JP3332541B2 - Dry hollow fiber membrane of cellulose derivative - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention 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 transmission speed does not decrease,
The present invention relates to a cellulose derivative hollow fiber membrane capable of maintaining a transmission rate before drying.

[0002]

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

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

[0004] Therefore, even when the hollow fiber membrane is in a dry state, it is necessary to keep the membrane structure unchanged and keep it moist enough to maintain the permeation rate. That is, the permeation rate can be maintained even after drying by impregnating the porous interior of the membrane with a humectant (or water retaining agent) after the formation of the hollow fiber membrane.

Glycerin or glycerin aqueous solution has been frequently used as a humectant for a porous membrane.
(For example, JP-A-47-11662 and JP-A-60-12072). However, when the glycerin content of the humectant is small, even if the glycerin-adhered porous membrane is dried and then immersed again in water, the permeation rate may be considerably lower than before drying, or the strength may be reduced. . On the other hand, when the glycerin content is high, the moisture absorbency of the porous membrane becomes too high, causing various inconveniences. For example, when modularizing a porous membrane, it is usual to seal the ends with a polyurethane-based adhesive or the like, but at that time, the humectant and the adhesive react and foam, resulting in a porous membrane. There is a problem that it is not possible to adhere sufficiently.

[0006] Japanese Patent Application Laid-Open No. 34435/1991 discloses that by incorporating a surfactant into a porous membrane, the water permeability after drying is not reduced. However,
The content of the humectant is particularly important for a hydrophilic membrane in which the affinity between the membrane material and water greatly affects membrane performance. For example, if the cellulose acetate porous membrane is immersed in a several wt% aqueous solution of sodium dodecyl sulfate and dried, the water permeability may be significantly reduced. In addition, when the concentration of the surfactant becomes several wt% or more, a large amount of the surfactant adheres to the porous membrane. Therefore, it is necessary to wash and remove the porous membrane for a long time with a large amount of water before using the porous membrane. Some inconveniences occur.

Examples of humectants used in cellulose acetate reverse osmosis membranes include DVKenneth et al., Industrial Engineering.
Chemistry, Product Research & Development Vol.8 N
o.1P84 (1969) and JP-A-53-92867 introduce 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 dried membrane. ing. However, when such a film contains an excessive amount of a humectant and the water concentration in the film is high, it is difficult to seal with an adhesive, and it is substantially impossible to manufacture a film module. On the other hand, if the moisture concentration in the membrane is too low, the water permeability of the dried membrane will decrease.

Further, Japanese Patent Application Laid-Open No. 56-129005 discloses a method containing 1,3-butylene glycol as a humectant for a cellulose acetate membrane. Yes, it is very difficult to determine an appropriate concentration of water contained in the membrane.

[0009]

Accordingly, the present invention provides an optimal humectant for a cellulose derivative hollow fiber membrane having a dense layer on both the inner and outer surfaces of the membrane, and also provides an amount of the humectant and a water concentration contained in the membrane. The problem is that, even if the membrane is dried, the permeation rate does not decrease even when the membrane is dried, the membrane can be easily handled during storage, transportation and processing, and further, there is no problem with the adhesive seal of the membrane even in modularization. And

[0010]

Means for Solving the Problems The present inventors have conducted intensive studies to solve the above-mentioned problems, and as a result, a polyhydric alcohol, an interface, and a cellulose derivative ultrafiltration membrane having a dense layer on the inner and outer surfaces of the membrane have been obtained. A mixed substance comprising three components of an activator and water is contained, and the water concentration in the mixed substance is 0.1 to 5% by weight.
The dry hollow fiber membrane in which the weight of the mixed substance is 0.1 to 1.5 times the weight of the polymer of the membrane can maintain the permeation rate before drying, and does not cause inconvenience in modularization. Heading, the present invention has been reached.

That is, the present invention relates to 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 comprising a polyhydric alcohol, a surfactant and water. A dry hollow fiber membrane of a cellulose derivative, characterized in that the water content of the mixed substance is 0.1 to 5% by weight and the weight of the mixed substance is 0.1 to 1.5 times the polymer weight of the membrane. About.

Hereinafter, the present invention will be described in more detail. 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 a 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, for example, propylene alcohol,
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 a fatty acid salt, a higher alcohol sulfate, an alkylnaphthalene sulfonate, an alkylbenzene sulfonate, and an alkyl phosphate. Examples of the cationic surfactant include an alkylamine salt, a quaternary ammonium salt, and a benzalkonium salt. As nonionic surfactants, polyoxyethylene alkyl ether, polyoxyethylene alkyl phenyl ether,
Examples include polyoxyethylene fatty acid esters, polyglycerin fatty acid esters, polyoxyethylene fatty acid amides, polyoxyethylene alkylamines, sorbitan fatty acid esters, and the like. Examples of the amphoteric surfactant include alkyl betaine, sulfo betaine, amino carboxylate, and alkyl amino acid salt. Among the above surfactants, higher alkyl sulfates, alkyl phosphates, alkylbenzene sulfonates, and some nonionic surfactants have low toxicity. It is preferable when used in the food field, medical field, water purification treatment and the like.

The hollow fiber membrane of the present invention is characterized in that the membrane has a dense layer on the inner and outer surfaces. 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 again has a minimum value on the outer surface. The pore diameter of the dense layer having the minimum value is the size of the ultrafiltration membrane region for separating 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 cut-off of 1 × 10 ³ to 1 ×.
A film 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, and cellulose ether compounds such as methyl cellulose and ethyl cellulose. Blend compounds in combination.

The hollow fiber membrane of the present invention is characterized in that the weight of the mixed substance comprising the three components of polyhydric alcohol, surfactant and water is 0.1 to 1.5 times the weight of the polymer of the membrane. If 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, so that the hollow fiber membrane is sealed with a polyurethane-based adhesive or the like to form a module. In this case, the mixed substance reacts with the adhesive to foam, and it is difficult to sufficiently join the hollow fiber membranes. On the other hand, when the weight of the mixed substance is less than 0.1 times the weight of the polymer, the permeation rate is significantly reduced. Therefore, the weight of the mixed substance may be 0.1 to 1.5 times the weight of the polymer, preferably 0.5 to 1.5 times.
It may be up to 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 mixed substance solution, the temperature of the mixed substance solution at the time of immersion, the drying temperature of the membrane, and the drying time. Although it can be changed by changing the composition of the mixed substance, it is most easily controlled. That is, the weight of the mixed substance increases as the composition of the polyhydric alcohol or the surfactant in the mixed substance, particularly the composition of the polyhydric alcohol increases.

The composition ratio of the polyhydric alcohol, the surfactant and the water in the mixed substance solution in which the hollow fiber membrane is immersed is particularly determined when the weight of the mixed substance in the dried membrane is 0.1 to 1.5 times the weight of the membrane polymer. Although not limited, polyhydric alcohol is 5-50wt
%, The surfactant is preferably 0.05 to 10% by weight, and the water is preferably 40 to 90% by weight. Further, if the moisture concentration in the mixed substance contained in the film is high, the adhesive foams at the interface between the polyurethane-based adhesive and the film, while if the water concentration is low, the permeation speed of the film after drying is reduced. In the present invention, it has been found that the fact that the water concentration is 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 described specifically. First, a cellulose derivative hollow fiber membrane obtained by a wet or dry-wet membrane forming method or the like is filled with a ternary mixed substance having a predetermined composition of a polyhydric alcohol, a surfactant and water. The method of filling is not limited, but the simplest 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, the hollow fiber membrane is dried to remove excess water inside the holes. The weight and moisture concentration of the mixed substance contained in the dried hollow fiber membrane of the present invention also vary 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 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 a cellulose acetate hollow fiber membrane
30-60 ° C is desirable. The drying may be performed until the content weight of the mixed substance reaches equilibrium. For example, when the cellulose acetate hollow fiber membrane is dried at 50 ° C., the drying may be performed for 5 hours or more.

Further, before using the hollow fiber membrane as a liquid separation membrane, the mixed substance can be removed from the membrane by immersing the dried hollow fiber membrane in water at room temperature for several hours or more. Transmission performance can be obtained. This immersion time can also be reduced by raising the temperature of the water to a level that does not reach 60 ° C.

Although the function 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 group part of the polyhydric alcohol have strong interaction with water, this water is apparently bound to the hollow fiber membrane via the surfactant and the polyhydric alcohol. Exists in. The water in the bound state 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 to give the hollow fiber membrane an appropriate water retention. The mixed substance can be easily removed from the hollow fiber membrane by immersing the membrane in water. In a hollow fiber membrane structure having a dense layer on the inner and outer surfaces of the membrane as in the present invention, generally, even if the membrane is immersed in a humectant, the rate at which the humectant diffuses throughout the porous interior of the membrane is significantly reduced. The mixed substance of the present invention can effectively perform the moisturizing action of the film even with such a film structure.

[0021]

As described above, even if 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 foaming of the adhesive does not occur, and sufficient sealing properties 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 A cellulose acetate (degree of acetylation: 60.5) polymer was stirred and dissolved in a solvent of dimethyl sulfoxide to prepare a film-forming dope (polymer concentration: 20% by weight). Temperature of this film dope
It was press-fitted into the sheath of a circular double-tube spinning nozzle at 90 ° C, and water was injected into the nozzle core as a coagulating liquid. The film forming dope discharged from the spinning nozzle opening has a space of 5 ° C. adjusted to 90 ° C.
After passing through a water bath, 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 and 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 diameter of 10 to 50 μm,
It had a large elliptical void with a major axis of 50-150 μm. The pure water permeation rate of this hollow fiber membrane (permeate water per unit time per unit membrane area when pure water at 25 ° C. is passed through the hollow at a pressure of 1 kg / cm ² ) is 320 liters / (m ² · hr).・ (Kg / cm ² ))
The molecular weight cut off was 150,000 (pore diameter of dense layer: 10 to 20 nm). After drying the film in a dryer at 50 ° C. for about 20 hours, the weight per 1 m length was 0.28 mg.

[0024] The hollow fiber membrane obtained above was used for glycerin
GL), a mixed solution of sodium dodecyl sulfate (hereinafter abbreviated as SDS) and water (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 the dried 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 based on the polymer weight of the membrane by the following equation.

[0026]

(Equation 1)

The moisture concentration in this mixed substance was determined by placing the dried film in a desiccator containing a large amount of phosphorus pentoxide,
For 1 week, and the moisture content of the dried film was further removed, and the weight was obtained from the difference between the weight of the film obtained and the weight of the original dried film.

After the dried membrane obtained as described above was immersed in a large amount of water for about 20 hours and the pure water permeation rate of the membrane was measured, the rate of decrease in the water permeation rate was only 5% of the water permeation rate before drying.
It was below. Further, when the dried film was sealed with a polyurethane adhesive, no foaming occurred at the film and the bonding interface. Table 1 shows the above results.

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

Example 3 The hollow fiber membrane of Example 1 before drying was prepared using 1,3-butylene glycol, sodium dodecyl sulfate and water each in an amount of 20 wt.
%, 0.5 wt%, and 79.5 wt%, except that it was immersed in a mixed solution, and the results are shown in Table 1.

Comparative Example 1 The same procedure as in Example 1 was carried out except that the hollow fiber membrane before drying was immersed in a 20% by weight aqueous solution of glycerin. The results are shown in Table 1.

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

Comparative Example 3 The procedure of Example 1 was repeated, except that the film 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 hollow fiber membrane before drying 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 in Example 1 was mixed with a mixed solution of glycerin, sodium dodecyl sulfate and water (mixing weight ratio: GL / SD).
(S / water = 20/10/70) except that the sample was immersed in the same manner as in Example 1. The results are shown in Table 1.

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

[0037]

[Table 1]

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-50-94079 (JP, A) JP-A-3-143534 (JP, A) JP-A-2-6830 (JP, A) JP-A 63-940 151333 (JP, A) JP-A-62-294419 (JP, A) JP-A-61-146306 (JP, A) JP-A-60-257808 (JP, A) JP-A-60-99260 (JP, A) JP-A-60-12072 (JP, A) JP-A-56-129005 (JP, A) JP-A-53-92867 (JP, A) JP-A-52-46699 (JP, A) JP-A-47-11662 (JP, A) JP-A-47-18777 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B01D 53/22 B01D 67/00-71/82 510 C02F 1/44

Claims (5)

(57) [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 comprising three components of a polyhydric alcohol, a surfactant and water. The water concentration in the mixed substance is 0.1 to 5% by weight, 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, which is twice as large. 2. The dense layer has a pore diameter of 1 to 50 nm.
A dry hollow fiber membrane of the cellulose derivative according to the above. 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 a cellulose derivative according to claim 1, wherein the surfactant is sodium dodecyl sulfate. 5. The dried 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.