JPH0582251B2 - - Google Patents

Description

[Detailed description of the invention]

(Technical Background) The present invention relates to a novel separation membrane made of a polysulfone resin containing a hydrophilic graft polymer. Membrane separation technology has attracted attention for its energy saving and compactness, and has made remarkable progress. Many types of polymers have been researched and developed as membrane materials for permselective separation membranes used in such systems, including cellulose-based, polyamide-based, polyacrylonitrile-based, polycarbonate-based, polyphenylene oxide-based, and polysulfone-based polymers. is used. Among them, hydrophobic polymers such as polysulfone, polycarbonate, polyphenylene oxide, and fluorine-containing polymers are originally used as engineering plastics, but they have poor heat resistance and mechanical properties. Due to its excellent properties, it is also being used as a material for separation membranes. Among these membrane materials, aromatic polysulfone membranes are attracting attention as they have high mechanical strength, excellent heat resistance, and chemical resistance. (Prior art and its disadvantages) However, aromatic polysulfone resin has low hydrophilicity and is a material that is difficult to wet with water, so separation membranes made of this resin have a significantly higher water permeation rate than separation membranes made of hydrophilic materials. is low, and overefficiency is poor. Therefore, various attempts have been made to improve the water permeability of aromatic polysulfone separation membranes. For example, Japanese Patent Application Laid-Open No. 104940/1983 describes a polysulfone separation membrane containing polyvinylpyrrolidone with a molecular weight of 100,000 or more and a method for producing the same. However 10
In this method, a hydrophilic polymer with a molecular weight of 1,000 or more is added to a membrane-forming solution (called a dope), which increases the polymer density of the dope. The hydrophilic polymer added to the membrane remains as it is throughout the membrane and is not removed even during subsequent use, resulting in an extremely dense structure and a reduction in water permeation rate. On the other hand, JP-A-54-26283 discloses a method in which polyethylene glycol having a molecular weight comparable to that of an oligomer is added to a polysulfone solution and used as a dope. However, this method uses water as a coagulation bath for membrane formation, and oligomer-level polyethylene glycol does not remain in the membrane but is completely eluted into the water, and the hydrophilicity of the polysulfone membrane cannot be substantially increased. , no significant improvement in water permeation rate can be expected. In addition, in JP-A-57-174104, a reactive functional group was introduced into the benzene ring of polysulfone polymer,
A method has been disclosed in which a wet film is formed from this polymer solution and then treated with a solution of a hydrophilic substance capable of reacting with the above-mentioned functional groups to perform crosslinking modification. However, the separation membranes obtained by this method are mostly limited to reverse osmosis membranes, and it is extremely difficult to produce a wide variety of separation membranes. Additionally, the benzene ring of polysulfone polymers generally has low reactivity, which limits the types of functional groups that can be introduced, and it is extremely difficult to control the rate of introduction. or heat resistance may decrease significantly. (Structure of the present invention) The present inventors have solved the above-mentioned problems and have developed a polysulfone resin that has a high water permeation rate and has heat resistance, chemical resistance, and high mechanical strength unique to polysulfone polymers. As a result of intensive research on separation membranes, we have invented a separation membrane made of hydrophilic polysulfone resin that contains a graft polymer in which a hydrophilic copolymer is used as the backbone polymer and a polysulfone polymer is used as the branch polymer. In other words, the present invention provides that the total degree of polymerization is 4 or more and 100 or less, of which the degree of polymerization of the hydrophilic component is 50 of the total degree of polymerization.
It is characterized by being wet film-formed from a solution of a hydrophilic polysulfone resin containing a graft polymer in which a hydrophilic copolymer accounting for % or more is the main polymer and a polysulfone polymer with a degree of polymerization of 30 to 100 is the branch polymer. Separation membrane made of polysulfone resin. ”. As the polysulfone polymer referred to in the present invention, aromatic polysulfone polymers having the structures of the following formulas () to () are representative.

[ka]

[ka]

[Chemical Formula] In the present invention, a polysulfone resin containing a graft polymer in which the ends of the polysulfone polymer described above are chemically bonded to a hydrophilic copolymer is used as a membrane material. In order to produce a polysulfone resin containing a graft polymer, a copolymer having a reactive functional group in its side chain is reacted with a polysulfone polymer having a functional group at its end that can react with the functional group. Alternatively, a polysulfone polymer having a vinyl group at the end is copolymerized with a vinyl monomer or oligomer. The following examples of combinations of specific reactive functional groups and end groups with which they can react can be cited from known organic chemical reactions. (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, or a sulfonyl halide group. (2) When the terminal group is a halogenated alkyl group or a halogenated aryl group: -(CH ₂ -) _o OM group (M is an alkali metal, n is 0
(a valence bond) or a positive integer), a functional group such as an amino group (which may be primary, secondary or tertiary). (3) When the terminal group is an amino group: Functional groups such as halogenated alkyl groups and acid halide groups. (4) When the terminal group is an epoxy group: Functional groups such as amino groups and alcoholate groups. (5) When the terminal group is a carbonyl group: _-NHNH2 group, a functional group such as a hydroxyl group. (6) When the terminal group is a carboxyl group: A functional group such as a hydroxyl group. In addition, the method for introducing terminal groups into polysulfone-based polymers and functional groups into copolymers may be carried out using known organic chemical reactions, and is not particularly limited. It is necessary to conduct the reaction under conditions that do not cause In the latter case, it is necessary to appropriately select whether to carry out the process before or after the copolymerization depending on the type of hydrophilic component, which will be described later. It is necessary to set appropriate reaction conditions so as not to change the polymerization degree in an unfavorable direction or to reduce the degree of polymerization. Of course, commercially available monomers, oligomers, or polysulfone polymers that already have reactive functional groups or terminal groups may be used as they are. The monomer or copolymer described above is reacted with a terminally reactive polysulfone polymer to produce a graft polymer or a polysulfone resin containing the graft polymer, which is a material for the separation membrane of the present invention. In this case, care must be taken to set reaction conditions such that only one side of the terminal group of the polysulfone polymer can react.
If both terminal groups participate in the reaction, a crosslinking reaction will occur, resulting in a gel-like substance insoluble in a solvent, which cannot be used in the wet membrane forming method for producing the separation membrane of the present invention. Therefore, either a reactive end group is introduced in advance into only one side of the polysulfone polymer, or only one of the two end groups is activated. Also, as with known grafting reactions, the polymer products produced by the above method are not always 100% grafted polymers.
In other words, both the unreacted polysulfone polymer and the graft polymer may coexist in the polymer product after the remaining monomer or remaining copolymer is 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 resin, is at least 20 mol% or more, preferably 40 mol% or more. If less than 20 mol% of the graft polymer is contained, the hydrophilicity of the polysulfone resin cannot be significantly improved, and therefore separation membranes made from such resins often have 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, the base polymer is a hydrophilic copolymer having a total polymerization degree of 4 or more and 100 or less, in which the polymerization degree of the hydrophilic component accounts for 50% or more of the total polymerization degree, and the polymerization degree is 30 or more.
It must be a graft polymer with polysulfone polymers of 100 or less as branch polymers. Therefore, when the total degree of polymerization of the backbone polymer is 4, the degree of polymerization of the hydrophilic component is 2 to 3, and the polysulfone polymer is bonded to other copolymer components through the terminal groups. Furthermore, if the degree of polymerization of the polysulfone-based polymer is less than 30, the heat resistance and mechanical strength of the polysulfone-based polymer cannot be fully exhibited. Furthermore, it is extremely difficult to increase the degree of polymerization of the polymer to greater than 100 using current polymerization technology.
On the other hand, controlling the degree of polymerization to 30 or more and 100 or less is technically and economically easy, and has great industrial advantages. Further, it is preferable that the hydrophilic component in the above-mentioned backbone polymer has one or more of the following structures as a repeating unit.

embedded image Here, R ₁ is hydrogen or a methyl group. Also, R ₂ is

【formula】

【formula】

【formula】

[Formula] (M is hydrogen, or an alkali metal or basic substance that ionically bonds with a carboxylic acid ion.)

[Formula] (R ₃ is an aliphatic hydrocarbon group having 1 to 20 carbon atoms),

[Formula] (R ₄ and R ₅ are each hydrogen or an aliphatic hydrocarbon group having 1 to 20 carbon atoms),

[Formula] or

[Formula] (n is an integer from O (valence bond) to 10. M is hydrogen, or an alkali metal or basic substance that ionically bonds with the sulfonate ion.)

[C] (R ₆ , R ₇ and R ₈ are each from 1 to 20 carbon atoms
is an aliphatic hydrocarbon group having 1, X is a halogen ion. ) or

[Chemical formula] (R ₉ is an aliphatic hydrocarbon group having 1 to 20 carbon atoms, n is an integer of 4 to 6, and 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 a polysulfone resin containing a graft polymer as described above. Polysulfone resin solution (hereinafter referred to as dope)
When the separation membrane to be produced is a high fractionation ultrafiltration membrane or precision filtration membrane, the resin concentration in the membrane is preferably 5% by weight or more and less than 30% by weight. When producing ultrafiltration membranes or reverse osmosis membranes with low fractionation properties, the content is preferably 10% by weight or more and 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 resin, but examples include N,N-dimethylacetamide, N,N-dimethylformamide, N-methyl-2-pyrrolidone, dimethylsulfoxide, 2- Examples include pyrrolidone. Moreover, a non-solvent, an electrolyte, etc. can also be added to such a polar organic solvent. In forming the separation membrane of the present invention from the dope described above, a conventional wet film forming method can be employed. To form a separation membrane in the form of a sheet or tube, a dope is applied to a thickness of several tens of microns to several hundred microns on a suitable support (for example, a glass plate or tube, nonwoven fabric, cloth, etc.) in the form of a sheet or tube. The membrane is cast by an appropriate method and then immersed in a coagulant bath to produce a separation membrane by sol-gel phase conversion. Furthermore, a hollow fiber separation membrane can be manufactured by spinning the dope through a hollow fiber forming nozzle using a known method. Coagulants used in film formation are non-solvents for polysulfone resins and easily mix with polar organic solvents, such as water, aqueous solutions of electrolytes such as salt and surfactants, aqueous solutions of polar organic solvents, or hydrophilic polysulfone resins. Examples include non-solvents or aqueous solutions thereof, and water is particularly commonly used. (Effects of the Present Invention) The characteristics of the separation membrane of the present invention are manifested by wet membrane formation of the hydrophilic polysulfone resin solution as described above. In other words, due to the presence of the hydrophilic graft polymer, microphase separation occurs during wet film formation into a component rich in hydrophilic backbone polymers and a component rich in polysulfone polymers.Moreover, since the aggregation speed of polysulfone polymers in water is extremely fast, hydrophilic The core polymer will be extruded onto the surface of the polysulfone polymer matrix. As a result, the microporous surface of the resulting separation membrane is rich in hydrophilic backbone polymer components, resulting in significantly improved hydrophilicity and extremely high water permeation rate of the separation membrane. Moreover, since the polymer matrix that essentially determines the structure of the separation membrane is made of polysulfone-based polymers, not only the mechanical strength of the separation membrane but also its heat resistance and chemical resistance are comparable to those of polysulfone-based polymers. You will reach a level where you can. Therefore, it can be effectively used in membrane separation operations under harsh conditions that conventional hydrophilic polymer-based separation membranes, such as separation membranes made of cellulose acetate, cannot withstand. Next, the present invention will be specifically explained with reference to Examples.
and ovalbumin rejection rate (Ro) are Lp = pure water permeability at 25°C (m ³ ) / effective membrane area (m ² ) ×
Water permeation time (days) x overpressure (Kg/cm ² ) (However, the Lp value after 10 minutes is L ⁰ _p , and the Lp after 3 hours is
Let the value be L ³ _p . ) β= ^L0 / _p − ^L3 / _p / ^L0 / _p ×100 and Ro=(1−ovalbumin concentration in permeated water/ovalbumin concentration in stock solution)×100. The contact angle of the film was determined by measuring the contact angle with water at 25° C. using an Elma goniometer type contact angle measuring device Model G-I. The degree of polymerization of the polymer was measured using a steam osmometer manufactured by KNAUER, and the structure and composition of the backbone polymer and graft polymer were determined by elemental analysis and NMR (100MHz
or 270MHz). The amount of superadsorption on the separation membrane was measured using a 150 ppm cytochrome C phosphate buffer solution (25°C). In other words, the concentration of the previous cytochrome C solution is
C ₁ ppm, volume V ₁ ml (approximately 50 ml), and a separation membrane with an effective membrane area of S cm ² (15.2 cm ² ) was used to apply a pressure of 3 Kg/
When filtered and concentrated to a volume of V ₂ ml (approximately 10 ml) in cm ² , the concentration of the concentrate is C ₂ ppm, the volume of the permeate is V ₃ ml,
Using a concentration C _{of 3} ppm, adsorption amount m on the separation membrane surface
(μg/cm ² ) can be calculated using the following formula.
However, in this case it is assumed that adsorption occurs over the effective membrane area. m=C ₁ V ₁ −C ₂ V ₂ −C ₃ V ₃ /S Example 1 Polysulfone polymer of the formula ( ) whose terminal end is a hydroxyl group (Victrex5003P, manufactured by ICI, degree of polymerization 52)
30g dimethyl sulfoxide (hereinafter referred to as DMSO) 200
ml and benzene chloride (hereinafter referred to as PhCl) at room temperature, and add 6.5 ml of 0.5N NaOH aqueous solution to this.
ml was added and reacted at room temperature for 2 hours to obtain solution A of polysulfone polymer with sodium phenolate type terminals. On the other hand, the backbone polymer has the following composition:

[Chemical] A random copolymer was synthesized by a known radical copolymerization method, and 14.5g of this was mixed with 100ml of DMSO and PhCl50.
ml of mixed solvent to obtain solution B. Slowly add the above solution A to this solution at room temperature, and
After reacting for 17 hours and 2 hours at 70°C, 0.2 ml of concentrated sulfuric acid was added to stop the reaction. Mix the reaction mixture with methanol/water = 80/20 (volume ratio)
After reprecipitation, the remaining hydrophilic backbone polymer was completely removed by Soxhlet extraction with ethanol for 7 hours. Analysis of the purified polymer product revealed that
It was found that the graft polymer had the following composition.

[Chemical] This graft polymer was dissolved in dimethylformamide (DMF) at a polymer concentration of 15% by weight, and this solution was cast onto a glass plate to a thickness of 400 μm, and the DMF was slowly evaporated at 90°C to form a non-porous material. A film was produced. After peeling off the film from the glass plate, immerse it in ethanol/water = 50/50 (volume ratio) for 24 hours.
After completely removing DMF, it was dried at 50°C for 24 hours and the contact angle was measured to be 66°. A film of the polysulfone-based polymer used in the above-mentioned graft reaction was prepared in a similar manner, and its contact angle was measured to be 73°, indicating that the above-mentioned graft polymer had significantly improved hydrophilicity. 15 parts by weight of this hydrophilic graft polymer was added to N-
After dissolving in 85 parts by weight of methyl-2-pyrrolidone, it was cast onto a glass plate to a thickness of 250 μm, and 30 seconds later, it was immersed in water at 10° C. to obtain a separation membrane. The amount of superadsorption of this separation membrane was measured to be 19 μg/cm ² , and no staining by cytochrome C was observed with the naked eye. In addition, when we measured the Lp of a polyester nonwoven fabric reinforced film obtained by wet film forming using a polyester nonwoven fabric instead of a glass plate during casting,
^15m3 / ^m2 ． Day. Kg/cm ² and the rate of decline β is 25
It was %. On the other hand, the elimination rate Ro of ovalbumin is
It was 100%. Comparative Example 1 A film was formed in the same manner as in Example 1, except that the polysulfone polymer used in the graft reaction in Example 1 was used instead of the graft polymer. The adsorption amount of the obtained membrane was as high as 74 μg/m ² , and the membrane surface was stained red by cytochrome C. On the other hand, Lp of the polyester nonwoven fabric reinforced membrane is 9m ³ /m ² .
Day. It was low at Kg/cm ² and β was 35%. Furthermore, the elimination rate Ro of ovalbumin was as low as 87%. Example 2 The backbone polymer has the following composition

[Chemical] A random copolymer was synthesized by a known radical copolymerization method, and 3.2g of this was mixed with 60ml of DMSO and 40ml of PhCl.
The graft reaction and purification were carried out in the same manner as in Example 1, except that solution B was prepared by dissolving it in a mixed solvent. It was found that the obtained graft polymer had the following composition.

[C] This graft polymer was formed into a film in the same manner as in Example 1, and the contact angle was measured.
It showed a low value of 54°, indicating that it was highly hydrophilic. This hydrophilic graft polymer was molded into a separation membrane in the same manner as in Example 1, and the membrane performance was evaluated: m = 26 μg/m ² , Lp = 33 m ³ /m ² . Day. Kg/cm ² , β
= 17% and Ro = 91%, which revealed extremely excellent performance. Example 3 The backbone polymer has the following composition

[Chemical] A random copolymer was synthesized by a known radical copolymerization method, and 2.9g of this was mixed with 60ml of DMSO and 40ml of PhCl.
A graft reaction was carried out in the same manner as in Example 1, except that solution B was prepared by dissolving the solution in a mixed solvent. After the reaction mixture was reprecipitated twice in acetone/water = 80/20 (volume ratio), the resulting graft polymer was analyzed and found to have the following composition.

[C] This graft polymer was formed into a film in the same manner as in Example 1, and the contact angle was measured.
It showed a low value of 67°, indicating that it was made hydrophilic. This hydrophilic graft polymer was molded into a separation membrane in the same manner as in Example 1, and the membrane performance was evaluated: m = 60 μg/cm ² , Lp = 12 m ³ /m ² . Day. Kg/cm ² , β
= 11% and Ro = 98%, which showed extremely excellent performance. Example 4 Random with the following composition as the backbone polymer

[Chemical formula] A copolymer was synthesized by a known radical copolymerization method, and a graft reaction was carried out in the same manner as in Example 1, except that 4.5 g of the copolymer was dissolved in 150 ml of DMSO and used as solution B. PhCl in the reaction mixture
After distilling off, the graft polymer was reprecipitated in ethanol/water = 15/85 (volume ratio), and the resulting graft polymer was analyzed and found to have the following composition.

[C] This graft polymer was formed into a film in the same manner as in Example 1, and the contact angle was measured.
It showed a low value of 54°, indicating that it was made hydrophilic. This hydrophilic graft polymer was molded into a separation membrane in the same manner as in Example 1, and the membrane performance was evaluated; m = 62 μg/cm ² , Lp = 12 m ³ /m ² ·day.
It had extremely excellent performance of Kg/cm ² and Ro=95%. Example 5 A random copolymer having the following composition as a backbone polymer was prepared by a known radical copolymerization method.

The grafting reaction was carried out in the same manner as in Example 1, except that 7 g of this compound was dissolved in 100 ml of DMSO and used as solution B. Next, the reaction mixture was dropped into a 10 wt% NaOH aqueous solution to form a flaky precipitate, and the mixture was stirred at 90°C for 5 hours to perform a saponification reaction. The precipitate was collected, washed with dilute hydrochloric acid and water, dried and analyzed, and it was found to be a graft polymer having the following composition.

[C] This graft polymer was formed into a film in the same manner as in Example 1, and the contact angle was measured.
It showed a low value of 56°, indicating that it was made hydrophilic. This hydrophilic graft polymer was formed into a separation membrane in the same manner as in Example 1, and the membrane performance was evaluated.
Lp=16m ³ /m ² , day・Kg/cm ² , β=31%, Ro=
It had an excellent performance of 96%. Example 6 A random copolymer having the following composition as a backbone polymer was synthesized by a known radical copolymerization method,

[Chemical formula] A graft reaction was carried out in the same manner as in Example 1, except that 15 g of this solution was dissolved in a mixed solvent of 100 ml of DMSO and 50 ml of PhCl and used as solution B. Furthermore, 3 g of 30 wt% trimethylamine aqueous solution was added to the reaction mixture to carry out a quaternization reaction, and then this reaction mixture was mixed with 700 ml of methanol and 40 wt% trimethylamine aqueous solution.
The mixture was added dropwise to a mixed solution of 14 ml of NaOH aqueous solution to form a flaky precipitate, and the mixture was stirred at 50°C for 5 hours to perform a saponification reaction. The precipitate was collected, washed with dilute hydrochloric acid and water, dried, and the polymer product was analyzed and found to be a graft polymer having the following composition.

[C] This graft polymer was molded into a separation membrane in the same manner as in Example 1, and the membrane performance was evaluated.
58μg/cm ² , Lp=9m ³ /m ²・day・Kg/cm ² , β=21
%, and Ro=99%.

Claims (1)

[Scope of Claims] 1. A hydrophilic copolymer with a total polymerization degree of 4 or more and 100 or less, in which the polymerization degree of the hydrophilic component accounts for 50% or more of the total polymerization degree, is used as the backbone polymer, and the polymerization degree is 30 or more.
1. A separation membrane made of a polysulfone resin, characterized in that it is wet-formed from a solution of a hydrophilic polysulfone resin containing a graft polymer having polysulfone polymers of 100 or less as branch polymers. 2. The polysulfone resin separation membrane according to claim 1, wherein the hydrophilic component has one or more of the following structures as repeating units. embedded image Here, R ₁ is hydrogen or a methyl group. In addition, R ₂ is [Formula] [Formula] [Formula] [Formula] (M is hydrogen, or an alkali metal or basic substance that ionically bonds with a carboxylic acid ion), [Formula] (R ₃ is a carbon atom (R ₄ , R ₅ are each hydrogen or an aliphatic hydrocarbon group having 1 to 20 carbon atoms.), [Formula] or [Formula] (n is an integer from O (valence bond) to 10. M is hydrogen, or an alkali metal or basic substance that ionically bonds with the sulfonate ion.), [Formula] (R ₆ , R ₇ and R ₈ are each from 1 to 20 carbon atoms
is an aliphatic hydrocarbon group having 1, X is a halogen ion. ) or [Chemical formula] (R ₉ is an aliphatic hydrocarbon group having 1 to 20 carbon atoms, n is an integer of 4 to 6, and X is a halogen ion). 3 The polysulfone polymer has the following () ~
The polysulfone-based resin separation membrane according to claim 1, characterized in that it has at least one type of repeating unit among (). [C] [C] [C]