JP2613764B2 - Separation membrane - Google Patents

Description

Description: BACKGROUND OF THE INVENTION The present invention relates to a novel separation membrane composed of a polysulfone resin containing a hydrophilic graft polymer.

Membrane separation technology has attracted attention in terms of energy saving and compactness, and has made remarkable progress. Various types of polymers have been researched and developed as membrane materials for the permselective separation membrane used in such systems, and polymers such as cellulose, polyamide, polyacrylonitrile, polycarbonate, polyphenylene oxide, and polysulfone polymers have been developed. Is used.

Among them, hydrophobic polymers such as polysulfone, polycarbonate, polyphenylene oxide, and fluorine-containing polymers are originally used as engineering plastics, but have excellent heat resistance and mechanical properties. As a result, they are also being used as materials for separation membranes.

Among these film materials, aromatic polysulfone-based films have been attracting attention as having high mechanical strength and excellent heat resistance and chemical resistance.

(Prior art and its disadvantages) However, since aromatic polysulfone resin is a material having low hydrophilicity and is hardly wetted by water, a separation membrane made of this resin has a significantly higher water permeation rate than a separation membrane made of a hydrophilic material. But the efficiency is poor.

Therefore, various attempts have been made to improve the water permeability of the aromatic polysulfone separation membrane.

For example, JP-A-58-104940 discloses a polysulfone-based separation membrane containing polyvinylpyrrolidone having a molecular weight of 100,000 or more and a method for producing the same. However, in this method in which a hydrophilic polymer having a molecular weight of 100,000 or more is added to a film-forming solution (referred to as a dope), the polymer density of the dope is increased, and polysulfone formed from such a dope is used. The added hydrophilic polymer remains as it is in the entire membrane of the system separation membrane, and is not removed during subsequent use, so that the system separation membrane becomes extremely dense and the water permeation rate is rather reduced.

On the other hand, JP-A-54-26283 discloses a method in which polyethylene glycol having a molecular weight of about an oligomer is added to a polysulfone solution and used as a dope. However, in this method, water is used as a coagulation bath for film formation, and polyethylene glycol of the order of oligomers is completely eluted in water without remaining in the film, and the hydrophilicity of the polysulfone film is not substantially increased. However, a remarkable improvement in water permeability cannot be expected.

In JP-A-57-174104, a functional group produced by a reaction is introduced into a benzene ring of a polysulfone-based polymer. After wet film formation from this polymer solution, the polymer is treated with a solution of a hydrophilic substance capable of reacting with the functional group. A cross-linking modification method is disclosed. However, the separation membrane obtained by this method is almost limited to a reverse osmosis membrane, and it is extremely difficult to produce a wide variety of classification membranes.

In addition, the benzene ring of polysulfone polymers generally has low reactivity, the types of functional groups that can be introduced are limited, and it is extremely difficult to control the introduction ratio. In some cases, the benzene ring is excessively hydrophilized, resulting in mechanical strength and heat resistance. Properties may be significantly reduced.

(Constitution of the present invention) The present inventors have solved the above problems and have a high water permeation rate, and a porsulfone-based resin having heat resistance, chemical resistance and high mechanical strength unique to polysulfone-based polymers. As a result of intensive studies on a separation membrane made of a resin, a separation membrane made of a polysulfone-based resin containing a hydrophilic graft polymer having a hydrophilic copolymer as a trunk polymer and a polysulfone-based polymer as a branch polymer was invented.

That is, in the present invention, a hydrophilic copolymer in which the total degree of polymerization is greater than 100, of which the degree of polymerization of the hydrophilic component accounts for 50% or more of the total degree of polymerization, is used as the trunk polymer, and the degree of polymerization is 30 or more and
A polysulfone-based resin separation membrane, which is formed by a wet membrane from a solution of a polysulfone-based resin containing a hydrophilic graft polymer having the following polysulfone-based polymer as a branch polymer. It is.

As the polysulfone-based polymer referred to in the present invention, an aromatic polysulfone-based polymer having a structure represented by the following formulas (I) to (III) is typical.

In the present invention, a polysulfone-based resin containing a graft polymer in which the terminal of the above-mentioned polysulfone-based polymer is chemically bonded to a hydrophilic copolymer is used as a film material. In order to produce a polysulfone-based resin containing a graft polymer, a copolymer having a reactive functional group on a side chain is reacted with a polysulfone-based polymer having a functional group capable of reacting with the functional group at a terminal. Alternatively, a polysulfone-based polymer having a vinyl group at the terminal is copolymerized with a vinyl-based monomer or oligomer. Specific examples of the combination of a reactive functional group and a terminal group capable of reacting with the functional group include the following examples from a known organic chemical reaction.

(1) When the terminal group is a hydroxyl group or an alkali alcoholate group: a functional group such as an acid halide group, an acid anhydride group, a glycidyl group, a halomethyl group, and a sulfonyl halide group.

(2) When the terminal group is a halogenated alkyl group or a halogenated aryl group: CH _{2 n} OM group (M is an alkali metal, n is O (valence bond) or a positive integer), amino group (this is , Secondary or tertiary).

(3) When the terminal group is an amino group: Functionality such as a halogenated alkyl group and an acid halide group.

(4) When the terminal group is an epoxy group: a functional group such as an amino group or an alcoholate group.

(5) When the terminal group is a carbonyl group: -NHNH ₂ group, hydroxyl group or other functional group.

(6) When the terminal group is a carboxyl group: a functional group such as a hydroxyl group.

The method for introducing a terminal group into the polysulfone-based polymer and a functional group into the copolymer may be performed by using a known organic chemical reaction, and is not particularly limited. In the former case, the degree of polymerization of the polysulfone-based polymer is reduced as much as possible. It is necessary to carry out the reaction under conditions that do not allow the reaction. In the latter case, it is necessary to appropriately select whether to perform before copolymerization or after copolymerization depending on the type of a hydrophilic component described later, and when performing after copolymerization, the functional group of the hydrophilic component is not preferable. It is necessary to set appropriate reaction conditions so as not to change in the direction or decrease the degree of polymerization.

Of course, a commercially available monomer, oligomer or polysulfone polymer having a reactive functional group or terminal group may be used as it is.

By reacting the above-mentioned monomer or copolymer with the terminal-reactive polysulfone-based polymer, a graft polymer or a polysulfone-based resin containing the graft polymer as a material of the separation membrane of the present invention is produced.

In this case, care must be taken that reaction conditions are set such that only one side of the terminal group of the polysulfone-based polymer can react. If both terminal groups take part in the reaction, a cross-linking reaction takes place, resulting in a gel which is insoluble in a solvent and cannot be used in the wet membrane formation method for producing the separation membrane of the present invention. Therefore, either a method of previously introducing a reactive terminal group to only one side of the polysulfone-based polymer or a method of activating only one of both terminal groups is applied.

Also, as is the case with known grafting reactions, polymer products prepared by the above methods are not always 100% grafted polymers. That is, both the unreacted polysulfone-based polymer and the graft polymer may be present in the polymer product after the residual monomer or the residual copolymer has been removed by a reprecipitation method or the like. In the present invention, it is necessary to adjust the conditions of the graft reaction so that the proportion of the graft polymer in the polymer product, that is, the hydrophilic polysulfone-based resin is at least 20 mol% or more, preferably 40 mol% or more. If the content of the graft polymer is less than 20 mol%, the hydrophilicity of the polysulfone-based resin cannot be improved so much, and the separation membrane produced from such a resin often has a low water permeation rate.

The structure and composition of the graft polymer also affect the hydrophilicity of the resin, that is, the water permeability of the separation membrane. In the present invention, a hydrophilic copolymer, in which the total degree of polymerization is greater than 100, of which the degree of polymerization of the hydrophilic component accounts for 50% or more of the total degree of polymerization, is used as a trunk polymer, and a polysulfone-based polymer having a degree of polymerization of 30 to 100 is used. It must be a graft polymer to be a polymer.

Therefore, for example, when the total degree of polymerization of the backbone polymer is 120, the degree of polymerization of the hydrophilic component is 60 or more, and the polysulfone-based polymer is bonded to a part or all of the other copolymerized components by a terminal group. In addition, the degree of polymerization of the polysulfone polymer is
If it is less than 30, the heat resistance and mechanical strength of the polysulfone polymer cannot be sufficiently exhibited.

In addition, it is extremely difficult to increase the degree of polymerization of the polysulfone-based polymer to more than 100 with current polymerization technology,
In contrast, controlling the degree of polymerization to 30 or more and 100 or less is technically and economically easy, and has great industrial advantages.

The hydrophilic component in the trunk polymer preferably has one or more of the following structures as a repeating unit.

Where R¹Is hydrogen or a methyl group, and R^TwoIs  (However, R^Three, R^Four, R^FiveAnd R⁶Represents carbon atoms 1 to
Aliphatic hydrocarbon groups having 20 groups, M is hydrogen, alkali gold
Genus or basic substance, n is an integer of 0 to 10, m is an integer of 4 to 6
Number, X Is a halogen ion. ).

In the present invention, the separation membrane of the present invention is manufactured by a wet membrane forming method using a solution of the polysulfone resin containing the graft polymer as described above.

The resin concentration in the polysulfone-based resin solution (hereinafter referred to as "dope") is 5% by weight or more and less than 30% by weight when the separation membrane to be produced is a high-fraction ultra- or ultra-fine membrane. Is preferred. In the case of producing a low-fraction ultra-permeability membrane or a reverse osmosis membrane, the content is preferably from 10% by weight to less than 40% by weight.

The solvent used is not particularly limited as long as it is an organic solvent that dissolves the hydrophilic polysulfone-based resin.For example, N, N-dimethylacetamide, N, N-dimethylformamide, N-methyl-2-pyrrolidone, dimethylsulfoxide, 2- Examples include pyrrolidone. Further, a solvent or an electrolyte may be added to such a polar organic solvent.

In forming the separation membrane of the present invention from the dope described above, a conventionally used wet film formation method can be employed.

In order to form the separation membrane into a sheet or a tube, a dope having a thickness of several tens to several hundreds of microns is coated on a suitable support in the form of a sheet or a tube (for example, a glass plate or a tube, a nonwoven fabric, a cloth, etc.). It is cast by an appropriate method and then dipped in a coagulant bath to produce a separation membrane by sol-gel phase conversion. Further, by spinning the dope through a hollow fiber forming nozzle by a known method, a hollow fiber separation membrane can be produced.

The coagulant used for film formation is a non-solvent of polysulfone resin and is easily mixed with a polar organic solvent. For example, an aqueous solution of an electrolyte such as water, salt, a surfactant, an aqueous solution of a polar organic solvent, or a hydrophilic polysulfone resin Examples thereof include a non-solvent and an aqueous solution thereof, and water is particularly generally used.

(Effects of the Present Invention) The characteristics of the separation membrane of the present invention are manifested by wet-forming a hydrophilic polysulfone-based resin solution as described above. That is, the presence of the hydrophilic graft polymer causes microphase separation into a component rich in a hydrophilic stem polymer and a component rich in a polysulfone polymer during wet film formation, and the aggregation speed of the polysulfone polymer in water is extremely high. The trunk polymer will be extruded onto the polysulfone-based polymer matrix surface. As a result, the microporous surface of the obtained separation membrane is rich in the hydrophilic stem polymer component, the hydrophilicity is remarkably improved, and the water permeability of the separation membrane is extremely high. Moreover, since the polymer matrix that substantially determines the structure of the separation membrane is formed from a polysulfone-based polymer, not only the mechanical strength of the separation membrane but also heat resistance and chemical resistance are comparable to those of the polysulfone-based polymer. Level. Therefore, it can be effectively used for a membrane separation operation under severe conditions where a conventional separation membrane based on a hydrophilic polymer, for example, a separation membrane made of cellulose acetate cannot withstand.

Next, the present invention will be specifically described by way of examples. The pure water permeability coefficient (Lp), the rate of decrease in Lp with time (β), and the rejection rate of ovalbumin (Ro) are respectively (Except the Lp value of the over 1 hour after ▲ L ¹ _p ▼, the Lp value after 3 hours ▲ L ³ _p ▼ to.) Is defined by

As for the contact angle of the film, the contact angle with water at 25 ° C. was measured with an Elma goniometer-type contact angle measuring device GI.

The degree of polymerization of the polymer was measured with a vapor osmometer manufactured by KNAUER, and the structures and compositions of the trunk polymer and the graft polymer were determined by elemental analysis and NMR (100 MHz or 270 MHz).

The amount of over-adsorption on the separation membrane was measured using 150 ppm cytochrome C.
This was performed using a phosphate buffer solution (25 ° C.).

That is, the concentration of the previous tyrochrome C solution was C ₁ ppm, the capacity was V ₁ m1 (about 50 m1), and the effective film area Scm ² (15.
2 cm ² ) Separation membrane with a pressure of 3 kg / cm ² and capacity V ₂ m1 (about 10 m1)
When concentrated and concentrated, the concentration C ₂ ppm after concentration, the volume of the permeate V ₃ m1, and the concentration C ₃ ppm, the amount of adsorption m on the separation membrane surface
(Μg / cm ² ) can be calculated by the following equation. However, in this case, it is assumed that the adsorption occurs in the effective film area.

(Examples) Next, the present invention will be described more specifically with reference to examples.

Example 1 A mixed solution of 60 g of polysulfone polymer (Victrex 5003p, manufactured by Imperial Chemical Industries, Ltd., degree of polymerization 52) of formula (I) having a hydroxyl group at its terminal is 400 m1 of dimethyl sulfoxide (hereinafter, DMSO) and 200 m1 of benzene chloride (hereinafter, phCl). At room temperature,
13 ml of 0.5N NaOH aqueous solution was added thereto and reacted at room temperature for 2 hours to obtain a solution A of a polysulfone-based polymer having a terminal of sodium phenolate.

On the other hand, it has the following composition (degree of polymerization 149) as a trunk polymer A random copolymer was synthesized by a known radical copolymerization method, and 50 g of this was dissolved in a mixed solvent of 200 ml of DMSO and 100 ml of PhCl to obtain a solution B. This solution was slowly added to the above solution A at room temperature, and reacted at room temperature for 1 hour and at 700 ° C. for 2 hours.
The reaction was stopped by adding 0.5 ml.

After the reaction mixture was reprecipitated with methanol / water = 80/20 (volume ratio), washing with methanol / water = 80/20 was repeated by centrifugation to completely remove the remaining unreacted hydrophilic stem polymer. When the polymer product after purification was analyzed,
It was a graft polymer having the following composition.

This graft polymer was dissolved in DMSO at a polymer concentration of 15% by weight, and the solution was cast on a glass plate to 400 μm.
DMSO was slowly evaporated at 0 ° C. to produce a non-porous film. After peeling the film from the glass plate, it was immersed in ethanol / water = 50/50 (volume ratio) for 24 hours to completely remove DMSO, dried at 50 ° C. for 24 hours, and measured the contact angle.
The value was as low as 57 °, indicating that the graft polymer was hydrophilic.

After dissolving 15 parts by weight of this hydrophilic graft polymer in 85 parts by weight of a mixed solvent mainly composed of N-methyl-2-pyrrolidone, it is cast on a polyester nonwoven fabric at a thickness of 150 μm, and immersed in water at 10 ° C. A separation membrane was obtained. When the amount of excessive adsorption m of this separation membrane was measured, it was 22 μg / cm ² , and no staining of the membrane surface with cytochrome C was observed even in the inner eye. ▲ L ¹ _p was 10 m ³ / m ² · day · kg / cm ² and β was 3%, indicating a high water permeation rate and stability over time.

Comparative Example 1 A film and a separation membrane were prepared in the same manner as in Example 1 except that the polysulfone polymer (Vict-rex5003p) used in the graft reaction of Example 1 was used instead of the graft polymer.

The contact angle of the film was 76 ° and was extremely hydrophobic. The separation membrane also showed a high adsorption amount of m = 74 μg / cm ^{2, and} the membrane surface was stained red with cytochrome C. On the other hand, ▲ L ¹ _p ▼ is as low as 7.1 m ³ / m ² · day · kg / cm ² and β
Was 20%, and the water permeation rate decreased significantly with time.

Claims (3)

(57) [Claims] 1. A polysulfone system having a total polymerization degree of more than 100, of which a hydrophilic copolymer occupying 50% or more of the total polymerization degree of a hydrophilic component as a trunk polymer, and having a polymerization degree of 30 or more and 100 or less. A separation membrane made of polysulfone-based resin, which is formed by a wet method from a solution of a polysulfone-based resin containing a hydrophilic graft polymer having a polymer as a branch polymer. 2. The method according to claim 1, wherein the hydrophilic component has one or more of the following structures:
Patent application characterized by having the above as a repeating unit
2. The separation membrane made of a polysulfone resin according to claim 1.Where R¹Is hydrogen or a methyl group, and R^TwoIs (However, R^Three, R^Four, R^FiveAnd R⁶Each represents a carbon atom of 1 to 20
Alicyclic hydrocarbon group, M is hydrogen, alkali metal
Or a basic substance, n is an integer of 0 to 10, and m is an integer of 4 to 6.
Number, X Is a halogen ion. ). 3. The polysulfone polymer has the following (I):
The polysulfone-based resin separation membrane according to claim 1, wherein the separation membrane has at least one type of repeating unit selected from (III) to (III).