JPH07194951A - Dry hollow fiber membrane made of cellulose derivatives - Google Patents

Abstract

PURPOSE:To obtain a hollow fiber membrane made of a cellulose derivative not decreased in the rate of water permeability after drying by adhering the hollow fiber membrane under wet condition with a specified substance. CONSTITUTION:An ultrafiltration membrane with a dense layer on the inner and outer surfaces of a hollow fiber membrane contains a mixed substance consisting of three components of a polyvalent alcohol, a surfactant and water in the membrane and the water concn. in the mixed substance is 0.1-5wt.% and the wt. of the mixed substance is 0.1-1.5 times to the wt. of the polymer in the membrane. It is thereby possible to keep the rate of water permeability and to seal sufficiently without generating foaming at the interface between the membrane and an adhesive in making a module.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a cellulose derivative hollow fiber membrane used for separating a liquid or a gas,
Specifically, even if the hollow fiber membrane is dried, the permeation rate does not decrease,
The present invention relates to a cellulose derivative hollow fiber membrane capable of maintaining the permeation rate before drying.

[0002]

2. Description of the Related Art In recent years, hollow fiber membranes have been increasingly used for the purpose of separating / purifying and concentrating liquids or gases in a very wide range of fields such as water treatment, food industry, pharmaceutical industry, and electronic industry. . In the wet or dry wet film forming method of polymer hollow fiber membranes, a polymer film forming solution is generally exposed to a low molecular weight non-solvent (for example, water) to separate into a polymer concentrated phase and a dilute phase. That is, so-called phase separation occurs and a hollow fiber membrane is formed. At this time, the hollow fiber membrane forms a porous structure of a certain size due to the polymer,
The film is formed with the non-solvent contained in the inside of the porous material. However, when such a hollow fiber membrane is dried as it is and the non-solvent escapes from the inside of the porous body, the porous structure of the membrane is irreversibly changed, and the permeation rate is often significantly reduced. Further, such a dry hollow fiber membrane itself becomes hard and brittle, and the mechanical strength is significantly lowered.

On the other hand, when the hollow fiber membrane is incorporated in a membrane module, stored, transported or processed, it is not only easier to handle when the hollow fiber membrane is dry to some extent, but the membrane is sealed with an adhesive. It is desirable that the concentration of water contained in the film is as low as possible when the module is made into a module.

Therefore, the hollow fiber membrane must be moistened to the extent that the permeation rate is maintained without changing the membrane structure even in the dry state. That is, the permeation rate can be maintained even after drying by impregnating the moisturizing agent (or water retaining agent) into the porous interior of the membrane after forming the hollow fiber membrane.

Conventionally, glycerin or an aqueous glycerin solution is often used as a moisturizing agent for porous membranes.
(For example, JP-A-47-11662 and JP-A-60-12072). However, if the glycerin content of the moisturizing agent is low, the permeation rate may be considerably lower than before drying or the strength may be lowered even if the porous film with glycerin attached is dried and then immersed in water again. . On the other hand, when the glycerin content is high, the hygroscopicity of the porous membrane becomes too high, which causes various problems. For example, when modularizing a porous film, it is usual to seal the ends with a polyurethane-based adhesive or the like, but at that time, the moisturizing agent and the adhesive react and foam, resulting in a porous film. There is a problem such as not being able to adhere sufficiently.

Further, Japanese Patent Laid-Open No. 3-143534 discloses that the inclusion of a surfactant in the porous membrane does not reduce the water permeability after drying. However,
The content of this moisturizing agent is particularly important in a hydrophilic membrane in which the affinity between the membrane material and water has a great influence on the membrane performance. For example, if the cellulose acetate porous membrane is immersed in an aqueous solution of several wt% sodium dodecyl sulfate and dried, the water permeability may be significantly reduced. Further, when the concentration of this surfactant becomes several wt% or more, a large amount of the surfactant adheres to the porous membrane, so it is necessary to wash and remove it with a large amount of water for a long time before using the porous membrane. There are some inconveniences.

As an example of a moisturizer used in a reverse osmosis membrane of cellulose acetate, Industrial Engineering of DV Kenneth et al.
Chemistry, Product Research & Development Volume 8 N
O.1P84 (1969) and JP-A-53-92867 disclose an aqueous solution containing glycerin, a surfactant and water, and it is known that this humectant does not reduce the water permeation rate of the membrane after drying. ing. However, when such a film contains an excessive amount of moisturizing agent and the water concentration in the film is high, it becomes difficult to seal the film with an adhesive and it becomes substantially impossible to manufacture the film module. On the other hand, if the water content in the membrane is too low, the water permeability of the membrane after drying will decrease.

Further, Japanese Patent Application Laid-Open No. 56-129005 discloses a method of containing 1,3-butylene glycol as a moisturizing agent for a cellulose acetate film. In this case, however, the same problem as described above occurs. Yes, it is very difficult to determine the appropriate water concentration contained in the membrane.

[0009]

Therefore, the present invention provides an optimum moisturizing agent for a cellulose derivative hollow fiber membrane having dense layers on both inner and outer surfaces of the membrane, and the amount and the water concentration of the moisturizing agent contained in the membrane. By determining the above, it is necessary to prevent the permeation rate from being decreased even when the membrane is dried, to facilitate the handling during storage, transportation and processing of the membrane, and to cause no inconvenience in the adhesive seal of the membrane even in the modularization. And

[0010]

Means for Solving the Problems As a result of intensive studies for solving the above problems, the present inventors have found that a cellulose derivative ultrafiltration membrane having a dense layer on the inner and outer surfaces of the membrane has a polyhydric alcohol and an interface. Contains a mixed substance consisting of three components, an activator and water, and the water concentration in the mixed substance is 0.1 to 5 wt%.
And the weight of the mixed substance is 0.1 to 1.5 times the polymer weight of the membrane, the dry hollow fiber membrane can maintain the permeation rate before drying, and does not cause inconvenience in modularization. Heading, arrived at the present invention.

That is, the present invention is an ultrafiltration membrane having a dense layer on the inner and outer surfaces of a hollow fiber membrane, which contains a mixed substance consisting of polyhydric alcohol, a surfactant and water. And the water concentration in the mixed substance is 0.1 to 5 wt%, and the weight of the mixed substance is 0.1 to 1.5 times the polymer weight of the membrane. Regarding

The present invention will be described in more detail below. One feature of the present invention is that a mixed substance composed of three components of a polyhydric alcohol, a surfactant and water is contained in the cellulose derivative hollow fiber membrane. The polyhydric alcohol used in the present invention is an alcohol having two or more hydroxyl groups in the same molecule, such as propylene alcohol, 1,
Examples thereof include dihydric alcohols such as 3-butylene glycol and polyethylene glycol, and trihydric alcohols such as glycerin.

The surfactant used in the present invention may be any of an anionic surfactant, a cationic surfactant, a nonionic surfactant and an amphoteric surfactant. Examples of the anionic surfactant include fatty acid salt, higher alcohol sulfate ester salt, alkylnaphthalene sulfonate, alkylbenzene sulfonate, alkyl phosphate ester salt and the like. Examples of cationic surfactants include alkylamine salts, quaternary ammonium salts, benzalkonium salts and the like. As the nonionic surfactant, polyoxyethylene alkyl ether, polyoxyethylene alkylphenyl ether,
Examples thereof include polyoxyethylene fatty acid ester, polyglycerin fatty acid ester, polyoxyethylene fatty acid amide, polyoxyethylene alkylamine, and sorbitan fatty acid ester. Examples of the amphoteric surfactant include alkyl betaine, sulfobetaine, aminocarboxylic acid salt, and alkyl amino acid salt. Among the above-mentioned surfactants, higher alkyl sulfate ester salts, alkyl phosphate ester salts, alkylbenzene sulfonates and some nonionic surfactants have low toxicity, so the hollow fiber membrane of the present invention is used. It is preferable when it is used in the food field, medical field, water purification treatment, etc.

The hollow fiber membrane of the present invention is characterized by having a dense layer on the inner and outer surfaces of the membrane. That is, the pore size of the film gradually increases from the minimum value on the inner surface toward the outer surface from the inner surface of the film, and has at least one maximum value,
It becomes a minimum again on the outer surface. The pore diameter of the dense layer, which is the minimum value, is the size of the ultrafiltration membrane region targeted for the separation of the polymer substance, and is usually in the range of 1 to 50 nm. Also,
The ultrafiltration membrane of the present invention has a molecular weight cutoff of 1 × 10 ³ to 1 ×.
Membrane that is 10 ⁶ .

The cellulose derivative according to the present invention includes cellulose ester compounds such as cellulose diacetate, cellulose triacetate, cellulose propionate, cellulose butyrate and cellulose phenylcarbanilate, cellulose ether compounds such as methyl cellulose and ethyl cellulose, and the like. Included are blended compounds that have been combined.

The hollow fiber membrane of the present invention is characterized in that the weight of the mixed substance consisting of the polyhydric alcohol, the surfactant and water is 0.1 to 1.5 times the weight of the polymer of the membrane. When the weight of this mixed substance exceeds 1.5 times the weight of the polymer, the hollow fiber membrane of the present invention has too high a water content, and therefore the hollow fiber membrane is sealed with a polyurethane adhesive or the like to form a module. In doing so, the mixed substance and the adhesive react and foam, which makes it difficult to sufficiently bond the hollow fiber membranes. On the other hand, if the weight of the mixed substance is less than 0.1 times the weight of the polymer, the permeation rate remarkably decreases. Therefore, the weight of the mixed substance may be 0.1 to 1.5 times the weight of the polymer, preferably 0.5.
It should be ~ 1.2 times. The weight of the mixed substance contained in the hollow fiber membrane of the present invention is the composition of the mixed substance, the time for immersing the hollow fiber membrane in the solution of the mixed substance, the temperature of the mixed substance solution at the time of immersion, the drying temperature of the membrane, and the drying time. It is possible to change the composition by changing the composition of the mixed substance. That is, the weight of the mixed substance is increased by increasing the composition of the polyhydric alcohol or the surfactant in the mixed substance, particularly the composition of the polyhydric alcohol.

The composition ratio of the polyhydric alcohol, the surfactant and the water in the mixed substance solution in which the hollow fiber membrane is dipped is particularly so long as the weight of the mixed substance in the dry membrane is 0.1 to 1.5 times the weight of the membrane polymer. Without limitation, polyhydric alcohol 5 to 50 wt
%, Surfactant is 0.05 to 10 wt%, and water is 40 to 90 wt%. Further, if the water content in the mixed substance contained in the film is high, the adhesive will foam at the interface between the polyurethane adhesive and the film, while if it is small, the permeation rate of the film after drying will decrease. In the present invention, it was found that the water concentration of 0.1 to 5 wt% with respect to the mixed substance solves both of the above problems.

Next, the method of the present invention will be specifically described. First, a cellulose derivative hollow fiber membrane obtained by a wet or dry wet film forming method or the like is filled with a three-component mixed substance having a predetermined composition of a polyhydric alcohol, a surfactant and water. The filling method is not limited, but the most convenient method is to immerse the hollow fiber membrane in a mixed substance having a predetermined composition. Usually, this immersion may be performed for 1 hour or more at room temperature, but the time can be shortened by increasing the temperature of the mixed substance. Next, this hollow fiber membrane is dried to remove excess water inside the pores. The weight and water content of the mixed substance contained in the dry hollow fiber membrane of the present invention also change depending on the drying conditions of the hollow fiber membrane. That is, the drying method may be hot air drying or vacuum drying, but it is necessary that excess moisture in the hollow fiber membrane can be removed and the weight of the membrane does not change even if the drying time is sufficiently long. Such a drying temperature should be lower than the glass transition temperature of the cellulose derivative used and higher than room temperature (25 ° C). For example, in the case of cellulose acetate hollow fiber membrane
30-60 ° C is desirable. The drying time may be such that the weight of the mixed substance reaches the equilibrium. For example, when the cellulose acetate hollow fiber membrane is dried at 50 ° C., it may be dried for 5 hours or more.

Further, before using the hollow fiber membrane as a liquid separation membrane, the dried hollow fiber membrane may be immersed in water at room temperature for several hours or more to remove the mixed substances from the membrane, which is the same as before drying. Transmission performance can be obtained. This soaking time can also be shortened by raising the temperature of the water so that it does not reach 60 ° C.

Although the operation of the present invention is not clear, it can be estimated as follows. That is, the hydrophobic portion of the surfactant in the mixed substance is adsorbed on the inner surface of the pores of the hollow fiber membrane, and at the same time, the hydrophobic portion also binds to the polyhydric alcohol. In addition, since the hydrophilic part of the surfactant and the hydroxyl part of the polyhydric alcohol have strong interactions with water, this water is apparently bound to the hollow fiber membrane via the surfactant and polyhydric alcohol. Exists in. This bound water is not completely removed even when the hollow fiber membrane is dried at a predetermined temperature, and does not change the porous structure even after drying in order to give the hollow fiber membrane an appropriate water retention property. The mixed substance can be easily removed from the hollow fiber membrane by immersing the membrane in water. In a hollow fiber membrane structure such as the present invention having a dense layer on the inner and outer surfaces of the membrane, generally, even when the membrane is immersed in a moisturizing agent, the rate at which the moisturizing agent diffuses throughout the porous interior of the membrane is significantly reduced. The mixed substance of the invention can effectively perform the moisturizing action of the film even in such a film structure.

[0021]

EFFECTS OF THE INVENTION Even when the hollow fiber membrane of the present invention is dried, the permeation rate can be easily made equal to that before drying by immersing the porous membrane in water. Further, when the porous membrane is made into a module, even if the end of the porous membrane is sealed with a polyurethane-based adhesive or the like, the adhesive does not foam and a sufficient sealing property can be obtained.

[0022]

EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

Example 1 Cellulose acetate (acetylation degree: 60.5) A polymer was stirred and dissolved in a solvent of dimethyl sulfoxide to prepare a film-forming dope (concentration of polymer: 20 wt%). Temperature of this film forming dope
It was pressed into the sheath of a circular double-tube spinning nozzle at 90 ° C., and water was injected as a coagulating liquid into the core of the nozzle. The film-forming dope discharged from this spinning nozzle port has 5
After passing cm, the mixture was coagulated while passing through a water bath at a temperature of 70 ° C., and immersed in a water bath at a temperature of 40 ° C. for several hours to completely replace the solvent in the hollow fiber membrane with water. The obtained hollow fiber membranes have inner and outer diameters of 0.8 mm and 1.3 mm, respectively.
It has a dense layer on both outer surfaces, and the inside of the film has a network structure with pores larger than the pores of the dense layer, with a minor axis of 10 to 50 μm,
It had an oval giant void with a major axis of 50 to 150 μm. The pure water permeation rate of this hollow fiber membrane (the permeated water amount per unit time and unit membrane area when pure water at 25 ° C was passed through the hollow at a pressure of 1 kg / cm ² ) was 320 liters / (m ² · hr).・ (Kg / cm ² ))
And the molecular weight cutoff was 150,000 (pore size of dense layer: 10 to 20 nm). Further, the weight per 1 m length after drying this film in a dryer at 50 ° C. for about 20 hours was 0.28 mg.

The hollow fiber membrane obtained above was treated with glycerin (hereinafter
GL), sodium dodecylsulfate (hereinafter abbreviated as SDS) and water mixed solution (mixing weight ratio: GL / SDS / water = 20)
/0.5/79.5) at 20 ° C for about 20 hours and then dried in a dryer at a temperature of 50 ° C and a humidity of 50% for about 20 hours.

The weight of this dry membrane per 1 m length was measured, and the weight of the mixed substance adhering to the hollow fiber membrane was determined as a value with respect to the polymer weight of the membrane by the following formula.

[0026]

[Equation 1]

The water concentration in this mixed substance was adjusted to 30 ° C. by placing the dry film in a desiccator containing a large amount of phosphorus pentoxide.
It was determined by the difference between the weight of the film obtained by further removing the water adhering to the dry film after standing for 1 week and the weight of the original dry film.

As a result of measuring the pure water permeation rate of the membrane obtained by immersing the dried membrane obtained as described above in a large amount of water for about 20 hours, the reduction rate of the water permeation rate was only 5% of the water permeation rate before drying.
It was below. Furthermore, when the dry film was sealed with a polyurethane adhesive, no foaming occurred at the film and the adhesive interface. The above results are shown in Table 1.

Example 2 The same as Example 1 except that the hollow fiber membrane before drying of Example 1 was immersed in a mixed solution of 30 wt%, 0.5 wt% and 69.5 wt% of glycerin, sodium dodecyl sulfate and water, respectively. The results were shown in Table 1.

Example 3 The hollow fiber membrane before drying of Example 1 was treated with 1,3-butylene glycol, sodium dodecyl sulfate and water at 20 wt each.
%, 0.5 wt% and 79.5 wt% were mixed, and the same procedure as in Example 1 was performed, and the results are shown in Table 1.

Comparative Example 1 The procedure of Example 1 was repeated, except that the hollow fiber membrane of Example 1 before drying was immersed in a 20 wt% aqueous solution of glycerin, and the results are shown in Table 1.

Comparative Example 2 The procedure of Example 1 was repeated except that the hollow fiber membrane of Example 1 before drying was immersed in a 40 wt% aqueous solution of glycerin, and the results are shown in Table 1.

Comparative Example 3 The procedure of Example 1 was repeated, except that the sample was immersed in a 20 wt% aqueous solution of sodium dodecyl sulfate before drying, and the results are shown in Table 1.

Comparative Example 4 The procedure of Example 1 was repeated, except that the undried hollow fiber membrane of Example 1 was immersed in a 20 wt% aqueous solution of 1,3-butylene glycol, and the results are shown in Table 1.

Comparative Example 5 A hollow fiber membrane before drying of Example 1 was mixed with glycerin, sodium dodecyl sulfate and water (mixed weight ratio: GL / SD).
S / water = 20/10/70) was carried out in the same manner as in Example 1 except that it was immersed, and the results are shown in Table 1.

Comparative Example 6 The procedure of Example 2 was repeated, except that the hollow fiber membrane was left to dry at room temperature (15 to 20 ° C.) for 13 hours, and the results are shown in Table 1.

[0037]

[Table 1]

Claims (5)

[Claims] 1. An ultrafiltration membrane having a dense layer on the inner and outer surfaces of a hollow fiber membrane, wherein the membrane contains a mixed substance consisting of polyhydric alcohol, a surfactant and water. The water content in the mixed substance is 0.1 to 5 wt%, and the weight of the mixed substance is 0.1 to 1.5 with respect to the polymer weight of the membrane.
A dry hollow fiber membrane of a cellulose derivative characterized by being doubled. 2. The pore size of the dense layer is 1 to 50 nm.
A dry hollow fiber membrane of the described cellulose derivative. 3. The polyhydric alcohol is glycerin or 1,3
-The dry hollow fiber membrane of the cellulose derivative according to claim 1 or 2, which is butylene glycol. 4. The dry hollow fiber membrane of the cellulose derivative according to claim 1, wherein the surfactant is sodium dodecyl sulfate. 5. The dry hollow fiber membrane of a cellulose derivative according to claim 1, wherein the hollow fiber membrane is a hollow fiber membrane formed by a wet or dry-wet method.