethylene, polypropylene, polysulfone, and polyimide. It is also possible to form the aromatic polyamide copolymer on a porous film material made of an inorganic compound. During the formation of the composite film, a compound having three or more reactive groups such as trimesic acid chloride, trimellitic acid chloride and 3-chlorosulfonylisophthalic acid chloride may be added in order to increase the strength of the film.

(Operation of the invention) The permselective membrane obtained by the present invention has not only excellent salt-excluding property and water-permeating property but also chlorine resistance as shown in Examples described later. Therefore, it is particularly suitable for desalination of seawater and brackish water. It is a suitable and useful membrane.

Hereinafter, the present invention will be described in more detail with reference to Examples.
The present invention is not limited to the embodiments.

Method for producing asymmetric membrane A 20% solution of the polymer obtained in the present invention in N, N'-dimethylacetamide (containing 5% LiCl) is prepared and coated on a glass plate in a thickness of 300 microns. 10 at 110 ° C in a constant temperature bath
Heat for a minute and evaporate the solvent. After cooling, it is immersed in water to form an asymmetric membrane of the polymer. This was peeled off from the glass surface and subjected to the following reverse osmosis membrane experiment.

Reverse osmosis membrane test method 3500 at 25 ° C using a normal continuous pump type reverse osmosis device
Using an aqueous solution containing 0 ppm NaCl as the stock solution, the operating pressure is 55 kg.
/ cm ² . For the evaluation of chlorine resistance, sodium hypochlorite and hydrochloric acid were added to the above aqueous solution to adjust pH to 6 and chlorine concentration to about 10 ppm, and the reverse osmosis performance was measured in the same manner as above. The reverse osmosis performance (salt exclusion rate (Rj), water permeation rate (FR)) was measured about 20 hours after the start of measurement, and the chlorine resistance of the water permeation membrane was evaluated from the difference with the reverse osmosis performance of the chlorine-free system. The smaller the difference, the better the chlorine resistance of the film.

Calculation of Salt Exclusion Rate The salt exclusion rate in the examples was determined by a usual method, that is, the following formula.

(Comparative Example 1) Synthesis of polyisophthaloyl metaphenylenediamine In a 500 ml four-necked round bottom flask equipped with a nitrogen inlet tube, a thermometer, and a stirring blade, 10.80 g (0.10 g) of metaphenylenediamine purified by distillation. ml) and 150 ml of dehydrated and purified NMP.

When the system becomes uniform by stirring, it is cooled to 0 ° C., and 0.1 mol (20, 30 g) of isophthalic acid chloride (IPC) is added at once as a powder while stirring. Wash off the reagent adhering to the container with 10 ml of NMP and adjust the molar ratio accurately. I
When PC is added, the temperature of the system rises to about 50 ° C. The mixture is stirred for about 1 hour while cooling, then returned to room temperature and further stirred for 2 hours to complete the reaction. The obtained solution was poured into about 1500 ml of methanol to obtain a polymer. After filtering the precipitate, it was purified by crushing and washing with a home mixer containing water. Then, the purified product was dried under reduced pressure for 24 hours. The yield at this time was about 85%. The viscosity is 1.35 (0.
Was _{5g / 1dl-H 2 SO 4} ).

Further, according to the above-mentioned method, the production of the asymmetric membrane of the obtained polymer and the reverse osmosis experiment were conducted.

(Comparative Example 2) Synthesis of polyisophthaloyl metaphenylenediamine / 3,5-diaminobenzoic acid terpolymer In Comparative Example 1, instead of metaphenylenediamine, a mixture of metaphenylenediamine and 3,5-diaminobenzoic acid (3 The copolymer was synthesized in the same manner except that 5,5-diaminobenzoic acid amount = 10 mol%) was used. Further, an asymmetric membrane was prepared according to the above-mentioned method and subjected to a reverse osmosis experiment.

(Comparative Example 3) Synthesis of polyisophthaloyl metaphenylenediamine / 2,4-diaminobenze sulfonic acid copolymer In Comparative Example 1, instead of metaphenylenediamine, metaphenylenediamine and 2,4-diaminobenzenesulfonic acid were used. The copolymer was synthesized in the same manner except that the mixture (amount of 2,4-diaminobenzenesulfonic acid = 10 mol%) was used. Further, an asymmetric membrane was prepared according to the above-mentioned method and subjected to a reverse osmosis experiment.

Comparative Example 4 Synthesis of Poly (isophthaloyl-4,4′-diaminodiphenylsulfone) Polymer In Comparative Example 1, instead of metaphenylenediamine, 4,
The copolymer was synthesized in the same manner except that 4'-diaminophenyl sulfone was used. An asymmetric membrane was prepared according to the method described above and subjected to a reverse osmosis experiment.

(Comparative Example 5) Synthesis of poly (terephthaloyl-4,4'-diaminodiphenylsulfone) polymer Comparative Example 4 was carried out in the same manner except that terephthalic acid chloride was used instead of isophthalic acid chloride. An asymmetric membrane was prepared according to the method described above and subjected to a reverse osmosis experiment.

Comparative Example 6 Synthesis of Poly (isophthaloyl-3,5-diaminobenzoic acid) Polymer In Comparative Example 1, instead of metaphenylenediamine, 3,
The copolymer was synthesized in the same manner except that 5'-diaminobenzoic acid was used.

Since the polymer is water-soluble, it was difficult to prepare an asymmetric membrane and measure reverse osmosis performance.

(Example 1) 1.9018 g (0.0125 mol) of 3,5-diaminobenzoic acid, 4,4 '
-Diaminodiphenyl sulfone 27.9979 g (0.1125 mol)
Under a nitrogen stream in a 500 ml four-necked flask equipped with a nitrogen introduction tube, a thermometer, and a stirrer. Further, 150 ml of N-methylpyrrolidone is added to this system to dissolve the monomer.

After thoroughly stirring, 25.3775 g (0.125 mol) of isophthalic acid chloride was quickly added under a nitrogen stream while cooling the entire reaction system with ice. After reacting under ice cooling for about 60 minutes, the temperature is returned to room temperature, and the reaction system is stirred for about 1 hour. After completion of the reaction, this solution is added to 1500 ml of methanol to precipitate the polymer. A series of purification steps of pulverizing the polymer with a household mixer, filtering, and washing with water were repeated several times to remove unreacted substances in the polymer and remove the solvent. Finally, the polymer was washed with methanol and dried under vacuum at about 140 ° C. for about 48 hours to be used for the production of the following asymmetric membrane. The yield of the obtained polymer was about 95%, and the reduced viscosity (ηsp / c) of the polymer was 1.65.
(0.5 g / dl N-methyl-2-pyrrolidone, 30 ° C.). According to the method described above, the asymmetric membrane of the obtained polymer was produced, and the reverse osmosis experiment was performed.

(Examples 2 and 3) The procedure of Example 1 was repeated, except that the amounts of 3,5 diaminobenzoic acid were changed to 30 mol% and 50 mol% based on the total amount of diamines. The reduced viscosities of the obtained polymers were 1.78 and 1.86, respectively.

(Examples 4 to 6) The same procedure as in Examples 1 to 3 was performed except that terephthalic acid dichloride was used instead of isophthalic acid dichloride in Examples 1 to 3. The reduced viscosities of the obtained polymers were 2.66, 3.07 and 2.06, respectively.

(Examples 7 to 9) In Example 2, a mixed acid component of isophthalic acid chloride / terephthalic acid chloride was used instead of isophthalic acid chloride, and the mixing molar ratio was 30/70, 50/50, 70/30. Was performed in the same manner as in Example 2. The reduced viscosities of the obtained polymers were 2.83, 2.18 and 1.97, respectively.

(Examples 10 to 12) In Example 2, in place of 4,4'-diaminodiphenyl sulfone, 3,3'-diaminodiphenyl sulfone / 4,4-
Using the mixed amine component of diaminodiphenyl sulfone,
The same procedure as in Example 2 was carried out except that the mixing molar ratio was 70/30, 50/50, 30/30/70. The reduced viscosities of the obtained polymers were 1.56, 1.78, and 1.95, respectively.

(Example 13) The procedure of Example 2 was repeated except that bis [4- (3-aminophenoxy) phenylsulfone was used instead of 4,4'-diaminodiphenylsulfone. The polymer obtained had a reduced viscosity of 2.58.

(Example 14) The procedure of Example 2 was repeated except that bis [4- (4-aminophenoxy) phenyl] sulfone was used instead of 4,4'-diaminodiphenylsulfone. The reduced viscosity of the obtained polymer was 2.87.

Film-forming properties of polymers according to Comparative Examples 1 to 6 and Examples 1 to 14,
The results of reverse osmosis experiments (salt exclusion rate Rj, water permeability FR) and chlorine resistance evaluation results of the obtained asymmetric membranes are summarized in Table 1.

The results of Table 1 show that the film-forming properties of the polymers obtained in Examples 1 to 14 of the present invention and the reverse osmosis performance (salt exclusion, water permeability) and chlorine resistance of the asymmetric membranes obtained from the polymers are in Comparative Examples 1 to 1. It is shown that it is superior to the film-forming property, reverse osmosis performance and chlorine resistance performance shown by 6.

(Effects of the Invention) The aromatic polyamide copolymer obtained by the present invention is excellent in solvent solubility and is excellent in film forming property on an asymmetric film. In addition, the asymmetric membrane obtained from the polymer is particularly excellent in salt exclusion and chlorine resistance.

Therefore, even when used for a long time for desalination of seawater containing chlorine, the excellent salt-removing property at the initial stage is maintained.

Claims (1)

[Claims] 1. An aromatic diamine compound (A) having at least one diphenylsulfone unit having the following general formula (excluding 3,3′-diaminodiphenylsulfone compound) and hydrogen on the benzene ring. A mixed diamine component mainly composed of an aromatic diamine compound (B) having at least one carboxyl group or a derivative thereof and having a molar ratio of the diamine compounds (A) and (B) of 95/5 to 40/60. A permselective membrane comprising an aromatic copolyamide obtained by reacting an aromatic polycarboxylic acid component with.