JPS6087803A - Polysulphone permselective film and its preparation - Google Patents

Abstract

PURPOSE:To prepare polysulphone permselective film having sulphonated surface by allowing a mixture of a poor solvent for a sulphonating agent behaving also as a nonsolvent for polysulphone, said reagent, and a good solvent for polysulpone to contact with a polysulphone permselective film. CONSTITUTION:Sulfuric anhydride, chlorosulfonic acid, or conc. sulfuric acid, etc. is used as sulfonating agent. A mixture of said sulfonating agent, a nonsolvent A for polysulphone behaving also as poor solvent for the sulfonating agent, and a good solvent B for both said sulfonating agent and polysulphone is allowed to contact with polysulphone film. Preferred solvent A is cyclohexane and preferred solvent B is methylene chloride. Preferred weight ratio A/B is 100/1-100/20. The concn. of the sulfonating agent may be optionally selected but >=3wt% is preferred. It is necessary to realize <=10<13>OMEGA-cm surface resistance for the sulfonated surface.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a selectively permeable membrane that can be used as a precision filtration membrane, an ultrapolar filtration membrane, or a reverse osmosis filtration 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 has excellent heat resistance, acid resistance, and alkali resistance, as well as 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, the amount of water permeation is low, especially when the molecular weight fraction is This is a major drawback when using a small film. 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 the characteristics of polysulfone are lost. Furthermore, along with the improvement in hydrophilicity, there arises a problem in film formation that solidification during wet i-removal is delayed. 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. 1983-1990).
Publication No. 397). However, it is difficult to control and start the sulfonation reaction 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 poor film forming properties and film properties. A problem arises with stable tickets. Furthermore, 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 Application Laid-Open No. 3629/1983). and 4\Kokai No. 55-48222).The method is only possible with special combinations of resins, the synthesis process is complicated, and since they have different repeating units, it is difficult to combine them. The problem of non-uniformity of the 11% properties due to separation arises.

The inventors conducted research to solve the above-mentioned problems with conventional sulfonated polysulfone, 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, the present invention provides the following advantages: (1) The surface resistance of the sulfonated table iJ1■ is 1o1
A surface sulfonated polysulfo/selective perms membrane characterized by a resistance of 3Ω-σ or less.

and (2) the sulfonation reagent is hydrothermal sulfuric acid and/or chlorosulfo/acid, and Liquid A, which is a poor solvent for the sulfonation reagent and a non-solvent for the polysulfone, has a 7% The membrane surface is sulfonated 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, which is a solvent, is 100/1 to 100/20. A method for producing a selectively permeable surface-sulfonated polysulfone membrane, characterized by the following.

The polysulfone (λ) used for sulfonation in the present invention may be any polysulfone (λ) that has 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 it is preferable from the viewpoint of heat resistance that the heat distortion temperature of the polymer is 150°C or higher at a load of 18.6 kg/cfA. , allyl group, aryl group, amino group, amide group, dil/4 group, acid amide, ketogysim,
Those substituted with functional groups such as epoxy or silanol groups and/or compounds containing these functional groups can also be used.

Furthermore, those in which these functional groups are used for crosslinking reactions and improve membrane properties can also be used.

The polysulfonoselective perms membrane used in the present invention is precision P]@
The membrane may be used for any purpose such as ultrafiltration, reverse osmosis, gas separation, etc. In addition, regarding the shape, flat membranes, medium-walled filamentous membranes, composite membranes using other sheets or porous materials as a support,
Furthermore, any composite membrane using a polysulfone membrane as a support can be used. Regarding the membrane structure, the surface layer is so dense that no pores can be seen even under an electron microscope, and the membrane is covered with a so-called skin layer, or the membrane is not covered with a skin layer, and the interior is porous and has a finger-like structure. can also be used.

Any method can be used to produce a selectively permeable membrane in which other functional groups or compounds are already bonded to the membrane surface. 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 process is mixed into a resin solution to form a porous membrane. Means the surface of layers and intramembranous tissues.

The degree of sulfonation of the surface sulfonated polysulfone selectively permeable membrane of the present invention must be such that it exhibits hydrophilicity, and it must exhibit a surface resistance of 100 cm or more. If the surface resistance of the surface sulfonated membrane is 10<13 >[Omega]-cm or more, no significant improvement in the hydrophilicity of the membrane is observed.

The permselective membrane of the present invention includes not only membranes in which the entire surface of the tissue is sulfonated, but also membranes in which the entire surface of the tissue 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 surface refers to particles on the order of microns or less.
Refers to membranes consisting of fine sea-like, island-like, or band-like sulfonated regions on the order of λ, or membranes in which part of the surface of the membrane is entirely sulfonated on a relatively large scale. The degree of sulfonation on the surface may vary depending on the portion, and also includes those in which the degree of sulfonation of the sulfonated portion changes continuously.

The surface-sulfonated polysulfone selectively permeable membrane of the present invention has many advantages as shown below.

(1) Since it is a charged membrane, a higher water permeation rate can be obtained compared to conventional polysulfone selectively permeable membranes.

(2) Since it is a charged film, it can drive away similarly charged solutes and colloids, thereby preventing the formation of a gel layer. Even if the pore diameter is larger than the ionic radius, inorganic salts can be blocked.

(3) Even in the case of substances with different charges, the gel layer structure may be rough in special cases, and as a result, the gel layer tends to peel off from the active surface of the membrane due to the flow of the solution, stabilizing the membrane performance. There are things to do.

(4) 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.

(5) There is no need to consider problems such as purification of sulfonated polysulfone in advance of synthesis of sulfonated polysulfone, resulting in a significant simplification of the process. Furthermore, sulfonated polysulfone solidifies slowly during wet film formation, making it difficult to form a film, 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.

(6) The range of application of partially sulfonated membranes can be expanded. That is, as in the past, a partially sulfonated membrane can be obtained by using a blend or copolymer of a polysulfone that is sulfone-rich and a non-sulfonated resin. From the viewpoint of compatibility, there are restrictions on the degree of sulfonation, type of resin, degree of polymerization, mixing ratio, etc. According to the present invention, unsulfonated polysulfone or polysulfone sulfonated to any 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 lacrimal properties that could not be obtained with conventional sulfonated polysulfone, and selection p (7) Sulfonated only in the skin layer, which could not be obtained with conventional sulfonated polysulfone. (If only the surface sulfonated polysulfone selectively permeable membrane is used, in which only the propensity tissue is sulfonated, it is possible to design a more advanced membrane performance. For example, if only the skin layer is sulfonated, the N' The deactivation of r-element can be kept to a minimum.Also, when only the internal structure is sulfonated, it is possible to prevent the permeate from adhering and staying inside the membrane structure.

(8) A surface sulfonated polysulfone separation membrane with a distribution of degrees 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. By sulfonating the membrane surface in parts of the module where a gel layer is likely to form or where water permeability is low due to pressure loss, etc., module performance can be improved without significantly changing other properties. I can do it.

(9) The sulfone group bonded to the membrane surface of the surface sulfonated polysulfo/membrane of the present invention may be further bonded to an alkali metal, and depending on the honation reagent, a sulfonyl chloride group (-3O2Ct) may be bonded to the membrane surface first in the sulfonation reaction. However, at that point, it is also possible to react 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 for modifying and compositing sulfonated membranes.

An example of the surface sulfonation method will be described below.

In the production of surface sulfonation membranes, commonly known sulfonation reagents such as sulfuric anhydride, phosphoric acid, concentrated sulfuric acid, etc. are used, and the sulfonation reaction can be carried out in either a solution system or a gas system. You can also do it with

Among these, conventionally known solution-based surface sulfonation for other resins involves dissolving the sulfonation reagent in a solvent that does not react with the sulfonation reagent, dissolves it, and does not degrade the resin. This is done by bringing the resin into contact with the resin. This solvent may vary depending on the resin, but for example, cyclohexane can be used. However, this results in non-uniformity. The reason for this is thought to be that the solubility of the sulfonated donor drug is low and sulfonation proceeds easily, resulting in non-uniformity in the concentration of the sulfonated reagent.

The inventors conducted extensive research in order to find a method that could stably perform surface sulfonation under relatively mild conditions, and came to invent the above-mentioned manufacturing method.

An example of the solvent A used in the present invention is cyclohexane, as described above. An example of solvent B is methylene chloride.

In particular, methylene chloride, dichloroethane, etc. are good solvents for polysulfone, but are poor solvents for sulfonated polysulfone, so only the surface is sulfonated.
It is thought that further progress into the interior is prevented. 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.

When the mixture of solvents A and B used in the present invention is less than 1/1, the concentration of the sulfonating reagent in the solution is low, and an improvement in the water permeability of the membrane, etc. is observed after contact with the membrane for a few minutes at room temperature. I can't do it. Moreover, if it is more than 100/20, the film will deteriorate.

The concentration of the sulfonation reagent can be arbitrarily selected depending on the solubility of the mixed solvent, but in order to immediately replenish the amount consumed by the sulfonation reaction, it is recommended to mix in a sulfonation reagent with a solubility higher than the solubility. * According to LFI, the mixing ratio of cyclohexane/methylene chloride is 94.
415.6, if chlorosulfonic acid is used as the sulfonating reagent, the degree of sulfonation should be at least 3% by weight, preferably at least 5% by weight.
Obtained quickly and stably. 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 a phase containing a high concentration of 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 highly concentrated phase has a high specific gravity and settles to the bottom in most solution systems, it is easy to prevent it from coming into 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. Further, an appropriate method can be selected depending on whether the entire surface of the membrane is sulfonated or only a portion thereof is sulfonated. For example, in the case of a flat membrane or a tubular membrane, it is possible to make it into a module after surface sulfonation, or to make it into a module and then surface sulfonation, but if the module has a metal part, the former method is possible. It is preferable to use the method. In addition, in the case of hollow fiber membranes,
Merely immersing the membrane in a sulfonation reagent solution will not result in sufficient surface sulfonation, especially on the inner surface, so it is appropriate to first create a module and then pass the sulfonation reagent solution through it, as described below. It is. To sulfonate only the internal membrane tissue, the undressing layer surface is required.

A substance that is insoluble in the sulfonation reagent is applied in advance to the
There is a method in which the layer is protected and then sulfonated, or a sulfonating reagent solution is allowed to penetrate from the opposite side while the surface of the undressing layer is in contact with a liquid that does not contain a sulfonating reagent. 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, conversely, fill the membrane tissue with a liquid that does not contain the sulfonating reagent and a substance that is not yet soluble in the sulfonating reagent solution, and then bring the membrane into contact with the sulfonating reagent solution. is selected. It is more effective to use a liquid that does not contain the sulfonating reagent and has poor compatibility with the sulfonating reagent solution and has a different specificity. g
In order to create a fine sulfonated region on one surface, it is appropriate to sulfonate the surface using a mixture or copolymer of a polysulfone having 12 repeating units that can be sulfonated and a resin that cannot be sulfonated. There is a method of using a sulfonation reagent solution that has a milky phase separation between a sulfonation reagent-rich layer and a non-sulfonation reagent-rich layer, but care must be taken to maintain the stability of the degree of sulfonation with respect to temperature. need to pay.

In order to obtain a surface sulfonated polysulfone with a distribution of degree of sulfonation within the membrane, in addition to using the above method, there is a method of partially immersing the membrane in a sulfonation reagent solution.λ Especially for hollow fiber membranes. By flowing a sulfonating reagent solution through one inlet and a liquid containing no sulfonating reagent through the other inlet at predetermined pressures, the degree of sulfonation can be distributed. Sulfonated membranes are often stabilized in the form of sulfonate sodium salts.

This can be done by immersing the membrane in a methanol or ethanol solution of thorium methylate for several minutes at room temperature after sulfonation.

Although the treatment reaction is mild, the sulfonating reagent also produces sodium salt, 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 surface-sulfonated polysulfone selectively permeable membrane of the present invention has the following advantages.

(A membrane with a high degree of sulfonation can be obtained quickly and stably.)

(2) A partially sulfonated selectively permeable membrane, which has not been previously available, can be produced.

(3) The shape and fractionation properties of the selectively permeable membrane are changed, and many St.
This is the βf ability applied to similar membranes.

(4) All of the sulfonating reagents used have low toxicity if they are neutralized 7 times. 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 polysulfone permselective membrane) Aromatic polysulfone P-1700 (manufactured by Union Carbide) 14
70 parts by weight to 86 parts by weight of N-methyl-2-pyrrolidone
Heat and dissolve at ℃ for 4 hours to prepare a resin solution. After defoaming, the resin solution was cast onto a glass plate at room temperature, and the plate was further immersed in water at 20°C to obtain a film with a thickness of 60 to 70 μm. This film is 1
After immersing in 8℃ ethyl alcohol for 10 minutes, 80℃, 30
After drying for several minutes, a flat dry polysulfone permselective membrane was obtained.

Next, cyclohexane/methylene chloride/chlorosulfonic acid are thoroughly stirred at a predetermined mixing ratio and then left to stand. A chlorosulfonic acid rich layer immediately settles to the bottom. 18
The above dried membrane is immersed in the supernatant solution at 0.degree. C. for 5 minutes to sulfonate the surface. Furthermore, it was immersed in an ethanol solution of 5% by weight of sodium methylate for 5 minutes, immersed in water extracted from the sodium salt, and washed with water to form a surface-sulfonated polysulfone selective diaphragm. :, j I got F.

) 1. The measurement results of surface resistance and water permeability are shown in Table 1.

(Measurement of l-plane resistance) l-shoulder? : [The sulfonated polysulfone selectively permeable membrane is immersed in methyl alcohol for 10 minutes, and then air-dried at 80°C for 30 minutes. The obtained dried film was sold at a temperature of 40℃ and a humidity of 90℃.
After 6 hours of dissipation, electrodes were placed concentrically on the membrane and J
The surface insulation resistance was measured according to the method shown in IS standard K-6911 (applied voltage DC-100VI).

Example 2 (Hollow fiber selectively permeable membrane) The same aromatic polysulfone used in Example 1 and N-
Mix a predetermined amount of methyl-2-pyrrolidone and lithium nitrate to fully prepare the resin solution. Next, a normal wet film forming method using water as a coagulating liquid was used to obtain a water permeability of 30 t/ty? hr
A polysulfone selectively permeable membrane (Ml) of ATM and IF7 (M2) having a water permeability of 10007/71jhratm were obtained. 50 modules each were made into modules, and these modules were further immersed in ethyl alcohol for 10 minutes and heated at 80°C for 3
It was air-dried for 0 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 was separated into two phases, the supernatant was placed at 18°C into the inner tube of a dry polysulfone hollow fiber membrane that had been made into a module.
Circulate for minutes. At this time, if the amount of the sulfonated sample solution is small, it is preferable to bring the liquid that has passed through the hollow fiber into contact with the chlorosulfonic acid sand 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 Efnol solution, and at the same time, the module is 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, thereby obtaining a hollow fiber-like surface-sulfonated polysulfone selectively permeable membrane. The measurement 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 = 515/90.

Table 3 shows the results of measuring the mechanical strength of the obtained membrane.

Table 3 Mechanical Properties of Hollow Fibers 8) a) Comparative Example 1 of FFL Moisture State Measurement A dry polysulfonate selectively permeable membrane in the form of a flat membrane was prepared in the same manner as in Example 1, and this was prepared without containing chlorosulfonic acid. 1
The sample was immersed in a predetermined mixed solution of cyclohexane and methylene chloride at 8°C for 5 minutes, and then immersed in ethyl alcohol and then water for 5 minutes each.

The water permeability and surface resistance of the obtained membrane were measured in the same manner as in Example 1. The results are summarized in Table 1. It can thus be seen that water permeability is improved by treatment with a sulfonating reagent.

Comparative Example 2 Dry polysulfone g in the form of hollow fibers was prepared in the same manner as in Example 2.
M1 and M2 modules were prepared and immersed in a mixed solvent of cyclohexane/methylene chloride = 9575 for 5 minutes, Example 2
Similarly, ethanol and water were immersed in that order for 5 minutes each, taking care to ensure that the fibers circulated inside the hollow fibers. Table 2 shows the measurement results of the water permeability of the obtained module and the mechanical strength of the hollow fiber.
, are summarized in Table 3.

Comparative Example 3 Using the same polysulfone as in Example 1, the method of No5bay et al. (J, AppL, Polym, Sci, 20
Polysulfones with various degrees of sulfonation were synthesized according to 1885 ('76)). The degree of sulfonation here refers to the number of sulfone groups present per repeating unit of polysulfone. Sulfonation degree 10
The resin contains 14% by weight of N-methyl-2-pyrrolidone.
We attempted to form a film in the same manner as in Example 1 using C25 as a solution, but the coagulation was slow and we were unable to obtain a good film. Although it was possible to form a film, it was possible to form a film only with a significantly low water permeability. I couldn't get it. Resins with sulfonation degree of 0 and 5 are 14-fold fi
Although it is possible to produce a flat membrane using t%, when attempting to produce a hollow fiber membrane using the same method as in Example 2, difficulties were encountered due to the slow coagulation. Moreover, the elastic modulus of the membrane was slightly less than 60% of that of the membrane without sulfonation. Although it is possible to fabricate a hollow fiber membrane using a resin with a sulfonation degree of 01, the water permeability obtained is 30 t/n for a non-sulfonated polysulfone hollow fiber membrane (Ml) formed under the same conditions. hr atm, 120 L/m'br atm, an improvement of about 4 times. As shown in Table 3, the mechanical strength of the membrane is lower than that of (Ml) with surface sulfonation.

The water permeability of the surface sulfonated material (Ml) is 2.
It can be seen that at 20t/l hour attn, there is almost no decrease in mechanical strength.

patent applicant Sumitomo Bakelite Co., Ltd.

Claims (2)

[Claims] (1) The surface resistance of the sulfonated surface is 1013Ω-
A selectively permeable surface sulfonated polysulfone membrane characterized by a surface sulfonated polysulfone permselective membrane having a CRN or less. (2) The sulfonating reagent is sulfuric anhydride and/or chlorosulfonic acid, and is a good solvent for both the sulfonating reagent and the polysulfone, and Liquid A is a poor solvent for the sulfonating reagent and a non-solvent for polysulfone. Surface sulfonation characterized by sulfonating the surface by bringing a polysulfone selectively permeable membrane into contact with a solution consisting of a mixed solvent and a sulfonating reagent whose mixing weight ratio A7B with liquid B is 100/1 to 100/20. A method for producing a polysulfone selectively permeable membrane.