JPH0122009B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a selectively permeable membrane that can be used as a precision membrane, an ultrafiltration membrane, or a reverse osmosis membrane, and a method for producing the same. The main objective is to provide a sulfonated polysulfone selectively permeable membrane with high mechanical strength. Polysulfone is heat resistant,
It has excellent acid resistance, alkali resistance, and high mechanical strength, making it useful as a membrane material or support for composite membranes.However, due to the hydrophobic nature of the resin itself, water permeability is low, making it especially suitable for membranes with a small molecular weight cutoff. This is a major drawback in some cases. A method is known in which polysulfone is sulfonated in advance for the purpose of making it hydrophilic, but the mechanical strength of sulfonated polysulfone decreases and one of the characteristics of polysulfone is lost. Furthermore, along with the improvement in hydrophilicity, there arises a problem in film formation that coagulation slows down during wet film formation. In order to maintain the mechanical strength of sulfonated polysulfone, a method has been proposed in which the degree of sulfonation is adjusted by the charging ratio of the sulfonation reagent (Japanese Patent Application Laid-Open No.
51-90397). However, it is difficult to control the sulfonation reaction and ensure that it is carried out uniformly, resulting in a wide distribution of molecules ranging from molecules in which almost all of the repeating units are sulfonated to molecules that are not sulfonated at all, resulting in stable film forming properties and film properties. A problem arises. In addition, a method has been proposed in which the degree of sulfonation is controlled by sulfonating a polymer that has both repeating units that can be sulfonated and repeating units that are not substantially sulfonated (Japanese Patent Laid-Open No. 55-36296 and Publication No. 55-48222). This method is only possible with a special combination of resins, the synthesis process is complicated, and the presence of different repeating units causes the problem of inhomogeneous membrane properties due to phase separation. The inventors conducted research to solve the above-mentioned problems with conventional sulfonated polysulfones, and found that sufficient hydrophilicity could be easily obtained by sulfonating only the surface of the polysulfone selectively permeable membrane without causing a decrease in mechanical strength. Based on this knowledge, we conducted various studies and completed the present invention. That is, in the present invention, the sulfonating reagent is sulfuric anhydride and/or chlorosulfonic acid, and liquid A is a poor solvent for the sulfonating reagent and a non-solvent for polysulfone, and a good solvent for both the sulfonating reagent and polysulfone. It is characterized by sulfonating the surface by bringing the polysulfone selectively permeable membrane into contact with a solution consisting of a mixed solvent and a sulfonating reagent whose mixing weight ratio A/B with liquid B is 100/1 to 100/20. This is a method for producing a surface-sulfonated polysulfone selectively permeable membrane. The polysulfone used for sulfonation in the present invention may have a molecular structure that can be sulfonated with a sulfonation reagent, and examples include the following repeating units. These monopolymers or copolymers thereof, and if necessary, copolymers with other repeating units and/or mixtures with other resins can also be used.
The degree of polymerization is not particularly limited, but the thermal deformation temperature of the polymer is 18.6Kg/ ^cm2 under a load.
The temperature is preferably 150°C or higher in terms of heat resistance.
Some of the aromatic rings or alkyl groups in the main chain are halogen, hydroxyl, thioalcohol, aldehyde,
carboxyl group, vinyl group, allyl group, aryl group, amino group, amide group, nitro group, acid amide,
Those substituted with functional groups such as ketoxime, epoxy or silanol groups and/or compounds containing these functional groups can also be used. Furthermore, those in which these functional groups are utilized for crosslinking reactions to improve membrane properties can also be used. The polysulfone selectively permeable membrane used in the present invention may be a membrane for any purpose such as precision filtration, ultrafiltration, reverse osmosis filtration, or gas separation. Regarding the shape, any of flat membranes, hollow fiber membranes, composite membranes using other sheet substrates or porous materials as a support, and composite membranes using a polysulfone membrane as a support can be used.
Regarding the membrane structure, membranes whose surface layer is covered with a so-called skin layer, which is so dense that no pores can be seen even under an electron microscope, or membranes which are not covered with a skin layer, and those whose interior is porous, also have a finger-like structure. You can also use some. It may be that other functional groups or compounds have already been bonded to the membrane surface, or that a crosslinking reaction has been carried out on the membrane surface layer. Any method can be used for producing the polysulfone selectively permeable membrane used for sulfonation in the present invention. Examples include a film forming method in which extrusion is followed by stretching, and a wet film forming method in which a resin solution is cast and then a drying step is added or not, and the material is immersed in a coagulating liquid. A method is known in which a substance to be dissolved and extracted in a subsequent step is mixed into a resin solution to form a porous membrane, but the present invention can be used as long as it does not cause an undesirable reaction with the sulfonation reagent. The surface of a selectively permeable membrane as used in the present invention means the outer surface layer of the membrane and the surface of the membrane's internal tissue. The degree of sulfonation of the surface-sulfonated polysulfone selectively permeable membrane of the present invention is necessary to exhibit hydrophilicity, and the surface resistance is preferably 10 ¹³ Ω-cm or less. The surface resistance of the surface sulfonated film is 10 ¹³ Ω−
cm or more, no significant improvement in the hydrophilicity of the membrane is observed. The selectively permeable membranes obtained by the method of the present invention include not only those in which the entire surface of the membrane tissue is sulfonated, but also those in which the entire surface of the membrane structure is sulfonated. For example, the surface of the skin layer is completely sulfonated, the surface of the skin layer is partially sulfonated, and the surface of the finger-like or porous microstructure within the membrane structure is fully or partially sulfonated. It also includes complexes of these compounds. Partially sulfonated surfaces are those that consist of fine sea-like, island-like, or band-like sulfonated regions on the order of microns or less, on the order of 10 Å, or those that are part of the surface of a film on a relatively large scale. is completely sulfonated. The degree of sulfonation on the surface may vary depending on the part,
It also includes those in which the degree of sulfonation of the sulfonated moiety changes continuously. The surface-sulfonated polysulfone selectively permeable membrane produced by the method of the present invention has many advantages as shown below. (1) Since only the surface is sulfonated, it is possible to prevent a decrease in mechanical strength, which was a problem with conventional sulfonated polysulfone selectively permeable membranes. Maintaining mechanical strength is also desirable in film forming and modularization processes. (2) Compared to the conventional method of synthesizing sulfonated polysulfone in advance, this synthesis step can be omitted. Therefore, there is no need to consider problems such as the use of a reaction solvent and its subsequent treatment, and the purification of sulfonated polysulfone, resulting in a significant simplification of the process. Furthermore, sulfonated polysulfone solidifies slowly during wet film formation, making film formation difficult, but this problem does not need to be taken into account. The surface sulfonation method of the present invention is extremely simple and easy to post-process. (3) The scope of application of partially sulfonated membranes can be expanded. In other words, the conventional method of obtaining a partially sulfonated membrane by using a blend or copolymer of a sulfonable polysulfone and a non-sulfonated resin is due to the degree of sulfonation and the resin. There were restrictions on the type, degree of polymerization, mixing ratio, etc. According to the present invention, unsulfonated polysulfone or polysulfone sulfonated to an arbitrary degree of sulfonation can be used, so restrictions in terms of compatibility are greatly reduced. With regard to the degree of sulfonation and combinations with other resins, many types of membranes are possible, so properties such as hypercharacteristics, hyperselectivity, anti-thrombotic properties, and biocompatibility that were not available with conventional sulfonated polysulfones can be obtained. Be expected. (4) By using a surface-sulfonated polysulfone selectively permeable membrane in which only the skin layer is sulfonated, or only the internal tissue is sulfonated, which has not been possible in the past, it is possible to design membranes with higher performance. For example, when only the skin layer is sulfonated, enzyme deactivation due to membrane permeation can be minimized. In addition, when only the internal tissue is sulfonated, it is possible to prevent permeate from adhering to and staying inside the membrane structure. (5) A surface sulfonated polysulfone separation membrane with a distribution of degree of sulfonation within the membrane has the following features when made into a module. For example, a permselective membrane whose end sealing portion is surface-sulfonated has improved affinity with the sealing resin. Furthermore, by sulfonating the membrane surface in areas within the module where a gel layer is likely to form or where water permeability decreases due to pressure loss, etc., module performance can be improved without significantly changing other properties. (6) The sulfone groups bonded to the membrane surface of the surface-sulfonated polysulfone membrane of the present invention may further include alkali metal, alkaline earth metal ions and their salts, and other compounds having functional groups capable of bonding with sulfone groups such as aziridyl groups. You can make it react. Depending on the sulfonation reagent, the sulfonyl chloride group (-
SO ₂ Cl) is bound to the membrane surface, and at that point it can be reacted with a compound having a functional group that can react with this sulfonyl chloride, such as an amine, epoxy, or hydroxyl group. These reactions can be effectively used to modify and compose sulfonated membranes. An example of the surface sulfonation method will be described below. Generally known sulfonating reagents such as sulfuric anhydride, chlorosulfonic acid, and concentrated sulfuric acid are used to produce surface sulfonated membranes, and the sulfonation reaction can be carried out in either a solution system or a gas system. good.
Among these, solution-based surface sulfonation of other conventionally known resins involves dissolving the sulfonation reagent in a solvent that does not react with the sulfonation reagent, dissolves it, and does not deteriorate the resin. This is done by contacting the resin. An example of such a solvent is cyclohexane, although it varies depending on the resin. However, when this is applied to polysulfone, the time required for sulfonation is long and unintended non-uniformity occurs in the degree of sulfonation. The reason for this is thought to be that the solubility of the sulfonating reagent is low and sulfonation proceeds easily, resulting in non-uniformity in the concentration of the sulfonating reagent. The inventors conducted research to find a method that could stably perform surface sulfonation under relatively mild conditions, and came to invent the above-mentioned production method. An example of the solvent A used in the present invention is cyclohexane, as described above. Also, solvent B
An example of this is methylene chloride.
In particular, methylene chloride, cycloethane, etc. are good solvents for polysulfone, but are poor solvents for sulfonated polysulfone, so only the surface is sulfonated and further progress into the interior is prevented. it is conceivable that. Both solvents A and B may have a single composition or may be a mixed solvent. Regarding the compatibility between solvents A and B, if they are compatible, sulfonation will be uniformly performed. The mixed weight ratio of the mixed solvent of solvents A and B used in the present invention is preferably A/B of 100/1 to 100/20.
100/3 to 100/8 is used. The concentration of the sulfonating reagent in a solution smaller than 100/1 is low, and no improvement in the water permeability of the membrane is observed even if the solution is brought into contact with the membrane for several minutes at room temperature. Moreover, if it is more than 100/20, the film will deteriorate. The concentration of the sulfonating reagent can be arbitrarily selected depending on the solubility of the mixed solvent, but it is practical to mix in a sulfonating reagent with a higher solubility so that the amount consumed by the sulfonation reaction can be immediately replenished. It is true. For example, cyclohexane/
In the case of a mixed solution in which the mixing ratio of methylene chloride is 94.4/5.6, if chlorosulfonic acid is used as the sulfonating reagent, it is better to use it at 3% by weight, preferably 5% by weight or more, as the degree of sulfonation will be faster and more stable. can be obtained. The sulfonation reaction easily proceeds in a few minutes at room temperature by simply bringing the membrane into contact with the sulfonation reagent solution, and there is no need for heating or long-term contact. When an excess of sulfonating reagent is present, as described above, the solution is heterogeneous. If the phase present at the concentration of the sulfonating reagent is brought into direct contact with the permselective membrane, it will cause deterioration of the membrane, so care must be taken. However, since the concentrated phase has a low specific gravity and settles to the bottom in most solution systems, it is easy to prevent contact with the membrane. An appropriate method for contacting the membrane with the sulfonating reagent can be selected depending on the shape of the membrane. Alternatively, the entire membrane surface may be sulfonated, or
Alternatively, appropriate means can be selected depending on whether partial sulfonation is desired. For example, in the case of a flat membrane or a tubular membrane, it is possible to perform surface sulfonation and then modularization, or modularization and then surface sulfonation.
If the module has metal parts, the former method is preferable. In addition, in the case of hollow fiber membranes, simply immersing the membrane in a sulfonating reagent solution will
In particular, since sufficient surface sulfonation of the inner surface is not carried out, it is appropriate to first form a module and pass a sulfonating reagent solution through it, as described below. To sulfonate only the internal membrane tissue, either coat the surface of the membrane with a substance that is insoluble in the sulfonation reagent to protect it before sulfonation, or bring the surface of the membrane into contact with a liquid that does not contain the sulfonation reagent. There is a method of penetrating the sulfonating reagent solution from the opposite side. The latter method is particularly suitable when the selectively permeable membrane is porous and does not have a skin layer. To sulfonate only the skin layer, the opposite method is to first fill the membrane tissue with a liquid that does not contain the sulfonating reagent or a substance that is insoluble in the sulfonating reagent solution, and then bring the membrane into contact with the sulfonating reagent solution. To be elected. It is more effective to use a liquid that does not contain a sulfonating reagent and has poor compatibility with the sulfonating reagent solution and has a different specific gravity. In order to create fine sulfonated regions on the membrane surface, it is appropriate to use a method of surface sulfonation using a mixture or copolymer of polysulfone having repeating units that can be sulfonated and a resin that does not undergo sulfonation. There is also a method of using a sulfonation reagent solution in which a sulfonation reagent-rich layer and a non-sulfonation reagent-rich layer are phase-separated into a milky state, but care must be taken to maintain the stability of the degree of sulfonation with respect to temperature. . In order to obtain surface sulfonated polysulfone with a distribution of degree of sulfonation within the membrane, in addition to the above method, there is a method of partially immersing the membrane in a sulfonation reagent solution. In particular, in the case of hollow fiber membranes, the degree of sulfonation can be distributed by flowing a sulfonating reagent solution from one inlet and a liquid containing no sulfonating reagent from the other inlet at a predetermined pressure. . In sulfonated membranes, sulfone groups are often stabilized in the form of sodium salts. This can be done by immersing the membrane in a methanol or ethanol solution of sodium methylate for several minutes at room temperature after sulfonation. Although the treatment reaction is mild, a sodium salt of the sulfonating reagent is also produced, so it is necessary to wash the membrane with water after the treatment reaction. Since it is a water-soluble salt, it is easy to wash with water. The method for producing a selectively permeable membrane with sulfonated polysulfone surface according to the present invention has the following advantages. (1) A membrane with a high degree of sulfonation can be obtained quickly and stably. (2) It is possible to produce a partially sulfonated selectively permeable membrane, which has not been previously possible. (3) The shape and fractionation properties of selectively permeable membranes can be changed and can be applied to many types of membranes. (4) All sulfonation reagents used have low toxicity if they are neutralized. An example of neutralization treatment is to use sodium salt.
Moreover, the solvent is industrially advantageous because it can be used as a solvent that is usually easily available and inexpensive. (5) It can also be applied to resins other than polysulfone. The present invention will be explained below with reference to Examples. Example 1 (Flat membrane polysulfone selectively permeable membrane) 14 parts by weight of aromatic polysulfone P-1700 (manufactured by Union Carbide) was dissolved in 86 parts by weight of N-methyl-2-pyrrolidone by heating at 70°C for 4 hours, and the resin solution was dissolved. make. After defoaming, the resin solution was cast onto a glass plate at room temperature, and then immersed in water at 20°C to a thickness of 60°C.
A 70μ membrane was obtained. This membrane was immersed in ethyl alcohol at 18°C for 10 minutes and then dried at 80°C for 30 minutes to obtain a dry polysulfone permselective membrane in the form of a flat membrane. Next, cyclohexane/methylene chloride/chlorosulfonic acid are thoroughly stirred at a predetermined mixing ratio and then left to stand. A chlorsulfonic acid rich layer immediately settles at the bottom. The above dried membrane is immersed in the supernatant liquid at 18°C for 5 minutes to sulfonate the surface. 5 more
The membrane was immersed in an ethanol solution of sodium methylate (wt%) for 5 minutes to form a sodium salt, and then immersed in water and washed with water to obtain a surface-sulfonated polysulfone selectively permeable membrane. Table 1 shows the measurement results of the surface resistance and water permeability of the membrane. (Measurement of surface resistance) The surface sulfonated polysulfone selectively permeable membrane is immersed in methyl alcohol for 10 minutes, and then air-dried at 80°C for 30 minutes. After the obtained dried film was left for 96 hours at a temperature of 40°C and a humidity of 90%, electrodes were placed concentrically on the film and the surface insulation resistance was measured according to the method shown in JIS standard K-6911. (applied voltage DC-100V1
minutes).

【table】

[Table] Example 2 (Hollow fiber selectively permeable membrane) The same aromatic polysulfone used in Example 1, N-methyl-2-pyrrolidone, and lithium nitrate were mixed in predetermined amounts to prepare a resin solution. Next, a polysulfone selectively permeable membrane (M1) with a water permeability of 30/m ² hratm and a membrane (M2) with a water permeability of 100/m ² hratm were created using the normal wet membrane manufacturing method in which water is coagulated and fixed.
I got it. 50 pieces were made into modules, and these modules were soaked in ethyl alcohol for 10 minutes.
It was air-dried at 80°C for 30 minutes to form a dry module. (Surface Sulfonation) As in Example 1, cyclohexane/methylene chloride/chlorosulfonic acid were thoroughly stirred at a predetermined mixing ratio and then allowed to stand. After the liquid is separated into two phases, the supernatant is circulated at 18° C. for 5 minutes through the inner tube of a modular dry polysulfone hollow fiber membrane. At this time, if the amount of the sulfonating reagent solution is small, it is advisable to bring the liquid that has passed through the hollow fiber into contact with the chlorosulfonic acid rich layer precipitated in the lower layer and circulate it through the hollow fiber again. Next, the module is immersed in a 5% by weight sodium methylate ethanol solution, which is simultaneously circulated inside the hollow fiber. After 5 to 10 minutes, the module was immersed in water, and water was similarly circulated through the hollow fibers for washing, yielding a hollow fiber-like surface-sulfonated polysulfone selectively permeable membrane. The rapid determination results of water permeability are summarized in Table 2. (Measurement of Membrane Strength) The selectively permeable membranes M1 and M2 were sulfonated and post-treated in the same manner using a sulfonating reagent of chlorosulfonic acid/methylene chloride/cyclohexane = 5/5/90. Table 3 shows the results of measuring the mechanical strength of the obtained membrane.

【table】

[Table] Comparative Example 1 A flat dry polysulfone selectively permeable membrane was prepared in the same manner as in Example 1, and one or both of methylene chloride and chlorosulfonic acid among cyclohexane/methylene chloride/chlorosulfonic acid was not included. The same treatment as in Example 1 was performed except for immersion in the solution. The measurement results of the water permeability and surface resistance of the obtained membrane are summarized in Table 1. It can thus be seen that the water permeability is improved by the sulfonation treatment. Comparative Example 2 Modules of hollow fiber dry polysulfone membranes M11 and M2 were prepared in the same manner as in Example 2, and immersed in a mixed solvent of cyclohexane/methylene chloride = 95/5 for 5 minutes. 5 each, being careful to circulate the water inside the hollow fiber in this order.
Soaked in minutes. The results of measuring the water permeability of the obtained module and the mechanical strength of the hollow fibers are summarized in Tables 2 and 3, respectively. Comparative Example 3 The results of measuring the water permeability and mechanical strength of the module obtained in the same manner as in Example 2, except that the ratio of chlorosulfonic acid/methylene chloride/cyclohexane was changed to 5/20/75, were table and third
Shown in the table. Comparative Example 4 Using the same polysulfone as in Example 1, Noshay
The method of et al. (J. AppL. Polym. Sci., 20 1885
('76)), polysulfones with various degrees of sulfonation were synthesized. The degree of sulfonation here refers to the number of sulfone groups present per repeating unit of polysulfone. Using a resin with a degree of sulfonation of 1.0, film formation was attempted in the same manner as in Example 1 using a 14% by weight solution of N-methyl-2-pyrrolidone, but coagulation was slow and a good film could not be obtained. When it is set to 25%, it becomes possible to form a film, but only a film with extremely low water permeability can be obtained. Although it is possible to fabricate a flat membrane using a resin with a degree of sulfonation of 0.5 at 14% by weight, attempts to fabricate a hollow fiber membrane using the same method as in Example 2 were still difficult due to slow coagulation. Moreover, the elastic modulus of the membrane was slightly less than 60% of that of the membrane without sulfonation. Degree of sulfonation
Although it is possible to fabricate a hollow fiber membrane using a resin with a diameter of 0.1, the water permeability obtained is 30% for a non-sulfonated polysulfone hollow fiber membrane (M1) produced under the same conditions.
/m ² hratm, whereas 120/m ² hratm
This is an improvement of about 4 times. As shown in Table 3, the mechanical strength of the membrane is lower than that of (M1) with surface sulfonation. Water permeability is surface sulfonated (M1)
It can be seen that the water permeability is 220/m ² hratm, and there is almost no decrease in mechanical strength.

Claims (1)

[Claims] 1 Liquid A, in which the sulfonating reagent is sulfuric anhydride and/or chlorosulfonic acid, is a poor solvent for the sulfonating reagent and a non-solvent for polysulfone, and Liquid B is a good solvent for both the sulfonating reagent and polysulfone. The mixing weight ratio A/B is 100/1
A method for producing a surface sulfonated polysulfone selectively permeable membrane, characterized in that the surface is sulfonated by bringing the polysulfone selectively permeable membrane into contact with a solution consisting of a mixed solvent and a sulfonating reagent in a ratio of ~100/20.