JPH07194950A - Preparation of hollow fiber-type separation membrane - Google Patents

Abstract

PURPOSE:To provide a method for obtaining conveniently, continuously and stably a hollow fiber-type separation membrane with excellent selective transmitting performance in relation to a method for preparing a separation membrane obtd. from a high polymer such as a gas separation membrane, a reverse osmosis membrane, an ultrafiltration membrane, a precision filtration membrane etc. CONSTITUTION:When a hollow fiber-type separation membrane 5 is obtd. by a dry-wet type film manufacturing method wherein after a high polymer soln. is extruded from a nozzle 1, it is coagulated in a coagulation bath 3 through a carrying part in air, the separation membrane 5 is prepd. by covering the high polmer soln. carried in the carrying part in air with a member 2 prepd. of a glass, a stainless steel etc., with an heat insulation structure so as to intercept the polymer soln. carried in the carrying part in air from the open air. As the film forming soln. carried in the carrying part in air is intercepted substantially from the open air, it is hardly influenced by the atmosphere of the open air and it is possible thereby to control the temp. of the atmosphere of the carrying part in air and the concn. of solvent vapor to be const. without special air conditioning and to obtain continuously and stably a high performance hollow fiber-type separation membrane.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for producing a hollow fiber type separation membrane used for separating solids or solutes from a liquid mixture, or selectively permeating and separating components in a gas mixture.

[0002]

2. Description of the Related Art Separation and concentration of a liquid mixture by a membrane method are more energy-saving than separation techniques such as distillation and do not change the state of substances, so that the concentration of fruit juice, the separation of beer enzymes, the food field, seawater, etc. Valuable materials from water purification fields or industrial wastewater such as drinking water, industrial water production by desalination, ultrapure water production in electronic industry, and aseptic water production in pharmaceutical industry and medical field. It has been widely used in various fields such as the recovery of lactic acid, and in particular, has seen rapid development in recent years. In addition, there are conventional cryogenic separation methods, adsorption methods, absorption methods, etc. as gas separation methods, but when using the separation membrane method compared to these technologies, the processing cost is low, the operation is simple, and the device efficiency is high. It has advantages such as high cost and easy maintenance, and research and development is also active.

These membrane separations can be accomplished by using a membrane to more selectively permeate certain components from the mixture. Therefore, the performance of the separation membrane is characterized by the permeation selectivity of the separation object as well as the permeation rate.
Permeation selectivity is defined by, for example, a salt removal rate in the case of a reverse osmosis membrane and by a separation coefficient in the case of a gas separation membrane. Similarly, the permeation rate is defined by the amount of permeated water and the amount of gas permeation per unit time.

Permeation selectivity is determined by the affinity (interaction) between the permeant and the membrane and the relationship between the molecular size of the permeant and the pore size of the membrane. In an ultrafiltration membrane or a microfiltration membrane that separates a permeate having a relatively large molecular size, the latter relationship, that is, the relationship between the molecular size of the permeate and the pore size of the membrane determines the permeation selectivity. On the other hand, in the case of a reverse osmosis membrane or a gas separation membrane, the permeation material has a molecular order size, so the permeation selectivity is also influenced by the interaction between the low-molecular permeation material and the membrane.

The site that exhibits such permeation selectivity is called the active layer and is generally formed on the surface of the membrane. Moreover,
The active layer is formed as thin as possible because it does not affect the transmission selectivity. As the molecular size of the separation target becomes smaller, the pore size of the active layer needs to be made smaller in order to improve the permeation selectivity. When the size becomes molecular order, the structure of the active layer needs to be made more compact. There is. The smaller the pore size of the active layer and the denser it is, the higher the permeation selectivity can be expected. However, the permeation rate of such an active layer also decreases because the permeation substance becomes a resistance at the same time. . The permeation rate is improved as the thickness of the active layer becomes smaller, the permeation resistance becomes smaller. This is why the thickness of the active layer is made as thin as possible.

In order for the membrane separation method to have industrial significance, it is important that the permeation selectivity is excellent and the permeation rate is high, or that the permeation selectivity and the permeation rate are well balanced. It is also important to have excellent durability such as mechanical strength, chemical resistance, and heat resistance under use conditions. Separation characteristics are improved by thinning the active layer, but the mechanical strength is lowered, so that it cannot be put to practical use as it is. Therefore, as a membrane structure, a structure in which a thin active layer is mechanically supported and a porous support layer is provided under the membrane is used, in other words, an asymmetric structure in which the pore size is larger from the surface to the back of the membrane is used. .

In general, an active layer and a support layer made of the same material are called an asymmetric membrane, and those made of different materials are called a composite membrane. The asymmetric membrane can be obtained by the phase inversion method, while the composite membrane is formed by the same operation as the asymmetric membrane to form a supporting film, and then the coating method, the interfacial polymerization method, the plasma polymerization method, etc. on the surface of the film. Can be obtained by forming an active layer.

As described above, the supporting membrane (mainly ultrafiltration membrane) of the asymmetric membrane or the composite membrane is formed by the phase inversion method, and the melted membrane forming method for obtaining the separation membrane by cooling the melted polymer. , A solvent or a solvent in some cases, but not a polymer but a non-solvent or a solvent prepared by adding an appropriate amount of a swelling agent to a solution of the polymer is used as a film-forming solution to evaporate the solvent in the air running part, and then the coagulation bath Of dry solvent and non-solvent in the solution, and a wet-type film-forming method that obtains a separation membrane by cooling if necessary, and a wet-type film forming method that does not include a solvent evaporation step in the dry-wet film-forming method Can be roughly divided into The present invention relates to a dry / wet film forming method among them.

In the dry-wet film-forming method, a solution in which a polymer is dissolved in a solvent or a solvent which may be dissolved in a solvent but does not dissolve a polymer or in which a suitable amount of a swelling agent is added is used as a film-forming solution. . As the non-solvent, a water-soluble low-molecular organic substance or a water-soluble polymer is generally used, for example, ethylene glycol, propylene glycol, polyglycols or polyvinylpyrrolidone is used, and an inorganic metal salt is widely used as a swelling agent. ing. These not only affect the state of polymer aggregation in the film-forming solution, but also affect the gelation rate of the film-forming solution in the coagulation bath. In other words,
These non-solvent and swelling agent are important components that affect the phase separation property of the polymer during membrane formation, and finally affect the selective permeability of the separation membrane.

Further, the evaporation condition and the coagulation condition of the solvent have a great influence on the selective permeability of the separation membrane. Specifically, when the evaporation temperature / time of the solvent, the component / temperature of the coagulant, etc. are changed, the physical structure of the obtained separation membrane is changed, so that the selective permeability of the separation membrane is changed. Therefore, in order to obtain a separation membrane having excellent selective permeability, it is necessary to optimize these conditions, and it is also necessary to devise a device so that the set conditions are kept constant.

[0011]

DISCLOSURE OF THE INVENTION The present invention relates to a support membrane of an asymmetric membrane or a composite membrane, or in other words, a separation membrane such as a gas separation membrane, a reverse osmosis membrane, an ultrafiltration membrane or a microfiltration membrane. The present invention relates to a production method, and provides a method for easily and stably obtaining a hollow fiber type separation membrane having excellent selective permeation performance.

[0012]

Means for Solving the Problems That is, according to the present invention, a solution containing a polymer is used as a stock solution for film formation, and the polymer solution is extruded from a die and then coagulated in a coagulating bath via an aerial traveling section. In the method for producing a separation membrane that obtains a hollow fiber type separation membrane by a dry-wet membrane production method, a method for producing a separation membrane, characterized in that the membrane-forming solution that travels in the aerial traveling portion is covered with a member having a heat insulating structure. It is provided.

Examples of the high molecular weight polymer in the present invention include polyamide, polyamide hydrazide, polysulfonamide, polyimide, polysulfone, polyether sulfone, and cellulose acetate, but are not limited thereto.

The die used in the present invention is not particularly limited as long as it can be formed into a desired hollow fiber type separation membrane, and for example, a multi-tube nozzle such as a three-split nozzle or a double-tube nozzle. Can be mentioned. The polymer solution is extruded from these spinnerets into the running part in the air. In this aerial running section, the formation of filaments starts when the solvent evaporates from the surface of the polymer polymer solution, and subsequently the polymer polymer solution is cooled in the coagulation bath and the filaments are formed by replacing the solvent with the coagulating liquid. Formation is complete.

By evaporating the solvent from the surface of the polymer solution, the separation active layer is formed first, and then the supporting layer is formed in the coagulation bath. Therefore, it goes without saying that the evaporation conditions of the solvent in the air running portion affect the compactness of the separation active layer on the surface of the polymer solution, but the surface layer formed here is the solvent and the coagulation liquid in the coagulation bath. Acts as a barrier for substitution, and thus the substitution rate changes depending on the thickness and density of the surface layer, and the coagulation rate of the polymer solution inside the surface layer also changes, affecting the asymmetric structure of the support layer. . In this way, the thickness and the density of the separation active layer of the separation membrane obtained by the conditions such as the evaporation temperature and the evaporation time of the solvent in the air running portion,
Since the pore size and porosity of the support layer are affected, it is necessary to optimize the evaporation conditions in order to obtain a high performance separation membrane. Further, in order to obtain such a film stably, it is important to control the evaporation conditions to be constant so as not to be affected by external factors such as the temperature and humidity of the atmosphere in the air running section.

As a method for positively controlling the evaporation conditions in the air running section, a method of discharging a high molecular polymer solution into a drying tower in which a heating gas flows and evaporating the solvent like a dry spinning method (Japanese Patent Publication No. Sho 53). No. 43-40) or a method of covering the air running part with a cylindrical material capable of blocking the outside air to keep the atmosphere constant with saturated solvent vapor (JP-A-47-4010). In the case of the former, since it is a membrane-forming method close to the dry spinning method, the membrane structure of the obtained hollow fiber separation membrane is likely to be homogeneous, and it is difficult to obtain a highly water-permeable separation membrane. In the latter case, the air temperature and solvent concentration in this part can be kept constant when the air running part is extremely short.However, if the air running part becomes long, the influence of the temperature of the outside air cannot be ignored. There is a limit to the applicable range of the length of the part.

The present invention controls the evaporation conditions of the solvent in the film forming solution running in these conventional air running parts, and the running film forming solution is made of glass, stainless steel or the like and substantially blocks the outside air. It is characterized in that it is covered with a member having a heat-insulating structure, which makes it possible to obtain a high-performance membrane having excellent asymmetry regardless of changes in outside air conditions.

[0018]

In a method for producing a separation membrane which obtains a hollow fiber type separation membrane by a dry-wet membrane formation method, a membrane-forming solution traveling in the air is covered with a member having a heat insulating structure so as to be substantially shielded from outside air. As a result, it is possible to control the temperature of the atmosphere and the concentration of solvent vapor in the air running part at a constant level without being affected by the atmosphere of the outside air and without particularly air conditioning. It is possible to obtain the film more stably.

[0019]

EXAMPLES The present invention will be described below with reference to examples and comparative examples, but the examples given here do not limit the present invention. Example 1 After sufficiently purifying a copolyamide obtained by a low temperature solution polymerization method from terephthalic acid dichloride, 70 mol% of 4,4'-diaminodiphenyl sulfone and 30 mol% of piperazine, 36 parts by weight of this copolymer was CaCl2. Dissolved in a DMAC solution containing 4 parts by weight (based on polymer) and 3.6 parts by weight diglycerin (based on polymer) at 80 ° C.,
It was used as a film forming solution. After defoaming this solution under reduced pressure, the solution was discharged from a three-division nozzle into a coagulation bath cooled at 4 ° C. through an in-air running portion to obtain a hollow fiber membrane. At this time, in the air running portion from the nozzle surface to the surface of the coagulating bath, a double cylindrical glass through a substantially vacuum portion so that the hollow fiber membrane running in this portion is substantially shielded from the outside air. The tube was attached. The spinning test was carried out for 24 hours, and a hollow fiber membrane for reverse osmosis membrane performance evaluation was sampled every hour. The obtained hollow fiber membrane was thoroughly washed with water and then heat-treated at 85 ° C. for 30 minutes to prepare a mini-module composed of 300 hollow fiber membranes having an effective length of 1 m. Each of these mini-modules was mounted in a reverse osmosis membrane performance evaluation cell, and a reverse osmosis experiment was carried out at a salt concentration in the feed liquid of 0.15%, a feed liquid temperature of 25 ° C., and an operating pressure of 30 Kg / cm ² , and 24 The reverse osmosis membrane performance was confirmed. The results obtained are shown in Table 1.

Comparative Example 1 A reverse osmosis membrane performance was evaluated by preparing a reverse osmosis hollow fiber membrane according to the procedure of Example 1. However, only a cylindrical glass tube was attached to the in-air running portion from the nozzle surface to the coagulation bath surface. The results obtained are shown in Table 1.

Example 2 Diaminodiphenylsulfone isophthalamide obtained by a low temperature solution polymerization method from isophthalic acid dichloride and 4,4'-diaminodiphenylsulfone was sufficiently purified, and then 25 parts by weight of this was added to 5 parts by weight of LiCl (polymer). In a DMAC solution containing 30 parts by weight of tetraethylene glycol (relative to the polymer) and 100 ° C.,
It was used as a film forming solution. After defoaming this solution under reduced pressure, it was passed through a tube-in-orifice nozzle, an air running section, and a temperature of 10 ° C.
A hollow fiber membrane was obtained by discharging into the coagulation bath cooled to above. At this time, a double-cylindrical glass tube provided with a suction port on the outside is attached to the air running part from the nozzle surface to the coagulating bath surface so that the hollow fiber membrane running in this part is substantially shielded from the outside air. From this suction port, a vacuum pump was used to substantially vacuum the portion sandwiched between the double glass tubes. The spinning test is 24
It was carried out for an hour, and a hollow fiber membrane for reverse osmosis membrane performance evaluation was sampled every hour. The hollow fiber membranes thus obtained were thoroughly washed with water and then heat-treated at 85 ° C. for 30 minutes to prepare mini-modules from the respective hollow fiber membranes. These hollow fiber membranes were attached to an ultrafiltration membrane performance evaluation cell, the dextran (molecular weight: 100,000) concentration in the feed liquid: 500 ppm, the feed liquid temperature:
The performance of 24 ultrafiltration membranes was confirmed at 25 ° C. and an operating pressure of 2 kg / cm ² . The obtained results are shown in Table 2.

Example 3 Diaminodiphenylsulfone terephthalamide obtained by a low temperature solution polymerization method from terephthalic acid dichloride and 4,4'-diaminodiphenylsulfone was sufficiently purified, and then 15 parts by weight of this was added to 5 parts by weight of LiCl (polymer). And (10) parts by weight of polyglycerin having an average molecular weight of 500 (based on the polymer) at 100 ° C. to obtain a film-forming solution. Next, this membrane-forming solution was defoamed, and then discharged from a tube-in-orifice nozzle adjusted to 35 ° C. to a coagulation bath that was also heated to 35 ° C. through an in-air running portion to obtain a hollow fiber membrane. At this time, in the air running portion from the nozzle surface to the coagulation bath surface, a cylinder having a heat insulating effect is provided through a substantially vacuum portion so that the hollow fiber membrane running in this portion is substantially shielded from the outside air. Attached stainless steel tube. Also, as a coagulation solvent in the coagulation bath, 30
% DMAC aqueous solution was used, and the same coagulating solvent was used for the core liquid forming the hollow portion. The spinning test is carried out for 24 hours,
Hollow fiber membranes for reverse osmosis membrane performance evaluation were sampled every hour. The resulting hollow fiber membrane is thoroughly washed with water and then at 90 ° C.
Heat treated for 20 minutes in water, outer diameter 500 μm, inner diameter 380
A hollow fiber type ultrafiltration membrane of μm was obtained. Mini-modules were prepared from these hollow fiber ultrafiltration membranes and subjected to ultrafiltration membrane performance evaluation. Dextran (molecular weight: 10
10,000) Concentration: 500 ppm, feed liquid temperature: 25 ° C., operating pressure: 2 Kg / cm ^{2 An} ultrafiltration experiment was conducted to confirm the performance of 24 ultrafiltration membranes. The obtained results are shown in Table 2.

Comparative Example 2 A hollow fiber type ultrafiltration membrane was prepared according to the procedure of Example 2 and the ultrafiltration membrane performance was evaluated. However, at the time of adjusting the hollow fiber type ultrafiltration membrane, no member was attached to the aerial traveling portion so that the hollow fiber membrane traveling in this portion was substantially shielded from the outside air. The obtained results are shown in Table 2.

[0024]

[Table 1]

[0025]

[Table 2]

From Tables 1 and 2, it can be seen that the average value of the membrane performance and the variation in the performance at 24 hours are smaller in the Examples than in the Comparative Examples.

[0027]

INDUSTRIAL APPLICABILITY According to the present invention, a solution containing a polymer is used as a stock solution for film formation, and the polymer solution is extruded from a die and then coagulated in a coagulating bath through an air running part to form a dry and wet film. In the method for producing a separation membrane to obtain a hollow fiber type separation membrane by a method, the method relates to a method for producing a separation membrane, characterized in that the membrane-forming solution traveling in the air running portion is covered with a member having a heat insulating structure, A high-performance separation membrane can be obtained easily and stably.

[Brief description of drawings]

FIG. 1 is an example of a method for producing a hollow fiber type separation membrane of the present invention.

[Explanation of symbols]

 1. Spinneret 2. A member having a heat insulating structure 3. Coagulation bath 4. Coagulation liquid 5. Hollow fiber type separation membrane

Claims (2)

[Claims] 1. A hollow fiber produced by a dry-wet film-forming method in which a solution containing a polymer is used as a stock solution for film formation, and the polymer solution is extruded from a die and then coagulated in a coagulating bath through an in-air running part. A method for producing a separation membrane, which comprises obtaining a mold separation membrane, wherein the membrane-forming solution running in the air running portion is covered with a member having a heat insulating structure. 2. The method for producing a separation membrane according to claim 1, wherein the member having the heat insulating structure is a double-cylindrical glass tube with a substantially vacuumed portion interposed therebetween.