JPS587324B2 - Manufacturing method of selectively permeable membrane - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a selectively permeable membrane, and in particular, to a method for manufacturing a selectively permeable membrane.

) The present invention relates to a method for producing a selectively permeable membrane made of a polyimide polymer having repeating units represented by:

In general, a membrane that selectively permeates a specific component in a liquid mixture such as a solution, emulsion, or suspension is called a selectively permeable membrane. It is an anisotropic membrane in which the skin layer is supported by a porous layer.

Representative of these membranes are semipermeable membranes for reverse osmosis and semipermeable membranes for ultraviolet filtration.

As is well known, semipermeable membranes for reverse osmosis can selectively separate small molecular substances such as sodium chloride as well as solvents from solutions containing substances with relatively small particle sizes. It is used for desalination of seawater and brine water, treatment of industrial wastewater, sewage purification, etc.

In addition, semipermeable membranes for ultrafurnace filtration can separate solvents and dispersion media from solutions and emulsions containing substances with relatively large particle sizes such as colloids, proteins, and microorganisms, or synthetic polymers. It is used for purification and concentration operations in the fields of food, medicine, brewing, fermentation, etc.

Conventionally, cellulose acetate has been typically used as a material for constructing such selectively permeable membranes.

When this cellulose acetate membrane is used for membrane separation treatment of aqueous liquid mixtures, it is an excellent membrane with high water permeation rate and high rejection rate for specific solutes, but it also has high resistance to heat, chemicals, and organic solvents. It is still not sufficient in terms of properties, mechanical strength, etc.

For this purpose, selectively permeable membranes made of condensation polymers such as polyimide, polyamide, polyimideamide, polybenzimidazole, polybenzimidazolone, etc., which are excellent in these respects, have been proposed.

Cellulose acetate membranes are made by dissolving cellulose acetate in a low boiling point solvent such as acetone together with a swelling agent to form a uniform membrane solution (
Hereinafter referred to as dope.

) and after applying it onto a suitable support substrate, some of the solvent is allowed to naturally evaporate from the dope, usually by leaving it at room temperature for a suitable period of time, and then applying it to a coagulation bath such as water. The cellulose acetate is immersed to coagulate and form a film.

However, the above-mentioned condensation polymers are generally not soluble in low-boiling point solvents such as acetone, and are not soluble in high-boiling point aprotic solvents such as N-methyl-2-pyrrolidone, dimethyl sulfoxide, dimethylacetamide, and dimethylformamide. Soluble only in polar organic solvents.

Therefore, when manufacturing a selectively permeable membrane from a dope in which a condensation polymer is dissolved in such a high boiling point solvent, the dope is applied to a support substrate and then heated to forcibly remove a portion of the solvent. It is necessary to evaporate the film, and conventionally, a method of forming a film by immersing it in a coagulating solvent after such heat treatment has been used.

The present inventors have already obtained a selectively permeable membrane from a polyimide polymer having a repeating unit represented by the above general formula by the above method (Japanese Patent Application Laid-Open No. 94477/1989).
, this membrane is an anisotropic membrane with a three-layer structure, which has a relatively dense porous layer under a skin layer as a surface layer, and a relatively coarse porous layer further under this, For example, in reverse osmosis, it has a sufficiently high practical salt removal rate, but the water permeation rate is not high enough for practical use.

In addition, the present inventors coated a dope containing the polyimide polymer on a support base material, and without heating, the polyimide polymer was difficult to dissolve and the organic solvent and water constituting the dope were removed. A selectively permeable membrane has also been obtained by immersing the polymer in a second organic solvent that is compatible with both for a short period of time, and then coagulating and molding the polymer in water (Japanese Patent Application Laid-Open No. 1983-1979-1). No. 71785), this membrane has a three-layer structure consisting of a relatively coarse porous layer under the skin layer, and a porous layer with large pores called a finger structure under this layer. When used in the method, it initially has a high water permeation rate, but as a result of the consolidation of the porous layer, especially the finger-like structure layer, the water permeation rate may even be halved after, for example, 24 hours of continuous operation. .

In addition, conventionally known selective permeable membranes made of polyimide are made of aromatic polyimide, which is insoluble in most organic solvents and therefore has organic solvent resistance. The membrane is necessarily a nuisance, and
This requires special technology and many steps.

For example, first, a polyamic acid soluble in an organic solvent is produced by reacting an aromatic tetracarboxylic acid anhydride with an aromatic diamine, and a solution of this polyamic acid is cast onto an appropriate support substrate to form a membrane structure. A method of manufacturing an aromatic polyimide film by dehydrating and cyclizing it by chemical reaction or heat treatment after formation has been disclosed (Strathmann, Des.
Alination, 26, 85 (1978)), this method has an additional step of converting an amic acid structure into an imide structure, as described above, but this conversion also does not necessarily proceed smoothly.

Therefore, the present invention generally aims to provide an improved method for producing a selectively permeable membrane made of a polyimide polymer, and in particular, it is an object of the present invention to The above-mentioned problems in the manufacturing method of a selectively permeable membrane made of a polyimide polymer having a polyimide polymer are solved, the porous layer under the skin layer as a surface layer is not made dense, and a finger-like structure is formed in the porous layer. , and form a relatively coarse porous layer, thus having a sufficiently high rejection rate (e.g., salt removal rate) and solvent permeation rate (e.g., water permeation rate) for practical purposes, and yet causing compaction. It is an object of the present invention to provide a method for producing a selectively permeable membrane that is difficult to use, can maintain a high permeation rate over a long period of time, and has excellent organic solvent resistance.

Another object of the present invention is to provide a method for producing a selectively permeable membrane with excellent organic solvent resistance, and in particular, to provide a simple and practical method for producing a polyimide polymer membrane.

The method for producing a selectively permeable membrane according to the present invention is mainly based on the general formula (where Rl represents a divalent organic group) having an imidization rate of at least 70% in a high boiling point aprotic polar organic solvent.

) A dope containing a polyimide polymer consisting of repeating units represented by ) is applied to a supporting base material, and a portion of the organic solvent is removed from the dope surface by heating the dope at a temperature at which the organic solvent does not exhibit a boiling phenomenon. After forced evaporation, the polymer is immersed for a short time in a second organic solvent that is difficult to dissolve and is compatible with both the organic solvent and water, and then coagulated in water. It is characterized by causing

Other objects and features of the present invention will become apparent from the following description.

The polyimide polymer used in the present invention mainly has the general formula (wherein Rl represents a divalent organic group).

) is a polyimide polymer consisting of repeating units represented by:

The polyimide polymer mainly composed of repeating units represented by the general formula (1) is 1, 2, 3, 4 monobutanetetracarboxylic acid (hereinafter referred to as BTC).

) and general formula H2N-R-NH2 (■) (However, Rl is the same as above.

) in substantially equimolar molar ratios, preferably using a solvent, usually at a temperature of about 100 to 300° C. for about 10 to 50 hours, and then dehydrated and condensed.

The above polymers can also be used to replace BTC with BTC imide-forming derivatives, i.e. BTC monoanhydride or dianhydride, BTC
It can also be produced using BTC lower alkyl esters such as C dimethyl ester, BTC amide, and the like.

Various kinds of diamines can be used as the diamine represented by the general formula (■).

As mentioned above, R1 is a divalent organic group, and is preferably an aromatic, aliphatic, alicyclic, or a combination of these hydrocarbon groups, or these hydrocarbon groups are bonded with a divalent bonding group. It is an organic group that has been

A preferred divalent aromatic hydrocarbon group is a phenylene group having 6 to 12 carbon atoms, and specific examples thereof include.

The bonding group X that forms a divalent organic group by bonding such an aromatic hydrocarbon group is, for example, (wherein R2 and R3 each independently have a carbon number of 1 to 10
represents an alkyl group or a cycloalkyl group having 3 to 10 carbon atoms.

) etc. A preferred example of the divalent aliphatic hydrocarbon group is the general formula (where R4 is a hydrogen atom, an alkyl group having 1 to 3 carbon atoms, or an alkoxy group having 1 to 3 carbon atoms, and R5 is a hydrogen atom or a C1 to 3 alkoxy group). 4 alkyl group, p and q are 1-
It is an integer of 6.

), an alkylene group represented by the general formula (where R6 is an alkyl group having 1 to 3 carbon atoms, and R7
is a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, and r is an integer of 1 to 10.

) can be mentioned.

In addition, examples of the bonding group Y that forms a divalent organic group by bonding a divalent aliphatic reverted hydrogen group include -O-, -S-, -(
CH2)y-O-(CH2CH2O)z-(CH2)y
-(However, y represents an integer of 0 to 5, and z represents an integer of 1 to 3.

) etc. The divalent alicyclic hydrocarbon group is preferably a cyclohexylene group having 6 to 12 carbon atoms, and specific examples thereof include.

Furthermore, such alicyclic hydrocarbon groups can be bonded together via the bonding group X to form a divalent organic group R1.

Therefore, specific examples of the diamine represented by the general formula (■) are m-phenylenediamine, p-phenylenediamine, 4,4'-diaminodiphenylmethane, 4,4'
-diaminodiphenylpropane, 4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl sulfide, 4,
4'-diaminodiphenyl sulfone, 3,3'-diaminodiphenyl sulfone, p-bis(4-aminophenoxy)benzene, m-bis(4-aminophenoxy)benzene, m-xylylenediamine, p-xylylenediamine, Hexamethylene diamine, heptamethylene diamine, octamethylene diamine, 4,4-dimethylheptamethylene diamine, 3-methoxyheptamethylene diamine, 2,11-diaminododecane, 1,4-diaminocyclohexane, di(4-aminocyclohexyl) methane,
4,4'-diaminodicyclohexyl ether, bis(
p-aminophenyl)bosphine oxide, bis(p-
Examples include aminophenyl)diethylsilane and bis(p-aminophenyl)dicyclohexylsilane.

These diamines may be used alone or as mixtures thereof.

In the method of the present invention, among the diamines represented by the general formula (■), the divalent organic group is an aromatic hydrocarbon group or two aromatic hydrocarbon groups are bonding groups -O-, -SO2
-, -CO-, -CH2- or -C(CH3)2-
Diamines, which are organic groups bonded with , and mixtures thereof are particularly preferably used.

When the divalent organic group is an aromatic hydrocarbon group, the selective separation ability of the resulting selectively permeable membrane at high temperatures is enhanced.

When the resulting permeable membrane is used for membrane separation treatment of aqueous liquid mixtures, the two aromatic hydrocarbon groups are -O-, -
Diamines bonded with hydrophilic groups such as SO2- and -CO- are particularly preferably used.

This is because these hydrophilic groups tend to increase the water permeation rate of the resulting permeable membrane.

The reaction between BTC and diamine is preferably carried out in a solvent.

Usually, N-alkyl-2-pyrrolidones such as N-methyl-2-pyrrolidone, dimethylacetamide, N-alkylpiperidones such as N-methyl-2-piperidone,
dimethylformamide, dihydroxybenzene, phenols such as phenol and cresol, preferably N
-Methyl-2-pyrrolidone and/or N-methyl-2-
Piperidone is used.

This is because these have particularly excellent solubility in BTC, diamines, and the resulting polyimide polymer, and have a high boiling point, so that the reaction can proceed rapidly at high temperatures.

Generally, the amount of solvent used is not particularly limited;
An amount sufficient to carry out the reaction uniformly may be used.

Usually, the total amount of BTC and diamine is 100 parts by weight (hereinafter referred to as
Unless otherwise specified, all parts are by weight.

) per 60 to 900 parts. In this way, a polyimide polymer mainly consisting of repeating units represented by the above general formula (■) is suitably used in the method of the present invention, but preferably this polyimide polymer consists essentially of the above-mentioned structure. It is composed of repeating units.

Such polymers contain BTC and diamine in a ratio of about 100 to 3
It is obtained by reacting at a temperature of 00°C.

On the other hand, when BTC and diamine are reacted at a lower temperature, for example, about 30 to 80°C, a polymer containing an amic acid bond, which is a precursor of an imide ring, ie, a polyimide polyamic acid is obtained.

This polyimide polyamic acid contains, for example, the following repeating units in addition to the repeating units represented by the general formula (■).

In the method of the present invention, it is permissible for the polyimide polymer to have a certain degree of amic acid structure.

That is, a polyimide polymer having an imidization rate of about 70% or more as defined by can be used.

However, the imidization rate of the polymer is preferably 90%.
Particularly preferred is a polyimide whose repeating units are 98 to 100%, that is, the structure substantially represented by the above general formula (■).

This is because if the imidization rate is less than about 70%, the resulting permeable membrane will have poor organic solvent resistance.

The polyimide polymer used in the present invention usually has 0
, 55 to 1.2, preferably 0.60 to 1.0 (measured value at 30°C).

Polymers with too low an intrinsic viscosity have poor self-supporting properties, that is, poor membrane-forming ability, and are difficult to form into membranes, making it difficult to form a good selectively permeable membrane.On the other hand, polymers with too high an intrinsic viscosity are This is because it is difficult to obtain a uniform dope from coalescence, and it is also difficult to form a good selectively permeable membrane.

Therefore, the polyimide polymer used in the present invention usually has an average molecular weight of 20,000 to 200.
000, preferably 30,000 to 100,000.

The organic solvent that constitutes the dope (hereinafter referred to as dope solvent).

) naturally dissolves the polyimide-based polymer, but the dope is also compatible with water so that the polymer in this dope will eventually coagulate on contact with water. It is required to have the ability to almost completely replace water when it is immersed in water together with the supporting base material.

Dope solvents that meet these requirements must have a high boiling point,
Usually, an aprotic polar organic solvent having a boiling point of about 130 to 320°C is preferably used, and specifically, N-alkyl-2-pyrrolidone such as N-methyl-2-pyrrolidone and N-ethyl-2-pyrrolidone -pyrrolidone, N-methyl-2-
Examples include N-alkyl-2-biperidones such as piperidone, dimethylformamide, dimethylacetamide, dimethylsulfoxide, tetramethylurea, sulfolane, and mixtures thereof.

Usually, a reaction solvent for BTC and diamine is used as a dope solvent, and after the reaction between BTC and diamine is completed, it is diluted or concentrated if necessary to form a dope.

Dope concentration (polymer concentration in dope) is usually 5 to 30
Weight % (Hereinafter, all % represents weight % unless otherwise specified.

), preferably 15 to 25%.

If the dope concentration is too low, the selectivity of the resulting permeable membrane will be poor, while if the dope concentration is too high, the dope viscosity will be too high, making it difficult to uniformly coat the support substrate, and the resulting permeable membrane will have poor selectivity. The permeation rate of the permeable membrane becomes low, making the permeable membrane impractical.

In addition, in relation to the dope concentration, the dope viscosity is generally
10 to 1000 poise, preferably 50 to 300 poise, particularly preferably 100 to 200 poise when applied to a supporting substrate
Adjusted to be a poise.

The dope prepared in this way is usually heated at a temperature of 10 to 40°C.
It is applied to a suitable support substrate at room temperature.

However, if desired, the dope can be applied to the support substrate in the temperature range of 40 to 150 DEG C., for example if the viscosity of the dope is too high in such a temperature range.

The supporting base material used is not particularly limited.

When smooth-surfaced plates and tubes made of materials such as glass, stainless steel, aluminum, polyethylene, and polypropylene are used as supporting substrates, the polyimide polymer is easily solidified after solidifying in a coagulating solvent. Since it is peeled off from the base material, sheet-like and tubular-like permeable membranes are obtained, respectively.

Furthermore, in the method of the present invention, sheet-like or tubular base materials of woven or non-woven fabrics made of organic fibers such as polyester fibers and acrylic fibers, and inorganic fibers such as glass fibers and carbon fibers may be used as supporting base materials. You can also do it.

The dope is applied onto such support substrates by any suitable means such as, for example, roll coating, spraying, dipping zone or casting bob application, and is integrated into these support substrates by forming a film. A composite permeable membrane with high strength can be obtained.

In addition, when the dope viscosity is high, Japanese Patent Application No. 50-1069
Preferably, the dope is applied onto the substrate by the method disclosed in Japanese Patent Application Laid-open No. 51-86078 or by a mechanical extrusion coating method.

The coating thickness of the dope on the support substrate varies depending on the intended use of the selectively permeable membrane and the type of substrate, but usually the thickness of the obtained permeable membrane is about 50 to 400 μm, preferably about 150 μm. It is adjusted so that it becomes ~250μ.

If the film thickness is too thin, the resulting permeable membrane will have poor strength for practical use; conversely, if it is too thick, the permselectivity will increase, but the permeation rate will decrease, making it impractical. This is because there will be a lack of

Obviously, the thickness of the permeable membrane obtained also depends on the doping concentration applied on the supporting substrate.

If the coating thickness of the dope is the same, the higher the dope concentration, the thicker the resulting permeable film will be.

When the supporting base material has a smooth surface like a glass plate,
For example, when the dope coating thickness is about 300μ, if the dope concentration is about 20%, a transmission film with a thickness of about 220μ can be obtained, and if the dope concentration is about 15%, a transmission film with a thickness of about 160μ can be obtained. A membrane is obtained.

The dope thus applied onto the support substrate is then heat treated according to the invention.

This heat treatment is usually carried out by blowing hot air onto the surface of the dope for a short period of time at a temperature at which the organic solvent constituting the applied dope does not exhibit a boiling phenomenon.

This is because if the boiling phenomenon of the dope solvent occurs, air bubbles will enter the selectively permeable membrane that is obtained, making it impossible to obtain the selectively permeable membrane that is the object of the present invention.

Therefore, the heat treatment is generally carried out at a temperature below the boiling point of the dope solvent, but there is no problem even if the heating temperature is above the boiling point as long as no boiling phenomenon occurs.

This heat treatment forcibly evaporates the dope solvent from the surface layer of the doped surface opposite to the doped surface that is in contact with the supporting substrate, and only this surface layer has an ultra-thin layer with a high concentration of polyimide polymer. This is to form.

Therefore, the temperature and time of the heat treatment in the present invention are determined to be sufficient to form the ultra-thin layer portion.

In other words, the temperature and time of the heat treatment in the present invention are as follows:
About 5-20% by weight of the coating dope, preferably about 1
It is determined to evaporate 0-15% by weight of solvent.

In the conventional so-called solvent evaporation method, that is, a method in which a dope is applied to a support base material, heat-treated, and immersed in water to form a film, it is necessary to obtain a reverse osmosis membrane with a salt removal rate of about 90% or more. This is in sharp contrast to the fact that 30-50% by weight of the solvent must be evaporated from the coating dope.

Taking a typical case as an example, in the solvent evaporation method, when the heating temperature is 120°C, a heating time of 6 to 8 minutes is desirable, but in the method of the present invention, about 1 minute is sufficient.

To explain the heat treatment in the method of the present invention more specifically, for example, when N-methel-2-pyrrolidone (boiling point 202°C) is used as the dope solvent, generally the diagonal line within the dotted line shown in FIG. The heat treatment is preferably carried out in the shaded area within the solid line.

In addition, dimethylformamide (boiling point 1
53°C), it is preferable to carry out the heat treatment in a region where the shaded area shown in FIG. 1 is moved vertically downward by the boiling point difference (202°C - 153°C = 49°C).

The same applies when other organic solvents are used as dope solvents.

If a solvent with a boiling point lower than 202°C is used, 202°C
It is preferable to carry out the heat treatment in an area where the hatched area in Figure 1 is moved vertically downward by the boiling point difference between It is preferable to carry out the heat treatment in an area where the hatched area in FIG. 1 is moved vertically upward by the boiling point difference between 202° C. and the boiling point of the solvent.

Furthermore, the heat treatment is generally preferably carried out at a high temperature for a short period of time, and at a low temperature for a long period of time.

For example, when N-methyl-2-pyrrolidone is used as the dope solvent, the heat treatment is performed at 180° C. for about 30 seconds and at 150° C. for about 1 minute.

Note that the time from creating the dope-coated support base material to heat treatment is usually within 5 minutes due to work constraints, but it is best to leave it for about 1 to 2 hours before heat treatment. Good too.

However, if the heat treatment is performed after being left for too long, it is difficult to obtain the selectively permeable membrane that is the object of the present invention.

If the dope-applied support substrate is left for too long, the applied dope will absorb moisture from the atmosphere, impairing its surface transparency and causing a cloudy phenomenon. It is best to heat treat it beforehand.

A permeable membrane formed from such a cloudy dope is not preferable because it does not have uniform properties over the entire membrane and also has low permselectivity.

After the heat treatment, the dope on the support substrate is treated with a second organic solvent (hereinafter referred to as dipping solvent) that is difficult to dissolve the polyimide polymer and has good compatibility with the dope solvent and water.

) for a short period of time. This immersion solvent is preferably
It does not dissolve the polyimide polymer at all or only swells it at most, and on the other hand, it has the function of displacing the dope solvent on the dope surface when the dope-coated support base material is immersed in the dipping solvent, and has the function of displacing the dope solvent on the dope surface. The dipping solvent is an organic solvent that has the function of almost completely, preferably completely replacing water when the process is finally coagulated and molded in water.

Particularly suitable immersion solvents in the present invention are organic solvents that are completely compatible with the dope solvent and water.

Therefore, the immersion solvent to be used strictly depends on the type of doping solvent used, but generally it has 1 to 1 carbon atoms.
5 aliphatic monohydric alcohol, C3-5 aliphatic polyhydric alcohol, C4-5 cyclic ether, C2-5
3, monomethyl and monoethyl ethers of these glycols, acetone, and mixtures thereof.

Specifically, methyl alcohol, ethyl alcohol, i
- Suitably selected from propyl alcohol, t-butyl alcohol, ethylene glycol, propylene glycol, glycerin, acetone, tetrahydrofuran, dioxane, methyl cellosolve, ethyl cellosolve, etc., and mixtures thereof.

To give an example of a preferred combination, when the dope solvent is N-methyl-2-pyrrolidone, the dipping solvent is tetrahydrofuran, t-butyl alcohol, ethylene glycol, or the like.

The immersion time of the doped support substrate in the immersion solvent varies depending on the type of immersion solvent and the immersion temperature, but is usually 0.
It is 5 seconds to 600 seconds, preferably 1 to 180 seconds.

If the immersion time is too short, the resulting selectively permeable membrane will have poor selective separation ability when used as a semipermeable membrane for reverse immersion or ultrafiltration; This is not preferable because the speed decreases.

The temperature of the dipping solvent during dipping is generally below the boiling point of the solvent.

Therefore, although it varies depending on the type of solvent used, it is usually 0°C.
-150°C, preferably 10°C - 80°C.

The time required for immersing the dope in the dipping solvent after heat treatment on the support base material is usually within 5 minutes due to work constraints, but within 1 to 2 hours, You can leave it for a while and then soak it.

If left for too long, the dope absorbs moisture from the atmosphere, resulting in poor dope dissolution, making it difficult to obtain a permeable membrane with excellent physical properties.

After the above-described treatments, the dope on the support base material is finally immersed in water and solidified.

It is undesirable to leave the dope-coated supporting substrate for too long after taking it out of the dipping solvent and immersing it in water because the permeation rate of the resulting selective permeable membrane will decrease. should be a time that can be practically used as a selectively permeable membrane.

Generally, it is coagulated and formed in water within 5 minutes, preferably within 1 minute, and particularly preferably immediately after the doped support substrate is removed from the dipping solvent, that is, within about 1 to 30 seconds.

The temperature of coagulation molding is not particularly limited, but it is generally carried out at a temperature below the boiling point of water, usually from 0°C to 80°C, preferably from 0°C to 50°C.

The time required for solidification molding varies depending on the solidification molding temperature, but is usually about 1 hour to 5 hours.

Note that the obtained selectively permeable membrane can be stored as it is in water, so in that case, the solidification molding step and the storage step become an inseparable series.

In addition, the selectively permeable membrane obtained is formed after coagulation in water.
It can be easily peeled off from a support base material with a smooth surface.

Next, in the method of the present invention, a swelling agent is preferably added to the dope in order to further increase the permeation rate of the resulting selectively permeable membrane.

The swelling agent must be soluble in the dope solvent and must also be soluble in the soaking solvent and water.

A group of swelling agents which are particularly preferably used in the present invention are the halides of alkali metals and alkaline earth metals, preferably lithium, potassium, sodium and magnesium, especially chlorides and bromides, as well as nitrates, sulfates and mixtures thereof. .

Representative examples include lithium nitrate, potassium nitrate, lithium chloride, potassium chloride, calcium chloride, calcium nitrate, and magnesium sulfate.

The amount of these inorganic swelling agents used varies depending on the dope concentration and the type of dope solvent, but is not particularly limited as long as these inorganic salts can be uniformly dissolved in the dope.

However, it is usually 200 parts or less, preferably 1 to 100 parts, particularly preferably 5 to 90 parts, per 100 parts of the polyimide polymer.

This is because if the amount of the inorganic swelling agent used is too large, it tends to impede the uniformity of the dope, and if the amount is too small, there is no sufficient addition effect.

For example, the inorganic swelling agent may be added as a solid to the dope and stirred with appropriate heating as necessary to uniformly dissolve it in the dope, or the swelling agent may be dissolved in the dope solvent in advance. This solution may then be added to the dope.

In this case, the solvent for dissolving the swelling agent may be different from the dope solvent in which the polymer is dissolved, as long as it is suitable as a dope solvent.

In addition, the general formula R9O-(CH2CHR8O)n-R10(■) (However, R8, R9 and R10 each independently represent hydrogen,
Represents a methyl group or an ethyl group, and n is 1 when R8 is hydrogen.
It is an integer of 1 to 5, preferably 2 or 3, and when R8 is a methyl group or an ethyl group, it is an integer of 1 to 3, preferably 1 or 2.

) and their mono- or di-lower alkyl ethers.

Specifically, (poly) such as ethylene glycol, diethylene glycol, triethylene glycol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol dimethyl ether, diethylene glycol monomethyl ether, diethylene glycol dimethyl ether, triethylene glycol monomethyl ether, etc. Mention may be made of (poly)propylene glycol and its methyl or ethyl ether derivatives, such as ethylene glycol and its methyl or ethyl ether derivatives, propylene glycol, dipropylene glycol, propylene glycol monomethyl ether, propylene glycol monoethyl ether.

Polyethylene glycol and its methyl and ethyl ether derivatives where n is 6 or more, and polypropylene glycol and its methyl and ethyl ether derivatives where n is 4 or more do not necessarily have sufficient solubility in the dope and are not uniformly soluble. This is not preferred because it may be difficult to obtain a suitable dope.

Furthermore, another group of swelling agents preferably used in the present invention has the general formula R11-(OH)m(■) (wherein R11 represents an aliphatic hydrocarbon group having 3 to 6 carbon atoms, and m represents 2 to 6 carbon atoms). It is an integer of 6.

) is a polyhydric alcohol represented by

Typically, chrycerin, 1,3-propanediol,
1,3-butanediol, 1,4-butanediol, 2
, 3-butanediol, 1,2,3,4,-butanetetraol, xylitol, sorbitol, pentaerythritol, and the like.

Polyhydric alcohols in which R11 has 7 or more carbon atoms are generally difficult to dissolve in dope, and are also difficult to obtain and produce, making them impractical.

The above glycol-based and polyhydric alcohol-based swelling agents are also
The amount used is not particularly limited as long as it dissolves in the dope solvent to give a uniform dope, but it is usually 300 parts or less, preferably 100 to 200 parts, per 100 parts of the polyimide polymer.

Similar to the inorganic swelling agents mentioned above, the above-mentioned glycol-based and polyhydric alcohol-based swelling agents tend to fail to obtain a uniform dope if the amount used is too large, and if the amount used is too small, it is difficult to obtain a sufficient addition effect. This is because there is a tendency to

Glycol-based and polyhydric alcohol-based swelling agents include, for example,
A suitable amount of this is added to a uniform solution prepared by dissolving a polyimide polymer in a dope solvent in advance, and stirred while heating at room temperature or at a temperature of about 80 to 150 °C as necessary to form a uniform dope. shall be.

Generally, glycol-based and polyhydric alcohol-based swelling agents are
There is an advantage that the dope using these is more stable than when using an inorganic swelling agent.

Further, in the method of the present invention, the above-described inorganic salt swelling agent,
It goes without saying that a mixture of two or more types of glycol-based swelling agents and polyhydric alcohol-based swelling agents may be used as the swelling agent.

A preferred mixed swelling agent is a mixture of a glycol-based swelling agent and a polyhydric alcohol-based swelling agent, and the mixture is used in an arbitrary ratio of 300 parts or less per 100 parts of the polyimide polymer.

A mixture of an inorganic swelling agent and a glycol-based or polyhydric alcohol-based swelling agent can also be used in a range of 300 parts or less per 100 parts of the polyimide polymer, but the amount of the inorganic swelling agent used is 200 parts per 100 parts of the polyimide polymer. part or less, preferably 100 parts or less.

As described above, in the method for producing a selectively permeable membrane according to the present invention, a dope containing a polyimide polymer is applied to a support base material, and then a part of the dope solvent in the dope surface layer is removed by heat treatment for a short time. Forced evaporation, followed by immersion in an immersion solvent, followed by immersion in water to coagulate the polymer,
It is used to form a film.

As described above, when the dope coated on the support substrate is immersed in water without heat treatment, the porous layer will contain finger-like structures with large pores, but in the method of the present invention, In this case, a thin film with a high polymer concentration is formed on the surface layer of the dope during the heat treatment of the dope, and furthermore, the supporting base Murakami's dope in this state is not immersed in water immediately.
Since the material is first immersed in an organic immersion solvent and then in water, the rate of replacement of the dope solvent with the immersion solvent and further with water is suppressed.

As a result, according to the method of the present invention, the formation of finger-like structures in the porous layer is suppressed, and in a preferred embodiment, almost no finger-like structures are formed.

However, on the other hand, the film obtained by the method of the present invention has a relatively dense porous structure, whereas the film obtained by the conventional method of heating the dope applied to the support base material and then immersing it in water has a relatively dense porous structure. The porosity of the membrane is relatively sparse.

Therefore, the selectively permeable membrane produced by the method of the present invention has a high water permeation rate and is unlikely to be compacted even after long-term use, so that the high water permeation rate can be maintained over a long period of time.

Furthermore, regarding the production of the polyimide polymer membrane described in detail above, the present invention has the following advantages.

That is, the polyimide polymer obtained from BTC and the diamine is dissolved in the above-mentioned high boiling point aprotic polar dope solvent and can form a uniform dope, so it is formed into a film at the polyamic acid stage. Unlike conventional aromatic polyimide permeable membranes which require an imidization step after forming a structure, this method does not require any additional steps after film formation, which is extremely advantageous industrially.

Furthermore, the permeable membrane obtained by the method of the present invention is particularly excellent in organic solvent resistance, and has a high permeation rate and excellent permselectivity.

Therefore, this selectively permeable membrane is suitable not only for membrane separation treatment of aqueous liquid mixtures but also for ultrafiltration of organic liquid mixtures, as well as for the treatment of organic industrial wastewater, food, pharmaceutical, fermentation, etc. It can be advantageously used in concentration and purification processes in fields such as brewing.

For example, the permeable membrane obtained by the method of the present invention is suitable for separating organic liquid mixtures containing organic solvents as exemplified below.

Namely, aromatic solvents such as benzene, toluene, xylene, and nitrobenzene, ether solvents such as ethyl ether, tetrahydrofuran, and dioxane, ketone solvents such as acetone and methyl ethyl ketone, and monohydric alcohol solvents such as methanol, ethanol, propanol, and butanol. , ethylene glycol, diethylene glycol, 1,3
- Polyhydric alcohol solvents such as butylene glycol, methyl cellosolve, ethyl cellosolve, polyhydric alcohol ether solvents such as diethylene glycol monomethyl ether, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, ethyl acetate, butyl acetate, ethyl propionate, ethylene glycol monomers and diacetate, ester solvents such as mono- and diacetate of diethylene glycol, dichloromethane, 1,
Halogenated hydrocarbon solvents such as 2-dichloroethane, trichlene, chloroform, bromoform, and chlorobenzene.

Next, in the method of the present invention, if necessary, other weights that are compatible with the dope and have self-supporting properties may be added for the purpose of improving the mechanical strength of the resulting permeable membrane. For example, polysulfone (Union Carbide Co., Ltd. P-1700, P-3500, etc.), polyphenylene oxide (General Electric Co., Ltd. PPO-53)
4 etc.) can be dissolved in a dope solvent together with a polyimide polymer to form a film.

The amount of such additionally added polymer should be 20 parts or less, preferably 5 parts or less, per 100 parts of the polyimide polymer constituting the dope.

This is because if 20 parts or more is added, the uniformity of the dope will be impaired.

Even when such a dope is used, the film forming conditions such as the dope concentration, viscosity, and amount of swelling agent added are preferably the same as those described above.

In the method of the present invention, for the purpose of improving the mechanical strength at high temperatures of the permeable membrane obtained as described above, after film formation, the membrane is heated at a temperature of about 100 to 400°C for 5 to
Heat treatment can also be performed for about 30 minutes.

This heat treatment may be performed using heated air, or by immersion in hot water or heated ethylene glycol.

If the treatment temperature is high, the treatment time may be short; if the treatment temperature is low, the treatment time may be lengthened.

For example, if the treatment temperature is 100°C, the treatment may be carried out for about 20 to 25 minutes, and if the treatment temperature is 350°C, the treatment may be carried out for several seconds to several tens of seconds.

The present invention will be described in detail below with reference to production examples of polyimide polymers and examples of the present invention, but the present invention is not limited to these examples in any way.

In addition, in the examples, the membrane performance of the selectively permeable membrane is 25°C.
Evaluation was made from the salt removal rate and water permeation rate defined by the following formulas at a temperature of .

Example 1 Production of polyimide polymer 20 liters equipped with a stirrer, nitrogen gas inlet, reflux tower with reaction product water removal device, and outer bath capable of heating up to 250°C
N-methyl-2-pyrrolidone (hereinafter referred to as NMP) was added to the reaction vessel.
That's what it means.

), 2.81 kg of BTC, and 2.40 kg of 4,4-diaminodiphenyl ether were charged, and then heated to about 70°C to uniformly dissolve them.

Xylene 1 was added to the thus obtained solution as a dehydrating azeotropic solution agent.
．． After adding 7 kg, the reactor was heated to a temperature of 175 to 195° C. under a nitrogen stream, and while xylene was refluxed, reaction product water distilled off by azeotropy was continuously extracted.

As the reaction progressed, the viscosity of the system increased, and 860 g of water was distilled off after about 35 hours.

After the reaction was completed, the azeotropic solvent xylene was distilled out of the system to finally obtain an NMP solution of the polyimide polymer with a solid content of 25% and a viscosity of 950 poise (value measured at 30°C with a B-type viscometer). Ta.

The intrinsic viscosity [η] of this polyimide polymer was 0.91 at a temperature of 30°C.

The imidization rate of this polyimide polymer was confirmed to be 99% or more by nuclear magnetic resonance spectrum and infrared spectrum.

Example 2 Production of polyimide polymer BTC 1.50 kg, diaminodiphenylmethane 1.2
Using 7 kg of NMP and 12.8 kg of NMP, an NMP solution of a polyimide polymer having a solid content of 18% and a viscosity of 57 poise (measured at 30° C. using a B-type viscometer) was obtained in the same manner as in Example 1 above.

The intrinsic viscosity [η] of this polyimide polymer was 0.58 at a temperature of 30° C., and the imidization rate was confirmed to be 99% or more from nuclear magnetic resonance spectra and infrared spectra.

Example 1 Preparation of dope (1) Polymer 1 was added to the polyimide polymer NMP solution obtained in Example 1 by adding finely ground lithium nitrate using a mortar.
A uniform dope A was prepared by adding 60 parts per 00 parts and stirring at a temperature of 100° C. for 5 hours.

Dopes B and C shown in Table 1 were prepared in exactly the same manner as this method.
and D were prepared.

(2) A 10% dimethylformamide solution of lithium chloride was added to the polyimide-based polymer NMP solution obtained in Example 2 and stirred, and 20% of lithium chloride was added per 100 parts of the polymer.
Dope E was prepared containing

Dopes F and G shown in Table 1 were prepared in exactly the same manner as this method.

For ease of comparison, Dopes A and E are also listed in Table 1.

(3) NMP of polyimide polymer obtained in Example 1
160 parts of diethylene glycol per 100 parts of this polymer was added to the solution, and the mixture was stirred at a temperature of 100° C. for 5 hours to prepare a uniform dope H.

Dopes ① and J shown in Table 1 were prepared in exactly the same manner.

Example 2 Evaluation of film formation and film performance (1) Using the polyimide polymer NMP solution obtained in Example 1 as a dope, a 300μ thick film was placed on a glass plate.
A dope-coated supporting base material was prepared by applying the dope to a thickness of
Heat treated for seconds.

It was taken out of the oven and immediately immersed in t-butyl alcohol (immersion solvent) at a temperature of 25° C. for 10 seconds.

20 seconds after taking it out from the immersion solvent, it was placed in a 1°C water bath and immersed for 2 hours.

The thickness of the obtained reverse osmosis membrane was 241μ.

This reverse osmosis membrane was set in a pressurized hatch-type measurement cell, and a sodium chloride aqueous solution with a concentration of 5000 ppm was supplied.
Water permeation rate and salt removal rate were measured under an operating pressure of 2 kg/cm2.

The results are listed in Table 3 below.

(2) Dope A was cast onto the inner surface of a glass tube with an inner diameter of 13.6 mm and a wall thickness of 3 mm to a coating thickness of 300 μm, and then the obtained dope-coated support base material (dope-coated glass tube) Hot air at a temperature of 120° C. was blown into the tube for 60 seconds. At this time, the glass tube was rotated at a speed of 50 revolutions per minute to prevent the dope from flowing down the tube wall to the bottom.

The glass tube coated with the dope and heat-treated in this manner was immediately placed in t-butyl alcohol (immersion solvent) at a temperature of 20° C., and immersed for 25 seconds.

5 seconds after taking it out of the immersion solvent, put it into 1℃ water,
It was immersed for 2 hours to form a film.

A tubular reverse osmosis membrane with an outer diameter of 12.8 mm and a membrane thickness of 215 μm was obtained.

This reverse osmosis membrane was inserted into a perforated stainless steel tube with an outer diameter of 13.0 mm and a wall thickness of 2 mm, and a sodium chloride solution with a concentration of 5000 ppm was passed through the membrane at a pressure of 42 kg/cm2, and the salt removal rate and water permeation rate were measured. .

The results are shown in Table 3.

(3) to (15) Table 2 (
3) to (9) and (13) to (15), and the above (
Reverse osmosis membranes shown in Table 2 (10) to (12) were obtained by the same method as in 2).

In order to facilitate comparison, the film forming conditions of (1) and (2) above are also shown in Table 2.

The water permeation rate and salt removal rate of the membrane thus obtained were
Shown in the table.

Example 3 The cross-sectional structure of the reverse osmosis membrane obtained in Example 2-(2) is shown in the scanning electron micrograph (200x magnification) of FIG.

The consolidation number was 0.021 when a 0.5% aqueous sodium chloride solution was continuously supplied to the membrane for 100 hours at 25° C. and an operating pressure of 42 kg/cm 2 .

Incidentally, the consolidation system number m is defined by the following equation.

Here, FO = water permeability after the first hour of pressurized operation, t
o = 1 (hour), F = water permeation amount after pressurized operation after t hours,
t=continuous operation time (hours).

Comparative Example 1 Polymer 100 was prepared from the NMP solution of the polyimide polymer obtained in Example 1 in exactly the same manner as in Example 1-(1).
A dope containing 75 parts per part of lithium nitrate was prepared.

This dope was applied to a thickness of 300μ on a glass plate, and
After being left for 0 seconds, it was placed in an air circulation heating oven at 115° C. and heat-treated for 420 seconds.

After taking it out of the oven and leaving it at room temperature for 60 seconds,
It was poured into water at 1° C. and immersed for 5 hours to form a film.

The thickness of this reverse immersion membrane was 115μ.

The cross-sectional structure of this film is shown in the electron micrograph (200x magnification) of FIG.

In addition, the compaction coefficient measured for this membrane in the same manner as in Example 3 was 0.015. A dope containing 10 parts of lithium nitrate per 100 parts of the polymer was prepared and coated on a glass plate to a thickness of 275 μm, and immediately poured into t-butyl alcohol at 25° C. and immersed for 10 seconds.

20 seconds after taking it out of the immersion bath, put it into 1℃ water,
A film was formed by immersion for 120 minutes.

This film has a thickness of 200 μm, and its cross-sectional structure is shown in the electron micrograph (200 times magnification) in FIG.

Further, as in Example 3, the compaction coefficient measured for this membrane was 0.087.

[Brief explanation of the drawing]

FIG. 1 shows that N is used as a doping solvent in the method of the present invention.
- It is a graph which shows the relationship between heating temperature and heating time in order to show the suitable area|region for heat processing when using methyl-2-pyrrolidone. Figures 2, 3, and 4 show the permeation obtained by the method of the present invention, the solvent evaporation method, and the solvent immersion method, respectively, using a polyimide polymer consisting of repeating units represented by the general formula (1). It is an electron micrograph showing the cross-sectional structure of the membrane.

Claims (1)

[Claims] 1. In a high-boiling aprotic polar organic solvent, at least 7
A dope containing a polyimide polymer mainly consisting of repeating units represented by the general formula (wherein R1 represents a divalent organic group) having an imidization rate of 0% or more is applied to a supporting substrate, and a After heating the dope at a temperature at which the organic solvent does not exhibit a boiling phenomenon and forcibly evaporating a part of the organic solvent from the dope surface, the polymer is difficult to dissolve and the organic solvent and water are mixed together. A method for producing a selectively permeable membrane, which comprises immersing it for a short time in a second organic solvent that is compatible with both, and then coagulating and molding it in water. 2 The second organic solvent is an aliphatic monohydric alcohol having 1 to 5 carbon atoms, an aliphatic polyhydric alcohol having 3 to 5 carbon atoms, or 4 carbon atoms.
5 cyclic ethers, glycols having 2 to 3 carbon atoms, monomethyl and cymonoethyl ethers of these glycols, acetone, and mixtures thereof. Production method. 3 The high boiling point aprotic polar organic solvent is N-methyl-2-
pyrrolidone, dimethylformamide, dimethylacetamide, or a mixture thereof, and the second organic solvent is proyl alcohol, butyl alcohol, glycerin, tetrahydrofuran, or ethylene glycol, or 2. A method for producing a selectively permeable membrane according to item 2. 4. The method for producing a selectively permeable membrane according to claim 1, wherein the polyimide polymer is a polyimide consisting essentially of repeating units represented by the above general formula. 5. The method for producing a selectively permeable membrane according to claim 1, wherein R is a divalent organic group containing an aromatic ring. 6. The method for producing a selectively permeable membrane according to claim 1, wherein R1 is. 7. A polyimide polymer containing 5 to 30% by weight of dope;
200 parts by weight or less of alkali metal and alkaline earth metal halides and nitrates per 100 parts by weight of this polymer;
Claims 1 to 6 contain an inorganic swelling agent selected from sulfates and mixtures thereof.
2. A method for producing a selective permeable membrane according to any one of paragraphs 1 and 2. 8. The method for producing a selectively permeable membrane according to claim 7, wherein the inorganic swelling agent is lithium chloride, potassium chloride, lithium nitrate, potassium nitrate, calcium nitrate, or a mixture of two or more thereof. 9 A polyimide polymer having a dove content of 5 to 30% by weight,
300 parts by weight or less of the general formula R9O-(CH2CHR80)n-R10 per 100 parts by weight of this polymer (however, R8
, R9 and R10 each independently represent hydrogen, a methyl group or an ethyl group, and n is an integer of 1 to 5 when R8 is hydrogen, and an integer of 1 to 3 when R8 is a methyl group or ethyl group. . 7. The method for producing a selectively permeable membrane according to any one of claims 1 to 6, characterized in that it contains a glycol-based swelling agent represented by: 10. Production of a selectively permeable membrane according to claim 9, wherein the glycol-based swelling agent is ethylene glycol, diethylene glycol, triethylene glycol, monomethyl ether thereof, or a mixture of two or more thereof. Method. 11 Dope contains 5 to 30% by weight of a polyimide polymer and 300 parts by weight per 100 parts by weight of this polymer of the following polyhydric alcohol swelling agent having 3 to 6 carbon atoms and 2 to 6 hydroxyl groups. A method for producing a selectively permeable membrane according to any one of claims 1 to 6, characterized in that: 12. The method for producing a selectively permeable membrane according to claim 12, wherein the polyhydric alcohol swelling agent is glycerin.